What are isoenzymes?
- Have different amino acid sequences but catalysed the same reaction
What types of short-term and long-term regulation of enzymes are there?
- Short-term: substrate and product concentration; change in enzyme conformation (Allosterically regulation, covalent modification, proteolytic cleavage)
- Long-term: change in rate of protein synthesis; change in rate of protein degradation
How does substrate concentration affect the rate of reaction?
- High concentration increases forward rate of reaction
How does product concentration affect the rate of reaction?
- High concentration of product inhibits the forward reaction
What type of curve do allosteric enzymes show and why?
- Sigmoidal
- In multi-subunit enzymes, substrate binding becomes subsequently easier
What do allosteric activators do?
- Increase the proportion of the enzyme in the R state
What do allosteric inhibitors do?
- Increase the proportion of enzyme in the T state
How is phosphofructokinase regulated?
- Allosterically regulated
Why is the regulation of phosphofructokinase important?
- Sets the pace of glycolysis
What activates phosphofructokinase?
- AMP
- Fructose-2,6-bisphosphate
What inhibits phosphofructokinase?
- ATP
- Citrate
- H+
Give 2 examples of covalent modification
- Phosphorylation (+ATP)
- Acetylation (+Acetyl CoA)
What type of enzymes add a phosphate group to proteins?
- Kinases
What type of enzymes remove a phosphate group from proteins?
- Phosphatases
How do kinase enzymes work?
- A phosphate group is removed from ATP which is transferred to the -OH group of Serine, Threonine or Tyrosine
How do phosphatase enzymes work?
- Remove phosphate groups by hydrolysis
Why do phosphate groups affect enzyme activity?
- Bulky, charged groups that significantly affect enzyme conformation and substrate binding
What is amplification?
- one enzyme activates other enzymes, which activates others,which means one signal is amplified very quickly - has a larger effect
What is proteolytic cleavage?
- enzymes secreted as zymogens (inactive protein precursors) and are cleaved by proteases to give the active enzyme
Give examples of digestive enzymes that undergo proteolytic cleavage
- Stomach: zymogen = pepsinogen, active enzyme = pepsin
- Pancreas: zymogen = chymotrypsinogen, active enzyme = chymotrypsin
- Pancreas: zymogen = trypsinogen, active enzyme = trypsin
- Pancreas: zymogen = procarboxypeptidase, active enzyme = carboxypeptidase
- Pancreas: zymogen = proelastase, active enzyme = elastase
Give examples of when proteolytic cleavage is used
- Digestive enzymes
- Protein hormones
- Blood clotting
- Developmental processes
- Apotosis
What is the overview of the blood clotting cascade?
Intrinsic pathway: Extrinsic pathway:
Damaged endothelial lining of Trauma releases tissue factor
Blood cells promotes binding (Factor III)
Of factor XII ⬇️ ⬇️
Factor X activation (common endpoint)
⬇️
Thrombin activation
⬇️
Formation of fibrin clot
What is good about the clot formation using a cascade?
- Allows formation of a clot from very small amount of initial factor
What type of feedback does thrombin do?
- Positive feedback
