NUTR 3210 Study Guide - Final Guide: Post-Translational Modification, Selenocysteine, Zwitterion
28 Apr 2018
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Protein Metabolism
• What are some qualities of protein?
- ~16% of daily calories; we don’t need protein – we need AA
- 21proteinogenic AA refers to an AA that can be incorporated into a protein
during translation
- All but selenocysteine part of the standard genetic code
- 9 AAs are essential/ indispensable
• Is distribution of macronutrients in the body equal?
- Distribution is NOT HOMOGENOUS but highly variable b/w tissues.
• What are the two types of AAs in the body?
1) Proteinogenic AAs:
- aka Standard AAs
- 20 encoded directly in eukaryote genome (except selenocysteine)
2) Non-proteinogenic AAs:
- aka Non-standard AAs
- formed by post-translational modification of AAs
- rarely used to make protein
• What’s the deal with AA enantiomers?
- D vs. L enantiomers
- All standard AA exist as enantiomers (except Glycine)
- L form of AA = naturally occurring
- D form can be made by post translational modification
• What’s the deal with Zwitterions?
- At physiological pH, relatively polar structure = AAs are ionized; they have
protonated amino group + deprotonated carboxyl group.
- No overall charge (except R)
- Increased polarity (AA are hydrophilic) = react in acid or base
• Can the terms ‘peptide’ and ‘protein’ be used interchangeably?
- No, a peptide is the linear linkage of AA. A protein is the 3D shape.
find more resources at oneclass.com
find more resources at oneclass.com
• Describe the 3 structures of protein?
- Primary: the linear, polypeptide sequence of DNA. Determined by DNA
sequence. AAs held together by peptide bonds (C-N) mediated by chaperons.
Counting of AAs always starts at amino end.
- Secondary: a-helix + B-pleated sheets (parallel or anti-parallel). Formed by
interactions that have nothing to do with side chains = H2-bonds.
- Tertiary: arrangement of 2^ structures. Formed by interactions b/w side chains
= disulfide bridges. A single polypeptide chain. Hydrophobic AAs inside of
protein.
- Quaternary: combination of 2 or + 3^ structures required to make protein
functional (subunits). Not all proteins have 4^ structure. Forms a multi-subunit
complex (multiple polypeptides, = insulin).
• What’s the difference between Native vs Denatured protein?
- Native protein = a protein in its normal 3D configuration.
- Denaturing happens in many ways: pH – temp. – salt
- Denatures = loses bioactivity. Can only affect 2^,3^,4^ (NOT 1^)
- Native albumin in egg = transparent + liquid. Denatured = white + hard.
• Classify the AAs in terms of Essentiality (Define essentiality)
- Essential AA (Indispensable): not made by the body/ not made quickly enough
- 9 AAs: LYS – THR – ISO – LEU – MET – PHE – TRP – VAL – HIS.
- Conditionally indispensable (born w/ problem): not normally required in diet.
- Phenylketonuria: error of metabolism = can’t breakdown Phe Tyr
- Phe build-up = mental retardation = supplement Phe with Tyr
- Tyr = conditionally indispensable for this protein
- Acquired indispensable (develop problem): may become indispensable under
metabolic stress
- Liver disease = impairs Phe + Met catabolism
- Tyr + Cys synthesized from Phe + Met catabolism ∴ Tyr + Cys = indispensable
- Non-Essential (completely indispensable): Can be synthesized in body; not
essential in diet.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
~16% of daily calories; we don"t need protein we need aa. 21proteinogenic aa refers to an aa that can be incorporated into a protein during translation. All but selenocysteine part of the standard genetic code. Distribution is not homogenous but highly variable b/w tissues: what are the two types of aas in the body, proteinogenic aas: 20 encoded directly in eukaryote genome (except selenocysteine: non-proteinogenic aas: All standard aa exist as enantiomers (except glycine) L form of aa = naturally occurring. At physiological ph, relatively polar structure = aas are ionized; they have protonated amino group + deprotonated carboxyl group. No, a peptide is the linear linkage of aa. Primary: the linear, polypeptide sequence of dna. Aas held together by peptide bonds (c-n) mediated by chaperons. Counting of aas always starts at amino end. Secondary: a-helix + b-pleated sheets (parallel or anti-parallel). Formed by interactions that have nothing to do with side chains = h2-bonds.
