Enzymes 2 Flashcards
Give an example of two enzymes that catalyse the same reaction?
Glucokinase and hexokinase
What reaction to glucokinase and hexokinase catalyse?
Glucose + ATP → Glucose-6-phosphate + ADP
Where is glucokinase found?
In the liver
Where is hexokinase found?
Everywhere other than the liver
What kinetic properties do glucokinase and hexokinase have (KM and vmax)
What does a graph of the activity of glucokinase and hexokinase look like and explain it?
Hexokinase is constantly working flat out whereas glucokinase can respond proportionally to blood glucose
Why does hexokinase have a low KM?
So it can respond proportionally to blood glucose
When [glucose] is low you don’t want the liver to break it down as you want it to be released into the blood
What is the difference between glucose-6-phosphate and glucose?
G-6-P cannot leave the cell
What do enzymes being found where they shouldn’t be indicate?
Tissue damage, enzymes may escape from damaged cells
How is enzyme activity measured in clinical scenarioes?
With an arbitory value
1U/ml o 100% = normal
What is an isozyme?
Different enzymes that catalyse the same reaction
Where are isoenzymes often found relative to each other?
In different tissues
Are isoenzymes coded for by the same gene?
No, they are products of different genes
What is electrophoresis?
Process where you can seperate out biological molecules
How does electrophoresis work?
Larger molecules get stuck and so move less than smaller molecules, charge also has an impact
What is creatine kinase (CK)?
An example of an isoenzyme which is a dimer made up from two polypeptide chains B and M
What is a dimer?
Oligomer consisting of two monomers joined by bonds that can be strong or weak, covalent or intermolecular
What is an oligomer?
Molecule complex of chemicals that consists of a few monomer units
What are the 3 isomorms that creatine kinase (CK) can form?
CK1 (BB)
CK2 (BM)
CK3 (MM)
How are enzymes used in diagnosis?
Measure activity and compare with normal
Sepperate differnt forms of enzymes by electrophoresis
Are enzymes restricted to interacting with one substance?
No, most enzymes can interact with a variety of substances
How does the KM vary between enzymes and their different substrates?
Changes for each substrate
What does catalysing a reaction with two or more substances normally involve?
The transfer of groups from one to the other
What ways can the catalyse of two or more substances with the transfer of groups occur?
Random order or ordered with ternary complex
No ternary complex formation
What does a random order reaction involving a ternary complex look like?
What does an ordered reaction involving a ternary complex look like?
With does a reaction with no formation of a ternary complex look like?
What is an example of an enzyme that uses an ordered sequential mechanism?
Lactate dehydrogenase for the reaction of pyruvate to lactate