CHEN EXAM 1 Flashcards
C-C single bond length
1.5 A
C=C double bond length
1.3-1.4 A
hydrogen bond length in biosystem
2-4 A
optimum van der waals distance
4.5 A
hydrophobic interactions
powered by the increase of entropy in water (favors increase in entropy)
how can you deprotonate dsDNA?
heat or increase pH, pH 9.9 most strands denatured (thymine), at 9.7 about half (guanine)
down syndrome
trisomy 21, 3 copies of chromosome 21 due to chromosome segregation error
TATA-box Binding Protein (TBP)
molecular structure conserved among archebaterium, plants, and humans
amino acid ionization states
both protonated (in acidic conditions): NH3+ and COOH
zwitterionic: NH3+ and COO-
both deprotonated (in basic conditions): NH2 and COO-
hydrophobic amino acids
GAPLIVYMWF
guanine, alanine, proline, leucine, isoleucine, valine, tyrosine, methionine, tryptophan, phenylalanine
polar amino acids
STYNQC
serine, threonine, tyrosine, asparagine, glutamine, cysteine
basic amino acids
KRH
lysine, argenine, histidine
acidic amino acids
DE
aspartic acid, glutamic acid
histidine
acts like a physiological pH sensor, pKa=6
can accept or donate protons at this pH
cysteine cross-linking
oxidation can induce disulfide bonds between two cysteines
occurs in insulin
sickle cell
substitution of valine for glutamic acid
change in primary structure affects function
survived due to malaria advantage
cis/trans configurations of amino acids
based on if the alpha carbons are on the same side (split by peptide bond)
trans is lower energy and favored
proline configurations
cis and trans have similar steric clashes so both isomers exist, isomerase can convert the proline from one configuration to another
C-N peptide bond length
1.32 A
C=N bond length
1.27 A
C-N single bond length
1.49 A
which angles in amino acids can be rotated and which are fixed?
peptide bond (C-N) is fixed due to partial double bond character/resonance
alpha C and NH3 (phi) can rotate, -80
alpha C and COO (psi) can rotate, 85
ramachandran plot
illustrates favorable and possible torsion angles
torsion angles
phi and psi angles in amino acids
how many DIFFERENT proteins are there in 1 human cell?
10,000 - 30,000
levels of protein structure
1: AA N to C sequence
2: a helix or beta sheet via hydrogen bonding
3: 3D folding via side chain interactions (noncovalent bonds, Cys disulfide bonds)
4: interaction of tertiary structures of 2+ polypeptide chains
alpha helix characteristics
right handed coil with protruding R groups
CO and NH groups H bond
3.6 residues/turn (3.6 AA/turn)
1.5 A/residues-rise (height of one AA)
5.4 A/turn-pitch (height of one turn)
beta sheets
distance between adjacent AAs: 3.5 A
antiparallel or parallel or mixed
antiparallel arises by hairpin folding of a single strand
twisted sheets, hydrophobic/hydrophilic faces
how can primary structures predict secondary structures?
identifying amphipathic helix (alpha helix has both polar and non polar)
beta strands have hydrophilic and hydrophobic faces
chameleon sequences
can adopt alpha helix or beta strand in different contexts
reserve/beta/hairpin turn
C-O group of residue i is H-bonded to the N-H group of residue i+3
polypeptide loops
part of antibody molecule
lie on protein surfaces
participate in interactions between proteins
protein motifs
common combinations of secondary structure present in many proteins, usually similar function
ex. helix turn helix in DNA binding proteins
coiled-coils
two right-handed alpha helices intertwine and form a left-handed super helix
stabilized by ionic and VDWs
heptad repeat & leucine zipper
3.5 residues per turn
allows side chain pattern to repeat every 7 AAs
2 helices interact through leucine side chain
collagen
rich in gly and pro
3 helical polypeptide chains form a superhelical cable
substitution mutation of Gly –> osteogenesis imperfecta
hemoglobin structure
2 alpha-globin, 2 B-globin subunits = heterotetramer
icosahedron
example of quarternary structure, 4 subunits of 60 each
many viruses: rhinovirus, coronavirus