Cellular Respiration Flashcards
What is ATP?
-Phosphorylated nucleotide
-Univeral energy currency
-Short term energy molecule
-Large so cannot diffuse across memb
-Can be hydrolysed by ATP synthase to release energy to form ADP + Pi + energy
Why is ATP needed by all living organisms?
(supply energy to drive metabolic reaction & other processes inside cells)
Muscle contraction
Anabolic reactions eg protein synthesis
Homeostasis
Active transport
Bulk transport eg. endocytosis, exocytosis
Bioluminescence
Cytokenesis
Chemical activation e.g. activation DNA nucleotides
Properties of ATP
-small and water soluble
-bond between adjacent phosphates is easily broken
-easily hydrolysed & reformed
Why is ATP called universal energy currency?
universal : found in all prokaryotes and eukaryotes
currency:
Terminal phosphate hydrolyses to release energy
So ATP links energy-releasing reactions to energy-consuming reactions
Coenzymes
How do they differ from co-factor
-Cofactors aid function of enzymes and can include organic or inorganic molecules
-Coenzymes sub-group
-Small, non-protein organic molecules which bind temporarily to AS
Coenzymes role in Redox reactions
Carry chemical groups between molecules to link reactions
What type of reaction are coenzymes usually involved in in respiration
oxidation
What happens to H atoms carried by coenzyme
-H splits into proton and e-
-Proton passes inner membrane of mitochondria
-Accumulates in inter membrane space to be used in oxidative phosphorylation to produce ATP
Where does reoxidation of coenzymes take place and why is this necessary
Cristae to combine more H atoms from the first 3 stages of respiration
NAD
(Coenzyme)
structure: adenine, ribose, Pi, Pi, ribose, nicotinamide
NAD is hydrogen carrier
Nicotinamide part accepts pair of hydrogen atoms.
NAD <-> red NAD (reversible)
Becomes oxidised when it donates 2H atoms
NAD+ + 2H+ 2e- -> red.NAD + H+
FAD
(coenzyme)
-similar to NAD
-acts as a hydrogen carrier
-Becomes red FAD when it accepts pair of H atoms
-Oxidised FAD when it donates pair of H atoms
CoA
-Adenosine triphosphate (ATP), cysteine, pantothenic acid
-carries 2C fragments (acetyl groups) from LR to KC
CoA + acetyl group <-> acetylCoA (aCoA)
Explain why living organisms do not contain much NAD or CoA at any one time
-They are both constantly recycled
-There is no net production or no net breakdown
Structure and Adaptation of mitochondrion
-Mitochondrial envelope. inter membrane space enables H+ to accumulate to generate proton motive force to form ATP production via chemiosmosis
-Cristae- large SA, site for oxidative phosphorylation
-Inner membrane impermeable to H+, outer permeable
-Matrix contains enzymes, lipid droplets, DNA plasmids
-Possess 70s ribosomes
Overview aerobic & anaerobic
Glycolysis common for both. Then:
Aerobic: LR, KC, OP
Anaerobic: LA pathway or fermentation
Location of glycolysis
why?
Cytosol
Requires specific enzymes only found there
Glycolysis function
Split glucose (hexose, 6C) into 2 triodes (3C) (pyruvate)
Source of glycolysis in plants
Amylose: unbranched polysaccharide, soluble. 1-4 alpha glycosidic
Amylopectin: branched polysaccharide, insoluble, 1-4 & 1-6 alpha glycosidic
Source of glycolysis in animals
Glycogen found in liver cells ad muscle cells
Many branches, many terminal end glc molecules, quickly hydrolysed to form glc
Glycolysis input
Glucose
2 ATP
2 NAD
Enzymes
Glycolysis output
2 Pyruvate
2 red NAD
4 ATP
Glycolysis in terms of net ATP
2 in, 4 out
Net gain of 2 ATP (gross of 4)
Substrate level phosphorylation occurs
give each stage of the conversion from a. glucose to pyruvate
Glucose (6C)
(ATP → ADP)
Glucose Phosphate
Fructose Phosphate
(ATP → ADP)
Fructose biphosphate
2 glyceraldehyde 3-phosphate (3C)
(2 Pi) (2 red. NAD→NAD)
2 glycerate 1,3-biphosphate
(2 ADP→ATP)
2 glycerate 3-phosphate
( 2 ADP→ATP)
2 pyruvate
what is phosphorylation? what is its use in glycolysis?
