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#amino acid

48 public questions tagged with this topic.

Biochemistry

Which one of the following side chains of an amino acid is responsible for fluorescence in proteins?

This outcome reflects enzyme catalysis and lipid structure, where substrate affinity, transition state stabilization and phospholipid composition govern function. Option A captures this correctly because it reflects catalytic efficiency and membrane organization, consistent with textbook descriptions and experimental observations in biochemistry.

Ref: Lehninger Principles of Biochemistry, Chapter 9, Lipids and Membranes, explains phospholipid components, glycerol, fatty acids, phosphate group and membrane structure providing foundation for lipid biochemistry.

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Biochemistry

Which one of the following amino acids is the most effective contributor of protein buffer?

In biochemistry, enzyme catalysis and lipid structure dictates that substrate affinity, transition state stabilization and phospholipid composition govern function. Therefore Histidine is correct as it reflects catalytic efficiency and membrane organization, supported by mechanistic studies and conserved across related systems.

Ref: Nelson and Cox, Lehninger Principles of Biochemistry, 7th Edition, Chapter 6, Enzyme Kinetics and Regulation, discusses Michaelis-Menten equation, transition state stabilization and allosteric control supporting enzyme function.

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Biochemistry - Part 2

In the active site of Transaldolase, which amino acid forms the Schiff base?

Mechanistically, enzyme catalysis and lipid structure involves substrate affinity, transition state stabilization and phospholipid composition govern function. This validates Lysine because it reflects catalytic efficiency and membrane organization, a pattern repeatedly demonstrated in biochemistry research.

Ref: Nelson and Cox, Lehninger Principles of Biochemistry, 7th Edition, Chapter 6, Enzyme Kinetics and Regulation, discusses Michaelis-Menten equation, transition state stabilization and allosteric control supporting enzyme function.

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Biochemistry

Which one of the following amino acids has pKa value near physiological pH?

This outcome reflects enzyme catalysis and lipid structure, where substrate affinity, transition state stabilization and phospholipid composition govern function. Option A captures this correctly because it reflects catalytic efficiency and membrane organization, consistent with textbook descriptions and experimental observations in biochemistry.

Ref: Lehninger Principles of Biochemistry, Chapter 9, Lipids and Membranes, explains phospholipid components, glycerol, fatty acids, phosphate group and membrane structure providing foundation for lipid biochemistry.

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Biochemistry

Which of the following amino acids is critical in the folding of proteins due to the slow isomerization of the peptide b

The principle of enzyme catalysis and lipid structure explains that substrate affinity, transition state stabilization and phospholipid composition govern function. Hence Proline fits best because it reflects catalytic efficiency and membrane organization, as documented in authoritative sources on biochemistry.

Ref: Berg et al., Biochemistry, 9th Edition, Chapter 13, Metabolism and Bioenergetics, covers glycolysis, citric acid cycle, oxidative phosphorylation and NADH-linked reactions detailing biochemical principles.

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Animal Tissue Culture 1

Which amino acid is a major energy source for cultured cells?

Glutamine addiction phenomenon observed in many cultured lines including HeLa, HEK293, and cancer cells reflecting elevated anaplerotic demand beyond energy generation. Glutaminase isoforms GLS kidney-type and GLS2 liver-type localized in mitochondria inner membrane convert L-glutamine to glutamate releasing ammonia via deamidation, glutamate dehydrogenase GDH or aminotransferases aspartate transaminase, alanine transaminase produce alpha-ketoglutarate feeding tricarboxylic acid cycle generating ATP via oxidative phosphorylation plus citrate exported via mitochondrial citrate carrier for ATP c

Ref: Newsholme Q J Exp Physiol 2003 glutamine anaplerosis TCA mTOR; Lodish MBoC GlutaMAX stable dipeptide ammonia avoidance.

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Lipid Link Protein

Which amino acid is commonly involved in myristoylation?

