8 Metabolism (HL) Flashcards
How do enzymes increase the rate of biochemical reaction?
Decreasing activation energy
Define exergonic reaction
Energy is released
Usually catabolic
Define endergonic reaction
Energy is absorbed
Usually anabolic
What are the two types of enzyme inhibition?
Competitive and non competitive
Describe competitive inhibition
Inhibitor is structurally similar to the substrate and directly binds to the active site
What occurs to the effects of the competitive inhibitor if substrate concentration increases?
Effects decrease
Describe non-competitive inhibition
Inhibitor binds to an allosteric site and changes the active site shape so the substrate can no longer bind
What occurs to the effects of the non-competitive inhibitor if substrate concentration increases?
No change
Give an example of a competitive inhibitor
Relenza
Drug which fights influenza by competitively inhibits the enzymes which triggers the release of virions from the infected cell
Give an example of a non-competitive inhibitor
Cyanide
Binds to the allosteric site on cytochrome oxidase (carrier molecule in the ETC of respiration)
Therefore ATP is not produced
Describe end-product inhibition
Final product inhibits an earlier step via non-competitive inhibition (temporarily inactivates the enzyme)
Which two sources can synthesise ATP from ADP?
Solar energy
Oxidative processes
What is the first step in the breakdown of carbohydrates?
Glycolysis
Where does glycolysis occur?
Cytosol
What happens in glycolysis?
Hexose (6C) -> Pyruvate (3C)
What are the 4 steps of glycolysis?
Phosphorylation
- 2ATPs phosphorylate the hexose making it more unstable
Lysis
- 6C sugar breaks into 2 triosephosphates (3C)
Oxidation
- H atoms are removed from each 3C (NAD+->NADH + H+) (2x NADH in total)
ATP formation
- 2 ATP molecules are synthesised per 3C molecule to produce pyruvate (4x ATP in total)
What is the net gain of H carrying molecules and ATP in glycolysis per hexose?
2 ATP (4 produced, 2 used)
2 (NADH + H+)
What happens after glycolysis in the absence of oxygen?
The pyruvate is converted to lactic acid
What happens after glycolysis in the presence of oxygen?
The pyruvate is transported to mitochondria for further breakdown
What is the second step of respiration (1st step unique to aerobic respiration)?
Links reaction
Where does the links reaction occur?
The pyruvate is transported into the mitochondrial matrix at the start of the reaction
What occurs to each pyruvate in the links reaction?
Decarboxylation (loss of a CO2)
Loss of 2H for NAD+ -> NADH + H+ creates a 2C which forms an acetyl group
Coenzyme A bonds to the acetyl group -> Acetyl CoA
What is the net gain of H carrying molecules and ATP in the links reaction per hexose?
2 (NADH + H+)
(as well as 2CO2)
1 of each per pyruvate
What is the third step of respiration?
Krebs cycle
Where does the Krebs cycle occur?
Mitochondiral matrix
What is the starting molecule that the Acetyl CoA binds to at the start of the Krebs cycle?
A 4C molecule called oxaloacetate
What is formed when oxaloacetate binds with the acetyl group of Acetyl CoA?
A 6C compound (citrate)
What happens to citrate (in which order) in the Krebs cycle?
Loss of 1x CO2 molecule
Loss of 2H (NAD+ -> NADH + H+)
(5C compound produced)
Loss of 2H (NAD+ -> NADH + H+)
Loss of 1x CO2 molecule
(4C compound produced)
1x ATP synthesised
Loss of 2H (FAD+ -> FADH2)
Loss of 2H (NAD+ -> NADH + H+)
Final Product -> Oxaloacetate (4C)
What is the net gain of H carrying molecules and ATP in the Krebb’s cycle per hexose?
2x ATP
2x FADH2
6x NADH + H+
(4x CO2)
(2 cycles - 1 per pyruvate)
What is the fourth and final stage of aerobic respiration?
Electron transport chain (oxidative phosphorylation)
Where does the electron transport chain in respiration take place?
Cristae (inner mitochondrial membrane folds)
What are the three steps of oxidative phosphorylation (resp ETC)?
