Which organisms have their cell wall made of polysaccharides and amino acids?

Which organisms have their cell wall made of polysaccharides and amino acids?

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I came across a question which somewhat goes like

In which of the following kingdom, most of the members have a cell wall made of polysaccharide and amino acids ? - Monera or Fungi.

To me it looks like both are correct answers because both are having hetero polymers of glucose and amine. Please enlighten me if I am wrong.

The correct answer is Monera.

It is so because their cell wall is made up of peptidoglycan.

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid. Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer.

Fungi is wrong because its cell wall is made of chitin which lacks amino acids.

Chitin $(C_8H_{13}O_5N)_n$ is a long-chain polymer of an N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is a characteristic component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulae of molluscs, and the beaks and internal shells of cephalopods, including squid and octopuses and on the scales and other soft tissues of fish and lissamphibians.

4 Bacteria: Cell Walls

It is important to note that not all bacteria have a cell wall. Having said that though, it is also important to note that most bacteria (about 90%) have a cell wall and they typically have one of two types: a gram positive cell wall or a gram negative cell wall.

The two different cell wall types can be identified in the lab by a differential stain known as the Gram stain. Developed in 1884, it’s been in use ever since. Originally, it was not known why the Gram stain allowed for such reliable separation of bacterial into two groups. Once the electron microscope was invented in the 1940s, it was found that the staining difference correlated with differences in the cell walls. Here is a website that shows the actual steps of the Gram stain. After this stain technique is applied the gram positive bacteria will stain purple, while the gram negative bacteria will stain pink.

Overview of Bacterial Cell Walls

A cell wall, not just of bacteria but for all organisms, is found outside of the cell membrane. It’s an additional layer that typically provides some strength that the cell membrane lacks, by having a semi-rigid structure.

Both gram positive and gram negative cell walls contain an ingredient known as peptidoglycan (also known as murein). This particular substance hasn’t been found anywhere else on Earth, other than the cell walls of bacteria. But both bacterial cell wall types contain additional ingredients as well, making the bacterial cell wall a complex structure overall, particularly when compared with the cell walls of eukaryotic microbes. The cell walls of eukaryotic microbes are typically composed of a single ingredient, like the cellulose found in algal cell walls or the chitin in fungal cell walls.

The bacterial cell wall performs several functions as well, in addition to providing overall strength to the cell. It also helps maintain the cell shape, which is important for how the cell will grow, reproduce, obtain nutrients, and move. It protects the cell from osmotic lysis, as the cell moves from one environment to another or transports in nutrients from its surroundings. Since water can freely move across both the cell membrane and the cell wall, the cell is at risk for an osmotic imbalance, which could put pressure on the relatively weak plasma membrane. Studies have actually shown that the internal pressure of a cell is similar to the pressure found inside a fully inflated car tire. That is a lot of pressure for the plasma membrane to withstand! The cell wall can keep out certain molecules, such as toxins, particularly for gram negative bacteria. And lastly, the bacterial cell wall can contribute to the pathogenicity or disease –causing ability of the cell for certain bacterial pathogens.


Structure Edit

Nutrition polysaccharides are common sources of energy. Many organisms can easily break down starches into glucose however, most organisms cannot metabolize cellulose or other polysaccharides like chitin and arabinoxylans. These carbohydrate types can be metabolized by some bacteria and protists. Ruminants and termites, for example, use microorganisms to process cellulose. [ citation needed ]

Even though these complex polysaccharides are not very digestible, they provide important dietary elements for humans. Called dietary fiber, these carbohydrates enhance digestion among other benefits. The main action of dietary fiber is to change the nature of the contents of the gastrointestinal tract, and to change how other nutrients and chemicals are absorbed. [7] [8] Soluble fiber binds to bile acids in the small intestine, making them less likely to enter the body this in turn lowers cholesterol levels in the blood. [9] Soluble fiber also attenuates the absorption of sugar, reduces sugar response after eating, normalizes blood lipid levels and, once fermented in the colon, produces short-chain fatty acids as byproducts with wide-ranging physiological activities (discussion below). Although insoluble fiber is associated with reduced diabetes risk, the mechanism by which this occurs is unknown. [10]

Not yet formally proposed as an essential macronutrient (as of 2005), dietary fiber is nevertheless regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake. [7] [8] [11] [12]

