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Alevel Biology > Respiration & Photosynthesis > Flashcards

Respiration & Photosynthesis Flashcards

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1
Q

Name 2 uses of ATP

A

ATP
Muscle contraction, blood circulation
Drive chemical reaction e.g. metabolic processes
Active transport and bulk transport

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2
Q

Why is ATP suitable as an energy source?

A
  1. Universal energy currency. ATP is a carrier of energy, does not store energy
  2. Readily soluble, highly mobile, can be transported readily/diffuses readily to point of need
  3. Serves as intermediary between energy yielding and energy requiring reactions
  4. Easy release of energy and easily reformed: ADP + Pi forms ATP during glucose oxidation, ATP can be easily hydrolysed to ADP + Pi
  5. Leading to energy released for cellular work
  6. ATP produced from a variety of reactions e.g. substrate level phosphorylation, oxidative phosphorylation and photophosphorylation
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3
Q

How is the mitochondrion adapted for its function?

A
  • Circular DNA: genes coding for mitochondrial specific enzymes; allows mitochondria to replicate independently of nucleus
  • Ribosomes: site for translation of essential mitochondrial specific proteins + EC of ETC can be produced
  • Enzymes in matrix: for link rxn and Krebs cycle
  • Compartmentalisation→ isolates Krebs cycle and OP from glycolysis in cytosol→ concentrates enzymes needed in a fixed compartment & provide optimal conditions→ improve efficiency (Krebs cycle in matrix, OP across cristae)
  • Inner membrane is highly folded to increases surface area for attachment of many ECs involved in ETC* and ATP synthase*
  • By being membrane bound, enzymes can be attached in an ordered sequence that facilitates transport of electrons. This improves efficiency;
  • P.lipid bilayer enclosing intermembrane space is impermeable to ions→ build up of protons→ proton gradient* across inner membrane→ production of ATP* from ADP, via chemiosmosis, by ATP synthase*
  • Selective permeability of mitochondrial double membrane to oxygen and pyruvate→ constant supply of these substrates; carbon dioxide to leave as a by-product
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4
Q

State the 4 steps in glycolysis

A
  1. Phosphorylation of glucose ⇒ fructose 1,6-bisphosphate (6C)
  2. Lysis
  3. Oxidation by dehydrogenation (remove H) ⇒ 1,3-bisphosphoglycerate
  4. Substrate-level phosphorylation
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5
Q

Describe what happens + purpose in glycolysis: phosphorylation of glucose

A
  • initial investment of 2ATP ==> fructose 1,6-bisphosphate
  • phosphofructokinase (PFK) catalyses addition of 2nd phosphate group
  • activates sugar–> more reactive and committed to the glycolytic pathway
  • -ve charge on glucose–> membrane impermeable to it, cannot diffuse across cell membrane–> trapped in cytosol
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6
Q

What is PFK enzyme activated and inhibited by?

A

Stimulated by AMP and ADP (allosteric activators)

Inhibited by excess ATP/citrate (allosteric inhibitor)

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7
Q

Describe what happens in glycolysis: lysis

A

fructose 1,6-bisphosphate (6C) lyses into 2 (3C): glyceraldehyde-3-phosphate (G3P) / triose phosphate (TP) / phosphoglyceraldehyde (PGAL)

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8
Q

What happens in glycolysis: oxidation by dehydrogenation?

A
  • G3P oxidised by dehydrogenation–> Coenzyme NAD (nicotinamide adenine dinucleotide) reduced to NADH
  • Energy used to add Pi
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9
Q

What happens in glycolysis: substrate-level phosphorylation?

A

1,3-bisphosphoglycerate dephosphorylated ⇒ pyruvate

Pi transferred to ADP → 2 x 2 ATP formed

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10
Q

What happens during link reaction?

A
  • 2 pyruvate + 2 NAD→ 2 acetyl CoA + 2 CO2 + 2 NADH
  • Pyruvate (3C) undergoes oxidative (by dehydrogenation) decarboxylation→ NADH + loss of CO2 + 2C compound
  • 2C + coenzyme A → acetyl coenzyme A (acetyl CoA)
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11
Q

What happens during Krebs Cycle?

A
  • Acetyl CoA (2C) + oxaloacetate (4C) → citrate (citric acid) (6C)
  • Citrate undergoes oxidative (via dehydrogenation) decarboxylation → α-ketoglutarate (5C) + NADH + CO2
  • Regeneration of oxaloacetate:
    > 1 decarboxylation→ 1 CO2
    > 3 dehydrogenation→ 2 NADH + 1 FADH2
    > 1 substrate level phosphorylation→ 1 ATP

1 glucose→2 acetyl CoA→ 2x(2CO2 + 3NADH + 1 FADH2 + 1 ATP)

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12
Q

What can ECs be inhibited by?

