12.2: Amino acid synthesis families - Biology

12.2: Amino acid synthesis families - Biology

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12.2: Amino acid synthesis families

Biology MCQ-06: Biochemistry: Amino Acids: Part 2 for JRF/NET Life Science Examination

(1). Which amino acid, among the 20 standard protein coding amino acids, is most abundantly occurs in proteins?
a. Glycine
b. Methionine
c. Serine
d. Leucine

(2). Which of the following amino acid is having more polarity?
a. Lysine
b. Arginine
c. Histidine
d. Aspartate

(3). Majority of enzyme’s active site usually contain one or more _____ residues.
a. Glycine
b. Tryptophan
c. Histidine
d. Arginine

(4). The following is the amino acid sequence of an alien polypeptide: ‘ AGQHIK X SKPWYVGLBUFF ’. The ‘ X ’ in the given sequence represents ___________.
a. Asparagine
b. Isoleucine
c. An ambiguous amino acid
d. An unknown amino acid

(5). Amino acid acting as a defensive molecule in plants:
a. Canavanine
b. Con-canavalin
c. Proline
d. All of these

(6). Which amino acid act as the precursor for the synthesis of the neurotransmitter serotonin?
a. Tyrosine
b. Tryptophan
c. Glycine
d. Arginine

(7). _____ is an exclusively ketogenic amino acid in human.
a. Valine
b. Methionine
c. Leucine
d. Proline

(8). pI of ___________ is near to physiological pH.
a. Lysine
b. Histidine
c. Arginine
d. Glutamic acid

(9). Which amino acid act as the precursor of dopamine?
a. Glycine
b. Aspartate
c. Valine
d. Tyrosine

(10). What is the molecular weight of Tryptophan?
a. 202 g.mol -1
b. 204 g.mol -1
c. 206 g.mol -1
d. 208 g.mol -1

(11). Amino acid which act as the precursor of IAA (indole 3-acetic acid) biosynthesis in plants is_____.

a. Tyrosine
b. Phenylalanine
c. Tryptophan
d. Methionine

(12). Amino acid involved in urea cycle____.

a. Ornithine
b. Citrulline
c. Arginine
d. Both (a) and (b)
e. All of these

(13). Which of the following amino acid have the buffering capacity at physiological pH?

a. Lysine
b. Arginine
c. Histidine
d. Aspartic acid

(14). Amino acid which act as the precursor of epinephrine synthesis is_____.

a. Glycine
b. Aspartate
c. Tyrosine
d. Valine

(15). Which amino acid act as the precursor of nitric oxide biosynthesis in animals?

a. Phenyl alanine
b. Arginine
c. Aspartate
d. Ornithine

(16). Which of the following is an essential amino acid?

a. Aspartic acid
b. Alanine
c. Leucine
d. Asparagine
e. All of these

(17). Which of the following is a non-essential amino acid?

a. Alanine
b. Histidine
c. Lysine
d. Methionine
e. All of these

(18). Which of the following amino acid is coded by a single codon?

a. Lysine
b. Arginine
c. Tryptophan
d. Phenylalanine

(19). First discovered amino acid is ____.

a. Asparagine
b. Aspartate
c. Glutamate
d. Glutamine

(20). Among the 20 standard protein coding amino acids, which was the last discovered amino acid?

a. Leucine
b. Isoleucine
c. Threonine
d. Serine

Answers with explanations

(1). Ans. (d). Leucine

(2). Ans. (b). Arginine

(3). Ans. (c). Histidine

Histidine has its pI near to physiological pH. The best buffering activity of an amino acid is at a pH which is equal to or near to its pI value (= isoelectric pH). Furthermore, an amino acid at its pI will be in zwitter ionic form and there it can act as both proton donor (acid) and proton acceptor. Since histidine’s pI is near to physiological pH, it can act as a good proton donor and proton acceptor at this pH. This is why the active site of many enzymes contains one or more histidine residues since most of the enzymatic reactions involve exchange of protons and electrons between enzyme and substrates.

Diethylpyrocarbonate (DEPC) which is used in laboratories to inactivate RNase enzyme will inactivate histidine residues in the active site and thereby it deactivate the enzyme.

(4). Ans. (d). An unknown amino acid

(5). Ans. (a). Canavanine

Concanavalin A (ConA) is a lectin isolated from a legume, jack bean (Canavalia ensiformis)

Lectins are protein which specifically binds to carbohydrates.

(6). Ans. (b). Tryptophan

(7). Ans. (c). Leucine

Leucine and lysine are the two amino acids in human which are exclusively ketogenic.

(8). Ans. (b). Histidine

(9). Ans. (d). Tyrosine

(10). Ans. (b). 204 g.mol-1

Tryptophan is the largest amino acid among ‘magic 20’.

Pyrrolysine is the largest proteinogenic amino acid with a molecular mass 255 g.mol -1

(11). Ans. (c). Tryptophan

Indole-3-acetic acid is the naturally occurring auxin in plants. Several pathways of auxin biosynthesis in plants are known and in most of them, tryptophan acts as the precursor. Tryptophan independent biosynthesis of auxin is also known to science now. IAA is synthesized from the indole ring of tryptophan in the young leaves and shoots.

