PAPER 2 Hardest Topics Flashcards
(16 cards)
Where does light dependent reaction happen?
- Thylakoid membrane where folded membranes contain photosynthetic proteins and electron carrier proteins which are embedded within these membranes, both being involved in the LDR.
Where does the Light independent reaction happen?
- Stroma (Fluid centre which contains enzymes involved in the light independent reaction)
4 key stages of Light Dependent Reaction
1) Photolysis
- Light energy is absorbed and splitts water into oxygen hydrogen and electrons
- H+ ions are picked up by NADP to form NADPH and this is used in the LIR
- The electrons pass along the electron carrier proteins
- Oxygen is used for respiration or diffuses out of the leaf through the stomata.
2) Photoionisation
- Light energy is absorbed by chlorphyll, electrons gain energy and are excited, causing electrons to leave to another energy level, leaving the cholorphyll
- Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis.
3) Chemiosmosis
- As electrons move, they release energy, which pumps protons into thylakoid lumen from the stroma via proton pump.
- Protons can move via facilitated diffusion to the stroma via an ATP synthase and this is the reason we have ATP production.
- Protons combine with co-enzyme NADP and becomed reduced.
4) Production of ATP and reduced NADP
Light independent reaction
- CO2 reacts with RuBP to form 2 GP molecules.
- This reaction is catalysed by the enzyme Rubisco.
- GP is reduced to TP using the energy from ATP.
- TP is converted into useful organic molecules or regeneration of RuBP.
What happens in glycolysis?
- Occurs in the cytoplasm
- Glucose converted to glucose phosphate (by ATP hydrolysis)
- Glucose phosphate converts into TP molecules.
- Redox reaction converts TP into 2 Pyruvate molecules via redox reactions. (reduction of 2 NAD molecules, using 4 ATP molecules)
Anaerobic respiration in animals and plants
ANIMALS
- Pyruvate is converted to lactate in a redox reaction of NADH.
- Regeneration of NAD so glycolysis can still continue.
- Lactate can damage cells.
PLANTS YEAST
- Pyruvate converted to ethanal, producing CO2 in the process, then ethanal is converted into ethanol in a redox reaction/
Link reaction
- Acetate is formed when Pyruvate loses carbon
- NAD -> NADH
- Acetyl coA when acetate combines with coA.
Matrix
- Acetyl coA reacts with a 4C carbon compound to form a 6C carbon compound.
- Redox reactions lead to 2 CO2, 3 NADH and 1 FADH2 and 1 ATP.
Oxidative phosphorylation in respiration
- Hyrodgen atoms released from reduced coenzymes
- Hydrogen atoms split in hydrogen ions and electrons.
- Electrons move down ETC
- Energy lost at each carrier is used to pump H+ ions into itnermembrane space, creating favourable conc gradient for diffusion of H+ into matrix via ATP synthase.
Oxygen as final electron acceptor but why?
- Oxygen accepts H+ ions and low energy electrons to form water
- If it didn’t happen, electron transport chain would stop and no pumping of hydrogen ions.
No diffusion of H+ ions so no ATP produced.
What happens when little O2 available?
- Too many hydrogen ions not being accepted by oxygen
SO - Respiration is stopped back to glycolysis as we need to remove the hydrogen atoms from NADH in oxidative phosphorylation to produce NAD, which is needed for glycolysis to continue.
Outline ultrafiltration
- First process of osmoregulation
- Efferent arteriole smaller in diamter than the afferent arteriole so hydrostatic pressure in the glomerular capillaries increases.
- Small molecules forced through 3 layer filter made out of capillary endothelium, basement membrane and podocytes.
- Proteins, RBCs too large
- Forms glomerular filtrate
Outline selective reabsorption
- Reabsorption of useful substances.
- They pass back into blood capillaries wrapped around the proximal convoluted tubule.
- Done by co-transport with sodium ions.
- Reabsorption lowers the water potential of blood so water moves out of the PCT into the capillaries by osmosis.
Outline osmoregulation
Main aim is to lower WP of the medulla so water can be reabsorbed at descending limb.
- Ascending limb is impermeable to water so water remains in the tubule, however sodium ions are pumped into the medulla by active transport. (lowers WP in medulla)
- Water moves out of descending limb (permeable to water) by osmosis.
- Descending limb isn’t permeable to ions so the filtrate becomes more concentrated.
- At the bottom of the ascending limb, sodium ions diffuse into medulla which further lowers the water potential in the medulla
Entire process of muscle contraction
1) At rest, tropomyosin blocks the myosin head from binding to the actin-myosin binding site so the myosin head cannot bind and myofilmanets can’t slide past each other.
2) Action potential reaches the neuromuscular junction
3) Acetylcholine diffuses over to the post synaptic membrane and binds to receptors.
4) Depolarisation of sarcolemma
5) Wave of depolarisation along T tubules
6) Calcium ions released intosarcoplasm
7) Calcium ions bind to troponin causing a change in shape pulling tropomyosin out of the binding site
8) Mysoin head binds to actin-mysosin site forming bridge
9) activates ATP hydrolase
10 Energy released causes bending
11) Another ATP binds to mysoin head and ATP hydrolyses causing breakage of the bridge
12) Myosin head binds to different actin-myosin head.
Second messanger model
- Explains the response of glucagon and adrenaline in restoring glucose to its original level
- Glucagon/adreanline bind to receptors on cell surface membrane
- Activates Adenylate Cyclase enzyme
- Catalyses production cAMP from ATP
- Protein kinase enzymes use cascade effect that lead to glycogenolysis.
