Ch 1: Amino Acids, Peptides, Proteins Flashcards
amino acids have 4 groups attached to the central alpha carbon
amino group
carboxylic acid group
hydrogen atom
R group
___ amino acids appear in the proteins of eukaryotic organisms
20
stereochemistry of alpha carbon for all aa in euk is
L
D-amino acids exist in
prokaryotes
all aa except ___ have (S) configuration
cysteine
all aa except ___ are chiral
glycine
nonpolar, nonaromatic
glycine alanine valine leucine isoleucine methionine proline
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Aromatic aa
Phenylalanine
Tyrosine
Tryptophan
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Polar aa
Serine Glutamine Threonine Asparagine Cysteine
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Positively Charged - basic aa
Lysine
Arginine
Histidine
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Negatively Charged - acidic aa
Aspartate
Glutamate
DE
pKa of a group is the pH at which half of the species is ____ ; HA = A-
deprotonated
aa exist in different forms at diff pH
low acidic pH, aa ___
pH near pI of aa ___
high alkaline pH, aa __
fully protonated
neutral zwitterion
fully deprotonated
isoelectric point (pI) of an aa w/o charged group can be calculated by
averaging the 2 pKa values
aa can be titrated:
titration curve nearly flat ____
nearly vertical when at the ____
at pKa values of the aa
pI of the aa
aa with charged side group can find pI by calculating
the average of two pKas of protonation/deprotonation of zwitterion
aa w/o charged sides have pI around
6
aa acidic have pI around
well below 6
aa basic have pI
well above 6
dipeptides have __ aa residues
tripeptides have __
oligopeptides ___
polypeptides __
2
3
less than 20
more than 20
forming a peptide bond is a
condensation or dehydration reaction
releasing one molecule of water
amide bonds are rigid due to
resonance
breaking a peptide bond is a
hydrolysis reaction
primary structure
linear seq of aa in a peptide and is stabilized by peptide bonds
secondary structure
local structure of neighboring aa, and is stabilized by h bonding between amino groups and nonadjacent carboxyl groups
2nd struc: alpha helices
clockwise coils around a central axis
2nd struc: beta pleated sheets
rippled strands that can be parallel or anti-parallel
proline can interrupt ___ because of rigid ___
2nd structure
cyclic structure
tertiary structure
3D shape of a single polypeptide chain and is stabilized by hydrophobic interactions, acid-base interactions (salt bridges), hydrogen bonding, and disulfide bonds
(3) hydrophobic interactions push hydrophobic R group to interior of protein which
inc entropy of the surrounding water molecules and creates a neg gibbs free energy
disulfide bonds (3)
occur when 2 cysteine molecules are oxidized and create a covalent bond to form cystine
quaternary structure is the interaction
between peptides in proteins that contain multiple subunits
can lead to denaturation of 3-D protein structure
heat and increasing solute conc
proteins w covalently attached molecules are ___ and the attached molecule is a ____ that may be _______
conjugated proteins
prosthetic group
metal ion, vitamin, lipid, carbohydrate, nucleic acid
