Skip to content
Login Register

#amino acid

41 public questions tagged with this topic.

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.

View Details
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 selenocysteine UGA recoding, illustrating dynamic codon redefinition regulated by metabolic state. Genome annotation reveals specialized amber codons within mtmB, mtbB, mtcB genes persisting despite termination signal in standard tables.

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

View Details
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, permitting methane formation. Limited distribution but strong catalytic benefit suggests evolutionarily recent codon capture where stop reassignment provided selective advantage for specialized anaerobic metabolism in niche environments.

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

View Details
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 element via selenophosphate pathway, not post-translational sulfur substitution. Similarity permits substitution maintaining tertiary fold but dramatically alters redox potentials and enzymatic rate acceleration crucial for antioxidant defense.

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

View Details
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 codon fidelity guided by Kozak context.

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

View Details
Translation in Prokaryotes and Eukaryotes

Initiator tRNA in prokaryotes carries which amino acid?

In prokaryotes, initiator tRNA is first aminoacylated with methionine then formylated at alpha-amino group by methionyl-tRNA formyltransferase using formyl-tetrahydrofolate as donor, generating N-formyl-methionine. Formylation blocks free amino terminus ensuring it can only form peptide bond as donor at N-terminus, establishing directionality, and enhances binding to IF2 and P site with higher initiation efficiency. After nascent chain emergence, peptide deformylase removes formyl group and methionine aminopeptidase may excise methionine, revealing mature N-terminus for many cytosolic proteins. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.

Ref: Watson Molecular Biology of the Gene, 7th ed., Chapter 15, Prokaryotic initiator fMet-tRNA and formylation by FMT

View Details
Mass Spectroscopy

Which amino acid has monoisotopic mass of 147.07?

Aromatic amino acids exhibit larger masses due to phenyl rings and contribute distinctive residues in peptide spectra. Phenylalanine molecular weight is 165.07 Da, residue mass after dehydration is 147.07 Da after subtracting water. Tyrosine residue mass is 163 Da, tryptophan 186 Da, histidine 137 Da. Observing mass difference of 147 Da between successive fragment ions indicates phenylalanine at that position during de novo sequencing. High-resolution mass spectrometry distinguishes phenylalanine from oxidized methionine which is isobaric near 147.03 Da, requiring accurate mass measurement for confident assignment in proteomics, critical for protein identification accuracy.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details
Mass Spectroscopy

Which amino acid has a monoisotopic residue mass of 99 Da?

Amino acid residue mass equals monoisotopic molecular mass minus water lost during peptide bond formation. Valine molecular mass is 117.07 Da; subtracting 18.0106 Da for H2O yields 99.06 Da residue mass. Lysine residue is 128 Da, glycine 57 Da, serine 87 Da. This 99 Da value creates diagnostic mass difference between consecutive b or y ions in tandem mass spectra when valine is present in sequence. Knowledge of residue masses enables manual de novo sequencing, validation of proteomic database search results, and understanding of mass spectrometry fragmentation ladders in peptide identification.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details
X Ray, IR Spectroscopy

Which amino acid has residue mass 147 Da in MS?

In peptide mass spectrometry, residue mass equals amino acid monoisotopic molecular mass minus mass of water eliminated during peptide bond formation, 18.015 Da. Phenylalanine molecular mass is 165.19 Da; subtracting water yields residue mass approximately 147.18 Da. This value is distinct from tyrosine residue 163 Da, arginine 156 Da and methionine 131 Da, allowing unambiguous assignment. Characteristic phenylalanine immonium ion at m/z 120 further confirms presence. Knowledge of residue masses enables database searching, de novo sequencing and accurate interpretation of b- and y-ion series in tandem spectra from proteolytic digests.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details
Amino Acids Structure

Which amino acid is the precursor of urea in the urea cycle?

Arginine is the correct answer because it serves as the specific precursor, synthetic product, or metabolic intermediate described in this question. Biosynthetic pathways in Amino_Acids_Structure follow precise enzymatic steps where specific substrates are converted to products through regulated metabolic reactions. Arginine occupies a key position in this metabolic pathway due to its chemical structure and reactivity. The other options (Glutamine, Asparagine, and Ornithine) are involved in different biosynthetic routes, serve as precursors for different end products, or participate in unrelated metabolic conversions.

Ref: Campbell Biology, Urry et al., 12th Ed.

View Details
Amino Acids Structure

Which amino acid contains a pyrroline ring in its structure?

Pyrrolysine accurately describes the structural composition or molecular organization asked about in this question. In Amino_Acids_Structure, knowledge of molecular structure is directly linked to understanding biological function. The specific arrangement of chemical components in Pyrrolysine determines its physical properties, biological activity, and interactions with other molecules. The other options (Proline, Ornithine, and Lysine) describe different structural arrangements, incorrect stoichiometry, or compositions of different biological molecules.

Ref: Campbell Biology, Urry et al., 12th Ed.

View Details
Amino Acids Structure

Which amino acid is the major contributor to protein fluorescence?

Phenylalanine is the scientifically accurate answer to this question. Within the study of Amino_Acids_Structure, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Phenylalanine directly address what is being asked. Among the other options, Tyrosine, Tryptophan, and Histidine do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

View Details