lecture 7 - Cellular energy generation and photosynthesis

Question 1

what i the equation of cellular respiration? and what is its Delta G value?

Answer 1

C6H12O6 + 6O2 –> 6CO2 + 6 H2O

Delta G = -686kcal/mol = -2870kJ/mol

Question 2

what does the graph of the energy released when a glucose molecule is broken down?

Answer 2

• the glucose molecule needs to be broken down in small steps
• at each step electrons are moved between reactants and products to enable breaking of chemical bonds.
  these reactions are called REDOX reactions
• this allows the controlled release of energy that can then be transformed into ATP

Question 3

what is the benefit of having NAD involved in cellular respiration?

Answer 3

• electron shuttle compound

- makes cellular metabolism more flexible (compare with the function of ATP)

Question 4

what is NAD?

Answer 4

NAD+ can transfer energy, 2 electrons and one proton around the cell

• using reduced NAD enables oxidised compounds to become more reduced
• NADH is the last phase of cellular respiration

Question 5

what is FAD?

Answer 5

• another electron acceptor used in cellular respiration
• the reduced form is FADH2
• structurally and functionally similar to NAD
• 2 hydrogens accepted in redox reaction
• 2 protons and 2 electrons

Question 6

what are the stages of cellular respiration?

Answer 6

• glycolysis
• pyruvate decarboxylation and the citric acid cycle
• oxidative phosphorylation

Question 7

describe glycolysis

Answer 7

• produces two molecules of pyruvate from 1 molecule of glucose
• produces 2 NADH and 2 ATP (net) by substrate-level phosphorylation

Question 8

what is substrate- level phosphorylation?

Answer 8

• production of ATP from ADP by direct transfer of a phospho-group from another molecule

Question 9

what happens in pyruvate decarboxylation?

Answer 9

• produces Acetyl-Co a and CO2.
• catalyzed by an enzyme complex called pyruvate dehydrogenase
• produces 1 NADH per pyruvate = 2 NADH

Question 10

what happens during the citric acid cycle?

Answer 10

• produces 2CO2 from 1 Acetyl CoA
• produces 1 FADH2, 3 NADH and 1 ATP by substrate phosphorylation per acetyl-CoA
• uses 8 individual enzymatic steps.

Question 11

what happens in oxidative phosphorylation?

Answer 11

the combination of two processes, that harness the redox potential in glycolysis, pyruvate decarboxylation and the citric acid cycle to generate ATP from ADP

• produces 30-32 ATP per glucose molecule
• Input NADH and FADH2
• consists of two phases (electron transport chain and chemiosmosis)
• uses 4+1 enzyme complexes.

Question 12

describe the electron transport chain

Answer 12

• four membrane protein complexes
• input: NADH and FADH2
• output: a proton gradient and H2O

Question 13

what role does oxygen play in the electron transport chain?

Answer 13

it is the final acceptor of electrons

Question 14

what is the equation of photosynthesis?

Answer 14

6CO2 + 6H2O + ENERGY (LIGHT) –> C6H1206 +6 O2

Question 15

What happens during photosynthesis?

Answer 15

two phases

• light reactions–> produces ATP and reducing power (NAD(P)H). happens in the thylakoids, membrane stacks in the chloroplasts
• dark reactions –> use energy (ATP) and reducing power (NAD(P)H) to produce sugars from CO2. happens in the stroma and cytosol

Question 16

what does it mean by dark reactions?

Answer 16

it does NOT mean that it occurs only at night, only that does not need light to proceed.

Question 17

what is NAD(P)+ used for in photosynthesis?

Answer 17

creating a proton gradient

Question 18

what are the similarities and differences between the final stage of respiration and photosynthesis?

Answer 18

differences
>oxidative phosphorylation
- consumes NADH/FADH2
- reduces oxygen to water
>light reactions (photosynthesis)
- produce NADPH
- produce oxygen from water
SIMILARITIES
- creates a proton gradient
- makes ATP via ATP synthase
-uses electron transport chain
- relies on membrane protein complexes.

Question 19

What is the Warburg effect?

Answer 19

> most cancer cells are defective in respiration
most cancer cells rely on glycolysis only for glucose oxidation. I.e., don’t need the citric acid cycle or oxidative phosphorylation