Biochem Exam 2 - Protein function

what are all the functions of proteins?

transport, structural, motor function, catalysis, immunity, regulation of gene expression

function of myoglobin

transport o2 throughout muscles

function of hemoglobin

transport o2 through blood

function of actin

forms myofilaments

function of tubulin

forms microtubules

function of keratin

forms intermediate filaments found in hair, nails, and skin

function of collagen

major protein in connective tissue

function of myosin

interacts with actin to facilitate muscle movement

function of kinesin

moves along microtubules to help transport cellular cargo

explain catalysis

enzymes accelerate chemical reactions

what is a heme

o2 binding component of myoglobin and hemoglobin
prosthetic group - specifically porphyrin

what is a prosthetic group

organic molecules bound to a protein that aids in protein function

what is the structure of heme

a porphyrin ring with iron in the center
iron is chelated by four nitrogen atoms

how many coordinate bonds does iron form?

6 total
4 nitrogen
1 o2
1 histidine residue

what is the function of His residues on a heme

stabilize the heme-o2 interaction
F8 his = coordinates directly with iron
E7 his = helps stabilize the bound o2 molecule

what is anemia and how is it treated?

iron deficiency
treated with iron supplements or iron rich diet

how can binding of o2 to myoglobin be described?

Mb + o2 = Mbo2

what does K stand for in this equation

dissociation constant = measure of how easily mbo2 falls apart and the po2 at which half the myoglobin is saturated
low k = strong bonding
high k = weak bonding

what does the myoglobin and o2 graph represent

hyperbolic trend

what happens when the oxygen conc and dissociation constant are equal?

binding is half maximal

what percentage are Mb and Hb identical in their primary sequence?

18%

which structure level are Mb and Hb similar?

secondary and tertiary

what does the similarity in structure and sequence between Mb and Hb indicate?

common evolutionary origin

how many heme groups can Hb and Mb bind to?

Hb = 4
Mb = 1

what is cooperativity?

when one subunit binds to o2 it triggers a conformational change that inc the affinity for the next

what type of graph data indicates cooperativity

sigmoidal

how is the deoxy (T) state represented

HbH+ + o2

how is the oxy (R) state represented

Hbo2 + H+

what is the relationship between ph and o2 affinity

as ph inc, o2 affinity inc

what is BPG

modulates Hb ability to bind to o2
negatively charged
only binds to Hb when in t/deoxy state
dec Hb’s o2 affinity which releases more o2 to tissues

at high altitudes does BPG inc or dec in people

inc to prevent hypoxia

What would be the expected result of a Lys residue being replaced by a Ser residue in the BPG binding site of hemoglobin?

BPG would bind less tightly because of the loss of a positive charge

In the ____ form of Hb, the iron atom is out of the plane of the porphyrin ring.

tense state

Deoxyhemoglobin is unfavorable to oxygen binding because it is in the _____ conformation

T

What statement regarding the fractional saturation of myoglobin is FALSE?

It increases linearly at all oxygen concentrations.

A plot of the binding of oxygen to myoglobin as a function of pO2 gives a _____ shape;  a similar plot for hemoglobin gives a _____ shape.

hyperbolic;  sigmoidal

How does CO₂ affect hemoglobin-oxygen binding?

CO₂ is converted to bicarbonate and H⁺ which promotes the deoxy state

explain the residue change in sickle cells

glutamate is replaced with valine
glutamate is neg charged while valine is nonpolar

explain sickle cell rbcs

less flexible so more likely to rupture
harder to pass through small capillaries can cause blockages
deoxygenated Hb becomes insoluble and forms polymers that aggregate

describe the structure of actin

globular actin subunits associate in a double chain to form microfilaments
microfilaments have a a pos and neg end
pos end has faster addition

what is treadmilling

when the rate of addition to one end matches the rate of removal at other end

describe the alpha tubulin

guanine nucleotide is buried and inaccessible

describe beta-tubulin

nucleotide is more exposed and can be hydrolyzed

describe the microtubule structure

alpha and beta tubulin join to create a heterodimer which is the fundamental unit of the microtubule which is hollow

how is the tubular structure able to be seen

cryoelectron microscopy

what drugs affect microtubules

colchicine = causes microtubules to depolarize
paclitaxel = prevents microtubule depolymerization

what is the structure of keratin

forms a coiled-coil structure made from alpha helices

what is the structure of collagen

made from 3 left handed gly-rich helical polypeptides that form a triple helix
covalently cross linked which stabilizes the structure
every 3rd aa is gly
30% of remaining aa are pro or hydroxyproline

what is the structure of myosin

two heads and a long tail

describe the sequence of events in the myosin-actin cycle

ATP binds to myosin, myosin release from actin, myosin binds to another actin subunit, release of P_i and ADP, stretched myosin returns to original conformation