8. Metabolism, Cell Respiration, Photosynthesis

Question 1

8.1 What is metabolism?

Answer 1

The chemical reactions of enzymes

Question 2

8.1 What are metabolic pathways?

Answer 2

The chain and/or cycle of enzyme-catalysed reactions

Question 3

8.1 Relationship between enzymes and energy

Answer 3

Enzymes reduce activation energy

Question 4

8.1 Types of inhibitors

Answer 4

Competitive: directly binds
- max rate of enzyme activity can be achieve but requires higher concentration

Non-Competative: binds to allosteric site, non-compettive
- max enzyme activity reduced

Question 5

8.1 What is end-product inhibition?

Answer 5

The final product of an enzyme binds to the allosteric site to stop reaction

Question 6

8.2 Rules of a redox reaction

Answer 6

Oxidation - loss of e-, (gain of O, loss of H)
Reduction - addition of e-, (loss of O, gain of H)

Question 7

8.2 What is an electron carrier?

Answer 7

A molecule that can accept or donate e-
- used to stager break down of energy so its not all lost

Question 8

8.2 NAD+ vs NADH

Answer 8

NAD+ is reduced to NADH (with 2 e-)

Question 9

8.2 What is phosphorylation?

Answer 9

The addition of a phosphate group

Question 10

8.2 Effects of phosphorylation

Answer 10

Molecules is more likely to react
Endogergonic recation - requires energy
Exogonic - removal of phosphate

Question 11

8.2 What is the first stage of glycolesis?

Answer 11

Phosphorylation: Glucose (6C) is phosphorylated by 2 ATP to form hexose biphosphate
- more unstable
- wont diffuse out of cell

Question 11

8.2 Where does glycolisis occur?

Answer 11

Cytoplasm

Question 12

8.2 What is the second step of glycolsis?

Answer 12

Lysis:
Hexose biphosphate (6C) is split into two triose phosphates (3C)

Question 13

8.2 What is the third step of glycolsis?

Answer 13

Oxidation:
The triose phosphates are oxidized giving the H+ to NAD to become NADH+ (2 are produced)

Question 14

8.2 What is the final step of glycolsis?

Answer 14

ATP formation:
The sugar molecules break down further into pyruvate and 2 ATP is created per molecule (4 total)

Question 15

8.2 Energy gain + loss of glycolisis

Answer 15

2 ATP used in beginning
4 ATP produced

Net: 2 atp

Question 16

8.2 Anaerobic conditinons + pyruvate

Answer 16

If oxegyn is not present pyruvate is broken down further becoming lactic acid (animals) or ethanol (plants/yeast) in the process of fermentation

Traditionally NADH+ is oxidized during aerobic respiration, but without oxygen this happens during fermentation instead

Question 17

8.2 What is the first step of aerobic respiration?

Answer 17

Link reaction:
Transport pyruvate to mitochondria

Steps:
1) Pyruvate is transported into the mitochondrial matrix by carrier protiens
2) Pyruvate is decarboxylated and becomes carbon dioxide molecule (waste product produced = Co2)
3) This molecule loses a H atom as NAD+ is reduced to NADH + H+, this becomes an acetyl group
4) The acetyl group combines with coenzyme A to become acetyle CoA

This happens twice with both pyruvate molecules

Question 18

8.2 Steps of Kreb Cycle

Answer 18

Also known as citric acid cycle

1) Acetyl CoA donates the Aceytl group to a 4C compound to become 6C (citrate). –CoA is released to become part of link reaction again

2) (processes during 5C)
- 6C is decarboxylated to form 5C, it then is oxidized twice (losing 4 total H) (NAD+ –> NADH + H+) x2

3) (process during 4C)
- 5C is decarboxylated again to form 4C
- One ATP molecule is produced via substrate level phosphorylation
- The molecule is oxidized twice again (losing 4 H total) first (FAD –> FADH2) then (NAD+ –> NADH + H+)

4C molecule is reused as its a cycle
This happens twice with the two Acetyl CoA molecules

Question 19

8.2 Products of Krebs Cycle

Answer 19

2 CO2 x 2 = 4 Co2
3 NADH + H x 2 = 6 NADH + H+
FADH2 x 2 = 2 FADH2
ATP x 2 = 2 ATP

Question 20

8.2 What is the electron transport chain?

Answer 20

A chain of electron carriers that pass along electrons

Question 21

8.2 Where does ETC occur?

Answer 21

The inner mirochondrial membrane
- Folds (cristae) increase the surface area for this process

Question 22

8.2 What is the term for the general procedure of the ETC

Answer 22

Oxidative phosphorylation
Energy derived from oxidization of carriers

Question 23

8.2 What is the first step of ETC?

Answer 23

Generating Proton Motor Force

1) NADH and FADH2 are oxidized releasing electrons and protons
2) Electrons are transfered to electron transport chain, consisting of several transmembrane carrier protiens
3) As electrons pass through the chain, they lose energy which is used by the protiens to pump H+ across the membrane from the matrix
4) The accumulation of protons in the innermatrix space creates a electrochemical gradient

