Metabolism and Photosynthesis Flashcards
Enzymes and Ea wrt Metabolism
- Ea is the energy input required to start a reaction
- When enzymes bind to substrates, substrates become altered lowering Ea
- They speed up reaction rate millions of times faster
Types of enzymatic reactions
Exergonic: reactants have more E than products, E released into system, catabolic
Endergonic: reactants have less E than products, E absorbed from system, anabolic
Enzyme Inhibitors
- Substances that bind to enzymes to reduce activity
- Two Types:
Competitive: bind to active site to block substrate chemically and structurally
Non-Competitive: Bind to anywhere other than active site, changes enzyme shape
End product inhibition
- The product of the last rxn in a pathway inhibits the enzyme that catalyzes the first, binds to the allosteric site and changes the shape of the enzyme
- Inhibited enzyme is called the allosteric enzyme
- Can be reversed when the product detaches
Overview of Cell Respiration
- Controlled release of E (ATP) from organic compounds
- glycolysis - link rxn - krebs - ETC - chemiosmosis
Redox Principle
- Oxidation of a molecule is linked to a reduction rxn where another molecule gains the lost e-
- OIL RIG
Electron Carriers (Redox)
- Molecules that accept and give up e- as needed
- E stored in organic molecules is transferred with proteins and e- to carrier molecules
- 2 H atoms from a molecule are oxidized
- One of the H atoms is split in an e- and an H+
- NAD+ accepts the e- -> NAD, H+ released
- NAD accepts the e- and H+ of the other H atom to become NADH
Phosphorylation
- Adding a phosphate group to an organic molecule
- Phosphorylated molecule is unstable and will react more easily in metabolic pathways - activated
Glycolysis
- ‘Sugar splitting’, Occurs in cytoplasm
4 Key Events:
1. Phosphorylation: 6C phosphorylated
2. Lysis: 6C split into 2 3C Pyruvates
3. Oxidation: H atoms from 3C reduce NAD+ to NADH, twice
4. ATP Formation: ATP synthesized from E released in intermediates, called substrate level phosphorylation, 4 ATP formed (2 per 3C)
Substrate Phosphorylation
Requires an enzyme that transfers a phosphate group for a high E substrate molecule to ADP
Results of Glycolysis
- 6C splits into 2 pyruvate molecules
- 2 NADH reduced via oxidation 2NADH + H+
- Net 2 ATP, 4 produced 2 used
Pyruvate
If O2 available: pyruvate moves to mitochondria where it is fully oxidized through cellular respiration
If O2 not available: Anaerobic respiration (fermentation) occurs, pyruvate turns to lactic acid in cytoplasm or ethanol and CO2 in plants
Link Reaction (Pyruvate Oxidation)
- Pyruvate converted into acetyl and attached to coenzyme A to form Acetyl coenzyme A
- Oxidative Decarboxylation is the splitting of CoA and CO2 by oxygen
- Yields 2 Acetyl COA per glucose molecule
Cell Respiration Using FAs
- CoA can oxidize the FA C chain and break it down to produce Acetyl CoA and 2 Carbons
- Acetyl CoA then enters Krebs
- Glycolysis not needed, but FA oxidation is slower than glycolysis
Kreb’s Cycle
- Occurs in the mitochondrial matrix
- 8 step process with 8 specific enzymes
- Cyclical, begins and ends with oxaloacetate
- SOme reactions prepare the molecule fo E harvesting later
- Uses NAD+ and FAD (reduced to FADH2) as e- carriers to ETC
- Net gain of 4 CO2, 2 ATP, 6 NADH and H+, 2 FADH2
Electron Transport Chain (metabolism)
- Series of proteins in inner mitochondrial membrane that transfer e- from NADH and FADH2 to O2
- e- pass from one complex to the nest to form H20 at the end
- As e- is transferred, E pumps H+ across the inner membrane to the intermembrane space
- Oxygen is the final e- acceptor forming H20
Chemiosmosis (metabolism)
- Production of ATP through the movement of ions down their electrochemical gradient through a semi-permeable membrane
- E in ETC moves H+ into the intermembrane space
- Creates a gradient, pH also changes, also called proton motive force
- H+ returns to matrix via ATP synthase
Summary of Oxidative Phosphorlation
- ETC located on inner mitochondrial membrane