Starch Edit

Starch is a glucose polymer in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of amylose (15–20%) and amylopectin (80–85%). Amylose consists of a linear chain of several hundred glucose molecules, and Amylopectin is a branched molecule made of several thousand glucose units (every chain of 24–30 glucose units is one unit of Amylopectin). Starches are insoluble in water. They can be digested by breaking the alpha-linkages (glycosidic bonds). Both humans and other animals have amylases, so they can digest starches. Potato, rice, wheat, and maize are major sources of starch in the human diet. The formations of starches are the ways that plants store glucose. [ citation needed ]

Glycogen Edit

Glycogen serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue. Glycogen is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach. [13]

Glycogen is analogous to starch, a glucose polymer in plants, and is sometimes referred to as animal starch, [14] having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α(1→4) glycosidic bonds linked, with α(1→6)-linked branches. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact and more immediately available as an energy reserve than triglycerides (lipids). [ citation needed ]

In the liver hepatocytes, glycogen can compose up to 8 percent (100–120 grams in an adult) of the fresh weight soon after a meal. [15] Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a low concentration of one to two percent of the muscle mass. The amount of glycogen stored in the body—especially within the muscles, liver, and red blood cells [16] [17] [18] —varies with physical activity, basal metabolic rate, and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy, to nourish the embryo. [15]

Glycogen is composed of a branched chain of glucose residues. It is stored in liver and muscles.

  • It is an energy reserve for animals.
  • It is the chief form of carbohydrate stored in animal body.
  • It is insoluble in water. It turns brown-red when mixed with iodine.
  • It also yields glucose on hydrolysis.

Schematic 2-D cross-sectional view of glycogen. A core protein of glycogenin is surrounded by branches of glucose units. The entire globular granule may contain approximately 30,000 glucose units. [19]

A view of the atomic structure of a single branched strand of glucose units in a glycogen molecule.

Galactogen Edit

Galactogen is a polysaccharide of galactose that functions as energy storage in pulmonate snails and some Caenogastropoda. [20] This polysaccharide is exclusive of the reproduction and is only found in the albumen gland from the female snail reproductive system and in the perivitelline fluid of eggs. [ citation needed ]

Galactogen serves as an energy reserve for developing embryos and hatchlings, which is later replaced by glycogen in juveniles and adults. [21]

Inulin Edit

Inulin is a naturally occurring polysaccharide complex carbohydrate composed of dietary fiber, a plant-derived food that cannot be completely broken down by human digestive enzymes.

Arabinoxylans Edit

Arabinoxylans are found in both the primary and secondary cell walls of plants and are the copolymers of two sugars: arabinose and xylose. They may also have beneficial effects on human health. [22]

Cellulose Edit

The structural components of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. Humans and many animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Certain animals such as termites can digest cellulose, because bacteria possessing the enzyme are present in their gut. Cellulose is insoluble in water. It does not change color when mixed with iodine. On hydrolysis, it yields glucose. It is the most abundant carbohydrate in nature. [ citation needed ]

Chitin Edit

Chitin is one of many naturally occurring polymers. It forms a structural component of many animals, such as exoskeletons. Over time it is bio-degradable in the natural environment. Its breakdown may be catalyzed by enzymes called chitinases, secreted by microorganisms such as bacteria and fungi and produced by some plants. Some of these microorganisms have receptors to simple sugars from the decomposition of chitin. If chitin is detected, they then produce enzymes to digest it by cleaving the glycosidic bonds in order to convert it to simple sugars and ammonia. [ citation needed ]

Chemically, chitin is closely related to chitosan (a more water-soluble derivative of chitin). It is also closely related to cellulose in that it is a long unbranched chain of glucose derivatives. Both materials contribute structure and strength, protecting the organism. [ citation needed ]

Pectins Edit

Pectins are a family of complex polysaccharides that contain 1,4-linked α- D -galactosyl uronic acid residues. They are present in most primary cell walls and in the nonwoody parts of terrestrial plants. [ citation needed ]

Acidic polysaccharides are polysaccharides that contain carboxyl groups, phosphate groups and/or sulfuric ester groups.

Pathogenic bacteria commonly produce a thick, mucous-like, layer of polysaccharide. This "capsule" cloaks antigenic proteins on the bacterial surface that would otherwise provoke an immune response and thereby lead to the destruction of the bacteria. Capsular polysaccharides are water-soluble, commonly acidic, and have molecular weights on the order of 100,000 to 2,000,000 daltons. They are linear and consist of regularly repeating subunits of one to six monosaccharides. There is enormous structural diversity nearly two hundred different polysaccharides are produced by E. coli alone. Mixtures of capsular polysaccharides, either conjugated or native are used as vaccines.

