Topic: Respiration/Photosyn Essay - Main Points!

Q) Distinguish photophosphorylation and oxidative phosphorylation

Main points
Key idea:	Location
Photophosphorylation · occurs at thylakoid membr (of chloroplast, plant cells) Oxidative phosphorylation · occurs at inner mitochondrial membr (of mitochondria, all euk cells)
Key idea:	Energy conversion
Photophosphorylation · Light energy converted to chemical energy (in the form of ATP) Oxidative phosphorylation · Chemical energy fr glucose converted to chemical energy (in the form of ATP)
Key idea:	Source of energy for ATP synthesis
Photophosphorylation · Originates fr light Oxidative phosphorylation · Originates fr oxidation of glucose
Key idea:	Involvement of light
Photophosphorylation · Light energy absorbed by photosyn pigments (of light harvesting complexes) · Excitation & displacement of energized e fr pri pigments (of rx centres of PSI & II) · Also required for photolysis of H2O, to generate e · Ref to replenish e lost fr PS II (during non-cyclic photophosphorylation) Oxidative phosphorylation · Light not required
Key idea:	Coenzymes
Photophosphorylation · NADP reduced to NADPH during light dep · NADPH required for reduction of glycerate-3-phosphate to triose phosphate (TP) · Some TP used to syn biomolecules (e.g. starch) + rest of TP to regenerate ribulose bisphosphate (RuBP) Oxidative phosphorylation · NAD & FAD reduced to NADH & FADH2 · which carry energized e to electron transport chain (ETC), for ATP syn
Key idea:	Source of electrons
Photophosphorylation · H2O (non-cyclic photophosphorylation) · PSI (cyclic photophosphorylation) Oxidative phosphorylation · NADH + FADH2 donate e to ETC
Key idea:	Oxygen
Photophosphorylation · not required · O2 produced as byproduct during photolysis of H2O · NADP+ - last e acceptor of light dep rx Oxidative phosphorylation · O2 - last e acceptor of ETC, hence required for continuous flow of e throu ETC + subseq ATP syn
Key idea:	Water
Photophosphorylation · Source of e in non-cyclic photophosphorylation (light dep rx) Oxidative phosphorylation   · H2O – byproduct, formed when O2 combines with e & H+
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic: Respiration/Photosyn/Cell Signalling Essay - Main Points!

Q) Using named examples, explain the advantages of metabolic pathways in cells

Main points
Key idea:	What is a metabolic pathway
· Ref to series of rx where product of one rx becomes substrate for next rx
Key idea:	Adv 1 : Allows a crucial molecule to be made from different sources
· Named example: Acetyl-CoA (of aerobic resp) · Acetyl-CoA as product of link rx which becomes substrate for Krebs cycle · Ref to its synthesis fr breakdown of glucose, fatty acids or aa throu other pathways; hence diff entry points to Krebs cycle
Key idea:	Adv 2 : End product inhibition + channel intermediate products to other pathways to make another product
· Named example: Glycolysis · Glucose mol oxidized throu a series of rxs (each rx catalyzed by an enz), form pyruvate, ATP & NADH · When ATP is sufficient, it acts as an allosteric inhibitor · Ref to it binding to an allosteric site on enz (phosphofructokinase) at initial part of glycolytic pathway, inhibits the enz · Result: Not only prevents formation of excess ATP but allows glucose-6-phosphate to be diverted to another pathway that makes glycogen
Key idea:	Adv 3 : Cell responds appropriately to its environmental conditions
· Named example: (fate of) Pyruvate when O2 absent · Will not enter mitochondrion (to combine w co-enzyme A to form acetyl-CoA) · Pyruvate reduced to lactate (in animals) or ethanol (in plants) in cytosol instead · Result: anaerobic respiration still proceed to yield 2 ATP/glucose
Key idea:	Adv 4 : A cyclical metabolic pathway allows its 1st substrate to be regenerated
· Named example: Krebs cycle & Calvin cycle · Result: (i) Krebs cycle (aerobic resp) - regenerate oxaloacetate, hence NADH produced continuously for ATP syn during oxidative phosphorylation (ii) Calvin cycle (light independent rx, photosyn) - regenerate RuBP for continuation of CO2 fixation · Ref to some phosphates made during reduction of glycerate-3-phosphates channeled to another pathway that synthesizes starch
Key idea:	Adv 5 : Crucial in cell signalling
· Named example: Insulin & glucagon signalling · Ref to binding of a signal mol (e.g. hormone) to its specific receptor, result: activation of signal transduction pathways + eventual cellular responses · Details: (i) Insulin binds to receptor tyrosine kinase, activation of several relay mol, in turn activate diff pathways · Ref to diff cellular responses due to binding of hormone to one target cell · Details: (ii) Glucagon binds to G-protein linked receptor, activation of many G proteins, in turn activate adenylyl cyclases · Ref to enz yield enormous amt of second messager cAMP · Each cAMP activates a protein kinase, in turn activates many other protein kinases · Result: phosphorylation cascade + ‘weak’ signal carried by a hormone greatly amplified (i.e. strong cellular response)
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) A rather challenging question as it requires a deeper understanding of the various concepts from different topics (e.g. respiration, photosynthesis and cell signaling). (v) The answer provided is more than sufficient to gain full credit for this question

Topic Respiration Essay - Main Points!

Q) Explain why anaerobic respiration produces so few ATP per glucose oxidized.

