transport proteins (3-4)

Question 1

what type of processes have negative value of gibbs free energy

Answer 1

exothermic, since they are loosing energy to the environement

Question 2

what is 0 celcius in kelvin

Answer 2

273

Question 3

what is the difference between a concentration gradient and electrochemical gradient

Answer 3

electrochemical gradient refers to charged solutes, concentration does

concentration gradient:
deltaG= RTln(c2/c1)

where c1 is initial concentration and c2 is conc on other side of membrane

electrochemical gradient:
delta G= RTln(c2/c1) + ZF (psi2-psi1)

where Z is charge of solute and psi2-psi1 is charge of new area relative to original area

Question 4

how do electrochemical gradients taken advantage of biologically

Answer 4

used as a source of free energy which can be used to do work ie active transport

commonly used ones are sodium and protons

Question 5

how is delta G calculated for sodium/potassium ATPase

Answer 5

since 3 sodium out for 2 potassium in

delta G worked out for 3x sodium going out + 2 x potassium going in + ATP hydrolysis

Question 6

what is mechanism for glucose transporter in gut

Answer 6

in the lumen of the small intestine

uses secondary active transport, is a sodium/glucose symporter

2 sodiums and 1 glucose in

Question 7

how does body store energy from food other than ATP

Answer 7

reduced co enzymes eg NADH or FADH2

used to drive electron transport chain

Question 8

what is the reduction potential

Answer 8

indicates the tendency for a compound to be reduced

(how likely it is to be reduced/oxidised)

a positive high value will accept electrons very easily, this process will be spontaneous and exothermic

Question 9

what is the gibbs free energy associated with redox reactions

Answer 9

delta G= -nF delta E

where delta G is the energy made available by the electron transfer

-nF is the number of electrons transferred x 96.5 kJ per mol per volt

delta E is the difference between the 2 reduction potentials

Question 10

in each cycle (pass of electrons) of the electron transport chain how many H+ ions are pumped across inner mitochondrial membrane

Answer 10

10 H+, for the cycle via NADH which reduces the 1 subunit, 10+ per NADH

6H+ for the pathway via FADH2, which reduces the 2 subunit, 6 H+ per FADH2

Question 11

what are electron carriers involved in electron transport chain in oxidative phosphorylation

Answer 11

ubiquinone, can carry 2 electrons and 2 H+, can accept/donate electrons one at a time or 2 at a time, also known as coenzyme Q

both cytochrome and iron-sulphur protein can only carry one electron at a time, no hydrogens, there are different varieties of each with different reduction potentials

Question 12

how do electron carriers interact with complex 3

Answer 12

a full oxidised coezyme Q offloads 2 electrons onto electron carriers, converting itself from QH2 to Q, the remaining 2 H+ are pumped across membrane into intermembrane space.

one electron from QH2 goes to iron sulphur protein and one goes to cytochrome bl

iron sulphur protein then offloads its electron to cytochrome C, reducing it

cytochrome bl offloads electron to cytochrome bh which offloads to an oxised coenzyme Q,Q which is then converted from Q to Q-, this is then converted back to QH2 via another QH2

overall reaction:
QH2 + 2cytochrome c (ox) + 2H+ goes to Q + 2cytochrome c (reduced) + 4 H+

Question 13

what are subunits in ATP synthase

Answer 13

a subunit: this is where protons enter however channel does not go all the way through so they do not go through

c subunits form a ring which rotates, protons from first half channel attach to these, ring turns and reaches other half channel on a subunit, allowing proton to pass through

gamma stalk is attatched to c subunits, rotates with c subunits

as gamma stalk rotates it interacts with beta subunits, catalysing conversion of ADP + phosphate to ATP

there are 3 beta subunits

Question 14

what are segments in ATP synthase

Answer 14

F0: embedded in inner mitochondrial membrane, contains ring of rotating c subunits and stationary c subunit contain proton half channels

F1: contains 3 beta subunits which are catalytic site of ATP synthase

flow of protons into matrix drives rotation of c ring, which causes activities of beta subunits to go through a cycle which results in formation of ATP

Question 15

how do a and c subunits interact

Answer 15

a channels creates a hydrophillic environment (relatively)

protons attatched to aspartate residues on c subunits are neutral when facing hydrophobic environment of membrane, when facing channel of a subunit protons dissociate and then flow into mitochondrial matrix where there is low concentration

direction of turn is energetically favourable so that it turns in the direction so that c subunits face the channel for the matrix before the one facing intermembrane space, since after offloading a proton aspartate residues are negatively charged, and so would not interact with hydrophobic membrane

difference between channels are that channel facing inter membrane space is has high proton concentration whilst one facing matrix has low proton concentration

(in ATP synthesis protons flow from intermembrane space to the matrix)

Question 16

what is proton gradient between mitochondrial matrix and intermembrane space, what is the charge gradient

Answer 16

ph intermembrane space: 7.2 (63.1 nM)

ph matrix: 8.6 (2.51 nM

matrix has relative charge of -0.14V (not mV) compared to intermembrane space

thus gibbs free energy associated with protons passing through is very negative/ exothermic (20kJ per mol of one proton)

Question 17

how does proton transport create ATP synthesis energetically

Answer 17

energy associated with one proton transport = -20kJ/mol

energy associated with 3 protons transported= -60kJ/mol

ATP formation = + 50kJ/mol

thus 3 protons transported can create 1 ATP formation with a free energy release of 10kJ/mol

Question 18

what happens to oxadative phosphorylation in absence of oxygen

Answer 18

proton gradient collapses

as matrix pH becomes more acidic ATP synthase could operate in reverse, pumping protons out and hydrolysing ATP, this backwards reaction is inhibited by inhibitory protein IF1, this becomes active at low pH and binds to ATP synthase

Question 19

what happens in brown adipose tissue in cold environments

Answer 19

thermogenin is a protein in inner mitochondrial membrane is a proton channel which reduces proton gradient by allowing protons back into matrix (against the electron transport chain)

this generates heat by increasing rate for glycolysis by allowing electron transport chain to work faster, using more reduced coenzymes, which causes previous metabolic pathways such as glycolysis and fatty acid oxidation which have lots of exothermic reactions, thus generating heat

when you are cold hormones stimulate thermogenin, this occurs particularly in brown adipose tissue

heat generated by this is called non shivering thermogenesis

Question 20

how do bacteria use proton gradients in the flagellar

Answer 20

flagellar motor; proton gradient is generated by redox reactions

in the flagellar motor there are several subunits; FliG subunits, MotA subunits and MotB subunits, there are many more of these subunits than the subunits in ATP synthase

FliG subunits form ring similar to c subunits of ATP synthase, rotation of this rind causes turn in bacterial flagella

protons enter channels facing the periplasmic space and leave via channels facing the cytoplasm, causing rotation, very similar to ATP synthase

rotation occurs very quickly