Cycle 4 - Metabolism Flashcards
State the photosynthesis equation and explain what is happening
- Water is oxidized, and loses its electrons to oxygen (requires light energy)
- CO2 is reduced (gaining electrons) to form carbohydrate
Ddescribe the thermodynamics of photosynthesis
- 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
Describe the structural features of the chloroplast
- 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
Describe the light reactions + chemiosmosis
- 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
Describe the structure and function of each photosystem
- 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
Describe how oxygenic photosynthesis evolved from anoxygenic photosynthesis
- 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
How does the redox potential of chlorophyll change upon photon absorption?
It’s redox becomes more negative; more likely/easier to take electrons from it
Distinguish between P680, P680* and P680+ and the processes that covert one to the other
- 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.
Describe the Calvin cycle
- 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
Describe glycolysis
- Location: cytoplasm
- Glucose is converted to G3P and then into pyruvate –> pyruvate dehydrogenase complex
- During this process, it releases ATP and NADH
Desribe the pyruvate dehydrogenase complex
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
Describe the citric acid cycle
- 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
Describe the electron transport system + oxidative phosphorylation
- 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
Why is it called oxidative phosphorylation?
- Oxidation: FADH2 and NADH are oxidized of their electrons
- Phosphorylation: ADP + Pi
Describe the relative potential energies for compounds in cell respiration
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
Why are proton gradients, in particular, used most often for ATP synthesis?
Protons can’t naturally defuse through the membrane because they are charged so they are forced to move through ATP synthase, making them an effective choice
Explain coupling and uncoupling the ETS with ATP synthesis and the physiology behind it
- Coupled: ATP synthase and ETS are coupled together (beside each other)
- Uncoupler: ATP synthase becomes inactivated
- Uncoupling proteins play a role in normal physiology, as in cold exposure or hibernation, because the energy is used to generate heat (see thermogenesis) instead of producing ATP.
- We control the gene expression of these proteins
Why are chemical uncouplers (ex., dinitropheonal) toxic?
- Dinitrophenol is an active ingredient in fat burners
- Uncoupling the proton pump prevents ATP from being synthesized; low levels of ATP can be dangerous
- Uncoupling causes temperature to rise and NAD+ to rise
How do cancer cells respirate?
- Using aerobic glycolysis
- Even under high oxygen, tumor cells always act like they are fermenting
- Tumours grow super fast, so they have a high glucose uptake to compensate for their low ATP
- As a result, hexokinase (converts glucose to pyruvate) goes up
- One guess as to why tumours use fermentation is because tumour cells are hypoxic; they have a low-oxygen environment
