1.6 Metabolism Flashcards
What is metabolism?
all the biochemical processes that occur in a living organism in order to keep it alive.
What are most biochemical processes catalysed by?
enzymes
What are the 2 categories metabolic pathways fall into?
catabolic and anabolic (biosynthetic)
What does catabolic mean?
Pathway involves the breakdown of larger,complex molecules into smaller, simpler ones and usually releasing energy.
What does anabolic mean?
Pathway which requires energy in order to build smaller molecules into larger more complex molecules
Give an examples of catabolic pathways (write out equation)(2)
Aerobic respiration
glucose+oxygen>carbon dioxide+water
ATP>ADP+Pi
Give an examples of anabolic pathways (write out equation)(2)
protein synthesis
amino acids>proteins
ADP+Pi>ATP
What do alternative pathways do? Give an example of a metabolic pathway?
bypass steps in the pathway e.g. glycolysis
How can you identify a reversible step?
double ended arrow head
Why would it not be efficient if enzymes were not available in biochemical processes, e.g. respiration & photosynthesis?
they would happen so slowly that life wouldn’t exist.
What are all biochemical processes catalysed by?
enzymes
What are found in all living cells?
enzymes
What do different cells produce?
different enzymes
What can enzymes either be?
intracellular or extracellular
What is meant by intracellular enzyme and give an example?
an enzyme that functions within the cell in which it is produced e.g. cytochrome oxidase which plays a key role in aerobic respiration / DNA polymerase
What is meant by extracellular enzyme and give an example?
an enzyme that is secreted by a cell and functions outside of that cell e.g. pepsin which plays a key role in digestion
Where are most enzymes made and via what process?
inside cells via protein synthesis
Give six properties of enzymes?
Lower activation energy required for a biochemical reaction to proceed.
Speed up the rate of a biochemical reaction
Take part in the reaction but remain unchanged at the end of the reaction, therefore can be reused.
They are made up of proteins
They are specific.
Work by induced fit model of action
What does the activity of enzymes depend on?
their flexible and dynamic shape.
What is the shape of the enzymes active site determined by?
the chemical structure and bonds in between the polypeptides in the amino acid chain.
What will an enzyme only work on?
one type of substrate
What are the molecules of the substrate complementary in shape to?
the enzymes active site.
What is the currently accepted model for enzyme action ?
induced fit model
Describe the induced fit model ?
The active site is flexible and changes very slightly when the substrate molecule enters allowing it to fit more closely around the substrate molecule. This reduces the activation energy required for the reaction to take place.
What does the substrate have?
a high affinity for the enzymes active site
If the reaction involves two or more substrates(i.e. is anabolic) what does the shape of the active site determine and what does this ensure?
the orientation of the reactants.This ensures the reactants are held together in a way that the reaction between them can occur.
Once a reaction has occured what do the products have?
a low affinity for the active site and are released.
What happens to the enzyme when the products are released?
it returns back to its original shape
How do enzymes increase the rate of biochemical processes?
by lowering the activation energy required for the reaction to proceed.
Once substrate molecules are in the active site what does the enzyme do?
act on the reactants to weaken the chemical bonds and they are described as being in a transition state. Which reduces the activation energy need for the reaction to occur.
Give 3 factors affecting enzyme activity?
Temperature
pH
substrate concentration
Describe stage 1 of the graph showing the effect of temperature on enzyme activity?
As the temperature increases the enzyme activity increases
Describe stage 2 of the graph showing the effect of temperature on enzyme activity?
The enzyme has reached its optimum temperature with maximum enzyme activity
Describe stage 3 of the graph showing the effect of temperature on enzyme activity?
As the temperature continues to increase the enzyme activity rapidly decreases
What is the working range and optimum pH for pepsin?
1-4
2.5
What is the working range and optimum pH for most enzymes e.g. amylase?
4-9
7
What is the working range and optimum pH for alkaline phosphatase?
9-12
10
Describe and explain the enzyme activity when the substrate concentration is very low?
the enzyme activity is low as there are not enough substrate molecules for the enzyme to act upon
Describe and explain the enzyme activity when the substrate concentration is increasing?