(12). Ans. (e). All of these

Urea cycle (also called ornithine cycle): a biochemical cycle in many animals including human to produce urea from ammonia. Urea cycle was the first discovered metabolic cycle by Hans Krebs and Kurt Henseleit in1932.

(13). Ans. (c). Histidine

Amino acids have best buffering activity in a pH equal to its pI. At this pH amino acids will be zwitter ionic in nature (with net charge zero) and they can act as both proton donor (acid) and proton acceptor (base). The pI of histidine is near to physiological pH and thus histidine can act as a good buffer at physiological pH (7.20 – 7.40).

(14). Ans. (c). Tyrosine

(15). Ans. (b). Arginine

Nitric oxide (NO) is one of the gaseous bio-signaling molecules in the cell. It is also called as Endothelium Derived Relaxing Factor (EDRF). NO is synthesized from the amino acid arginine by the enzyme nitric oxide synthase in the endothelial cells of blood vessels. NO is a vasodilating agent and it relaxes the smooth muscle cells and thereby enhances blood flow through blood vessels.

(16). Ans. (c). Leucine

(17). Ans. (a). Alanine

(18). Ans. (c). Tryptophan

(19). Ans. (b). Aspartate

Aspartate was discovered from Asparagus racemosus by Plisson in 1827.

(20). Ans. (c). Threonine

Threonine was discovered in 1930 by William Cumming Rose

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Molecular Biology of the Cell. 4th edition.

All eucaryotic cells have an endoplasmic reticulum (ER). Its membrane typically constitutes more than half of the total membrane of an average animal cell (see Table 12-2). The ER is organized into a netlike labyrinth of branching tubules and flattened sacs extending throughout the cytosol (Figure 12-35). The tubules and sacs are all thought to interconnect, so that the ER membrane forms a continuous sheet enclosing a single internal space. This highly convoluted space is called the ER lumen or the ER cisternal space, and it often occupies more than 10% of the total cell volume (see Table 12-1). The ER membrane separates the ER lumen from the cytosol, and it mediates the selective transfer of molecules between these two compartments.

Figure 12-35

Fluorescent micrographs of the endoplasmic reticulum. (A) Part of the ER network in a cultured mammalian cell, stained with an antibody that binds to a protein retained in the ER. The ER extends as a network throughout the entire cytosol, so that all (more. )

The ER has a central role in lipid and protein biosynthesis. Its membrane is the site of production of all the transmembrane proteins and lipids for most of the cell's organelles, including the ER itself, the Golgi apparatus, lysosomes, endosomes, secretory vesicles, and the plasma membrane. The ER membrane makes a major contribution to mitochondrial and peroxisomal membranes by producing most of their lipids. In addition, almost all of the proteins that will be secreted to the cell exterior—plus those destined for the lumen of the ER, Golgi apparatus, or lysosomes𠅊re initially delivered to the ER lumen.


A physiologically-significant increase in the rate of muscle protein synthesis requires adequate availability of all amino acid precursors. The source of EAAs for muscle protein synthesis in the post-absorptive state is the free intracellular pool. Intracellular free EAAs that are available for incorporation into protein are derived from muscle protein breakdown. Under normal conditions about 70% of EAAs released by muscle protein breakdown are reincorporated into muscle protein. The efficiency of reincorporation of EAAs from protein breakdown back into muscle protein can only be increased to a limited extent. For this fundamental reason, a dietary supplement of BCAAs alone cannot support an increased rate of muscle protein synthesis. The availability of the other EAAs will rapidly become rate limiting for accelerated protein synthesis. Consistent with this perspective, the few studies in human subjects have reported decreases, rather than increases, in muscle protein synthesis after intake of BCAAs. We conclude that dietary BCAA supplements alone do not promote muscle anabolism.

Applications of synthetic peptides

The invention of peptide synthesis in the fifties and sixties spurred the development of different application areas in which synthetic peptides are now used, including the development of epitope-specific antibodies against pathogenic proteins, the study of protein functions and the identification and characterization of proteins. Furthermore, synthetic peptides are used to study enzyme-substrate interactions within important enzyme classes such as kinases and proteases, which play a crucial role in cell signaling.

In cell biology, receptor binding or the substrate recognition specificity of newly discovered enzymes can often be studied using sets of homologous synthetic peptides. Synthetic peptides can resemble naturally occurring peptides and act as drugs against cancer and other major diseases. Finally, synthetic peptides are used as standards and reagents in mass spectrometry (MS)-based applications. Synthetic peptides play a central role in MS-based discovery, characterization and quantitation of proteins, especially those that serve as early biomarkers for diseases.

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The synthesis of an unnatural amino acid, 1-amino-3-[2-(1,7-dicarba-closo-dodecaboran(12)-1-yl)ethyl]cyclobutanecarboxylic acid, was achieved. This new potential BNCT agent was prepared via the monoalkylation of m-carborane with 4-bromobutene to produce 4-m-carboranyl-1-butene, which was then subjected to a 2 + 2 cycloaddition using dichloroketene. The resultant boronated cyclobutanone was reductively dechlorinated prior to the formation of the corresponding hydantoin, which was hydrolized to the title compound in excellent yield.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Watch the video: Amino acids: Building Blocks of Proteins (May 2022).