Bacteria and many other microbes, including fungi and algae, often secrete polysaccharides to help them adhere to surfaces and to prevent them from drying out. Humans have developed some of these polysaccharides into useful products, including xanthan gum, dextran, welan gum, gellan gum, diutan gum and pullulan.

Most of these polysaccharides exhibit useful visco-elastic properties when dissolved in water at very low levels. [23] This makes various liquids used in everyday life, such as some foods, lotions, cleaners, and paints, viscous when stationary, but much more free-flowing when even slight shear is applied by stirring or shaking, pouring, wiping, or brushing. This property is named pseudoplasticity or shear thinning the study of such matters is called rheology.

Viscosity of Welan gum
Shear rate (rpm) Viscosity (cP or mPa⋅s)
0.3 23330
0.5 16000
1 11000
2 5500
4 3250
5 2900
10 1700
20 900
50 520
100 310

Aqueous solutions of the polysaccharide alone have a curious behavior when stirred: after stirring ceases, the solution initially continues to swirl due to momentum, then slows to a standstill due to viscosity and reverses direction briefly before stopping. This recoil is due to the elastic effect of the polysaccharide chains, previously stretched in solution, returning to their relaxed state.

Cell-surface polysaccharides play diverse roles in bacterial ecology and physiology. They serve as a barrier between the cell wall and the environment, mediate host-pathogen interactions. Polysaccharides also play an important role in formation of biofilms and the structuring of complex life forms in bacteria like Myxococcus xanthus [24] .

These polysaccharides are synthesized from nucleotide-activated precursors (called nucleotide sugars) and, in most cases, all the enzymes necessary for biosynthesis, assembly and transport of the completed polymer are encoded by genes organized in dedicated clusters within the genome of the organism. Lipopolysaccharide is one of the most important cell-surface polysaccharides, as it plays a key structural role in outer membrane integrity, as well as being an important mediator of host-pathogen interactions.

The enzymes that make the A-band (homopolymeric) and B-band (heteropolymeric) O-antigens have been identified and the metabolic pathways defined. [25] The exopolysaccharide alginate is a linear copolymer of β-1,4-linked D -mannuronic acid and L -guluronic acid residues, and is responsible for the mucoid phenotype of late-stage cystic fibrosis disease. The pel and psl loci are two recently discovered gene clusters that also encode exopolysaccharides found to be important for biofilm formation. Rhamnolipid is a biosurfactant whose production is tightly regulated at the transcriptional level, but the precise role that it plays in disease is not well understood at present. Protein glycosylation, particularly of pilin and flagellin, became a focus of research by several groups from about 2007, and has been shown to be important for adhesion and invasion during bacterial infection. [26]

Periodic acid-Schiff stain (PAS) Edit

Polysaccharides with unprotected vicinal diols or amino sugars (where some hydroxyl groups are replaced with amines) give a positive periodic acid-Schiff stain (PAS). The list of polysaccharides that stain with PAS is long. Although mucins of epithelial origins stain with PAS, mucins of connective tissue origin have so many acidic substitutions that they do not have enough glycol or amino-alcohol groups left to react with PAS.

Types of Polysaccharides (3 Types)

The following points highlight the three main types of Polysaccharides. The types are: 1. Food Storage Polysaccharides 2. Structural Polysaccharides 3. Mucosubstances.

Type # 1. Food Storage Polysaccharides:

They are those polysaccharides which serve as reserve food. At the time of need, storage polysaccharides are hydrolysed. Sugars thus released become available to the living cells for production of energy and biosynthetic activity. There are two main storage polysaccha­rides— starch and glycogen.

It is the storage polysaccharide of most plants. Human beings obtain it from cereal grains (e.g., rice, wheat), legumes (pea, gram, beans), potato, tapioca, banana etc. It is polyglucan homosaccharide and is formed as an end product of photosynthesis. Starch is stored either inside chloro­plasts or special leucoplasts called amyloplasts. Starch oc­curs in the form of microscopic granules called starch grains.

Starch grains may occur singly or in groups. The two types are known as simple and compound starch grains. Starch grains may be rounded, oval, polygonal or rod shaped in outline (Fig. 9.6). Each grain has a number of shells or layers arranged in con­centric or eccentric fashion around a proteinaceous point called hilum.