The enzyme activity increases because the enzymes now have something to act upon
Why does the line level off on the graph conveying the effect of substrate concentration?
enzyme activity activity becomes constant because there are more substrate molecules present than active sites to combine with. Thus, enzyme concentration because the limiting factor.
What do metabolic pathways often involve?
a group of enzymes
What does the activation of the first enzyme in the pathway simulate?
the production of a metabolite which activates the next enzyme and so on.
What are most reactions?
reversible
What does the direction a reaction proceeds in depend on?
the relative concentrations of reactants and products
What doe metabolic pathways rarely occur in?
isolation and are often linked to other pathways
What do enzymes often work in groups as?
multi-enzyme complexes
Give 2 examples of multi-enzyme complexes
DNA polymerase
RNA polmerase
What does a metabolic pathway have?
several stages each controlled by enzymes and involving the breakdown or build-up of one metabolite into another
As enzymes are made up of protein, what can each enzyme be coded for by?
a particular gene
What are genes for some enzymes?
continuously expressed. These enzymes are always present in the cell
What can the action of some enzymes be controlled by?
the expression of the gene
What does controlling the action of some enzymes by the expression of the gene help prevent?
resources being wasted allowing enzymes to only be made when required. The genes are effectively switched on and off.
What is lactose?
a sugar found in milk
What E.coli only use glucose for?
respiration once it has been released from lactose
When can glucose be released from lactose?
when lactose is digested by the enzyme B-galactosidase
What is lactose composed of?
glucose and galactose
What does E.coli’s chromosome contain?
a gene that codes for B-galactosidase
When is E.coli found do produce B-galactosidase?
when lactose is present
When is the gene which codes for B-galactosidase switched on and off?
depending on the presence or absence of lactose
What is the process called when genes are switched on and off ?
enzyme induction
What is an oberon?
a section of DNA which consists of one or more structural genes (e.g. to for an enzyme) and an operator gene which controls the structural gene. The operator gene is, in tun, affected by a repressor molecule which is coded for by a regulator gene
What are some metabolic pathways required to do?
operate continuously
How is the control of metabolic pathways which need to operate continuously brought about by?
regulating the action of their enzymes in several ways
Give 2 ways in which enzyme action can be regulated?
by signal molecules
by inhibitors
What signal molecules do?
trigger a series of events within a cell
Where do intracellular signal molecules come from and what can they affect? give an example?
within the cell and they can affect the cell’s metabolism e.g. transcription factors
Where do extracellular signal molecules originate from?give an example?
outwith the cell, they are produced by other cells e.g. epinephrine
What is an inhibitor?
a substance which decreases the rate of an enzyme-controlled reaction. They can even bring the reaction to a complete halt.
What are the 2 types of inhibitors?
competitive inhibitors
non-competitive inhibitors
What do competitive inhibitor molecules have?
a similar molecular structure to the substrate of an enzyme so they compete with the molecules of the substrate for the enzyme’s active site.
What happens if the competitive inhibitor molecule becomes attached to the active site?
the active site becomes blocked preventing the substrate from occupying the active site, causing a reduction in the rate of reaction
What do non-competitive inhibitors do?
they don’t combine with the enzyme’s active site, instead they attach to another non-active (allosteric) site on the enzyme, which causes the shape of the active site to become indirectly altered, which prevents the substrate combining with the enzyme
What does the degree of enzyme inhibition vary with?
the type of inhibitor
What are competitive inhibitors affected by?
the concentration of the inhibitor
the concentration of the substrate
What are non-competitive inhibitors only affected by?
the concentration of the inhibitor
If the end product in a metabolic pathway accumulates what can it do?
bind to the first enzyme (allosteric site) in the pathway and reduce the efficiency of conversion of metabolites
When the end product can bind to the first enzyme what is it another means of and what does it work by?
means of regulation and works by negative feedback, preventing wasteful conversion and accumulation of intermediates and final products.
Give an example of feedback inhibition by an end product?
during respiration, the enzyme PFK can be inhibited by high concentrations of ATP or citrate