Question 24

8.2 What is the second step of ETC

Answer 24

ATP Synthesis via chemiosmosis 1) Protons move down the generated gradient and diffuse back to matrix 2) This is known as chemiostatis and is facilitated by ATP synthase 3) This causes the ATP synthase rotation, leading to the synthesis of ATP

Question 25

8.2 What is the final step of ETC

Answer 25

Reduction of Oxygen 1) De-energized electrons need to be removed from chain 2) Oxygen acts as final receptor accepting electrons 3) Oxygen binds with protons reentering matrix to become water

Question 26

8.2 Reactants and Products of ETC

Answer 26

6 O2 --> 32 ATP 6 H2O

Question 27

8.2 ATP Production throughout process

Answer 27

(1 glucos, 2 pyruvate) Glycolsis: 2 ATP Link Reaction: none Kreb Cycle: 2 ATP ETC: 34 ATP Net: 38 ATP

Question 28

8.2 Mitochondria Structure

Answer 28

Outer Mitochondrial Membrane: - seperates mitochondria from the rest of the cell Inner Mitochondrial Memrbane: - location of ETC + ATP synthase - folds for max surface (cristae) Intermbrane Sprace: - small for proton build up Matrix: - krebs, enzymes

Question 29

8.3 Where do light dependent reactions happen?

Answer 29

Membrane discs in chloroplast called thylakoids

Question 30

8.3 What do light dependent reactions use?

Answer 30

Photosynthetic pigments organized into photosystems embedded in thylakoid membrane

Question 31

8.3 What is the first step of light dependent reactions?

Answer 31

Excitation of Photosystems w/ Light E- -Photosystems are classified according to max absorption wavelengths (PS I = 700nm, PS II = 680 nm) 1) When a photosystem absorbs light energy electron within the pigment become energised 2) These electrons are transfered to carrier protiens in thylakoid membrane

Question 32

8.3 What is the second step of light dependent reactions?

Answer 32

Production of ATP via ETC 1) Excited electrons from Photosystem II are transferred to electron transport chain in thylakoid membrane 2) ATP is synthesized as the protons return to stroma via ATP synthase (chemiosmosis) - this process is photophosphorylation 3) The newly de-energersied electrons from Photosystem II are taken into Photosystem I

Question 33

8.3 What is the final step of light dependent reactions?

Answer 33

Reduction of NADP+ and Photolysis of water 1) Excited electrons from Photosystem I may be transferred to carrier molecule and used to reduce NADP+ --> NADPH (needed in light independent reactions) 2) Electrons in Photosystem 1 are replenished from Photosytem 2 3) Electrons in photosystems 2 are replaced by electrons from water via photolysis --> water is split by light energy into H+ and oxygen (waste)

Question 34

8.3 What are the two types of photophosphorylation?

Answer 34

Cyclic and non-cyclic

Question 35

8.3 What is photophosphorylation?

Answer 35

Production of ATP with light dependent reactions

Question 36

8.3 What is cyclic photophosphorylation?

Answer 36

Only photosystem I is involved, no NADP+ is reduced The de-energized electron returns to photosystem I, no need for water

Question 37

8.3 What is non-cyclic photophosphorylation?

Answer 37

Requires both photosystems, NADPH is synthesized from Photosystem I, requires water

Question 38

8.3 Cyclic vs Non-Cyclic Photophosphorylation

Answer 38

Cyclic can be used to produce steady ATP w/ sunlight, however since ATP cannot be stored Non-Cyclic is needed for synthesis of organic molecules and long-term energy storage

Question 39

8.3 What is the calvin cycle?

Answer 39

The light independent reactions w/ three main steps

Question 40

8.3 Where does the calvin cycle occur?

Answer 40

The stoma

Question 41

8.3 What is the first step of the calvin cycle?

Answer 41

Carbon Fixation 1) The cycle starts with ribulose biphosphate, RuBP (5C) 2) Rubisco (RuBP carboxylase) catalyses attachement of CO2 to RuBP 3) The resulting 6C compound is unstable and breaks down into two 3C compounds glycerate-3-phosphate (GP) Cycle requires 3 RuBP = 6 GP

Question 42

8.3 What is the second step of the calvin cycle?

Answer 42

Reduction of GP 1) GP is converted into triose phosphate (TP) using ATP and NADPH 2) Reduction of NADPH provides hydrogen atom while ATP hydrolysis provides energy 6 GP per cycle = 6 ATP and 6 NADPH utilized

Question 43

8.3 What is the final step of the calvin cycle?

Answer 43

Regeneration of RuBP 1) One TP may be used to form half a sugar molecule, two cycles are required for one simple monomer 2) The remaining 5 TP's are combined to regenerate RuBP (5 x 3C = 3 x 5C) 3) The regeneration of RuBP requires energy from ATP 5 TPs --> 3 RuBP + 3 ATP used

Question 44

8.3 Structure of chloroplast

Answer 44

Thylakoids : flatted discs with small internal volume, max SA for ETC Grana: stacks of thylakoids Lamella: Connects granas Stroma: Central cavity that contains approriate enzymes and pH