Proteins Flashcards
midterm 1
Protein roles in the body (6 of them)
- mechanical support
- control of growth & differentiation
- catalysis
- transport/storage
- nerve propagation
- immune protection
Protein roles in the eye (5 of them)
- support structure & clarity of the cornea
- participate in variable light refraction of the lens
- initiate transduction of light into electric signaling
- generate IOP
- lyse bacteria in the precornial tear film
peptide bond
-covalent bond between amino group of one AA and the carboxylate group of another
-dehydration synthesis (condensation rxn): H2O molecule is released
peptide bond properties in proteins
partial double-bond character, rigid and planar, trans configuration, uncharged but polar
what causes protein degradation in the body? lens? cornea?
- proteases
- caspases
- matrix metalloproteinases (MMP)
Protein structure
defines the function, determined by the sequence of AA
Primary structure of a protein
a unique sequence of amino acids
required for understanding:
1. structure of a protein
2. mechanism of action/function
3. relationship to other proteins w/ similar physiological roles
secondary structure of a protein
“local folding” from repeated H bonding within a chain
common arrangements: a-helix, B-pleated sheets
globular vs fibrous protein structure
globular: mixed secondary structure
fibrous: mainly one kind of secondary structure
alpha helix structure
- stabilized by hydrogen bonds between atoms of the polypeptide back bone
- very stable
- R-groups are outside the helix
-ex. keratin
Beta sheet
- H bonding to adjacent chains
-gives a flattened structure - either parallel or antiparallel
tertiary structure
-entire 3D structure of a single-chain polymer
-refers to final arrangement of domains
- stabilized by side chains: ionic bridges, H bonds, disulfide bonds, hydrophobic interactions
quaternary structure
spatial arrangement of a macromolecule’s individual subunits
protein denaturation definition
protein alteration from its native form
- unfolding and disorganization of a protein’s secondary, tertiary, and quaternary structures
- WITHOUT hydrolysis
protein denaturation causes and result
causes: heat, detergents, strong acids/bases
results: loses function, may be reversible though
molecular chaperones
chaperones bind reversibly to unfolded polypeptide segments and prevent misfolding/premature aggregation
heat shock proteins
major class of molecular chaperones
- synthesized in response to heat shock, or other stresses in cells
fibrous protein
proteins characterized by polypeptide chains in a stiff, elongated strand or sheet, tend to form fibers
fibrous examples and function
keratin, collagen, elastin
- resist stretching and provide shape and tensile strength
- structural role, rather than dynamic
collagen structure
collagen molecule: 3 alpha-chain polypeptides coiled around each other (triple helix)
collagen fibril: many collagen molecules
collagen fibers: may collagen fibrils
vit c in collagen
hydrolyzes proline to hydroxy proline, critical for collagen formation
type I collagen location
major connective tissues of skin, bone, tendon, blood vessels, and corneal stroma
type II collagen location
cartilage, vitreous
type III collagen location
found along type I in skin, arteries, and muscle, also in iris
type IV collagen location
basement membranes of various tissues (descemet’s membrane, lens capsule)
elastin
fibrous, insoluble protein, present w/ collagen in the CT
responsible for elasticity
elastic fibers: elastin core & microfibrils
marfan’s syndrome
mutations in the fibrillin gene causes autosomal dominant trait
clinical manifestations: disorders of cardiovascular, musculoskeletal, and ophthalmic systems
CT fibrous components
collagen & elastin
CT cellular components
fibroblasts, keratocytes
CT ground substance
GAG (glycosaminoglycans), proteoglycans, glycoproteins
- bind tissue together and provide support for the organs and other structures of the body
glycosaminoglycans (GAG) structure and classes (6)
long unbranched polysaccharides, highly hydrophilic
1. hyaluronate (vitreous humor)
2. chondroitin sulfate (vitreous humor)
3. dermatan sulfate (cornea)
4. keratan sulfate (cornea)
5. heparan sulfate
6. heparin
proteoglycans
core protein to which at least 1 GAG chain is covalently attached
participate w/ collagen and elastin, in the organization of the extracellular matrix
globular proteins
folded into a spherical shape, water-soluble protein characterized by a compact structure
globular protein functions (3 of them)
enzymes, transporters, regulatory proteins (metabolic pathways and gene expression)
Hemoglobin
brings O2 from the lungs to the tissue
4 subunits each containing a heme prosthetic group
- 4 binding sites, which are Fe
Heme
site for reversible oxygen binding
- Fe2+ for both hemoglobin and myoglobin
- Fe2+ is oxidized to Fe3+
-protein portion prevents permanent oxidation
hemoglobin binding
oxygen binding alters the structure of the entire hemoglobin
- T “taut” state (deoxyhemoglobin)
- R “relaxed” state (oxyhemoglobin)
- hemoglobin is an allosteric protein and has cooperative binding
T to R transition
iron shifts from being “domed” to being planar configuration
myoglobin
heme protein found in heart and skeletal muscle
acts as oxygen reservoir and oxygen carrier for O2 transport within muscle cells
myoglobin binding
one O2 binding site (1 heme molecule)
non-cooperative binding of oxygen
oxygen pressure on Hb rxn
rxn favors oxyhemoglobin w/ an increase in oxygen pressure (lungs)
rxn favors deoxyhemoglobin with decrease in oxygen pressure (tissues)
myoglobin vs hemoglobin curves
myoglobin: parabolic curve
hemoglobin: sigmoidal curve
sigmoidal curve means
cooperative interaction between binding sites
rightward curve means? caused by?
rightward shift means lower oxygen affinity
caused by “allosteric effectors”
1. increase in pCO2
2. increase in temp (exercise/fever)
3. decrease in pH (exercise)
4. increase in [2,3-BPG]
5. combo of these
2,3-biphosphoglycerate (2,3-BPG)
abundant in RBC’s
modulates oxygen dissociation from Hb
-binds to deoxy-Hg and stabilizes the T state, which decrease O2 affinity and promotes O2 release
leftward shift means? caused by?
means an increase of O2 affinity
caused by positive allosteric effectors or allosteric activators, ex. oxygen and carbon monoxide
Bohr effect
reduction in O2 binding w/ lowered pH (increased [H+]) or increased pCO2
-both stabilize the T-state
CO2 to bicarbonate
-for efficient transport, CO2 is converted to carbonic acid in the RBC’s by carbonic anhydrase
- then spontaneously loses a H+ to become bicarbonate
principal buffers in the blood
bicarbonate-carbonic acid: plasma
hemoglobin: RBC’s
Protein functional groups: both
flow of CO2 in the body
CO2 in tissues is converted to bicarbonate and transported to the lungs, then converted back to CO2 in the lungs and eliminated there
2 types of acidosis
acidosis: when pH <7.35
respiratory acidosis: can’t efficiently expire CO2 (acid) from lungs
metabolic acidosis: kidney’s reduced ability to retain bicarbonate (base)
2 types of alkalosis
alkalosis: when pH >7.45
metabolic alkalosis: kidney’s hyper ability to retain bicarbonate
respiratory alkalosis: eliminates too much CO2 from lungs
