Regulation of enzyme activity Flashcards
Why regulate the activity of enzymes?
Our cells monitor and regulate the activity of enzymes so they only function at times needed.
How many stages of enzyme regulation are there
5 stages
What are the two disadvantages of Altering [Enzyme] as a means of regulation
- Takes time to get increase in [Enzyme].
- Takes time for [Enzyme] to decrease - most enzymes have an appreciable half-life in the cell (> 100 hours)
What happens in the allosteric control stage 1
- Enzymes have allosteric sites, signal regulation molecules bind to them on the enzyme
2.The binding causes change in the activity of the enzyme
3.Allosteric enzymes & proteins observe cooperativity meaning the binding of a molecule onto the site will affect affinity of the other site for binding e.g Haemogloblin
What happens in reversible covalent modification stage 2 ?
- Activity of enzymes are controlled and regulated by creating a covalent bond modification on the enzyme
- E.g Phosphoryl group is put onto the enzyme through ATP
- Protein kinase catalyse the transfer of Phosphoryl group from ATP to enzyme activiting or in activating
- Removal of Phosphoryl group uses Protein phosphatase
E+ ATP –> protein kinase E-P+ ADP
<– Protein phosphatase
What happens in Protrolytic cleavage stage 3 ?
- Many enzyme are produced by cell in the body in their inactive form which is known as zymogen or proenzyme
- To activate zymogen or proenzyme protease molecules are used to cleave at the special sites
- Once zymogen or proenzyme are activated they can carry out their function until they are inhibited by an irreversible inhibitor
4.Digestive enzymes such as chytrotrypsin and trypsin as well as blood clotting cascade use this regulation
What happens in enzyme concentration stage 4?
Regulation transcription of the specific genes, can control the amount of enzymes produced
What happens in Isoenzymes ?
- Isoenzymes differ in their sequences of amino acid, 3D structure and enzyme kinetics but they are used to carry out the same reaction
- Multiple forms of the same type of enzymes carry out the same type of function
- Isoenzymes are controlled by regulating molecules
- Isoenzymes e.e lactate dehydrogenase is used anaerobic cellular respiration
What are the two types of isoenzymes
- Cardiac muscle
- skeletal muscle cells
What graph line does allosteric enzyme and normal enzymes have?
Allosteric- sigmoidal curve
Normal- Hyperbolic curve
What is the information of protein kinase ?
- About 30% of human proteins are modified by kinase activity.
- Involved in regulating the majority of signal transduction pathways.
- Human genome encodes > 500 protein kinases
How many protein phosphatase are encoded in human genome?
250
What are the advantages of reversible covalent modification?
- inter-conversion of the enzyme from low activity to high activity forms (and vice versa) is enzyme-catalysed – rapid change in the concentration of active enzyme in response to an external signal.
- reversible modification allows a more controlled response to various metabolic circumstances than irreversible covalent modification.
What are the two inter convertible forms of enzymes?
Tense (T)- Low activity form
Relaxed(R)- High activity form
These differ their affinity for given ligands
The equilibrium between the T- and R-state depends on the relative binding of the allosteric regulators
What is the property of allosteric enzymes?
Heteroallostery- Allosteric enzymes reversibly bind regulatory ligands (called“effectors”, “activators” or “inhibitors”) which are structurally distinct from the substrates or products of the enzyme-catalysed reaction
