8. Metabolism, Cell Respiration, Photosynthesis Flashcards
8.1 What is metabolism?
The chemical reactions of enzymes
8.1 What are metabolic pathways?
The chain and/or cycle of enzyme-catalysed reactions
8.1 Relationship between enzymes and energy
Enzymes reduce activation energy
8.1 Types of inhibitors
Competitive: directly binds
- max rate of enzyme activity can be achieve but requires higher concentration
Non-Competative: binds to allosteric site, non-compettive
- max enzyme activity reduced
8.1 What is end-product inhibition?
The final product of an enzyme binds to the allosteric site to stop reaction
8.2 Rules of a redox reaction
Oxidation - loss of e-, (gain of O, loss of H)
Reduction - addition of e-, (loss of O, gain of H)
8.2 What is an electron carrier?
A molecule that can accept or donate e-
- used to stager break down of energy so its not all lost
8.2 NAD+ vs NADH
NAD+ is reduced to NADH (with 2 e-)
8.2 What is phosphorylation?
The addition of a phosphate group
8.2 Effects of phosphorylation
Molecules is more likely to react
Endogergonic recation - requires energy
Exogonic - removal of phosphate
8.2 What is the first stage of glycolesis?
Phosphorylation: Glucose (6C) is phosphorylated by 2 ATP to form hexose biphosphate
- more unstable
- wont diffuse out of cell
8.2 Where does glycolisis occur?
Cytoplasm
8.2 What is the second step of glycolsis?
Lysis:
Hexose biphosphate (6C) is split into two triose phosphates (3C)
8.2 What is the third step of glycolsis?
Oxidation:
The triose phosphates are oxidized giving the H+ to NAD to become NADH+ (2 are produced)
8.2 What is the final step of glycolsis?
ATP formation:
The sugar molecules break down further into pyruvate and 2 ATP is created per molecule (4 total)
8.2 Energy gain + loss of glycolisis
2 ATP used in beginning
4 ATP produced
Net: 2 atp
8.2 Anaerobic conditinons + pyruvate
If oxegyn is not present pyruvate is broken down further becoming lactic acid (animals) or ethanol (plants/yeast) in the process of fermentation
Traditionally NADH+ is oxidized during aerobic respiration, but without oxygen this happens during fermentation instead
8.2 What is the first step of aerobic respiration?
Link reaction:
Transport pyruvate to mitochondria
Steps:
1) Pyruvate is transported into the mitochondrial matrix by carrier protiens
2) Pyruvate is decarboxylated and becomes carbon dioxide molecule (waste product produced = Co2)
3) This molecule loses a H atom as NAD+ is reduced to NADH + H+, this becomes an acetyl group
4) The acetyl group combines with coenzyme A to become acetyle CoA
This happens twice with both pyruvate molecules
8.2 Steps of Kreb Cycle
Also known as citric acid cycle
1) Acetyl CoA donates the Aceytl group to a 4C compound to become 6C (citrate). –CoA is released to become part of link reaction again
2) (processes during 5C)
- 6C is decarboxylated to form 5C, it then is oxidized twice (losing 4 total H) (NAD+ –> NADH + H+) x2
3) (process during 4C)
- 5C is decarboxylated again to form 4C
- One ATP molecule is produced via substrate level phosphorylation
- The molecule is oxidized twice again (losing 4 H total) first (FAD –> FADH2) then (NAD+ –> NADH + H+)
