respiration Flashcards
structure of mitochondria
- Spherical or rod shaped structures surrounded by a double membrane
- the outer membrane is smooth
- the inner membrane is highly
convoluted with infoldings called
cristae which project into matrix - Between the membranes is the
intermembrane space - matrix is semi-fluid and
contains circular DNA, 70S
ribosomes, phosphate granules &
enzymes for aerobic respiration - ATP synthase complex on inner
membrane projects into matrix
function of mitochondria
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
main processes in respiration and their location
glycolysis in cytosol
link reaction in mitochondriol matrix
krebs cycle in mitochondriol matrix
oxidative phosphorylation in the cristae
describe phosphorylation of glucose in glycolysis
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
outcome of phosphorylation of sugar in lysis
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
describe process of lysis in glycolysis
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
what can also occur during lysis of glycolysis
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
what occurs during oxidation by dehydrogenation during glycolysis
glyceraldehyde-3-phosphate (G3P/TP) undergoes
oxidation/dehydrogenation and phosphorylation to form 1,3 bisphosphoglycerate
NAD is reduced to NADH
reduction of NAD to NADH equation
NAD+ + 2e- + H+ = NADH
describe substrate level phosphorylation in glycolysis
- 1,3 bisphosphateglycerate is dephosphorylated to form glycerate
- the 2 phosphate groups on 1,3 bisphosphateglycerate are transferred by enzymes to 2 ADP molecules, forming 2 ATP
summary of glycolysis
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
what happens during link reaction
- 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
total products at the end of link reaction
2 NADH, 2 CO2, 2 acetyl CoA
describe oxidative decarboxylation in link reaction
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
describe krebs cycle
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
*
products at the end of krebs cycle
6 NADH + 2 FADH2 + 2 ATP + 4 CO2 are produced at the end of 2 cycles
why is decarboxylation needed
CO2 is removed as a waste product
all 6 carbons of glucose are removed as CO2
describe oxidative phosphorylation
- Oxidative phosphorylation occurs on the folds of the inner membrane of mitochondria
= cristae*; - NADH donates electrons to first electron carrier of the electron transport chain* found
on the cristae; - The electron carriers alternate between reduced and oxidized states as they accept
and donate electrons; - Each successive carrier has a higher electronegativity;
- Each FADH2 donates electrons to the chain at a lower level and hence generates 2 ATP compared to 3 ATP generated by NADH;
- 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; - 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*. - This process is known as chemiosmosis*;
* and produces 90% of the ATP during aerobic respiration. - 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.
products at the end of oxidative phosphorylation
from 1 NADH: 3 ATP
from 1 FADH2: 3 ATP
from 10 NADH and 2 FADH2: 34 ATP form
amount of ATP at the end of repsiration
34 + 4 = 38
how does NADH produce more ATP than FADH2
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
role of NADH and FADH2
- 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 - 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
- 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
role of oxygen in aerobic respiration
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
what happens when oxygen is absent
- 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.
describe alcoholic fermentation
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
describe lactatic acid fermentation
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
how is mitochondria suited for its role in repsiration
