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Cell Biology > Photosynthesis and Carbon Assimilation > Flashcards

Photosynthesis and Carbon Assimilation Flashcards

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1
Q

Define metabolism

A

the totality of an organism’s chemical reactions

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2
Q

What does metabolism arise from?

A

Arises from interactions between molecules

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3
Q

A metabolic pathway has …

A

…many steps

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4
Q

What does the metabolic pathway begin with?

A
  • Begin with a specific molecule and end with a product
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5
Q

Each step in the metabolic pathway catalysed by a _____ ______

A
  • Each step in the metabolic pathway catalysed by a specific enzyme
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6
Q

Catabolic pathways break down…

A

…complex molecules into simpler compounds, releasing energy

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7
Q

Examples of catabolic pathways?

A

Glycolysis, Krebs Cycle

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8
Q

Examples of anabolic pathways?

A

Photosynthesis

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9
Q

Anabolic pathways build…

A

….complicated molecules from simpler ones.
- Consume energy

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10
Q

The capture of solar energy and its conversion to chemical energy is the …

A

…ultimate source of nearly all biological energy.

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11
Q

Photosynthetic organisms use …

A

…solar energy to form ATP and NADPH that are used to as energy sources to make carbohydrates and other compounds.

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12
Q

Photosynthesis takes place in:

A

higher plants
varieties of bacteria
algae

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13
Q

THe photosynthetic process in higher plants is shown in two processes which are…

A
  • light-dependent reactions (light reactions)
  • carbon-assimilation reactions (“dark reactions” – misleading, also take place in the light! sometimes called “light independent reactions”)
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14
Q

The photosynthesis process is similar in all organisms and based on the redox process:

A

CO2 + H2O –> O2 + (CH2O)

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15
Q

Where do Light dependent and carbon assimilation reactions take place?

A

In the chloroplast

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16
Q

Chloroplasts have their own…

A

…dna

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17
Q

CHloroplasts are surrounded by…

A

a double membrane (two membranes)
(an outer and inner membrane)

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18
Q

Chloroplasts contain…

A

….thylakoids

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19
Q

WHat are thylakoids?

A

Flattened membrane surrounded vesicles

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20
Q

What are thylakoids arranged in?

A

Arranged in stacks called GRANA

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21
Q

THe outer membrane of chloroplasts is permeable to…

A

…small ions

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22
Q

The inner membrane of chloroplasts ecloses a…

A

…compartment

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23
Q

In the thylakoids membranes (called lamellae) are the…

A

…photosynthetic pigments and enzyme complexes that perform light reactions and ATP synthesis

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24
Q

What makes us see a colour (EG: Green)?

A

White light is absorbed and only the green light is reflected by the pigment.
A pigment is a chemical (or cocktail of chemicals) that absorbs visible in all
Regions EXCEPT at 500-560 nm (see examples below).

25
Q

The exact colour you see depends on…

A

…the precise wavelengths absorbed

26
Q

What colour is not absorbed by plants for photosynthesis?

A

Green

27
Q

Electromagnetic waves are made of …

A

…photons

28
Q

What are photons?

A

(particles of energy - no mass)

29
Q

electromagnetic waves travel at the…

A

…speed of light - but differ in frequency and wavelength

30
Q

How does light absorption work?

A

A molecule struck by a photon with the right frequency and wavelength will absorb the photon´s energy and achieve an excited state

31
Q

If the energy of the photon exactly matches the energy required to excite an electron to a higher energy level…

A

…it is absorbed and the electron moves to the excited state

The electron now possesses more energy.

32
Q

The excited electron soon returns to the …

A

…ground state (it decays), giving off the absorbed energy as either light (fluorescence) or heat, but in photosynthesis, the energy released is captured by another energy absorbing molecule.

33
Q

How is energy transferred across the antenna to the reaction center?

A

As energy

34
Q

The energy irradiated (given off) is always…

A

…of a longer wavelength (lower energy) than the energy absorbed.

35
Q

Pigments in the Thylakoids are arranged in functional arrays which are…

A

…PHOTOSYSTEMS

36
Q

Each photosystem has…

A

~200 molecules of chlorophylls
~50 molecules of carotenoids

37
Q

The majority of pigment molecules in the system are called:

A

LIGHT HARVESTING or
ANTENNA MOLECULES

38
Q

What do LIGHT HARVESTING or
ANTENNA MOLECULES do?

A

absorb light energy and transmit it to the reaction centre

39
Q

What occurs at the reaction center?

A

Photochemical reaction here converts the energy of a photon initiating electron flow.

40
Q

An electron acts as an…

A

…energy store in each antenna molecule and reaction centre using its physical quantum state to define it

41
Q

If we have a line of electrons in adjacent antenna molecules…

A

… the excited state passes not the electron

42
Q

Chloroplasts have two different types of…

A

… photochemical reaction centres acting in tandem

43
Q

Describe the Z Scheme

A
  • Electrons that originate from water are fed into reaction centre P680 (photosystem II)
  • They are excited by excitons, where they are passed via several electron carriers to photosytem I and its reaction centre P700
  • Here they are excited again before being passed along more electron carriers eventually to NADP to form NADPH
44
Q

The electron transport chains are located within the …

A

…thylakoid membrane

45
Q

WHat happens within the thylakoid membranes in photosystems?

A

the energy of electron transport is used to pump protons across the membrane from the stroma to the inside of the thylakoid membrane.

46
Q

ATP Synthesis by Photophosphorylation

A
  • PS I and PS II move electrons from H2O to NADP+
  • Energy from this process is conserved as:
    1. NADPH
    2. H+ gradient
      (electrochemical potential)
47
Q

How much ATP is synthesised by photophosphorylation?

A

O2 + 3 ATP + 2 NADPH

48
Q

What is the difference between the number of protons required to make 1 ATP in mitochondria and chloroplasts?

A

None (no difference)

49
Q

Is the light reaction strictly anabolic?

A

No

50
Q

Is the calvin benson reaction strictly anabolic?

A

Yes

51
Q

Describe Carbohydrate biosynthesis.

A

Plants are able to take the most oxidised form of carbon (CO2) and reduce it with water to make carbohydrates using the energy derived from the light-dependent reactions of photosynthesis

52
Q

CO2 is the…

A

…SOLE source of carbon atoms required for biosynthesis of all other plant biomolecules

53
Q

What is CO2 assimilation?

A

CO2 assimiliation where CO2 is incorporated into a three-carbon compound called 3-phosphoglycerate

54
Q

Carbon Assimilation occurs in …

A

… 3 stages

55
Q

What are the three stages of the Calvin-Benson Cycle?

A

1) CO2 –> biomolecules
2) Reduction of 3 Phosphoglycerate —> Glyceraldehyde 3-phosphate
3) Regeneration of Ribulose 1,5-bisphosphate

56
Q

The light-dependent reactions (the Z-scheme) creates …

A

…equal amounts of NADPH and ATP.

  • We need more ATP than NADPH!!
57
Q

How can we obtain more ATP than NADPH?

A

This can be achieved by cyclic electron flow in the Z-scheme prevents NADPH formation and boosts ATP production to provide the relative proportions for glyceraldehyde 3-phosphate production.

58
Q

Cyclic flow balances…

A

…ATP and NADPH production for carbon assimilation

59
Q

What is produced in Cyclin electron flow?

A

Electrons are pumped continuously
around Photosystem I.
- ATP is generated (Cyt b6f)
- no O2 is produced
- no NADPH is produced

3:2 ratio of ATP:NADPH

Cell Biology (19 decks)

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