4C molecule is reused as its a cycle
This happens twice with the two Acetyl CoA molecules
8.2 Products of Krebs Cycle
2 CO2 x 2 = 4 Co2
3 NADH + H x 2 = 6 NADH + H+
FADH2 x 2 = 2 FADH2
ATP x 2 = 2 ATP
8.2 What is the electron transport chain?
A chain of electron carriers that pass along electrons
8.2 Where does ETC occur?
The inner mirochondrial membrane
- Folds (cristae) increase the surface area for this process
8.2 What is the term for the general procedure of the ETC
Oxidative phosphorylation
Energy derived from oxidization of carriers
8.2 What is the first step of ETC?
Generating Proton Motor Force
1) NADH and FADH2 are oxidized releasing electrons and protons
2) Electrons are transfered to electron transport chain, consisting of several transmembrane carrier protiens
3) As electrons pass through the chain, they lose energy which is used by the protiens to pump H+ across the membrane from the matrix
4) The accumulation of protons in the innermatrix space creates a electrochemical gradient
8.2 What is the second step of ETC
ATP Synthesis via chemiosmosis
1) Protons move down the generated gradient and diffuse back to matrix
2) This is known as chemiostatis and is facilitated by ATP synthase
3) This causes the ATP synthase rotation, leading to the synthesis of ATP
8.2 What is the final step of ETC
Reduction of Oxygen
1) De-energized electrons need to be removed from chain
2) Oxygen acts as final receptor accepting electrons
3) Oxygen binds with protons reentering matrix to become water
8.2 Reactants and Products of ETC
6 O2 –> 32 ATP 6 H2O
8.2 ATP Production throughout process
(1 glucos, 2 pyruvate)
Glycolsis: 2 ATP
Link Reaction: none
Kreb Cycle: 2 ATP
ETC: 34 ATP
Net: 38 ATP
8.2 Mitochondria Structure
Outer Mitochondrial Membrane:
- seperates mitochondria from the rest of the cell
Inner Mitochondrial Memrbane:
- location of ETC + ATP synthase
- folds for max surface (cristae)
Intermbrane Sprace:
- small for proton build up
Matrix:
- krebs, enzymes
8.3 Where do light dependent reactions happen?
Membrane discs in chloroplast called thylakoids
8.3 What do light dependent reactions use?
Photosynthetic pigments organized into photosystems embedded in thylakoid membrane
8.3 What is the first step of light dependent reactions?
Excitation of Photosystems w/ Light E-
-Photosystems are classified according to max absorption wavelengths (PS I = 700nm, PS II = 680 nm)
1) When a photosystem absorbs light energy electron within the pigment become energised
2) These electrons are transfered to carrier protiens in thylakoid membrane
8.3 What is the second step of light dependent reactions?
Production of ATP via ETC
1) Excited electrons from Photosystem II are transferred to electron transport chain in thylakoid membrane
2) ATP is synthesized as the protons return to stroma via ATP synthase (chemiosmosis) - this process is photophosphorylation
3) The newly de-energersied electrons from Photosystem II are taken into Photosystem I
8.3 What is the final step of light dependent reactions?
Reduction of NADP+ and Photolysis of water
1) Excited electrons from Photosystem I may be transferred to carrier molecule and used to reduce NADP+ –> NADPH (needed in light independent reactions)
2) Electrons in Photosystem 1 are replenished from Photosytem 2
3) Electrons in photosystems 2 are replaced by electrons from water via photolysis –> water is split by light energy into H+ and oxygen (waste)
8.3 What are the two types of photophosphorylation?
Cyclic and non-cyclic
8.3 What is photophosphorylation?
Production of ATP with light dependent reactions
8.3 What is cyclic photophosphorylation?
Only photosystem I is involved, no NADP+ is reduced
The de-energized electron returns to photosystem I, no need for water
8.3 What is non-cyclic photophosphorylation?
Requires both photosystems, NADPH is synthesized from Photosystem I, requires water
8.3 Cyclic vs Non-Cyclic Photophosphorylation
Cyclic can be used to produce steady ATP w/ sunlight, however since ATP cannot be stored Non-Cyclic is needed for synthesis of organic molecules and long-term energy storage
8.3 What is the calvin cycle?
The light independent reactions w/ three main steps
8.3 Where does the calvin cycle occur?
The stoma
8.3 What is the first step of the calvin cycle?
Carbon Fixation
1) The cycle starts with ribulose biphosphate, RuBP (5C)
2) Rubisco (RuBP carboxylase) catalyses attachement of CO2 to RuBP
3) The resulting 6C compound is unstable and breaks down into two 3C compounds glycerate-3-phosphate (GP)
Cycle requires 3 RuBP = 6 GP
8.3 What is the second step of the calvin cycle?
Reduction of GP
1) GP is converted into triose phosphate (TP) using ATP and NADPH
2) Reduction of NADPH provides hydrogen atom while ATP hydrolysis provides energy
6 GP per cycle = 6 ATP and 6 NADPH utilized
8.3 What is the final step of the calvin cycle?
Regeneration of RuBP
1) One TP may be used to form half a sugar molecule, two cycles are required for one simple monomer
2) The remaining 5 TP’s are combined to regenerate RuBP (5 x 3C = 3 x 5C)
3) The regeneration of RuBP requires energy from ATP
5 TPs –> 3 RuBP + 3 ATP used
8.3 Structure of chloroplast
Thylakoids : flatted discs with small internal volume, max SA for ETC
Grana: stacks of thylakoids
Lamella: Connects granas
Stroma: Central cavity that contains approriate enzymes and pH