Starch consists of two com­ponents, amylose and amylopectin (Fig. 9.7). Amylose is more soluble in water than amylopectin. In general, 20-30% of starch consists of amylose and the rest as amylopectin. Waxy starch of some vari­eties of Maize and other cereals consists en­tirely of amylopectin. On the other hand, the starch of some varieties of Pea having wrinkled surface may have as much as 98% of amylose.

Both amylose and amylopectin are formed by the condensation of α -D-glucose (pyranose forms). Amylose is in the form of a continuous straight but helically arranged chain where each turn contains about six glucose units.

The suc­cessive glucose units are linked together by 1-4 α-linkages, that is, the link is between carbon atom 1 of one and carbon atom 4 of the other (Fig. 9.8). A molecule of water is lost during the formation of the linkage. A straight chain of amylose consists of 200-1000 glucose units.

Amylopectin contains a large number of glu­cose units (2000-200,000). Besides a straight chain it bears several side chains which may be branched further.

Branching is usually at intervals of about 25 residues. At the place of origin of a side chain, the carbon atom 6 of a glucose residue of a straight chain is linked to the carbon atom 1 of the first glucose unit of side chain (1-6 α-link- age). Wolform and Thompson (1956) have also reported 1 → 3 linkages in case of amylopectin.

Amylose fraction gives blue-black colour with iodine solution (Iodine-Potassium iodide solution) while amylopectin fraction gives red-violet colour.

It is the polysaccharide food reserve of animals, bacteria and fungi. Glycogen is popularly called animal starch. Glycogen is mainly stored inside liver (up to 0.1 kg) and muscles. In shape the complex carbohydrate appears as ellipsoid flattened granules that lie freely inside the cells. The polysaccharide gives reddish colour with iodine. Chemi­cally, it is similar to starch.

It has about 30,000 glucose residues and a molecular weight of about 4.8 million. Glucose residues are arranged in a highly branched bush like chains. There are two types of linkages 1-4 α -linkages in the straight part and 1-6 linkages in the area of branching. The straight part is helically twisted with each turn having six glucose units. The distance between two branching points is 10-14 glucose residues.

It is a fructan storage polysaccharide of roots and tubers of Dahlia and related plants. Inulin is not metabolized in human body and is readily filtered through the kidney. It is, therefore, used in testing of kidney function, especially glomerular filtration.

Type # 2. Structural Polysaccharides:

They are polysaccharides that take part in forming the structural frame work of the cell walls in plants and skeleton of animals. Structural polysaccharides are of two main types: chitin and cellulose.

It is the second most abundant organic substance. Chitin is a complex carbohydrate of heteropolysaccharide type which is found as the structural component of fungal walls and exoskeleton of arthropods. In fungal walls, chitin is often known as fungus cellulose. Chitin is soft and leathery. Therefore, it provides both strength and elasticity. It becomes hard when impregnated with certain proteins and calcium carbonate.

In chitin, basic unit is not glucose but a nitrogen containing glucose derivative known as N-acetyl glucosamine. Chitin has an un-branched configuration. Monomers are joined together by 1- 4 β-linkages (Fig. 9.9). Adjacent residues lie at 180°. Molecules occur in parallel and are held together by hydrogen bonds.

It is fibrous homopolysaccharide of high tensile strength which forms a structural element of cell wall in all plants, some fungi and protists. Tunicin of tunicates (=ascidians) is related to cellulose (also called animal cellulose).

In absolute terms, cellulose is the most abundant organic substance of the biosphere forming 50% of carbon found in plants. Cotton fibres have about 90% of cellulose while wood contains 25-50% cellulose. The other materials of the cell wall include lignin, hemicellulose, pectins, wax, etc.

Cellulose molecules have un-branched and linear chains unlike the branched and helical chains of starch and glycogen. A chain of cellulose molecule contains 6000 or more glucose residues.

The successive glucose residues are joined together by 1-4 β-linkages (Fig. 9.10). Consequently alternate glucose molecules lie at 180° to each other. Hydroxyl groups of glucose residues, therefore, project in all directions. The molecular weight of cellulose ranges between 0.5 to 2.5 millions.

Cellulose molecules do not occur singly. Instead a number of chains are arranged in close antiparallel fashion. The molecules are held together by intermolecular hydrogen bonds between hydroxyl group at position 6 of glucose residues of one molecule and glycosidic oxygen between two glucose residues of the adjacent molecule.

There is also intermolecular strengthening of the chain by the formation of hydrogen bonds between hydroxyl group at position three and oxygen atom of the next residue. About 2000 cellulose chains or molecules are packed together to form a micro fibril visible under the electron microscope.