Generating a proton motive force
ATP Synthesis vis chemiosmosis
Reduction of oxygen
Describe the process of generating a proton motive force (resp ETC)
Hydrogen carriers are oxidised and release high energy electrons (e-) and protons (H+)
e- are transferred to the ETC
e- pass through the chain and lose energy as they do which pumps H+ from the matrix
H+ accumulates in the intermembrane space (electrochemical gradient)
Describe ATP synthesis via chemiosmosis as a step of the respiration ETC
H+ ions will diffuse back into the matrix (chemiosmosis) which is facilitated by ATP synthase thus triggering the synthesis of ATP
Describe the reduction of oxygen as a step of the respiration ETC
O2, H+ and the de-energised e- are lost through water synthesis
What is the yield of one hexose sugar in the electron transport chain?
32 ATP
What is the final yield of aerobic respiration of one hexose?
6x CO2
10x NADH
2x FADH2
36x ATP
Where does the light dependent part of photosynthesis occur?
Thylakoid
Where does the light independent part of photosynthesis occur?
Stroma
What are the three steps of light dependent photosynthesis?
Excitation of photosystems
Photophosphorylation
Reduction of NADP+ and photolysis of water
Describe excitation of photosystems as a step of light dependent photosynthesis
Photosystem pigments in the thylakoid membrane absorb light and electrons in them become excited
The excited electrons are transferred to carrier molecules in the thylakoid membrane
What wavelength does PSI absorb?
700nm
What wavelength does PSII absorb?
680nm
Describe (non-cyclic) Photophosphorylation as a step of light dependent photosynthesis
Excited e- from PSII are transferred through the membrane and lose energy as they do, translocating H+ ions into the thylakoid
Chemiosmosis occurs as the H+ ions return to the stroma via ATP synthase, synthesising ATP (from ADP + Pi)
Deenergised e- from PSII are taken up by PSI
Describe the reduction of NAD+ and photolysis of water as a step of light dependent photosynthesis
Excited e- from PSI may be transferred to a carrier molecule to reduce NADP -> NADH (for the light independent reaction)
Electrons lost from PSII are replaced via photolysis of water (H+ used in chemiosmosis and O is a byproduct)
Describe the reduction of NAD+ and photolysis of water as a step of light dependent photosynthesis
Excited e- from PSI may be transferred to a carrier molecule to reduce NADP -> NADH (for the light independent reaction)
Electrons lost from PSII are replaced via photolysis of water (H+ used in chemiosmosis and O is a by-product)
Describe cyclic photophosphorylation
Involves only PSI and no reduction on NADP+
e- cause chemiosmosis from PSI but re-enter PSI and are re-energised
Where does the Calvin cycle occur?
Stroma
What are the three steps of the Calvin cycle?
Carbon fixation
Reduction of GP
Regeneration of RuBP
What is the initial (and final) molecule in the Calvin cycle?
RuBP (5C)
Describe carbon fixation as a part of the Calvin cycle?
RuBP carboxylase catalyses 3RuBP+3CO2-> 3(6C) compound-> 6x GP (3C)
What does GP stand for (photosynthesis)?
Glycerate - 3- phosphate
Describe reduction of GP as a part of the Calvin cycle?
6(ATP-> ADP + Pi) and 6(NADPH->NADP+ + H+) converts 6GP to 6TP (3C)
What does TP stand for (photosynthesis)?
Triose phosphate
Describe Regeneration of RuBP as a part of the Calvin cycle?
1 out of 6TPs is removed to produce half a sugar
3(ATP -> ADP + Pi) converts The other 5TP into 3x RuBP
How many RuBP are involved in each Calvin cycle?
3
(2 cycles per glucose)
How many Calvin cycles are required for a full sugar to be synthesised?
2
How many CO2 are needed to produce a full sugar in the Calvin cycle?
6
Describe a chloroplast
Stroma (central cavity)
Thylakoids - flattened dinks with high SA:Vol
Grana - Thylakoids in stacks to increase SA:Vol
Lamella - connect and separate granum
