Lecture Nine - Metabolic regulation Flashcards
What is metabolism?
The sum of all chemical reactions in an organism.
Large amounts of energy lost.
About 40% efficiency.
Involves biosynthesis and degridation reactions.
Every stage produces heat as a biproduct = a loss of chemical energy in the form of heat.
What are biosynthesis and degridation reactions?
Biosynthesis = anabolic = e.g. new tissue produced.
Degridation = catabolic.
What are enzymes?
Proteins with speific 3D structure.
Are vital to transformation of energy.
Speed up or slow down (stabilize) reactions.
Heat can do the same but would kill the cell.
E.g. Catalase:
Is found in nearly all living organisms that are exposed to oxygen.
Enzymes speed up reactions by lowreing the activation energy.
It catalyses the decomposition of hydrogen peroxide to oxygen and water.
Hydrogen peroxide is a harmful byproduct of aerobic metabolism.
Note that a reactino will still occur without an enzyme, just usually too slowly to allow the organism to live.
Show and explain how enzymes can be organismed into teams in metabolic pathways.
Sequential reactinos. Theoretically reversible, but products are typically removed/used.
How can metabolic regulation occur?
Changing the number of enzymes (gene expression).
Changing the activity of enzymes (competitive).
Changing the activity of enzymes (allosteric).
Putting enzymes in different compartements of the cell.
These are feedback mechanisms.
What is positive feedback?
The enhancing or amplification of an effect by its own influence on the process which gives rise to it.
What is negitive feedback?
The diminution or counteraction of an effect by its own influence on the process giving rise to it, as when a high level of a particular hormone in the blood may inhibit further secretion of that hormone, or where the result of a certain action may inhibit further performance of that action.
What is an unregulated enzyme and competitive inhibition?
An unregulated enzyme is one with an active site where the substrate binds, may also have an alosteric site.
A competitive inhibitor is an enzyme which can have its substrate plus a product of a past reaction bind in its active site.
What is allosteric inhibition and allosteric activation?
An allosteric inhibitor binds to the allosteric site and changes the shape of the enzyme so that the substrate CANNOT bind to the active site.
An allosteric activator binds to the allosteric site and changes the shape of the enzyme so that the substrate CAN bind to the active site.
What is cooperativity?
Form of allosteric regulation.
Substrate itself causes activation of enzyme.
Why is there specific localisation of enzymes and substrates?
Specific localisation (compartements) of enzymes and substrates (e.g. in separate cells).
Increases efficience.
Keeps enzymes and substrates in close contact.
Allows more specific control.
E.g. Mitochondria are a good exampe of how localisation of enzymes and substrates can help cellular efficiency.
What are rate limiting enzymes?
One step (enzyme) in pathway.
Causes a bottleneck.
Regulation of its acitivity determines overall reaction rate.
Are most effective if they are the first step in teh reaction series.
What are isozymes/allozymes?
Slighly different forms of an enzyme.
Each of two or more enzymes with identical function but different structure.
May come from different genes/alleles.
Differing levels of activity and/or regulation.
Important in metabolic regulation.
E.g. Lactate dehydrogease (LDH).
5 different forms found in vertebrates.
Combinatinos of two polypeptide chains ‘M’ and ‘H.’
Encoded by two genes ‘LDH1 and LDH2.’
Thus, M4, M3H, M2H2 and H4 isozymes.
Different characteristics of activity in different tissues.
What are some examples of feedback control in cellular respiration?
Respiration increases or decreases with cellular demand.
Phosphofructikinase is the pacemaker.
Balance of products/fuels controlled by a variety of enzymes.
What is homeostasis?
The regulation of a constant internal environment (within tolerable limits) despite an external or internal deviation.
Integration of metabolic pathways.