(1) Cellulose constitutes the bulk of human food. However, due to being polymer of β-glucose, cellulose is not acted upon by amylases present in human digestive juices. In humans, cellulose has a roughage value which keeps the digestive tract in functional fitness.

(2) Cellulose is an important constituent of diet for ruminants like cows and buffaloes. The stomach of ruminants contain micro-organisms capable of digesting or breaking down cellulose. Termites and snails also possess micro-organisms in their gut for this purpose.

(3) Microbes are used in producing soluble sugars from cellulose. The sugars are then allowed to undergo fermentation for obtaining ethanol, butanol, acetone, methane, etc.

(4) Cellulose rich wood is employed in building furniture, tools, sports articles, paper etc.

(5) Depending upon the percentage of cellulose present in the fibres, the latter are used in textiles (e.g., Cotton, Linen), preparation of sacs (e.g., Jute) or ropes (e.g., Hemp, China Jute, Deccan Hemp).

(6) Rayon and cellophane are formed of cellulose xanthate.

(7) Cellu­lose acetate is obtained by treating wood pulp with acetic acid, acetic anhydride and a catalyst. Cellulose acetates are used in preparing fibres for double knits, tericot, wrinkle proof, and moth proof clothing. Cigarette filters are also prepared from these fibres. Other uses of cellulose acetates include preparation of plastics and shatter proof glass.

(8) Cellulose nitrate is used in propellent explosives.

(9) Carboxymethyl cellulose is used as emulsifier and smoothening reagent of ice creams, cosmetics and medicines.

Type # 3. Mucosubstances:

Mucilage, mucus or slime forming substances are called mucosubstances. They are of two types, mucopolysaccharides and mucoproteins (= glycoproteins).

They are slimy substances or mucilages which possess acidic or aminated polysaccharides formed from galactose, mannose, sugar derivatives and uronic acids. Mucopolysaccharides or mucilages are quite common in both plants and animals.

They can be observed by cutting the unripe fruits of Okra (Lady’s finger, vern Bhindi) or soaking the husks or seeds of Plantago ovata (Plantain, vern. Isabgol). Mucopolysaccha­rides occur inside the plant cell walls, outside the cells or bodies of bacteria, blue-green algae and many aquatic plants, cementing layer between cells, inside body fluids, connective tissues and cartilages.

The important functions of mucopolysaccharides are as follows:

(1) They bind proteins in the cell walls and connective tissue.

(2) Water is held in the interstitial spaces due to mucopolysaccharides.

(3) Mucopolysaccharides occur in the cell walls of bacteria and blue-green algae. They form a layer of mucilage around them as well as other aquatic plants and protects the organisms against rotting effect of water, prevents desiccation, growth of epiphytes and attack of pathogens.

(4) They provide lubrication in ligaments and tendons.

(5) As keratan sulphate (acetyglucosamine + galactose + sulphuric acid) they occur inside skin and cornea providing both strength and flexibility.

(6) Chon­droitin sulphate (glucuronic or iduronic acid + acetyl aminogalactose) is the mucopolysaccharide found in the matrix of cartilage and connective tissue for support and elasticity.

(7) Hyalu­ronic acid (glucuronic acid +acetyl glucosamine) is the mucopolysaccharide met in extracellular fluid of animal tissues, vitreous humor of eye, synovial fluid, cerebrospinal fluid, etc. It also occurs in cementing material between animal cells as well as inside cell coat.

(8) Husk of Plantago ovata contains mucilage which is used medicinally in treating intestinal problems. It relieves irritation. Mucilage present in Aloe barbadensis reduces inflammation. It is also purgative.

(9) Mucopolysaccharide heparin (α-1, 4 glucosamine + glucuronic acid) is blood anticoagulant.

(10) Agar. Marine brown and red algae, called sea weeds, yield mucopolysac­charides of commercial value, e.g., agar, alginic acid, carragenin, etc.

Agar (agar-agar) is polymer of D-galactose, 3-6 anhydro L-galactose having sulphate esterification after every tenth galactose unit. It is used as culture medium in the laboratory, as laxative, stiffening, stabilising and emulsifying agent. It is obtained from cell wall of some red alae like Gracilaria, Gelidium and Gelidiella.

Pectin (Pectic Compounds):

It is an acidic polysaccharide that occurs in the matrix of cell wall and middle lamella (as calcium pectate). Pectin is soluble in water and can undergo ↔ sol gel interchange. Pectin is formed of galacturonic acid, galactose, methylated galacturonic acid and arabinose. It is used in making Jelly and Jams.

