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y1 genes, molecules and cells s2 > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Photosynthesis is broken up into two stage, what are they?

A

Light and dark reactions

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2
Q

What are they key features of the chloroplast

A
  • Chloroplast envelope
  • Granum
  • Thylakiod
  • Stroma
  • Nucleiod + Ribosomes
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3
Q

The light dependent reactions happens …

A

At the Thylakoids (stacks of grana)

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4
Q

What is the name of the principel photoreceptor

A

Chlorophyll
(highly conjugated molecule)

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5
Q

The absorption of photons by chlorophyll cause …

A

Transition from HOMO to LUMO
This energy is then immediately transmitted back OR photoionisation can occur

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6
Q

Plant photosynthesis is a …… process

A

non-cyclic

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7
Q

How many photosystems are used in photosynthesis

A

2

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8
Q

There are two reaction centres consisting of ‘special pairs’ of cholophyll molecules:
They are….

A
  • Photosystem II - oxidises H₂O (absorbs lights ~680nm)
  • Photosystem I - reduces NADP⁺ (absorbs light ~700nm)
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9
Q

Electrons move from photosystem II to photosystem I by

A

The electron transport chain
Operate in electrical series using redox reactions

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10
Q

When the electrons move from photosystem II to photosystem I, what is the name of the complex they travel through

A

Cytochrome b₆f
When electrons travel through this, it generates a proton gradient

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11
Q

What is the function of photosytem II within the electron transport chain

A
  • Catalyses the transfer of e⁻ from H₂O to plastoquinone
  • Photoxidation at PSII will lead to the reduction of plastoquinone (Q) to plastoquinol (QH₂)
  • This will then gain 2 protons forming QH₂
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12
Q

The PSII reaction centre once oxidised using plastoquinone, how is is reduced again

A
  • Utilises the oxygen evolving complex (containing Mn) to oxidise water (- 4e⁻)
  • Forms oxygen
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13
Q

Why when reducing plastiquinone to form 2QH₂ does it create a proton gradient

A

The protons to form it will be taken from the stoma

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14
Q

What reaction occurs at Cytochrome b₆f complex

A

Catalyses the transfer of electrons from plastoquinol (QH₂) to plastocyanin (Pc)
The plastoquinone formed is then reduced again in an addition cycle - further increases proton gradient

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15
Q

What happens at photosystem I

A
  • A photon of light with excite the electrons within the chlorophyl - photoxidation to A0
  • Electrons move onto Ferredoxin
  • Used to for 2NADPH catalysed by Fd-NADP⁺ reductase
  • Also increases proton gradient by uptake of protons from stoma
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16
Q

The result of the light dependent reactions is a transmembrane proton gradient
Where is the [H⁺] concentration greatest?

A

Greater [H⁺] in the thylakoid lumen

17
Q

The proton gradient is capitalised upon by

A

The chloroplast ATP synthase
Couples dissipation of proton gradient to enzymatic synthesis of ATP

18
Q

Per absorbed photon, how much ATP is produced from non-cyclic photosynthesis

A

Produces 1 ATP per absorbed photon

19
Q

At saturating light intensity: there is a proton gradient of ~3.5pH
Why?

A
  • Evolution of oxygen through lysis of H₂O will produce 4 protons
  • Transport of e⁻ through Cytochrome b₆f will translocate 8 protons into Lumen
  • NADP⁺ being reduced in the stroma
20
Q

The dark reaction of photosynthesis can be considered to have 2 stages

A

Production and Recovery

21
Q

Which two enzyme are part of the control for the dark reactions

A
  • Fructose bisphosphatase
  • Sedoheptulose bisphosphatase
22
Q

What is the name of the enzyme which fixes CO₂

A

Ribulose Bisphosphate Carboxylase (RuBP carboxylase)
(slow enzyme so is about 50% of leaf proteins)

23
Q

Rubsico is impacted by pH
Why?

A
  • Works best in alkaine pHs (protons are being removed from the stroma in the light dependent reaction)
  • (Mg²⁺ effux will balance membrane charge and stimulate RuBP)
24
Q

What compound will bind to RuBP carboxylase in the dark, to inhibit its activity

A

CA1P
(2-carboxyarabionitol-1-phosphate)

25
Q

How do FBPase & SBPase respond to NADPH

A

As the light reactions starts, NADPH will be generated
Hence FBPase and & SBPase will be stimulated by NADPH

26
Q

Thioredoxin contains a reversible reducible disulphide group
How does this affect the regulation of the dark reaction

A

Reduced thioredoxin activates FBPase and SBPase

27
Q

What is the primary output of photosynthesis

A

GAP (glyceraldehyde-3-phosphate)
Used in multiple pathways inside and outside the chloroplast with being a precursor to higher order carbohydrates

28
Q

How is glucose stored within the cell or the plant

A

α-amylose as a starch component
Driven by PPi hydrolysis

29
Q

What can GAP go on to form to aid in the structure and function of the plant cells

A

Sucrose - primary energy molecule
Cellulose - structural molecule

y1 genes, molecules and cells s2 (12 decks)

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