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BIO1011 > Powering Life: Capturing Light to Build Carbohydrates > Flashcards

Powering Life: Capturing Light to Build Carbohydrates Flashcards

1
Q

types of energy

A

Light
Chemical
Heat

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2
Q

photo autotroph

A

organisms that harness light energy to synthesis organic compounds from inorganic carbon compounds.
Usually sugars
Plants, algae and cyanobacteria do this

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3
Q

photosynthesis location

A

In plants, it occurs in the chloroplast

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4
Q

light dependent reaction

A

Chlorophyll absorbs light energy for the cytolysis of water
Splitting water releases to oxygen gas and protons and electrons
Protons drive ATP production by chemiosmosis
Electrons pass down the electron transport chain to produce NADPH

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5
Q

light independent reaction

A

ATP and NADPH are the sources of chemical energy for the Calvin cycle
Enzyme rubisco is used - most abundant protein on the planet
Carbohydrates are created

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6
Q

redox reactions summary

A

Redox reactions: electrons are transferred from one reactant to another.
Gaining an electron (and energy) is reduction
Losing and electron (and energy) is oxidation (electron donor)
OIL RIG
Adding electrons reduces charge

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7
Q

equation of photosynthesis and reduction and oxidation

A

Energy + 6CO2 + 6H2O —> C6H12O6 + 6O2

CO2 is reduced to C6H12O6
H2O is oxidised to O2

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8
Q

what is the photic zone in oceans?

A

Photic zone: surface to 100m in an ocean where sun can still reach.

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9
Q

where does the electron transport chain take place? bacteria and eukaryotes

A

Electrons move between large protein complexes embedded in specialised membranes
In bacteria - in the membrane or membranes in the cytoplasm
Eukaryote - in chloroplasts

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10
Q

electron transport chain - thylakoid membrane, grana, lumen, stroma

A

Thylakoid membrane: highly folded membrane in chloroplasts where electron transport chain is located and where light is captured.

Grana: stacks of thylakoid membranes connected by membrane bridges.

Lumen: a single interconnected compartment within thylakoid membranes.

Stroma: region surrounding the thylakoid membranes where carbohydrate synthesis takes place.

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11
Q

what is the Calvin cycle?

A

Calvin cycle: 15 chemical reactions that synthesis carbohydrates from CO2.

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12
Q

steps of Calvin cycle

A

Carboxylation - CO2 is added to a 5 carbon molecule
Reduction - energy and electrons are transferred to the compounds formed in step 1
Regeneration of the 5-carbon molecule needed for carboxylation

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13
Q

step 1 of the Calvin cycle

A

Incorporation of CO2 is catalysed by the enzyme rubisco
CO2 is added to 5-carbon sugar ribulose 1,5-bisphosphate (RuBP) by ribulose bisphosphate (rubisco)

Carboxylase: an enzyme that adds CO2 to another molecule.

Rubisco:
RuBP and CO2 diffuse into its active site
Once occupied, RuBP and CO2 can enter without energy (spontaneously)
6 carbon compound is produced and it immediately breaks into two 3-phosphoglycerate (3-PGA) molecules
First stable products of the Calvin cycle

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14
Q

step two of the Calvin cycle

A

Nicotinamide adenine dinucleotide phosphate (NADPH): reducing agent in the Calvin cycle.
Moves freely in the stroma
Energy and electrons are only transferred to NADPH with a specific enzyme, allowing for control over the fate of the electrons.
Two NADPH and two ATP are required for each CO2 (because of the two 3-PGA)

Reduction of 3-PGA:
ATP donates a phosphate group to 3-PGA
NADPH transfers two electrons plus one proton (H+) to the phosphorylated compound which releases Pi.

Forms 3-carbon carbohydrate molecules called triose phosphates (true product of the Calvin cycle)
Triose phosphates are exported from the chloroplast and glucose and sucrose are assembled in the cytoplasm
Most triose phosphate are used to regenerate RuBP
1 in 6 triose phosphate molecules is moved to the cytoplasm

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15
Q

step 3 of the Calvin cycle

A

12 out of 15 reactions that make up Calvin cycle
Five 3-carbon triose phosphate to three 5-carbon RuBP
ATP required

Total Energy usage for Calvin cycle:
2 NADPH
3 ATP
For each CO2

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16
Q

why does the Calvin cycle require light?

