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Topic 8: Metabolism, Cell respiration and photosynthesis - Coggle Diagram
Topic 8: Metabolism, Cell respiration and photosynthesis
Metabolic pathways
Metabolism - describes the sum total of all chemical reactions that occur within an organism in order to maintain life
- Metabolic processes are controlled and coordinated by a series of enzyme-catalysed reactions
- Metabolic pathways are typically organised into chains or cycles
Enzyme action
Every chemical reaction requires a certain level of energy in order to proceed , this is called the activation energy
Enzymes speed up reaction rates by lowering the activation energy threshold (destabilise substrate bonds = increase product conversion)
- If reactants contain more energy than the products, the reaction is exergonic as energy is released (catabolic reactions)
- If reactants contain less energy than the products, the reaction is endergonic as energy is absorbed (anabolic reaction)
Enzyme inhibition
Competitive inhibition:
- Inhibitor is structurally similar to the substrate
- It directly blocks the active site of the enzyme
- Increasing substrate concentration will reduce inhibition
Non-competitive inhibition:
- Inhibitor is not structurally similar to the substrate
- It binds to an allosteric site (not the active site)
- It induces a conformational change in the active site
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Feedback inhibition
Metabolic pathways can be controlled by feedback inhibition, where a product inhibits an earlier step, this ensures product levels are always tightly regulated
Rational drug design
Inhibitors can be used to treat infectious diseases by targeting the enzymes involved in pathogenesis, inhibitors can be identified by database mining or constructed via combinatorial chemistry techniques
Photosynthesis
Photosynthesis converts light energy from the sun into stored chemical energy
- the conversion of light energy into chemical energy requires energy transfer molecules and ATP
- This process requires photosynthetic pigments, which are found in chloroplasts in most eukaryotic cells
Chloroplasts
The structure of a chloroplast is adapted to the function it performs:
- Granum are made up of stacks of thylakoids to increase the surface area available for the electron transport chain
- The thylakoid lumen is very small (maximises the electrochemical gradient that results from proton accumulation
Cell respiration
Cell respiration converts stored chemical energy into an immediate and usable energy molecule (ATP)
- The conversion of energy between stored and usable forms requires energy transfer molecules
- The majority of ATP is produced via aerobic respiration which occurs within the mitochondria of a cell
Mitochondria
The structure of a mitochondria is adapted to the function it performs:
- The inner membrane is folded into cristae to increase the surface area available for the electron transport chain
- The intermembrane space is very small
- The mitochondrial matrix contains suitable enzymes and an appropriate pH for the krebs cycle to occur
- The outer membrane contains the necessary transport proteins for shuttling pyruvate into the mitochondria
Electron tomography
Electron tomography is a technique by which a 3D image of an internal cellular structure can be generated, samples are repeatedly imaged at different angles
Redox reactions
Biological energy can be stored or released by redox reactions:
- Oxidation Is the Loss of electrons/hydrogen (OIL)
- Reduction Is the Gain of electrons/hydrogen (RIG)
Oxygen is the opposite
Electron carriers transfer chemical energy via redox reactions
organic molecules are oxidised to form reduced carriers
the reduced carriers may then be oxidised to form ATP
Glycolysis
Aerobic respiration is preceded by glycolysis (anaerobic), glucose is broken down to form 2 pyruvate molecules
The process of glycolysis involves 4 basic stages:
- Glucose is phosphorylated by ATP (becomes less stable)
- The 6C sugar splits into 2 triose phosphates (3C)
- 3C sugars are oxidised to form reduced carriers (NADH)
- A small amount of ATP is produced (net gain = 2 ATP)
Aerobic respiration
Link reaction:
- Pryruvate transported from cytosol to mitochondrial matrix
- Pyruvate oxidised to produce a reduced carrier (NADH)
- Pyruvate decarboxylated to form acetyl CoA
Krebs cycle:
- Acetyl CoA is combined with a 4C compound (forms 6C)
- 6C compound broken down into original 4C
- This involves oxidation reactions (NADH/FADH² formed)
- There is also a small yield of ATP (one per cycle)
Electron transport chain:
- Reduced carriers are oxidised at the electron transport chain
- The energy is used to make ATP (via oxidative phophorylation)
- 32 ATP molecules are made from the reduced carriers
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Stages of photosynthesis
Photosynthesis is a 2 step process:
- The light dependent reactions occur in the thylakoids and convert light energy into chemical energy (ATP + NADPH)
- The light independents reactions occur in the stroma and use this chemical energy to make organic compounds
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Lollipop experiment
The light independent reactions were elucidated by Melvin Calvin used a 'lollipop'- shaped apparatus
- Radioactive CO² was incorporated to identify the different carbon compounds