N-myristoylation is co-translational irreversible modification attaching 14-carbon saturated fatty acid myristate from myristoyl-CoA to target protein. N-myristoyltransferase NMT recognizes N-terminal sequence Met-Gly-X-X-X-Ser/Thr after methionine aminopeptidase removes initiator methionine, exposing glycine at position 2 for amide bond formation. The glycine requirement is absolute; replacement with other residues abolishes myristoylation. Myristate anchor provides weak membrane affinity that often cooperates with additional palmitoylation or polybasic cluster to stably tether proteins to in

Ref: Resh, Biochim Biophys Acta 1999, N-myristoylation mechanisms; Farah et al., J Biol Chem 2020, NMT specificity.

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MOLECULAR EVOLUTION

Conservative amino acid substitution changes:

Biochemical properties reflects key principle in quiz on molecular evolution, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Biochemical properties aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Biochemical properties fits helps integrate natural selection, environment.

Ref: Li, Molecular Evolution, Neutral Theory and Molecular Clocks.

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Eukaryotes gene regulation

Pyrrolysine is encoded by which codon?

In most organisms UAG amber codon terminates translation via release factor RF1 or eRF1 mediated hydrolysis. Methanogenic archaea capable of methylamine metabolism recode specific UAG codons to pyrrolysine when downstream PYLIS element and high PylRS levels present. Release factor competition determines outcome; high Pyl-tRNAPyl availability favors elongation producing full-length methyltransferase essential for methanogenesis from methylamines. Remaining genomic UAG instances still terminate translation normally, ensuring proteome integrity. This context-dependent reassignment parallels selen

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: Pyrrolysine Encoding by UAG Codon

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Eukaryotes gene regulation

Pyrrolysine is known as the

Genetic code expansion natural example pyrrolysine discovered in methylamine methyltransferase genes of methanogenic archaea and certain Gram-positive bacteria demonstrates additional proteinogenic amino acid beyond canonical twenty. Featuring bulky pyrroline ring connected via isopeptide bond to lysine epsilon-amino group, pyrrolysine designated twenty-second amino acid. Coding requires dedicated amber suppressor tRNAPyl and pyrrolysyl-tRNA synthetase PylRS recognizing UAG codon only within specific mRNAs. Incorporation expands catalytic versatility for methanogenesis from methylamines, permi

Ref: NCBI Bookshelf, Genetic Code Expansion: Pyrrolysine – 22nd Amino Acid Discovery

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Eukaryotes gene regulation

Selenocysteine contains which atom instead of sulfur?

Chemically selenocysteine represents cysteine analogue where chalcogen sulfur replaced by heavier selenium, generating selenol side chain -SeH instead of thiol -SH. Selenium larger radius, higher polarizability, pKa approximately 5.2 versus cysteine 8.3, rendering selenolate anion predominant at physiological pH, conferring superior nucleophilicity, leaving group ability, and resistance to irreversible overoxidation forming selenenic acid reversible. This explains enhanced catalytic rate of glutathione peroxidases, thioredoxin reductases, and deiodinases. Selenium originates from dietary trace

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 3: Selenocysteine – Selenium vs Sulfur Chemistry

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Translation in Prokaryotes and Eukaryotes

Initiator tRNA in eukaryotes carries

Eukaryotic cytosolic initiator tRNA carries unformylated methionine, distinguishing cytosolic machinery from bacterial and mitochondrial systems. Met-tRNAiMet is delivered by ternary complex eIF2 GTP Met-tRNAi to 40S P site within 43S pre-initiation complex during scanning initiation. Methionine remains first amino acid but often removed co-translationally by methionine aminopeptidases depending on second residue. Lack of formylation reflects distinct eIF2 recognition and insensitivity to initiator specific antibiotics, yet preserves N to C synthesis polarity and requirement for AUG start codo

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 7, Eukaryotic initiator Met-tRNAiMet without formylation

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