A

Light independent but…
NADPH and ATP are supplied by photosynthetic electron transport chain
Some enzymes are regulated by cofactors activated by the photosynthetic electron chain

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17
Q

radioactive CO2

A

Radioactive CO2 in unicellular green alga
Boiling alcohol halted enzyme reactions
Carbon compounds produced by photosynthesis were radioactively labeled
Then shorten exposure of CO2 so that only one compound is labelled and thus 3-PGA is the initial product
Then determined first step was addition of CO2 to RuBP

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18
Q

carbohydrates stored as starch

A

If sugars accumulated, osmosis would make water fill cell
Converted to starch which is not soluble
Can use the starch as a source of carbohydrates at night

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19
Q

light dependent stage - chlorophyll

A

Chlorophyll: major photosynthetic pigment.
Green - poorly absorbs green wavelengths
Large, light absorbing head that has a magnesium atom - alternating single and double bonds (efficiency in absorbing light)
Long hydrocarbon tail - binds molecules to integral membrane proteins in the thylakoid membranes

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20
Q

light dependent stage and visible light

A

Visible light: is part of the electromagnetic spectrum that we can see (400-700nm), 40% of sun’s energy.
Pigments absorb some wavelengths and reflect light they don’t absorb

21
Q

light dependent stage and photosystems

A

Photosystems: protein-pigment complexes that are functional and structural and absorb light energy and use it to drive the electron transport chain.

22
Q

light dependent stage and accessory pigments

A

Accessory pigments: pigments other than chlorophyll.
Orange-yellow carotenoids which absorb light poorly absorbed by chlorophyll
Allows a broader spectrum of light to be absorbed
Protect the electron transport chain from damage

23
Q

electron transport chain in solution

A

Chlorophyll molecule absorbed visible light and an electron is excited to a higher energy level
Light (fluorescence) and heat energy is rapidly released
Electron returns to ground state

24
Q

electron transport chain in a cell

A

Energy is transferred ti an adjacent chlorophyll molecule instead of being lost as heat
Energy level is raised in adjacent chlorophyll
Efficient energy transfer - little is lost
Moved from molecule to molecule
Finally transferred to a specially configured pair of chlorophyll molecules known as the reaction centre

25
Q

electron transport chain reaction centre

A

Reaction centre: where light energy is converted into chemical energy as a result of excited electron’s transfer to adjacent molecules.
Directly involved in electron transport
Antenna chlorophylls transfer energy to the reaction centre - make the chain more efficient
When excited, reaction centres transfer an electron to an adjacent molecule that acts as an electron acceptor
Reaction centre is oxidised
Adjacent molecule is reduced
Chain of redox reactions results in NADPH
Reaction centre must gain an electron to absorb light again

26
Q

electron transport chain and water

A 
Abundant in cells
O2 is created from removing electrons 
O2 diffuses easily 
Lots of energy to pull electrons from it
Require two photosystems - first gives energy to remove electrons from water, the second allows electrons to be transferred to NADP+
Split to make H+ and O2 (on lumen side)
27
Q

electron transport chain and photosystems

A

Large increase of energy as electrons pass through two photosystems
At every other step there is a slight decrease in energy - exergonic reactions and so electrons move in one direction through the redox reactions (would require an input of energy to go other way)
Photosynthetic electron transport chain is called Z scheme sometimes (up and down in energy)

28
Q

photosystem II

A

Supplies electrons to the beginning of the electron transport chain
It is oxidised and able to pull electrons from water
Not a strong enough reductant to reductant to form NADPH
Enzyme that pulls electrons from water is located on lumen side of II

29
Q

photosystem I

A

Energises electrons with a second input of energy so they can reduce NADP+
Not a strong enough oxidant to split water
NADPH is formed when electrons are passed from I to a membrane associated protein called ferredoxin (Fd)
Enzyme ferredoxin-NADP+ reductase catalyses the formation of NADPH by transferring two electrons from two molecules of reduced ferredoxin to NAPD+ as well as a proton from the surrounding solution

NADP+ +2e- + H+ ——> NADPH

30
Q

major protein complexes and the electron transport chain

A

Include two photosystems
Cytochrome-b6 f complex (cyt) - electrons pass through it between photosystem II and I
Plastoquinone (Pq) - lipid soluble, carries electrons from II to cyt by diffusing through the membrane
Plastocyanin (Pc) - water-soluble protein, carries electrons from cyt to I by diffusing through thylakoid lumen

31
Q

synthesis of ATP and the electron transport chain

A

Synthesis of ATP:
Synthesised by ATP synthase - transmembrane protein powered by a proton gradient from the lumen to the stroma
Oxidation of water releases proteins into the lumen
Cyt and Pq function as a proton pump together that is functionally and evolutionarily related to proton pumping in cellular respiration

Steps:
Transport of two electrons and two protons by diffusion of Pq from the stroma of II to the lumen of cyt
Transfer of electrons within cyt to a different molecule of Pq which results in more protons coming from the stroma to the lumen

Concentration of protons is 1000x greater in lumen than stroma (3 pH units difference)
Accumulation is used to power the synthesis of ATP by oxidative phosphorylation