A
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13
Q

All ECs are cytochrome complexes, can be inhibited by cyanide

A

All ECs are cytochrome complexes, can be inhibited by cyanide

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14
Q

What are the functions of ETC?

A
  • Generate proton motive force to produce ATP

- Regeneration of coenzymes NAD and FAD so that they can pick up more …

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15
Q

What are the functions of NAD and FAD?

A
  • *High energy e– from oxidation of organic mlcs in glycolysis, link reaction and Krebs cycle are transferred to NAD and FAD, reducing them→ NADH, FADH2
  • *Are coenzymes, serving as mobile e– carriers, to transport high-energy electrons from organic molecules to ETC, reducing ECs
    > e– passes down ECs; protons liberated establish proton gradient→ phosphorylation of ADP into ATP
    >1 NADH = 3 ATP, 1 FADH = 2 ATP through OP
  • *NADH and FADH2 are re-oxidised, regenerating NAD and FAD for them to pick up more e- and protons from glycolysis, link rxn and Krebs cycle
  • Anaerobic: regeneration of NAD allow glycolysis to continue
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16
Q

Describe what happens during oxidative phosphorylation

A
  1. NADH from glycolysis, link rxn & Krebs cycle donates high energy electrons to 1st EC of ETC→ 1st EC reduced; NADH oxidised to NAD, NAD is regenerated and can pick up e– and protons from glycolysis, link rxn and Krebs cycle
  2. 1st reduced EC transfers e– to next EC and reduces it, itself reoxidised
  3. Transfer of e– continues until it combines with H+ and molecular oxygen, the final electron acceptor → metabolic H2O in matrix
    - Catalysed by *cytochrome oxidase
  4. Flow of high energy e– down increasingly EN ETC releases energy to pump H+ from the mitochondrial matrix, across the inner mitochondrial membrane, into intermembrane space, via some of the ECs.
    - Proton gradient created, as p.lipid bilayer of inner mitochondrial membrane is impermeable to ions e.g. H+
  5. H+ diffuses down its conc gradient through ATP synthase→ ATP synthase activated, ATP is produced from ADP and inorganic phosphate, via chemiosmosis
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17
Q

Explain the importance of O2

A
  • Act as final e– acceptor at the end of ETC, by combining w e– and H+ to form water→ re-oxidises ETC so e– carriers NADH and FADH can continue donating e– to ETC→ allow e– flow→ allow OP to continue to generate ATP by chemiosmosis
  • NAD & FAD regenerated when NADH and FADH donates e– to ETC, allowing NAD and FAD to pick up more e– and protons from glycolysis, link reaction and Krebs cycle, allow these to continue
  • Reduction of O2 to water removes H+ from matrix→ contribute to generating proton gradient across inner mitochondrial membrane
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18
Q

Explain what is meant by chemiosmosis

A
  • mechanism where energy stored in the form of a proton gradient across a membrane is used to drive ATP synthesis
  • movement of chemicals (H+) down conc gradient via ATP synthase embedded in the inner membrane of mitochondrion
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19
Q

1 NADH or FADH generates how much ATP?

A

1 NADH–> 3 ATP (or 2.5)

1 FADH2–> 2 ATP (or 1.5)

20
Q

How much ATP, NADH, CO2 and FADH2 is generated in glycolysis, link rxn, Krebs cycle, OP and in total respectively? (per mlc of glucose)

A

ATP NADH CO2 FADH2
Glycolysis 2 net 2 0 0
Link rxn 0 0 2 0
Krebs cycle 1x2 3x2 2x2 1x2
OP 30 (NADH) 10 6 2
+4 (FADH2)
Total: 38 ATP

21
Q

Why do different cell types produce <38 ATP?

A
  • Mitochondrial membrane impermeable to NADH from glycolysis → NADH passes e– and protons to NAD or FAD inside mitochondrion via shuttle system
  • Diff shuttle system/pass to FAD→ 2 ATP produced instead of 3
22
Q

What is the function of alcohol fermentation and lactic acid fermentation?

A
  • Produce small yield of energy: net 2 ATP produced per glucose in glycolysis. Produces 1/19 of ATP from aerobic respiration
  • Regenerate NAD from NADH, ensuring a steady supply of NAD for glycolysis to continue to produce 2 ATP
23
Q

Explain how anaerobic conditions occur

A

No O2, no final e– acceptor to accept e– from ETCs → ECs remain reduced; NADH and FADH remain reduced and can no longer donate e– to ETC→ OP stops→ NAD & FAD not regenerated in OP to pick up more e– and protons from link rxn, Krebs cycle and OP→ link reaction, Krebs cycle stops→ anaerobic conditions

24
Q

Describe alcohol fermentation

A
  1. Decarboxylation of pyruvate→ ethanal (2C) + CO2
    • pyruvate decarboxylase
  2. Ethanal reduced to ethanol by alcohol dehydrogenase. NADH recycled, NAD regenerated for glycolysis to continue
    (Ethanal is the final electron acceptor here)
25
Q

Describe what happens in lactic acid fermentation

A

Pyruvate, the final electron acceptor, is reduced → lactic acid/lactate. NAD regenerated
- lactate dehydrogenase

26
Q

Why does lactic acid fermentation occur during exercise?