-Addition of a phosphate group from molecule
-Supplied from ATP
-Adds negative charge to glc. Repelled by hydrophobic core of ppl bilayer of csm, so cannot diffuse out)
Substrate Level Phosphorylation
- accounts for 10% of ATP in aerobic respiration
-Involves direct additional of phosphate group to ADP to produce ATP
-Does not involve ETC
Where does the Link Reaction occur
why?
Mitochondrial matrix
CoA and other enzymes are only found here
How does pyruvate reach mitochondrial matrix?
moves across the mitochondrial envelope through specialised intrinsic protein through A.T.
What 3 types of reactions are involved in the LR
Oxidation: e- removed from pyruvate (H gained by CoA)
Reduction: NAD gains protons (and e-)
Decarboxylation: Co2 removed from pyruvate
This is all called: oxidative decarboxylation
Mechanism of LR
______________⬈ CO2
Pyruvate + CoA -> aCoA
______________⬊2e- & 2H+
NAD -> red. NAD
Occurs TWICE per glc
A C is removed from pyruvate, forming CO2, to turn it into a 2C acetate. During the conversion into acetate, H is also removed and is picked up by NAD to form red. NAD. Acetate is combined with CoA to form aCoA.
Procucts of LR (per 1 glc)
2CO2
2aCoA
2red NAD
How can fats be converted into a CoA molecule
Hydrolysis of fatty acids hydrocarbon tail can release 2C fragments
Each 2C fragment can make 1 CoA
Process: B-oxidation
Where does K cycle take place
Mitochondrial matrix
What is K cycle controlled/ limited by?
Since it is a series of enzyme controlled reactions, limited by:
[S], [E], [I], Temp, pH
Krebs Cycle
aCoA (2C) combines with 4C
⇩ out CoA
Citrate (6C)
⇩. out CO2
⇩. NAD-> red NAD
5C
⇩ out CO2
⇩ NAD-> red NAD
⇩ADP+P= ATP
4C
⇩ FAD-> red FAD
4C
⇩ NAD -> red NAD
oxaloacetate
Products of KC
Per cycle
1 ATP
2 CO2
3 red NAD
1 red FAD
Per glc
2 ATP
2 CO2
6 red NAD
2 red FAD
Recap of ATP, redNAD, redFAD
per glc
ATP: 2 net Glycolysis, 2 Krebs
red NAD: 2 Glycolysis, 2LR, 6 Krebs
red FAD: 2 Krebs
Main points K cycle
-oxaloacetate is regenerated for KC to continue
-Most important products (NAD & FAD)- reduced hydrogen carriers
-Substrate level phosphorylation occurs- direct production of ATP
- No O2 been used yet (But KC can only continue in presence of O2 as oxidised NAD & FAD required)
What is the purpose of red NAD and red FAD
Co enzymes that act as hydrogen carriers to ETC
Allows ATP production via oxidative phosphorylation
Oxidative phosphorylation
-Accounts for 90% of ATP production of aerobic respiration
-Is the combined effect and outcome of both the electron transport chain and chemiosmosis
Where does oxidative phosphorylation take place
Cristae of mitochondria
What molecules are involved in the ETC
red NAD
red FAD
e- carriers
Oxygen
ETC: what are e- carriers?
Specialised carrier globular proteins
accept/donate e-
Have quaternary structure (prosthetic group)
ETC
-Consists of series of redox reactions using specialised proteins
-Dehydrogenase enzyme interacts with reduced H carrier
-H atoms released from co-enzyme and split into H+ and e-
-E- flow down ETC
-Energy released as e- flow from one carrier to another
-Energy used to pump proton into inter membrane space
-Generates proton gradient
-At the end, oxygen acts as final e- acceptor to form H2O (in absence of O, ETC stops)
NB: only red NAD from Krebs enters at first carrier
Chemiosmosis def
movement of ions across partially permeable membrane, down their electrochemical gradient
Chemiosmosis outline
-proton pumping leads to accumulation in inter membrane space
-Creates proton motive force
-Protons flow down electrochemical gradient through ATP synthase (stalked particles) into matrix
-This flow of protons releases energy
-Energy used to ADP + Pi-> ATP
-Protons react with O to form h2o- maintains proton gradient
Products of Chemiosmosis (ATP)
red NAD from Krebs: 3 (2.5)
red FAD from Krebs: 2 (1.5)
red NAD from glycolysis: 2 (1.5)
red NAD from LR: 2 (1.5)
ATP
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation
as substrate-level phosphorylation?
