Plants Lecture 1 – The Light Reaction of Photosynthesis Flashcards Preview

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Flashcards in Plants Lecture 1 – The Light Reaction of Photosynthesis Deck (26)
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1
Q

Light energy → ______ + ______ (this lecture)
which needs to happen to then allow
CO2 + H2O → ________ (next lecture)

A

ATP + NADPH

Carbohydrates

2
Q

What is the chromophore?

A

The absorbing molecule

3
Q

The energy in a quantum of light must = the energy required ________

A

to excite the chromophore

4
Q

If the chromophore loses energy it falls back down to its _____ state and gives off 4 things. What are they?

A

Ground state

Heat, fluorescence, exciton transfer, charge transfer

5
Q

What are the 2 sources of energy that drive ATP synthesis?

A
  1. Chemical bonds of nutrients (food)

2. Sunlight

6
Q

Photosynthesis can be divided into 2 types/phases of reactions. What are they? Where do each of them occur in the plant?

A
  1. Light-dependent reactions - thylakoid membranes (this lecture)
  2. Carbon-assimilated reactions - stroma (next lecture)

A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen.

7
Q

Thylakoids stack to form _____?

A

Grana

8
Q

Structure of chlorophyll = a _______ cage + a _____ atom

A

Tetrapyrrole cage + a Mg atom (in heam it is Fe though)

9
Q

What is the main pigment used in red algae and cyanobacteria?

A

Phycobilins

10
Q

Carotenoids are accessory pigments. What are 2 of their roles?

A
  1. Capture more light at wavelengths that chlorophyll can’t

2. Protect against ROS (particularly singlet oxygen - a type of ROS)

11
Q

What does a pigment’s action spectra help to tell us?

A

It tells us the wavelength at which a pigment most strongly absorbs and hence is most active at.
They help us deduce which pigment is responsible for a particular light-induced biological effect.

12
Q

What part of thylakoid membranes do the first photosynthetic steps occur? What is it made up of?
What happens here starting from when light is absorbed?

A

Photosystems which are found in the thylakoid membranes. Spinach ones comprise ~200 chlorophyll + ~50 carotenoid molecules.
2 chlorophyll molecules form the REACTION CENTRE in the middle and the leftover chloropgyll + carotenoids form ANTENNA MOLECULES.
The AMs absorb light and pass it into the middle to the RC.

13
Q

In the Reaction Centre, _____ energy is converted to ____ energy.

A

Light –> chemical

14
Q

The Antenna Molecules surrounding the Reaction Centre in Photosystems can bind to specific proteins to form specific structures. What are 2 of these structures?

A
  1. CORE COMPLEX around the RC
  2. LIGHT-HARVESTING COMPLEXES (LHC) around the outside of the CC e.g. LHCII which comprises 36 chlorophyll + 6 lutein molecules
15
Q

Once light reaches one of the Chls in the RC, an electron is promoted to a higher/lower energy level. This electron is then _____ to a nearby ____ ____ (which is part of the chloroplast electron transport chain and is negatively charged) and is replaced by an electron from a neighbouring ____ ____.

This continuously happens (electron passed out, one comes in to take its place, setting up a series of ____ ____. This is known as ____ ______.

A

higher, donated, electron acceptor
electron donor

redox reactions, charge separation

16
Q

Photosynthetic electron transport allows ______ + ______.

A

Proton pumping (across the thylakoid membrane) + ATP synthesis

17
Q

The cytochrome bc1 complex is analogous to _____ in the mitochondrial electron transport chain. This complex acts as a pump pumping protons across the thylakoid membrane to create a proton gradient which is required to form ____.

A

Complex III

ATP

18
Q

If we precisely orientate our photosystems (most importantly the chromophores ) we can prevent _________ by the process of ____ _____.

A

the excited state of the RC decaying to its ground state.

internal conversion.

19
Q

The reactions that occur in charge separation are _____ and ____ ____. This makes them irreversible.

A

Fast and thermodynamically downhill (negative delta g)

20
Q

Does each photosystem have the same wavelength of light that is absorbs or different?

A

Different

21
Q

What wavelengths do PSI and PSII absorb at?

A

PSI: 700nm
PSII: 680nm

** Both in red light **

22
Q

Is it PSI or PSII that rips electrons from water?

Where does this electron go?

A

PSII
Goes through PSII then the electron goes out into the electron donor and then into the Cytochrom b6f complex and into PSI. It then moves through PSI and onto another electron acceptor which then moves it onto NADP+ converting it to NADPH.
*** This is the Z-scheme

23
Q

Often photosystems work in parallel to maximise efficiency. PSI and PSII work together in a Z-_____

A

Z-scheme

“Electrons are transferred from H20 to NADP+ in a ‘Z-scheme’.”

24
Q

__ electron is transferred from H2O to NADP+ for every __ photons absorbed.
__ molecule of O2 is formed for every __ photons absorbed.

A

1, 2.

1, 8.

25
Q

Cyclic electron transfer occurs when electrons from the ______ move back to the ______ complex, resulting in the production of more ___ and less ___.

A

Ferrodoxin, cytochrome b6f complex, more ATP, less NADPH.

26
Q

PSII is a dimer/trimer. Each monomer in the dimer/trimer consists of ___ proteins. The ability to split water by this complex is dependent on the complex _____. This mechanism is similar to that found in the photo system of purple _____.

PSI is a dimer/trimer. Each monomer in the dimer/trimer consists of ___ proteins.

A

Dimer, 19, Mn4CaO5, purple bacteria

Trimer, 16