Download 6-metabolic-pathways

Human Cells
Metabolic pathways
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What do you already know?
 Write down 3 things you know about metabolic pathways
already.
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What you will be learning
 What metabolic pathways are.
 How metabolic pathways are controlled.
 Why it is necessary to control metabolic pathways.
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Metabolism in cells
 Cell metabolism is the whole, vast array of biochemical
reactions taking place in a cell.
 It is complex but controlled and integrated.
 Enzymes play a vital role by catalysing these biochemical
reactions.
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Metabolic pathways
 There are 2 types of metabolic pathways
 Anabolic pathways are biosynthetic (building up)
processes that require energy (e.g. building proteins)
 Catabolic pathways involve the breakdown of complex
molecules and usually release energy (e.g. respiration)
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Metabolic pathways
 Some metabolic pathways have reversible and irreversible
steps
 One reason for this is that the enzyme controlled
reactions produce new molecules that can act as
regulatory molecules
 Some metabolic pathways have alternative routes
 Alternative routes mean cells can make use of alternative
chemicals for metabolic pathways
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Control of metabolic pathways –
enzymes are key
 Enzymes control the rate of reactions in metabolic
pathways
 The absence or presence of particular enzymes will
determine whether a reaction can proceed or not
 Enzymes allow the activation energy for a chemical
reaction to be lowered so that the reaction is more
likely to take place
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Control of metabolic pathways –
enzymes are key
 Enzymes are produced by gene expression
 Some genes for enzymes are continuously expressed
 These enzymes are always present in cells
 The presence of a substrate or the removal of a product
will effect the rate of reaction and it’s direction
 The presence of a substrate will often drive the reaction
forward
 The presence of the end product will often slow or stop a
metabolic pathway
 Many metabolic reactions are reversible
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Control of metabolic pathways –
enzymes are key
 Enzymes react with their substrates at an active site
 The active site allows the enzyme to be specific for a
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substrate
The substrate will have a affinity (chemical attraction) for
the active site
The active site is flexible and as the substrate combines
with it, the site changes shape slightly
This change of shape allows the active site to fit very
closely to the substrate
This is called INDUCED FIT
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Control of metabolic pathways –
enzymes are key
 Enzymes allow the correct orientation of the substrate or
substrates at an active site due to their shape
 Enzymes lower the activation energy for a reaction to
take place
 Enzymes produce products that have a low affinity for the
active site so they are released
 Enzymes can be utilised many times in a metabolic
pathway
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Factors affecting enzyme activity
 These include:
 Substrate concentration
 End product inhibition
 Multi enzyme complexes
 Inhibitors
 Signal molecules
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Substrate concentration
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End product inhibition
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Multi enzyme complexes
 This is when there are a number of enzymes working
together to make a process happen.
 An example of this is DNA polymerase and RNA
polymerase activity
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Enzyme inhibitors
 Inhibitors are molecules that will decrease the rate of an
enzyme controlled reaction
 Competitive inhibitors – bind to the active site directly so
are in direct competition with the substrate
 Increasing the substrate concentration will increase the
rate of reaction as more sites will be occupied by the
substrate than the inhibitor
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Enzyme inhibitors
 Non competitive inhibitors
 These become attached to another part of the enzyme
NOT the active site
 They alter the shape of the active site so the substrate
can no longer bind to it
 This slows the rate of reaction
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Uses of enzyme inhibitors
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Signal molecules
 Enzyme activity can be controlled by signal molecules
 If the signal molecule originates and has it’s effect within
a cell then they are called INTRACELLULAR signal
molecules
 If the signal molecule originates from one cell and have
their effect somewhere else they are called
EXTRACELLULAR signal molecules
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Gene expression discovered
 LAC OPERON theory
 Jacob and Monod
 E. coli and it’s use of lactose as an alternative substrate
for respiration
 Enzyme needed is β galactosidase to breakdown lactose
into glucose and galactose
 Enzyme only produced when lactose is present
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What do you know now?
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What is metabolism?
What are anabolic reactions?
What are catabolic reactions?
What molecules control metabolic pathways?
What is an active site?
What is induced fit in reference to enzymes?
What is activation energy?
How do enzymes change activation energy?
What are competitive inhibitors?
What are non competitive inhibitors?
What is the effect of substrate concentration on enzyme
reactions?
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