Chapter 8 Flashcards
Metabolism, cell respiration and photosynthesis
Metabolic pathway
any chain or cycle of linked reactions catalysed by enzymes; are linked, enzymatically catalysed reactions
- some are linear, and some are cyclic
- pathway can be complex , w/ many intermediate products before an end product is produced
- some are linked to other metabolic pathways
Activation energy
minimum energy that reacting particles need to possess for a reaction to take place
- enzymes speed up reactions by lowering the activation energy
Enzyme inhibitors
Two types:
- competitive
- non-competitive
Competitive inhibitor
competes w/ substrate for the same active site
- maximum rate of reaction is eventually the same as the reaction without inhibitor
- when substrate conc. increases, rate will increase
- because, there’s more available substrate than inhibitor
- hence, there’s a greater chance of substrate binding to enzyme’s active site and forming product
Non-competitive inhibitor
bind at a site away from the active site
- rate of reaction levels off and never reaches same level it would without inhibitor
- because all enzyme molecules to which inhibitor is attached are effectively blocked from reacting w/ substrate- due to modification of their active site
- hence, fewer enzyme molecules, free of inhibitor, are available to catalyse the reaction
Properties of competitive inhibitor
- It is chemically quite similar to the substrate
- It binds to active site of the enzyme
- Binding of inhibitor to enzyme doesn’t modify its active site
- As conc. of substrate is increased, effect of inhibitor on reaction is reduced
Properties of non-competitive inhibitor
- It has no similarity to the substrate.
- It binds to the enzyme at a site other than active site
- Binding of inhibitor to enzyme modifies its active site, hence preventing binding of substrate- if it does bind, enzyme won’t be able to catalyse reaction
- Increasing conc. of substrate doesn’t decrease impact of inhibitor- hence, rate of reaction is lower than normal at all substrate concentrations.
End-product inhibition
when the enzymes that catalyse the first reaction of the pathway are allosterically inhibited by the end product of the pathway
Allosteric site
a binding site on the surface of an enzyme other than the active site
- in non-competitive inhibition, when inhibitor binds to an allosteric site, it blocks activity of the enzyme
Allosteric inhibition
- binding of a regulatory molecule (usually, the end product of the pathway) to allosteric site changes overall conformation of the enzyme
- this can either enable the substrate to bind to the active sire or prevent binding of the substrate
Synthesis of isoleucine from threonine
- isoleucine can bind to the enzyme that catalyses the first step of the pathway in a non-competitive way
- it binds allosterically to the enzyme and changes conformation of the active site
- hence, substrate can no longer bind to the enzyme
Formula for rate of reaction
Rate (1/s) = 1/ t
t= time taken in seconds
Redox reactions
- involve one compound being oxidised, while another is reduced
- involve gain or loss of e-
- makes electrons carriers of energy that can be used for other processes
Redox reactions and electron carriers
- redox reactions are usually coupled to an e- carrier eg. NAD (Nicotinamide Adenine Dinucleotide)
- reactions often transfer 2 hydrogen atoms to carrier
- e- that are lost from one substance in oxidation are needed or used in another part of the cell
- the reduced NADH+ H+ is transferred to a mitochondrion
- it’s used in electron transport chain to generate ATP
NADP vs. NAD
NADP (Nicotinamide Adenine Dinucleotide Phosphate)
- main carrier for photosynthetic reactions
NAD (Nicotinamide Adenine Dinucleotide)
- used for bulk of respiration reactions
Oxidation
- gain of oxygen
- loss of hydrogen
- loss of electrons
Reduction
- loss of oxygen
- gain of hydrogen
- gain of electrons
Phosphorylation
the addition of a phosphate group to a molecule
- makes whole molecule less stable
- makes it more likely to react or break down into smaller molecules
Glycolysis
the reaction in the cytoplasm where glucose is broken down to pyruvate in a series of linked catalytic steps
Link reaction
In aerobic respiration:
- pyruvate is converted to acetyl coenzyme A
- this is transferred to mitochondria, where it enters the Krebs cycle
- link reaction because it links glycolysis to Krebs cycle
Process of glycolysis
Glycolysis is the first step of cellular respiration and occurs in all organisms
- glycolysis is a metabolic pathway which gives a small yield of 2 ATP and 2 reduced NADH+ H+
- at the end of the glycolytic pathway, 2 molecules of pyruvate are formed
- they’re linked to acetyl CoA in the link reaction if oxygen is available
- this is a decarboxylation reaction as carbon is lost as carbon dioxide
- as pyruvate loses hydrogen, it’s oxidised to acetyl CoA
- overall, conversion of pyruvate to acetyl CoA involves both decarboxylation and oxidation reactions
Krebs cycle
- next step in catabolic breakdown of glucose
- takes place in the mitochondrial matrix
- the acetyl group that enters the Krebs cycle is successively oxidised- it loses hydrogen atoms and e-
- the hydrogen atoms lost are picked up by hydrogen carriers, either NAD or FAD, which are themselves reduced
- oxidation of acetyl group is coupled w/ a loss of CO2 (decarboxylation)
Electron transport chain
- all oxidation reaction in cytoplasm in cytoplasm and mitochondrial matric are linked to electron carriers
eg. NAD and FAD - reduced forms of these molecules carry energy released by oxidation to cristae of mitochondria - they give off e- and hydrogen ions to special protein complexes
- in inner mitochondrial complex, ATP synthase uses a hydrogen ion gradient to synthesis ATP
- both NADH+ H+ and FADH2 release e- to different complexes in ETC, along w/ release of H+ ions into mitochondrial matrix
- e- are successively transferred from one e- carrier to the next along ETC, until they reach cytochrome oxidase, where e- are combined w/ oxygen and hydrogen to form water
- transfer of e- along ETC involves a drop in energy state of e-, energy is released
- this energy is used to pump H+ ions across inner mitochondrial membrane into inter-membrane space
Chemiosmosis
- involves pumping of protons (H+ ions) into intermembrane space of mitochondria by using energy released by e- transport along ETC
- this is followed by diffusion of protons into the matrix down a conc. gradient through ATP synthase to produce ATP
- As the last electron acceptor of ETC, oxygen helps maintain hydrogen gradient in the matrix by binding w/ free protons to form water
- Oxygen accepts electrons and binds protons at the same time to form water
- Each molecule NADH + H+ and FADH2 can give rise to 3 and 2 ATP molecules, respectively
- main reason FADH2 generates fewer ATP molecules, is because it donates its electrons to ETC at a later step