A

Muscle contracts creates very high demand for ATP→ high rate of glycolysis depletes limited supply of NAD→ OP unable to replenish NAD quickly enough to meet ATP→ additional system, anaerobic respiration via lactic acid fermentation, needed to regenerate NAD

27
Q

What is the role of carotenoids (accessory pigments)?

A

photoprotective role, absorb & dissipate excess light energy that could damage chlorophyll

28
Q

How is the structure of chloroplast adapted for photosynthesis?

A
  • Thylakoids
    > Stacked as granum→ provides a large sf area to embed many photosynthetic pigments/chlorophyll mlcs for light absorption, ETC & ATP synthase so ATP can be produced as protons flow down their gradient via chemiosmosis
    > Hydrophobic core of p.lipid bilayer impermeable to protons→ accumulate protons→ maintain proton gradient for ATP synthesis, essential to chemiosmosis
    > Maintains sequential arrangement of photosystems and ECs of ETC for the flow of electrons
  • Starch grains: store starch formed
  • Circular DNA: contains genes that code for ATP synthase, ETC, RuBisCO, other chloroplast specific enzymes/proteins→ only chloroplast has RuBisCO and can carry out Calvin cycle
  • Ribosomes: translation of chloroplast specific proteins/enzymes
  • Enzymes in stroma involved in Calvin cycle
29
Q

What does the absorption spectrum show?

A

Each pigment has its own specific spectrum
Each pigment has a different number, height and breadth of peaks
Pigments don’t absorb green light strongly (absorb red & blue light most)

30
Q

Compare the absorption spectrum and action spectrum

A

both are similar (wavelengths of peaks and troughs coinciding), but does not exactly match the combined absorption spectrums of chl a, chl b and carotenoid

31
Q

What is the role of accessory pigments?

A

broadens spectrum of wavelength of light over which photosynthesis can occur

32
Q

Describe the structure of PSI and PSII

A
  • Reaction centre: 2 special chl a + primary electron acceptor
  • Surrounded by light-harvesting complex: accessory pigment molecules (e.g. chl a/b, carotenoids) bound to proteins

PS II: contain P680 (special chl a), absorbs light of wavelength 680 nm
PS I: contains P700 (special chl a), absorbs light of wavelength 700 nm

33
Q

What is the role of NADP?

A
  • The final e– acceptor in the non-cyclic LD rxn, reduced to NADPH
  • A coenzyme, carrier for protons and high energy e– from PS in LD stage to Calvin cycle in stroma
  • e– carried in NADPH used in Calvin cycle in stroma, to reduce GP to G3P→ NADP is regenerated to carry out its role as e– carrier in LD
34
Q

Describe non-cyclic photophosphorylation

A
  1. A photon of light is absorbed by a chl mlc in light harvesting complex of PS II/I→ e–is excited to a higher energy level. Drops to its ground state, energy released is passed on to the next pigment molecule. Energy is relayed from pigment to pigment, via resonance transfer of energy until it reaches one of the special chl a, P680/P700, in the reaction centre of PS II/I.
  2. P680/P700 emits an excited e–, which is captured by the primary electron acceptor
  3. There is hence an electron hole in PSII. Photolysis and splitting water in enzyme catalysed rxn releases e- and H+ in thylakoid space
    • mlc oxygen formed as by product
  4. e– from the primary e acceptor is then passed down a series of (increasingly EN) ECs
  5. Flow of e– down ETC releases energy through redox rxns, which is used to actively pump H+ from the stroma to the thylakoid space→ proton gradient
  6. Chemiosmosis: H+ diffuse down the proton gradient back into the stroma via ATP synthase, & ADP is phosphorylated to ATP.
  7. Meanwhile, P700 absorbs energy, excited e emitted and captured by primary e acceptor–> e- hole, filled by displaced e from PSII
  8. e from PSI passed down 2nd ETC, accepted by NADP, the final e acceptor, reduced to NADPH by NADPH reductase
35
Q

Describe cyclic photophosphorylation

A
  1. A photon of light is absorbed by a chl mlc in light harvesting complex of PS I→ e–is excited to a higher energy level. Drops to its ground state, energy released is passed on to the next pigment molecule. Energy is relayed from pigment to pigment, via resonance transfer of energy until it reaches one of the special chl a, P700, in the reaction centre of PS I.
  2. Cyclical flow of e-: e– from the primary e acceptor is transferred to the middle of the ETC linking PSII and PSI, transported down ETC and recycled back to PSI
  3. Flow of e– down ETC releases energy through redox rxns, which is used to actively pump H+ from the stroma to the thylakoid space→ proton gradient
  4. Chemiosmosis: H+ diffuse down the proton gradient back into the stroma via ATP synthase, & ADP is phosphorylated to ATP.