It is a mixture of polysaccharides of xylans, mannans, galactans, arabino-galactans and glucomannans. Hemicellulose occurs in the cell wall where it forms a link between pectic compounds and cellulose micro fibrils.

Peptidoglycan (Murein, Mucopeptide):

It is formed of heteropolysaccharide chains cross-linked by short peptides (generally tetra peptides). Heteropolysaccharide chains are formed of two alternate amino-sugar molecules, N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM).

It is a complex formed of lipid and polysaccharide which forms the outer membrane of Gram -ve bacteria. There is a glycolipid responsible for endotoxic activity, a core polysaccharide and an antigen specific variable chain. Lipopolysaccharide induces fever, shock and other toxic effects.

Mucoproteins (glycoproteins):

The protein with conjugated monosaccharide’s form mucus. These are found in stomach, nasal secretion, intestine, vagina and are antibacterial and protective in function.

Which organisms have their cell wall made of polysaccharides and amino acids? - Biology

The composition of the cell wall varies from that organism that has it. Thus it is different when considering a fungus, a bacterium, or a plant. In bacteria, the cell wall is made of a substance called “peptidoglycan.” The “peptide” part of the substance is from short chains of amino acids called peptides. Amino acids are a major building block of life and are what make up proteins. The “glycan” part is long chains of sugars which along with the peptides make up the mesh of the cell wall.

In plants, the cell wall is mostly made up of various sugars such as cellulose. These sugars are connected in a way such that your body can’t digest them and are also known as “dietary fiber”. Fungi have cell walls made of sugars too, but different ones than you would normally find in a plant. All of these cell walls are made of very different molecules than the cell membrane which is mostly made up of lipids (fats are a type of lipid).

A variety of organisms have cell walls. Plant cell walls are made of mostly of cellulose, hemicellulose, and pectin. There compounds make a rigid cell wall that gives the plant structure to support itself.

Fungi and other organisms like diatoms have cell walls made of different compounds such as chitin and silica.

Animal cells, on the other hand, don't have cell walls and as a result don't have very rigid structures.

Cell walls are usually found in plants, fungi, and various prokaryotes (bacteria, etc.. It is a tough, yet flexible structure that provides structure, protection, and permeability to the cells. Also, it is used to maintain the pressure inside the cells and prevent the cells from over-expansion. The material which makes up cell walls differs in various cell types. Bacterial cell walls are made up of peptidoglycan, a material made from 2 different polysaccharides - N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG).

Cell walls of fungi are composed of chitin, which made up of many N-acetylglucosamines (NAG).

A plant cell wall is composed of cellulose, a complex sugar. Algae and different members of archaea have cell walls composed of different materials. Although the cell walls in all of these organisms are created from different materials, they serve the same function.

That depends on the cell. Plant cell walls are made out of cellulose. Fungal cell walls are made of chitin, the same stuff that insect skeletons are made of. Bacterial cell walls are made out of peptidoglycan, which is a mixed protein-sugar material unique to bacteria. Animal cells don't have cell walls.

Very interesting question. In plants, cell walls are made up of a material called cellulose. It is an extremely tough structural molecule that is very hard to digest. In fact, there are very few animals that can actually eat and digest cellulose. When you read about foods that are high in fiber, they are referring to the tough cellulose in the plant walls. Fiber is good for you but you don't really digest much of it.

The answer to your question depends on which kind of organism we are talking about. The main kinds of organisms that have cell walls are plants, fungi, and certain prokaryotes (bacterial type cells).

In plants, cell walls are mainly comprised of complex polysaccharides (sugar-based polymers) molecules such as cellulose, hemicellulose, and pectin. In between these polysaccharides are lignin, a complex biopolymer made of alcohols that contributes to the structural integrity of the cell wall by crosslinking with the different polysaccharides. Plant cell walls also have various proteins and enzymes embedded in the the wall and as surface accessories which provide various support and functionality in the cell wall.

Fungal cell walls contain different polysaccharides from plants: chitin, glucans, and mannans. They also contain various proteins. However, the composition of fungal cell walls can vary widely between different species.

Bacterial cell walls fall under two main categories: gram positive and gram negative. Gram positive walls are thick, and have many layers of peptidoglycans (protein+sugar) and teichoic acids (polysaccharides). Gram negative walls on the other hand are thin, only have a few peptidoglycans, and are surrounded by a second lipid (fats) membrane consisting of lipopolysaccharides and lipoproteins.

