Topic 3 Flashcards
conformation
spatial arrangement of proteins
3D structure of a protein determined by?
amino acid sequence
stabilization of protein structure
non-covalent interactions
protein functions
enzyme catalysis protein-protein/carb/lipid interaction transport structural support buffer signal transduction
non-covalent interactions
hydrogen bonds
ionic bonds
hydrophobic interactions
structural protein classification
fibrous
globular
intergral
fibrous proteins
insoluble
supports structure
e.g. collagen, keratin
globular proteins
water soluble
e.g. myoglobin, hemoglobin
integral membrane proteins
embedded in membrane
supports structure and/or function or both
e.g. membrane bound enzymes, receptors, ion channels
amino acid polymerization
condensation reaction to form peptide bond
water released
protein configuration
carbonyl & amino groups have trans configuration d/t partial double bonds
exception: proline has cis configuration (6%)
primary structure
amino acid sequence of its poly peptide chains
derived by covalent peptide bond formation; disulfide linkage
change can alter biologic activity
secondary structure
3D structure w/o regard to the conformation of side chains
2 types: α-helix, β-sheet
hydrogen bonds cause bends/folds
α-helix
spiral configuration
side chains directed outward
stabilized by hydrogen bonds
right-handed more thermodynamically stable
β-sheet
laterally stacked chains extended not condensed
proline must be present
glycine often found w/in 4 positions of proline
antiparallel β-sheet
strands that extend in opposite directions
most stable
parallel β-sheet
strands that extend in the same direction
less stable d/t distorted H-bonding
mixed β-sheet
common, consisting of both parallel and antiparallel sheets
tertiary structure
overall 3D structure
helices and sheets combined to form motifs
quaternary structure
3D arrangement composed of multi polypeptides
subunits joined by non covalent interactions
disulfide linkages sometimes formed
e.g. hemoglobin, insulin, collagen, immunoglobulins
native proteins
proteins in their functional and folded conformations
marginally stable at physiologic conditions
function of structure in native proteins
specific structural stability
specific functions
solubility
fluctuating flexibility of conformation allowing diffusion of small molecules
denaturation
loss of native structure
denaturation factors
heat
pH
certain reagents (detergent/bile salt, urea, alcohols, weak bless, some non-enzymatic modifications)
polypeptide folding
fold rapidly in a systematic stepwide manner
some undergo assisted folding
defective folding results in diseases
renature
under proper conditions, unfolded proteins can refold spontaneously
permanent denaturation
extreme pH
heat (>100C)
myoglobin
monomer (single polypeptide) muscle tissue oxygen STORAGE Fe2+ can bind one O2 higher affinity for O2 releases O2 when tissue becomes hypoxic hyperbolic O2 saturation curve
heme
present in myoglobin, hemoglobin, and other proteins
oxygen can bind to a heme prothetic group
metmyoglobin
oxidized myoglobin
cannot bind oxygen
hemoglobin
tetramer
RBCs
oxygen TRANSPORT
binds 4-O2 molecules (allosteric, cooperative binding)
high affinity O2 in lungs, low affinity O2 in tissue
sigmoidal O2 saturation curve
right shift Bohr effect
decrease pH increase PCO2 increase temp increase 2,3-BPG reversed in lungs
effect of pH
decrease in pH promotes release of O2
effect of 2,3-biphosphoglycerate
product of glycolysis
binds to deoxyhemoglobin
decreases O2 binding affinity of Hb
left shift Bohr effect
increase pH
decrease PCO2
decrease temp
decrease 2,3-BPG
fetal hemoglobin (HbF)
tetramer of α2γ2
does not bind 2,3-BPG
higher affinity for O2 than HbA
sickle cell hemoglobin (HbS)
tetramer of α2β2
one nucleotide change in the β-change:
glutamate –> valine at position 6
β-chain of HbS has very low affinity for O2