Main points
Key idea:	Effect of the lack of oxygen during anaerobic respiration
· O2 as last e acceptor of electron transport chain (ETC) · Anaerobic respiration - no O2 to accept e + H+ at end of ETC · Result - flow of e throu ETC disrupted, no ATP produced via oxidative phosphorylation, NAD + FAD remain reduced, NAD+ + FAD not re-generated to participate in link rx + Krebs cycle · Ref to no ATP produced in Krebs cycle via substrate level phosphorylation
Key idea:	To regenerate NAD+ for glycolysis
· Cytoplasmic NADH reduce pyruvate (fr glycolysis) to ethanol in plants/yeast or lactate in animals · Result: re-generates NAD+ for glycolysis to proceed to produce 2 ATP/ glucose via substrate level phosphorylation · Ref to glucose incompletely oxidized
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Cellular Respiration: Q) How does one glucose molecule produce 38 ATP via substrate level phosphorylation and oxidative phosphorylation?

Substrate level phosphorylation (4 ATP)

In glycolysis, net gain of 2 ATP

In the Kreb cycle, net gain of 2 ATP (cycle rotates twice per glucose)

Oxidative phosphorylation (34 ATP)
10 NADH are formed : glycolysis (2), link reaction (2) and Krebs cycle (6)

2 FADH₂ are formed from Krebs cycle

Since 1 NADH produces 3 ATP while 1 FADH₂ produces 2 ATP, 34 ATP are produced

Total no. of ATP / glucose = 4 + 34 = 38

Topic Respiration / Photosynthesis Essay - Main Points!

Q) Distinguish Calvin cycle and Krebs cycle

Main points
Key idea:	Site of occurrence
Calvin cycle: Occurs at stroma of chloroplast  Krebs cycle: Occurs at mitochondrial matrix
Key idea:	Starting material
Calvin cycle: Ribulose bisphosphate (RuBP) ; eventually regenerated Krebs cycle: Oxaloacetate ; eventually regenerated
Key idea:	Substrate
Calvin cycle: CO2 used to convert RuBP to an unstable 6C compound that breaks down to form glycerate-3-phosphate + ref to carbon fixation Krebs cycle: Acetyl-CoA combines w oxaloacetate, to form citrate
Key idea:	Role of CO2
Calvin cycle: CO2 as substrate Krebs cycle: CO2 released due to decarboxylation rx
Key idea:	Role of O2
Calvin cycle: Not required Krebs cycle: Occurs only when O2 present
Key idea:	Electron carriers
Calvin cycle: NADPH as e donors ; to reduce glycerate-3-phosphate to glyceraldehyde-3-phosphate Krebs cycle: NAD+ and FAD as e acceptors ; to oxidize intermediates of cycle
Key idea:	ATP
Calvin cycle: Requires energy throu hydrolysis of ATP Krebs cycle: ATP syn throu substrate level phosphorylation
Key idea:	Products
Calvin cycle: For every 3 mol of CO2 that enter cycle,1 glyceraldehyde-3-phosphate is made Krebs cycle: Gives rise to 2 ATP, 6 NADH, 2 FADH2 per glucose molecule*
Key idea:	Nature of the process
Calvin cycle: Anabolic ; syn of hexose phosphates that give rise to starch Krebs cycle: Catabolic ; oxidation of acetyl-CoA throu a series of decarboxylation +  dehydrogenation rx
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Glyceraldehyde-3-phosphate is a triose phosphate (v) Clarification of worked solution – Each rotation of the Krebs cycle gives rise to 1 ATP, 3 NADH, 1 FADH2. For every glucose oxidized, the cycle rotates twice.

Topic Membrane Essay - Key Points!

Q) Discuss the functional significance of membranes in photosynthesis and respiration

Main points
Key idea:	Increase surface area for attachment of electron carriers + stalked particles
· Due to infolding of inner mitochondrial membranes (IMM)(to form cristae) + thylakoid membr of chloroplast · Ref to electron transport chain (ETC) · Ref to stalked particles – consist of hydrophilic protein channels embedded in membr + ATP synthase at tip of struc
Key idea:	Flow of energized e throu ETC
· Energized e flow throu ETC + ref to down an energy gradient · Energy released during transfer of e, used to pump H+ (protons) · Ref to fr mitochondrial matrix to intermembrane space · Ref to fr chloroplast stroma to thylakoid space
Key idea:	Establish proton gradient
· Ref to membr being impermeable to H+ · Results: H+ (proton) conc gradient a/x IMM and thylakoid membrane · H+ flow back into matrix or stroma throu stalked particles by facilitated diffusion, where ATP synthase catalyzes phosphorylation of ADP to form ATP
Key idea:	Membranes compartmentalize enzymes
· Enz involved in : i) link rx + Krebs cycle w/n matrix of mito ii) light indep rx (i.e. Calvin cycle) w/n stroma of chloroplast
Key idea:	Membranes facilitate reactions
· Maintain optimal cond for various rx w/n organelles · Membranes - in close proximity to mitochondrial matrix and chloroplast stroma, for oxidative phosphorylation and photophosphorylation, to occur efficiently
Key idea:	Outer and inner mitochondrial membranes create intermembrane space
· Ref to H+ entering intermembrane space fr matrix – required for H+ (proton) conc gradient, then syn of ATP (as described)
Key idea:	Attachment of photosynthetic pigments on thylakoid membrane
· Ref to photosynthetic pigments (e.g. chlorophyll) functionally grouped into  photosystem I or II · Ref to maximizing absorption of light + photoactivation of chlorophyll - excitation, subsequent displacement of energized e fr rx centres of photosystems · Energized e flow throu ETC, leads to syn of ATP (as described)
Key idea:	Permeability of membranes
· Ref to both outer and inner membr of organelles being permeable substrates or products of cellular respiration and photosyn · E.g. O2, CO2, H2O, ADP, inorganic phosphate and ATP · Ref to mitochondrial membr being permeable to pyruvate fr glycolysis + pyruvate = substrate for link rx in matrix of mitochondrion
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The proton gradient gives rise to the proton motive force which is the source of potential energy for the synthesis of ATP.