Nucleic acids

The final of the four molecules of life are the nucleic acids. There are two types of nucleic acids that are essential to all life. These are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

DNA is a very well-known type of molecule that makes up the genetic material of a cell. DNA is responsible for carrying all the information an organism needs to survive, grow and reproduce.

RNA is a lesser-known molecule but it also plays an important role in cells. RNA molecules are used to translate the information stored in DNA molecules and use the information to help build proteins. Without RNA, the information in DNA would be useless.

Nucleic acids are long chains made from many smaller molecules called nucleotides. Each nucleotide is made of a sugar, a base and a phosphate group.

The two differences between DNA and RNA are their sugars and their bases. DNA has a deoxyribose sugar while RNA has a ribose sugar. DNA has four different bases – adenine (A), thymine (T), guanine (G), and cytosine (C). RNA has three of the same bases but the thymine base is replaced with a base called uracil (U).

Last edited: 31 August 2020

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Structure of the Plant Cell Wall

Plant cell walls are three-layered structures with a middle lamella, primary cell wall and secondary cell wall. The middle lamella is the outermost layer and helps with cell-to-cell junctions while holding adjacent cells together (in other words, it sits between and holds together the cell walls of two cells this is why it's called the middle lamella, even though it is the outermost layer).

The middle lamella acts like glue or cement for plant cells because it contains pectins. During cell division, the middle lamella is the first to form.

Bacteria Kingdom

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The Bacteria Kingdom, formerly called monera, are single celled prokaryotic organisms. Bacteria encompass two domains: eubacteria and archaea. Eubacteria and archaea have very different cell walls. They are also distinguished by their DNA - the DNA of archaea has histone proteins while that of eubacteria does not.

Under traditional classification schemes Monera is the name of the Kingdom of Bacteria but in most modern textbooks, scientists due to the big diversity in the group that we normally call bacteria because there are such diversity, scientists are starting to split that into two other groups called Domains. One of these Domains is called Eubacteria, the other Domain is called Archea. So what are some of the characteristics of the Eubacteria or "true bacteria" well they're all prokaryotic which you should know what that means? They have cell walls made of a mesh between polysaccharides and amino acids called peptidioglycan.
They have what is called naked DNA what does that mean, just means it doesn't have the histone proteins that Eurkaryotic DNA like ours is wrapped around to help organize it. They have what I sometimes call "prokaryotic-style" ribosomes which if you really want to look at the details of, go ahead and Google it but most of the time you don't need to know that. And what are some examples of it, this is a huge group with huge diversity within it, it includes the photosynthetic cyanobacteria that are a major source of oxygen and food in many ecosystems. There is the nitrogen-fixing bacteria that are in our soil that help provide materials for our plants. There's lots of different kinds of Eubacteria.
The Domain Archea is a little bit unusual, now they're all prokaryotic however they have unusual cell walls made out of not peptidioglycogen but these weird other polysaccharides, even their cell membranes have unusual phospholipids within them. They don't have naked DNA like majority of the prokaryots do instead they have histone proteins wrapped around their DNA. They have "Eukaryotic-style" ribosomes, these two factors are one of the major reasons why scientists now think that ultimately the eukaryotes like ourselves and plants ultimately evolve from the Archea. Now they also have a number of different roles in the environment, many of them are Methanogens which means they're the things that in your large intestine and especially in the large intestine of things like cows. They're the things breaking down some of the undigested polysaccharides to produce methane. Halogens they inhabit really weird unusual environment and the Halogens they love salty water because by living in that kind of environment they're able to avoid competition from a lot of the other creatures. So usually they get lumped together into this group called extremophiles which simply means they love the extreme environments, and those are the bacteria.


  • A biomolecule [biological molecule] is any molecule that is present in living organisms –– microorganisms, plants and animals.
  • They are mostly made up of carbon, oxygen, hydrogen and nitrogen.
  • Proteins, carbohydrates, lipids, and nucleic acids [DNA and RNA] are Macromolecules or Macro-biomolecules.
  • Other small molecules such as vitamins, primary metabolites, secondary metabolites, etc. are also biomolecules.
  • Most biomolecules are organic compounds.

Metabolism == the chemical processes that occur within a living organism to maintain life.

Metabolite == a substance formed in or necessary for metabolism.

Primary metabolite == Metabolite that is directly involved in normal growth, development, and reproduction. Eg: ethanol, lactic acid, and certain amino acids.

Secondary metabolite == Metabolites that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolites does not result in immediate death, but rather in long-term impairment. Eg: ergot alkaloids, antibiotics, etc.

