Proteins Flashcards
proteins
- polymers composed of AA
- provide structure, regulate metabolism, hormone control, catalyst
amino acids
-amine group and carboxyl group attached to am alpha carbon (w an R group)
Fischer projection of an AA
drawn with the amino group on the left (L-enantiomer)
zwitterions
-AA in the form of a neutral ion, having both positive and negative charges
amphoteric
-AA act as either bases or acids depending on the environment
isoelectric point (pI)
-intermediate pH at which the AA is electrically neutral
titration of AA
- when adding base, the carbonyl group loses its proton first, then the amino group loses its acidic proton
- 2 moles of base must be added to deprotonate one mol of AA
- buffering capacity is greatest at the 2 dissociation constants (Ka1 and Ka2)
Henderson-Hasselbalch equation
pH=pKa+log([CB]/[CA])
non polar AA
- R-groups are saturated hydrocarbons
- hydrophobic
polar AA
- R-groups are polar, uncharged
- hydrophilic
acidic AA
- R-group contains a carboxyl group
- negative charge
basic AA
- R-group contains an amino group
- positive charge
peptides
-composed of AA subunits (residues) linked by peptide bonds
reactions of peptides
-peptide bonds b/w carboxyl group and amino group is formed via condensation reaction (water is lost)
trypsin
protein that cleaves at the carboxyl end of arginine and lysine
amino-terminal (N-terminal)
terminal AA with a free alpha-amino group, on left
carboxyl-terminal (C-terminal)
terminal with a free carboxyl group, on right
primary structure of proteins
-sequence of AA
determined using a lab procedure called sequencing
secondary structure
- local structure of the neighboring AA, governed by H bond interactions
- alpha helix and beta sheet
alpha helix
-rod-like structure in which the peptide. chain coils clockwise, H bonds b/w carboxyl O atoms and amine H atoms 4 residues away
beta pleated sheet
- peptide chains lie along each other in rows; rippled
- H bonds b/w carbonyl O atoms and amine H atoms
tertiary structure
-3D shape of the protein
disulfide bond
2 cysteine molecules become oxidized to form cystine, create loops in tertiary structure
fibrous proteins
- sheets or long strands
- collagen
globular protein
- spherical in shape
- myoglobin
quaternary structure
- ways in which more than one polypeptide subunit arranges
- ex: Hb
conjugated proteins
-derive part of their function from covalently attached molecules called prosthetic groups (at least one portion is not made of protein)
lipoproteins, glycoproteins, and nucleoproteins
proteins with lipid, carbohydrate, and nucleic acid prosthetic groups
denaturation (melting)
-process in which proteins lose their 3D shape and revert to random-coil state
renature
-regain structure and function if the reagent is removed
