Biochemistry Part 4 Flashcards
What are the parameters used to describe the relationship between concentration of substrate and rate of catalysed reaction?
Vmax and Km
What makes the enzyme-substrate complex unstable?
The activation energy barrier
What is the michaelis constant equivalent to?
Substrate concentration where the initial reaction is half maximal
Where is Vmax on a line weaver burke plot?
Intersection of the straight line with the Y axis
Where is Km on the lineweaver burke plot?
Intersection with the X axis
Define Vmax
Maximum velocity of a reaction
Define Km
Concentration in moles of S which gives 1/2 of Vmax
What does a low Km indicate?
An enzyme only needs a little substrate to work at half-maximal velocity
What does a high Km indicate?
Enzyme needs a lot of substrate to work at half-maximal velocity
Describe the Km of the hexokinase in red blood cells
0.05mM glucose
Low Km maintains energy production in RBC by glycolysis even if glucose level falls dramatically
Describe the Km of glucokinase in the liver
High Km enables glucose sensing and homeostasis.
Its abundance in liver is regulated by insulin.
Excess blood glucose is metabolised
What are prolyl hydrolyses?
Prolyl hydrolyses are oxygen sensors which require O2 as a substrate to regulate the HIF transcription factor
High Km for O2- even high than atmospheric oxygen levels
How do genes help us survive hypoxia?
Prolyl hydrolyses activate the transcription factor hypoxia inducible factor
Transcribes genes for;
- RBC synthesis
- Blood vessel growth
- Anaerobic survival pathways
What happens in Von Hippel Lindau syndrome?
Excessive blood vessel growth
Haemangiomas in brain
Subcutaneous haemangious track spinal cord
What does competitive inhibition do to Vmax and Km?
Vmax does not change
Km varies
How can methanol poisoning be treated?
Substrate for alcohol dehydrogenase: causes conversion to formaldehyde
ADH has a Km for ethanol 20x greater than methanol
Treat with 40% ethanol in combination with dialysis and ventilation
What does non-competitive inhibition do to Vmax and Km?
Vmax varies
Km does not change
What is a rate limiting enzyme?
When the end product acts as an inhibitor of the slowest enzyme in the pathway (usually near the beginning)
When is feedback inhibition prevalent?
Common mechanism of allosteric control
What is feedback inhibition useful for?
Control mechanism, it avoids build ups of intermediates
Do allosteric enzymes follow the michaelis-menten kinetics?
No
Increasing substrate results in a sigmoidal curve instead of hyperbola
Give an example of allosteric regulation?
Binding of oxygen to haemoglobin
Controlled by
- H+
- CO2
- 2,3 bisphosphoglycerate a side product of glycolysis