Alkaloid == any of a class of nitrogenous organic compounds of plant origin which have pronounced physiological actions on humans. Eg: morphine obtained from opium poppy.

Eukaryotic Cell Walls

Eukaryotic organisms, such as algae, fungi, and higher plants, have multilayered cell walls composed in large part of either cellulose or chitin . Cellulose and chitin are polysaccharides , meaning they are composed of many linked sugar molecules. Cellulose is a polymer of glucose , which contains only carbon, hydrogen, and oxygen, while chitin is a polymer of N-acetylglucosamine, a sugar that contains nitrogen as well. Both cellulose and chitin are linear, unbranched polymers of their respective sugars, and several dozen of these polymers are assembled into large crystal-like cables, called microfibrils, that spool around the cells.

Cellulose microfibrils form the scaffold of all plant cell walls. At least two types of primary walls are found among the species of flowering plants (angiosperms). In the Type I walls of eudicots and some monocots, the microfibrils are tethered together by sugars called xyloglucans, and this framework is embedded in a gel of pectins , another type of polysaccharide. The pectins establish several of the wall's physical characters, such as electrical charge, density, porosity, enzyme and protein distribution, and cell-to-cell adhesions . Pectins are used commercially to thicken jellies and jams. The Type II walls of cereal grains and other monocot relatives tether the microfibrils with different sugars, and is relatively pectin-poor. The hardness of wood comes from lignin , which is impregnated between the cellulose microfibrils. Lignin is a phenolic compound, chemically related to benzene.

The cell walls of fungi are diverse among the taxonomic groups, but most contain chitin microfibrils embedded in a polysaccharide matrix and covered with a loose coating of additional molecules combining sugars and peptides (amino acid chains). However, the cell walls of the Oomycetes contain cellulose instead of chitin. Different groups of fungi can be distinguished partly by the composition of their cell wall components.

Cellulose forms a substantial part of the microfibrillar framework of most algae, although some contain other polysaccharides instead. These microfibrillar networks are embedded in a thick gel of polysaccharides of immense diversity. Three important classes of algae, the Chlorophyceae (green), Rhodophyceae (red), and Phaeophyceae (brown), can be distinguished to a certain extent based on their polysaccharide constituents. Alginic acid and fucans are found in brown algae, whereas agarose and carrageenan are found predominately in red algae. Several of these polysaccharides are used as thickening and stabilizing agents in a variety of foods.


The bacteria are kept under the Kingdom Monera. They are prokaryotic and possess cell wall. The cell wall is composed of polysaccharides and amino acids. Bacteria can be autotrophic and heterotrophic. The autotrophic bacteria can be chemosynthetic or photosynthetic. The heterotrophic bacteria can be saprophytic or parasitic.

Based on their shape, bacteria are classified into four types:

  1. Spherical bacteria are called Coccus (pl.: cocci),
  2. Rod-shaped bacteria are called Bacillus (pl.: bacilli),
  3. Comma-shaped bacteria are called Vibrium (pl.: vibrio) and
  4. Spiral shaped bacteria are called Spirillum (pl.: spirilla)

Archaebacteria: These are believed to be the oldest living beings. The archaebacteria live in some of the harshest habitats like sulphur springs, volcanic crater, etc. The different structure of their cell wall helps them in surviving in extreme conditions. Based on their habitats, the archaebacteria are classified as follows:

  1. Halophiles: They live in extremely salty areas.
  2. Thermoacidophiles: They live in hot spring.
  3. Methanogens: They live in marshy areas. They also live in the guts of the ruminant animals. They are responsible for production of methane from the dung of these animals.

Eubacteria: They are also called the ‘true bacteria’. They possess a rigid cell wall, and a flagellum (in motile bacteria). The cyanobacteria are also called ‘blue-green algae’ because they contain chlorophyll. The cyanobacteria can be unicellular or filamentous. They can live solitary or in colonies. The colony of cyanobacteria is usually surrounded by a gelatinous sheath. Some of the cyanobacteria are capable of nitrogen-fixation, e.g. Nostoc and Anabaena.

Heterotrophic: These are the most abundant organisms in nature. Most of them have economic significance for human beings. While many of them are beneficial for humans, many others are quite harmful.

Reproduction in Bacteria:

Bacteria usually reproduce by binary fission. Under unfavourable conditions, they reproduce by spore formation. They also reproduce by adopting a primitive type of DNA transfer from one bacterium to another. This is similar to sexual reproduction.