32
Q

cyclic electron transport

A

Four electrons transported in the photosynthetic electron transport chain (reduce NADP+) does not transport enough protons into the lumen to produce three ATP
Another pathway for electrons is needed

Cyclic electron transport: electrons from photosystem I are redirected from ferredoxin back into the electron transport chain by Pq.
Electrons eventually return to I - pathway is cyclic in contrast to linear movement of electrons from water to NADPH
As electrons are picked up by Pq, protons are taken in from the stroma to the lumen and are used to synthesis ATP

33
Q

evolution of photosynthesis

A

New source of energy

Released oxygen into the atmosphere

34
Q

early cells and early reaction centres

A

UV damages DNA and other macromolecules
Earliest interaction may have been evolution of UV-absorbing compounds
Mutations lead to variants that may have been able to transfer electrons like a reaction centre
Could not have used chlorophyll because it is a complex pathway of at least 17 steps
Intermediate compounds leading to chlorophyll may have been used

Early reaction centres:
Use light energy to move electrons from an electron donor outside the cell to an electron-acceptor within the cell
Synthesise carbohydrates
First electron donor might have been Fe2+ which was in the ocean
May have been cyclic and not needed a donor
Light driven electron transport could have been coupled with movement of protons across the membrane allowing for the synthesis of ATP

35
Q

water as an electron donor

A

Ancient forms had one photosystem - not enough to split water
Must have oxidised things like H2S - must live in such environments and do not produce O2
Cyanobacteria were first to evolve ability to use water - two photosystems in a single photosynthetic electron transport chain
Genetic material associated with with one photosystem might have been transferred to a bacterium that already had a photosystem
Or genetic material for photosystems was duplicated and overtime they diverged slightly (duplication and divergence)
Photosynthesis could not occur anywhere there was water and sun

36
Q

endosymbiosis

A

Cyanobacterium ingested by a eukaryotic cell and lost ability to survive outside and evolved into a chloroplast
Two membranes

37
Q

prokaryotic structures for photosynthesis

A

Unfolded regions of the plasma membrane (can be called thylakoids)
Photosynthetic pigments imbedded in the membranes and organised into one or more photosystems

38
Q

oxygenic photosynthesis

A

Plants and cyanobacteria
H2O is split and supplies the electron to the reaction centre
Oxygen is realised as a byproduct

39
Q

an oxygenic photosynthesis

A

Bacterial phototrophs
Compounds other than water are used as electron donors such as hydrogen sulphide or thiosulfate
Does not produce oxygen

40
Q

oxygen catastrophe

A

Photosynthetic organisms produced so much oxygen and ran out of carbon dioxide
Everything nearly died

41
Q

electromagnetic spectrum and visible light

A

Electromagnetic energy: kinetic energy (light is a form of electromagnetic energy).
Energy is either kinetic or potential

Visible light: the part of the spectrum that we can see.
Each colour is a different wavelength
Violet and blue have the most energy, red and orange have the least

42
Q

what are the benefits of grana? why are they stacked?

A

Increased surface area to volume ratio
Can accomodate a large amount of light harvesting pigments
Large separation between light systems
PPT for extra point

43
Q

how do electrons travel through the electron transport chain?

A

Redox reactions
Electrons move from PSII to PSI through an electron transport chain
Good diagram on the slide

44
Q

ideal conditions for photosynthesis

A

Sunlight
Lots of water
CO2
Plants have adapted to their environments
Optimal temperature and pH for the enzymes

45
Q

how is photosynthesis different in aquatic environments?

A

Some wavelengths can’t penetrate as deep
Brown, green and red algae are observed
There are a range of algal pigments
Blue light (lots of energy) gets deepest in water column
Micro and macro algae have evolved a range of pigments to absorb light at different depths
The colour of the algae is the wavelength it reflects
Deepest algae is a red algae which is about 295m but water has to be very clear
These organisms are eukaryotes and they all have chlorophyl a (may have some accessory pigments too)

46
Q

can photosynthesis occur in deep sea habitats with hydrothermal vents?

A

Mariana trenches with black smokers
Yes - anoxygenic photosynthesis in bacteria
Does not produce oxygen
Hydrogen sulphide can be the electron donor

47
Q

green sulphur bacteria

A

2391m
H2S or elemental sulphur, no oxygen, CO2 and light
Geothermal light (not visible)
Contain bacteria chlorophylls and carotenoid pigments

48
Q

DCIP

A

DCIP (blue) accepts electrons produced from light reactions and is reduced and made colourless
Measure rate at which it loses colour to estimate rate
Measure with a spectrophotometer (decrease in absorbance) - do not say absorption

49
Q

wavelengths and photosynthesis

A

Different wavelengths drive photosynthesis differently
Plants use blue and red parts
Carotene and some more minor pigments might absorb green lights
Chloroplasts reflect most green light and absorb the others

BIO1011 (12 decks)

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