Cycle 4 - Metabolism Flashcards
1
Q
State the photosynthesis equation and explain what is happening
A
- Water is oxidized, and loses its electrons to oxygen (requires light energy)
- CO2 is reduced (gaining electrons) to form carbohydrate
2
Q
Ddescribe the thermodynamics of photosynthesis
A
- Energy comes from absorption of photons of light
- Photosynthesis is endergonic (requires light energy)
- We maintain low energy by building up molecules to decrease entropy, thus free energy is increases as we do this
3
Q
Describe the structural features of the chloroplast
A
- Thylakoid - electron transport takes place on the membrane
- Lumen (space inside thylakoid) - high concentration of H
- Stroma (space outside thylakoid) - low concentration of H
- Circular genome - encodes an important protein called D1
- D1 is a protein that is encoded by the chloroplast genome and is synthesized in the chloroplast
4
Q
Describe the light reactions + chemiosmosis
A
- Location: thylakoid membrane
- Pigments are found in PSII (P680) and PSI (P700)
- Light ejects electrons from this system and enable them to travel down until they are re-excited at PSI and picked up by NADP+ to form NADPH
- This powers the H+ pumps which push H+ into the lumen
- Water is split to supply electrons to PSII and add to the H+ concentration
- Products: NADPH and ATP –> Calvin cycle
5
Q
Describe the structure and function of each photosystem
A
- The function of a photosystem is to trap photons of light and use the energy to oxidize a reaction centre chlorophyll, with the electron being transferred to the primary electron acceptor
- Each contains an antennae complex or light-harvesting complex
- Light is absorbed and converted into chemical energy
- The energy is transferred to the reaction centre
- Each contains an antennae complex or light-harvesting complex
6
Q
Describe how oxygenic photosynthesis evolved from anoxygenic photosynthesis
A
- Anoxygenic photosynthesis features only one photosystem, either type II with PSII or type I with PSI
- They use H2S as a source of H+ because it is easy to split
- They make ATP, NADPH, but only require one photosystem
- Cyanobacteria somehow got both type I and type II photosystems together, leading to oxygenic photosynthesis
- This extra strength enabled the splitting of water; if you can use water, you can live almost anywhere
- Leads to an explosion of plant life all around the planet
7
Q
How does the redox potential of chlorophyll change upon photon absorption?
A
It’s redox becomes more negative; more likely/easier to take electrons from it
8
Q
Distinguish between P680, P680* and P680+ and the processes that covert one to the other
A
- PSII is constantly being damaged by light and needs to be repaired.
- P680* = excited
- P680+ is when an electron is lost, which is highly oxidizing and then steals an electron from water to return to its normal state
- Bound to protein D1, which it destroys over time.
9
Q
Describe the Calvin cycle
A
- Location: stroma
- CO2 enters the system and undergoes carbon fixation using rubisco
- It transistions to PGA then to G3P; it is reduced to produce NADP+ and ADP
- G3P goes to make glucose and bring it to –> glycolysis
- Extra G3P under go regeneration to make RuBP and continue the cycle
10
Q
Describe glycolysis
A
- Location: cytoplasm
- Glucose is converted to G3P and then into pyruvate –> pyruvate dehydrogenase complex
- During this process, it releases ATP and NADH
11
Q
Desribe the pyruvate dehydrogenase complex
A
Location: cytoplasm, ends at matrix
- Pyruvate enters the complex and is acted upon by pyruvate kinase
- Pyruvate is cleaved of CO2, oxidised to produce NADH, and CoA is added to produce Acetyl-CoA –> citric acid cycle
12
Q
Describe the citric acid cycle
A
- Location: matrix
- Acetyl-CoA moves through the system; it loses its CoA which goes back to be reused
- NADH, FADH2, ATP, and CO2 are produced during this cycle –> ETS
13
Q
Describe the electron transport system + oxidative phosphorylation
A
- Location: inner mitochondrial membrane
- NADH and FADH2 drop off their electrons which move down the system, pumping the protons into the intermembrane space
- The electrons are picked up by oxygen to produce water, the final electron acceptor
- H+ ions move through ATP synthase to produce ATP
14
Q
Why is it called oxidative phosphorylation?
A
- Oxidation: FADH2 and NADH are oxidized of their electrons
- Phosphorylation: ADP + Pi
15
Q
Describe the relative potential energies for compounds in cell respiration
A
Glycolysis
- Makes glucose-6-phosphate which has more free energy due to the addition of phosphate
- Results in pyruvate; less free energy than glucose
Citric acid:
- CoA binds to pyruvate to make Acetyl-CoA with even less free energy
- CO2 is removed from pyruvate as well, thus it has lower potential energy than pyruvate
ETS:
- NAD+ has low free energy, NADH has high free energy
- The free energy of NADH is used to move electrons down the ETS
- Each step sees the release of free energy which pumps the hydrogens into the intermembrane space
