Question

Can someone please help with questions 14, 16,& 20

Name two sulfur amino acids. IgG. IgA and IgM antibodies are proteins that arc stabilized by disulfide bonds. Explain the formation of this type of bond and the type. Explain one of the posttranslational modification that happens to collagen. Deficiency of Vitamin C (ascorbate) can cause Scurvy. Explain the mechanism. D-serine is a neurotransmitter. Explain the stereochemistry and the enzymatic conversion of substrate into product. Methionine can also be classified as an _____ amino acid in terms of its physical property. Describe the posttranslational modification of Histone proteins. Explain the physical changes that would happen upon phosphorylation, acetylation and methylation of lysine and arginine residues of histone proteins. Prothrombin, one of the clotting factor is post translationally modified by ____ and it allows the protein to form _____ interaction with _____. Gamma-Carboxylation of glutamate residues of prothrombin requires the cofactor _____. Whether a functional group is going to be protonated or deprotonated depends the _____ value of the compound and the _____ of the medium/solvent. Imidazole ring of histidine residue of proteins can engage in acid-base catalysis effectively under physiological conditions of the cell. Explain.

Answer 1

14. Background knowledge: Stereochemistry is the study of isomers, which are molecules with the same atoms (elements) and in the same amount( same molecular formula), but ordered differently (in a different spatial location). D-Enantiomers are molecules with a chiral atom that are mirror images, and therefore can't overlap, in the same sense as the right feet wouldn't fit in the left shoe. D-Serine is a dextro isomer (amino group on the right side of the chiral carbon) of serine, being L-serine the common form. It's a glycine agonist (same response) that binds to the N-methyl-D-aspartate receptor (NMDAR), and in fact, it triggers a more potent response than glycine itself. Hypofunction of NMDA neurotransmission has been found to be linked to schizophrenia, therefore D-serine administration has been used as treatment. D-serine is one of the few Da amino acids that naturally exist in humans. D-serine is synthesized from L-serine by serine racemase (SRR).

16. Posttranslational modification refers to the changes that a protein suffers after being synthesized. Both amino acids, lysine, and arginine carry a positive charge. Phosphorylation: A kinase transfer a phosphate to the target amino-acid of the histone, which adds significant negative charge to the histone. As DNA has a negative charge, this will cause the DNA to loose around that histone, which gives space for transcription factors to bind, increasing gene expression. Acetylation: histone acetyltransferases transfer of an acetyl group to the target amino-acid on the side chain, which neutralizes lysine/arginine's positive charge, weakening the histone-DNA interaction, increasing gene expression. Methylation: As methylation doesn't change the charge, it can either repress (lysine 9) or allow (Lysine 4) gene expression.

20. The imidazole ring in the side chain of histidine has by far the highest catalytic propensity of all the amino acids, due to its unique property of having a pKa close to neutral (∼6-7), allowing the imidazole to interconvert between charged and uncharged forms and making it an ideal group for engaging in acid/base catalysis at neutral pH.