respiration

Question 1

structure of mitochondria

Answer 1

1. Spherical or rod shaped structures surrounded by a double membrane
2. the outer membrane is smooth
3. the inner membrane is highly
   convoluted with infoldings called
   cristae which project into matrix
4. Between the membranes is the
   intermembrane space
5. matrix is semi-fluid and
   contains circular DNA, 70S
   ribosomes, phosphate granules &
   enzymes for aerobic respiration
6. ATP synthase complex on inner
   membrane projects into matrix

Question 2

function of mitochondria

Answer 2

Acts as the site for certain stages of aerobic respiration to generate energy in the form of ATP
1) Inner mitochondrial membrane is highly folded & hence increases surfacearea for oxidative phosphorylation
2) Mitochondrial matrix is the site of the
link reaction & the Krebs cycle

Question 3

main processes in respiration and their location

Answer 3

glycolysis in cytosol
link reaction in mitochondriol matrix
krebs cycle in mitochondriol matrix
oxidative phosphorylation in the cristae

Question 4

describe phosphorylation of glucose in glycolysis

Answer 4

involves initial investment of 2 ATP molecules
1 phosphate group from each of the 2 ATP phosphorylates sugar into fructose 1,6 bisphosphate
reaction is catalysed by phosphofructokinase

Question 5

outcome of phosphorylation of sugar in lysis

Answer 5

activates the sugar, making it more reactive and commiting it to the glycolytic pathway
confers a negative charge to glucose so that it is impermeable and cannot diffuse across the cell membrane and is trapped within the cytosol

Question 6

describe process of lysis in glycolysis

Answer 6

1 molecule of fructose-1,6- bisphosphate (6C) lyses to form
2 molecules of glyceraldehyde-3-phosphate (G3P/TP)(3C)
so all products formed in subsequent reactions are doubled

Question 7

what can also occur during lysis of glycolysis

Answer 7

dihydroxyacetone phosphate is also formed from lysis
G3P and dihydroxyacetone phosphate are isomers of each other and can be converted from one from to the other by an isomerase, but formation of G3P is favoured

Question 8

what occurs during oxidation by dehydrogenation during glycolysis

Answer 8

 glyceraldehyde-3-phosphate (G3P/TP) undergoes
oxidation/dehydrogenation and phosphorylation to form 1,3 bisphosphoglycerate
NAD is reduced to NADH

Question 9

reduction of NAD to NADH equation

Answer 9

NAD+ + 2e- + H+ = NADH

Question 10

describe substrate level phosphorylation in glycolysis

Answer 10

1. 1,3 bisphosphateglycerate is dephosphorylated to form glycerate
2. the 2 phosphate groups on 1,3 bisphosphateglycerate are transferred by enzymes to 2 ADP molecules, forming 2 ATP

Question 11

summary of glycolysis

Answer 11

glucose + 2ADP + 2Pi + 2 NAD = 2 pyruvate + 2ATP + 2 NADH

for each glucose molecule, 2 ATP is used up, 4 ATP is produced and the net ATP produced is 2

Question 12

what happens during link reaction

Answer 12

• If O2 is present, pyruvate is actively transported into the mitochondrial matrix from cytosol via a transport protein embedded across the mitochondrial double membrane
• 2 pyruvate mlcs (3C) undergo oxidative decarboxylation to form 2 acetyl CoA mlcs (2C)
• 2 NADH + 2 CO2 are produced

Question 13

total products at the end of link reaction

Answer 13

2 NADH, 2 CO2, 2 acetyl CoA

Question 14

describe oxidative decarboxylation in link reaction

Answer 14

decarboxylation: 1 carbon atom is removed from 1 molecule of pyruvate in the form of CO2
Oxidative: acetyl group is oxidised and attached to coenzyme A to form acetyl coA
electrons lost from oxidation is used to reduce NAD to NADH

Question 15

describe krebs cycle

Answer 15

When 1 glucose molecule is oxidised, 2 Acetyl CoA
mlcs form and enter the Krebs cycle. Thus 2 turns of
the Krebs cycle is necessary to oxidise 1 mlc of glucose.
1. Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C)
2. Citrate (6C) is converted to α-ketoglutarate (5C) by
oxidative decarboxylation
* α-ketoglutarate (5C) then goes through oxidative decarboxylation to NADH and CO2, substrate level phosphorylation to form ATP & oxidation to form NADH and FADH2 and is converted to oxaloacetate (4C) as a result
*When oxaloacetate (4C) is regenerated ATP, NADH &
FADH2 are also produced and one cycle is complete
*