Used Produced. Gain
2. 4 2
0 0 0
0 2. 2
0 0 0
ATP direct
(from chemiosmosis)
- 2 red. NAD from glycolysis
- 2 red. NAD from link reaction
- 6 red. NAD from Krebs cycle
- 2 red. FAD from Krebs cycle?
Used Produced. Gain
0 4 3
0 4 3
0 18 15
0 4 3
Theoretical yield & ATP production
1 glc molecule has potential to produce 36 ATP
Rarely achieved as ATP used to:
-Move pyruvate to matrix
-pump protons into inter membrane space
-shuttle H from red NAD produced in glycolysis to matrix
Also, some protons leak across mitochondrial membrane reducing the proton motive force, so less ATP made
Role of oxygen
-Acts as final e- acceptor
-accepts protons to form water
-Enables ETC to continue
-Which in turn allows chemiosmosis to take place
-Increased ATP production
Where can anaerobic respiration take place?
Whta is its principle?
only in skeletal muscles
enables glycolysis to continue to ensure 2 ATP is made per glc
Lactate fermentation
-H atoms removed from red. NAD
-Join with pyruvate to make lactate
-so red. NAD deoxidised back to NAD
-Can then be re-used in glycolysis
-Enables low rate of substrate level phosphorylation
Role of pyruvate in lactate fermentation
Pyruvate acts as an alternative hydrogen acceptor
Fate of lactate
- Build up causes inhibition of glycolysis, cramp & fatigue
-Lactate transported to liver in plasma
-lactate is oxidised back to pyruvate by lactate dehydrogenase (when O is available again) so reversible
-1/5 respired anaerobically
-4/5 converted to glucose and stored as glycogen
Alcoholic fermentation
-Pyruvate is decarboxylated to form ethanal & CO2 by pyruvate decarboxylate
-Ethanal acts as H acceptor and removes H from red. NAD
-Forms ethanol and is catalysed by Ethanol dehydrogenase
-Oxidises red NAD back to NAD so it can be used in glycolysis
why is yeast considered a ‘facultive anaerobe’?
it can survive in both anaerobic and aerobic conditions (although growth is faster in aerobic)
What type of aerobic respiration in yeast?
alcoholic fermentation
why is alcoholic fermentation considered wasteful for the yeast?
As the chemical potential energy is trapped in ethanOl so wasteful
What is a respiratory substrate
an organic molecule that can be broken down in respiration to produce ATP
why do different respiratory substrates produce different amounts of ATP?
have different amounts of hydrogen
∴ different number of H+ that can be pumped into the IMS
∴ different proton motive forces generated
∴ different numbers of ATP molecules can be produced
name two cells that only use glucose as a respiratory substrate
Mature RBC
Human brain cells
how are carbohydrates converted and used as respiratory substrates?
-Glycogen/ amylose/ amylopectin can be hydrolysed to glc
how are proteins converted and used as respiratory substrates?
-Excess amino acids deaminated
-remainder of molecule converted to glycogen or lipids for energy storage
-during starvation, proteins can be hydrolysed to release amino acids
how are lipids converted and used as respiratory substrate?
-triglycerides can be hydrolysed into 3 fatty acids and 1 glycerol
-glycerol is converted to glc
-Hydrocarbon fatty acid tail hydrolysed during B oxidation to release 2C fragments (acetyl)
-each acetyl can join with CoA to form aCoA to join Krebs
Define Respiratory Quotient
The ratio of the volume of CO2 produced by a respiring organism to that of oxygen consumed by an organism, tissue cell IN A GIVEN PERIOD OF TIME
RQ formula
volume CO2 released/ volume O2 taken up
what does the RQ indicate?
the type of respiratory substrate being used
what is the RQ value for anaerobic conditions?
infinite
RQ value for subrates aerobically
carbohydrates 1
proteins 0.8-0.9
lipids 0.7
EQ Outline the stage of aerobic respiration that occurs in the cytoplasm
-Glycolysis
-Phosphorylation of glucose
-Splitting of fructose biphosphate into two triose phosphate (3C)
-Each 3C Oxidised to form pyruvate
-net 2 atp production & 2 red. NAD formed