- H atoms transfer to ETC by e-carriers
- e-carriers release e-, transferred b/w complexes, E released
- Pumps H+ across the membrane, where they accumulate
- H+ return to matrix via ATP synthase
- Produces ATP via chemiosmosis
- Oxygen is final acceptor, forms H20
Photosynthesis overview
6CO2 + 6H2O -> C6H12O6 + 6O2
- Consists of two stages, light-dependent and independent
Light Dependent Reactions Overview
- Takes place in the thylakoids
- Converts light energy into ATP and NADPH
Consists of:
1. Photoactivation
2. Photolysis
3. ETC
4. Chemiosmosis
5. ATP synthesis
6. Reduction of NADP to NADPH and H+
Photoactivation
- E light used to excite e- in a chlorophyll pigment
- e- can leave the pigment molecule and move through the ETC
- Occurs in photosystems
- E passed inward when absorbed until it reaches the rxn centre
- e- becomes energized and moves to a higher e- level
- Rxn centre is oxidized
Photolysis
- breaking apart of H2O using light E to produce H+ and e-
- e- replace e- lost during photoactivation in PSII
- H+ build up in a gradient in the lumen used in chemiosmosis to create ATP
- O2 is a waste prouct
Photosystems
- Large complexes of protein and pigment within the thylakoid membrane
- two types: PSII and PSI, PSII used first, PSI second
- both contain pigments to collect light E and a special pair of chlorophyll in the rxn centre
ETC (photosynthesis)
- series of molecules transferring e- via redox rxns, fuels pumping of H+ across a membrane
- Creates a protein gradient in thylakoid membrane
- Two ETC, one for each PS
- Transfer of e- in PSII builds H+ gradient
- Transfer of e- in PSI reduces NADP -> NADPH
Chemiosmosis and ATP Synthesis
- Movement of H+ down gradient is coupled with ATP synthesis
- Occurs at ATP synthase, a molecule in the thylakoid membrane
- H+ flows down into the stroma
- ADP is joined by a P
Reduction of NADP to NADPH and H+
- Formation of e- carrier NADPH using e- from PSI at the end of PSI ETC
- e- excited out of rxn centre, given to e- carrier NADP, become NADPH
Cyclic e- Transport / Phosphorylation
- NADP can run out, PSII will shut down
- e- energized in PSI will return to first acceptor in ETC
- Transfered down chain, pumps H+ across membrane re-energized by PSI
Light Dependent Summary
- Occurs in the thylakoid membrane, inside is lumen, outside is stroma
- Light E captured by light pigments in the chloroplast
- PSII generates ATP via Chemiosmosis
- PSI generates NADPH
- Splitting H2O maintains the flow of e- through PS
- O2 released as waste
Light Independent Reactions Overview
- Enzymes in stroma synthesize carbs from CO2 using ATP and NADPH
- 3 Steps: Carbon fixation, Reduction, Regeneration
- 6 turns of Calvin cycle produce 1 glucose molecule
Carbon Fixation
- Adding C from an inorganic molecule to an organic
- C from CO2 used to build carbs
- Occurs in stomata
1. CO2 enters plant via stomata and diffuses into stroma
2. CO2 attaches to RuBP(5C), becoming rubisco (6C)
3. 6C splits into two glycerate-3-phosphates (GP 3C) - 3 RuBP + 3 CO2 -> 6 GP
Reduction
- ATP and NADPH used to reduce GP into triose phosphate (TP) in stroma
- e- and H+ from NADPH become part of the carb
Regeneration
- Using ATP, some Tp are used to regenerate RuBP
- Must be regenerated so C Fixation can occur again, occurs in stroma
- Remaining TP stay in system to enable system to prepare for more CO2
Structure and function of chloroplasts
Thylakoids: volume to increase H+ gradient as H+ accumulates, a large area of light absorbing capacity
Grana: Stacks of thylakoids to increase surface
Stroma: Central cavity with enzymes for calvin cycle, surrounds thylakoids so NADPH and ATP is close to enzymes
PS: Pigments arranged in PS in the thylakoid membrane to maximize light absorption
Melvin Calvin and the Lollipop
- Supplied algae with Carbon 14 to determine which C compounds were present
- Used chlorella algae in a glass lollipop vessel
- Added H14^CO3
- Killed algae at intervals by dropping it into methanol
- Analyzed samples using 2D chromatography and Autoradiography