Question 16

products at the end of krebs cycle

Answer 16

6 NADH + 2 FADH2 + 2 ATP + 4 CO2 are produced at the end of 2 cycles

Question 17

why is decarboxylation needed

Answer 17

CO2 is removed as a waste product
all 6 carbons of glucose are removed as CO2

Question 18

describe oxidative phosphorylation

Answer 18

1. Oxidative phosphorylation occurs on the folds of the inner membrane of mitochondria
   = cristae*;
2. NADH donates electrons to first electron carrier of the electron transport chain* found
   on the cristae;
3. The electron carriers alternate between reduced and oxidized states as they accept
   and donate electrons;
4. Each successive carrier has a higher electronegativity;
5. Each FADH2 donates electrons to the chain at a lower level and hence generates 2 ATP compared to 3 ATP generated by NADH;
6. the energy released from electron transport through the series of carriers is coupled to the active pumping of H+
   into the intermembrane space. This generates a proton gradient/ proton motive
   force across the mitochondria membrane;
7. The proton motive force is used to phosphorylate ADP. As protons diffuse back into the
   matrix via the ATP synthase complex, ADP is phosphorylated to ATP*.
8. This process is known as chemiosmosis*;
   * and produces 90% of the ATP during aerobic respiration.
9. transfer of electrons in electron carriers continue until they combine with oxygen* as the final electron acceptor* having the highest electronegativity;
   * 2e- +2H+ + 1/2O2 → H2O.

Question 19

products at the end of oxidative phosphorylation

Answer 19

from 1 NADH: 3 ATP
from 1 FADH2: 3 ATP
from 10 NADH and 2 FADH2: 34 ATP form

Question 20

amount of ATP at the end of repsiration

Answer 20

34 + 4 = 38

Question 21

how does NADH produce more ATP than FADH2

Answer 21

NADH donates electrons earlier/at lower energy level in the ETC which results in more energy being released as the donated electrons transfer down the ETC
more energy released to pump more H+ which ultimately leads to more ADP being phosphorylated into more ATP via chemiosmosis

Question 22

role of NADH and FADH2

Answer 22

1. The high-energy electrons yielded from the oxidation of organic food such as carbohydrates, fats and proteins in glycolysis, link reaction
   and Krebs cycle are transferred to NAD and FAD, reducing them and forming NADH and FADH2
2. They are coenzymes which serve as mobile electron carriers which transport the high-energy electrons from organic molecules to the electron transport chain in the inner mitochondrial membrane
3. By passing their electrons to the electron transport chain, NADH and FADH2 are oxidized, regenerating NAD and FAD, allowing them to pick
   up more electrons and protons from glycolysis, link reaction and Krebs cycle

Question 23

role of oxygen in aerobic respiration

Answer 23

By acting as the final electron acceptor at the end of the ETC where it combines with electrons and protons to form water, O2 re-oxidises the
ETC so that the electron carriers NADH and FADH2 can continue donating their electrons to the chain, thereby allowing oxidative
phosphorylation to continue to generate ATP
2. NAD and FAD are regenerated when NADH and FADH2 donate electrons to the ETC, allowing NAD and FAD to pick up more electrons and
protons from glycolysis, link reaction and Krebs cycle
3. Reduction of oxygen to water removes H+ from the matrix, contributing to the generation of a proton gradient across the inner mitochondrial membrane

Question 24

what happens when oxygen is absent

Answer 24

• In the absence of oxygen (O2),
  1. no final e - acceptor to accept electrons from the electron transport chain (ETC).
  2. oxidative phosphorylation cannot occur: Electron carriers remain reduced and so
  NADH and FADH2 can no longer donate electrons to the ETC.
  3. In absence of oxidative phosphorylation, there is no regeneration of NAD & FAD and hence no electron acceptors for
  the link reaction & Krebs cycle cannot occur .
• In the absence of oxygen, glycolysis can still occur as the NAD needed for glycolysis is regenerated from fermentation reactions.
• Alcoholic fermentation occurs in yeasts while lactate fermentation occurs in muscles of
  animals.
  Both fermentation reactions regenerate
  NAD from NADH in order to keep glycolysis
  going. ATP is only produced from glycolysis.

Question 25

describe alcoholic fermentation

Answer 25

glycolysis
There is an initial ATP investment of 2 ATP per glucose molecule during the conversion
of glucose to fructose 1,6-bisphosphate by phosphofructose kinase;
4. Substrate level phosphorylation* will yield a total of 4 ATP per glucose molecule
when 1,3-bisphosphoglycerate is converted to pyruvate;
5. with a net of 2 ATP molecules* produced for each glucose molecule oxidised;

fermentation
6. Pyruvate is reduced by pyruvate decarboxylase to ethanal (with a release of CO2)
which is further reduced by alcohol dehydrogenase* to ethanol with the regeneration
of NAD+ in yeast, so ethanal is the final electron acceptor
;
8. NAD+ regenerated ensures steady supply of NAD is used for
glycolysis to continue

Question 26

describe lactatic acid fermentation

Answer 26

There is an initial ATP investment of 2 ATP per glucose molecule during the conversion
of glucose to fructose 1,6-bisphosphate by phosphofructose kinase;
4. Substrate level phosphorylation* will yield a total of 4 ATP per glucose molecule
when 1,3-bisphosphoglycerate is converted to pyruvate;
5. with a net of 2 ATP molecules* produced for each glucose molecule oxidised;

fermentation
7. In mammal NAD+ can be regenerated by reducing pyruvate in presence of lactate
dehydrogenase* to lactate, so lactate is the new final electron acceptor
8. NAD+ regenerated ensures steady supply of NAD is used for
glycolysis to continue

Question 27

how is mitochondria suited for its role in repsiration