No NADPH produced

36
Q

Why is cyclic photophosphorylation necessary?

A

Non-cyclic→ ATP and NADPH produced in roughly equal amts

Calvin cycle uses more ATP than NADPH. Cyclic rxn makes up the difference by producing only ATP

37
Q

Compare non-cyclic and cyclic photophosphorylation

A

S

  • energy lost from flow of e used to pump H+ across membrane, proton gradient
  • ADP phosphorylated to ATP via ATP synthase, using energy from flow of protons down their gradient via chemiosmosis
  • both on membranes

D

  • PS involved
  • Conditions
  • Pathway of e–
  • Source of e– / e– donor
  • Last e– acceptor
  • Products

S/D: Contributing to high H+ in thylakoid space

  • S–> pumping of H+, lack of permeability of membrane
  • D–> photolysis of water + reduction of NADP into NADPH VS no photolysis and reduction
38
Q

Describe the 3 phases of Calvin cycle

A
  1. Carbon fixation
    - CO2 + RuBP, catalysed by RuBisCO → unstable 6C, which immediately breakdown→ 2 GP
  2. Reduction
    - NADPH is the reducing power used to reduce GP to G3P, the basic sugar used to synthesise other carbs & the 1st sugar formed in photosynthesis and end-product of Calvin cycle
    - 6 NADPH → 6 NADP+ per GP
    - ATP needed: 6 ATP→ 6 ADP + Pi per GP
  3. RuBP regeneration
    - 5 mlc G3P + 3 ATP (needed) → 3 RuBP + 3 ADP
39
Q

Compare LD and LID

A 
Location
Conditions
Reactions involved
Reactants
Products
By-products
40
Q

Define limiting factor

A

any factor that directly affects a process and hence rate of reaction, if its magnitude is changed

41
Q

Explain the effect of light as limiting factor on the rate of photosynthesis

A
  • LD stage, photoactivation: light excites e– in photosynthetic pigments to higher energy state
  • Rate of photosynthesis high under wavelengths of light about 700nm (red light) & about 470 nm(blue light)
  • Light intensity rarely limiting during daylight hrs
  • Light compensation point*, photosynthetic rate = respiration rate→ amt of CO2 given out during respiration = amt of CO2 fixed during LID of photosynthesis ⇒ no net gain in dry mass, no growth
42
Q

Explain the effect of no light on ant of GP and RuBP

A

No light→ no LD and photolysis of water, no O2 → no NADPH and ATP to reduce GP to G3P + C fixation still occurs→ GP still made ⇒ net increase in GP

lack of G3P for regeneration, & RuBP regeneration slows + RuBP carboxylated and converted to GP, as carbon fixation doesn’t require ATP or NADPH and can continue→ net drop in RuBP

43
Q

Explain effect of CO2 as limiting factors on rate of photosynthesis

A
  • CO2 is used in carbon fixation of RuBP catalysed by RuBisCO*;
  • Since atmospheric [CO2] is at a low level of 0.04%, CO2 becomes a limiting factor of photosynthesis;
  • Increased [CO2] will increase rate of photosynthesis: ↑ [CO2] → ↑ freq of effective collisions* between CO2, RuBP and RuBisCO→ ↑ enzyme-substrate complex* formed per unit time→ ↑ rate of C fixation, which ↑ rate of Calvin cycle
    → ↑ synthesis of GP and G3P→ faster use of NADPH and ATP→ more glucose produced; faster regeneration of NADP→ faster rate of photolysis and O2 production
44
Q

What happens when there’s a high O2 concentration?

A

Photorespiration:

  • RuBisCO accepts O2 as competitive inhibitor
  • RuBP splits into GP (3C) and glycolate (2C), glycolate converted to CO2
  • no ATP produced
45
Q

Compare respiration and photosynthesis

A 
Metabolism
Energy
Location
Conditions
Oxygen
CO2 & H2O
Major rxns
e– carrier
High [H+]
Dry mass
46
Q

Compare PP and OP

A 
Location (S/D)
Energy
- Source
- Light needed?
- Energy conversion
Flow of e-- 
- no. of ETC
- e-- pathway
- e-- donors
- e-- acceptor
By-product
Proton gradient
- Chemiosmosis (S)
- Direction
- What contributes
47
Q

Compare Calvin cycle and Krebs cycle

A 
Nature
Location
CO2 fate
Role of coenzymes
ATP role
Substance regenerated
Rxns

Alevel Biology (16 decks)

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