lecture 13 - carbohydrate metabolism Flashcards
What are the two main features of ATP?
- thermodynamically unstable
- kinetically stable
What is thermodynamic stability?
concerned with the direction/ feasibility of the process
What is kinetic stability?
concerned with the rate
What happens under cellular conditions to ATP hydrolysis
Get doubles the amount of energy
What is intermediary metabolism?
- chemistry achieved in small steps
- Each step catalysed by enzymes
What are the two mechanisms by which glucose can enter cells?
- Facilitated diffusion transporters ( the GLUT family)
- Sodium linked active transporters ( The SGLT family)
What does GLUT 4 do?
Translocates through multiple intracellular compartments
What does insulin do to GLUT 4?
insulin receptors signalling stimulated GLUT 4 exocytosis
An overview of the first half of Glycolysis
(reactions 1-5)The hexose glucose is phosphorylated and cleaved to yield 2 molecules of triose glyceraldehyde - 3- phosphate
The second half of glycolysis
The two molecules go glyceraldehyde -3-phosphate are converted in to pyruvate.
What does glucose turn into in the first step of glycolysis?
Glucose- 6 - phosphate
What is the name of the enzyme in the first reaction of glycolysis ?
hexokinase
what occurs in the first reaction glycolysis?
A phosphate group is added to the C6
Why are magnesium ions needed in the first step of glycolysis?
Complexing with the phosphate oxygen atoms, shield the negative charge
why does hexokinase perform an induced fit, enclosing ATP and glucose?
must be shielded from water , to make suer phosphate isn’t simply cleaved off by ATP
what are the two parts of human hexokinase?
- Regulatory domain
- kinase domain
Where are hexokinases found?
Most tissues in the body
where is glucokinase found?
in the liver
`How are Hexokinases 1-3 regulated?
build up of G6P , enzyme inhibited . This occurs when there is too much ATP . If the cell does not need ATP , then it also does not take up glucose
what does Glucose - 6 - phosphate turn into in the second reaction of glycolysis?
Fructose - 6 - phosphate . From aldose to ketose
What is the enzyme for reaction 2 of glycolysis?
Phosphoglucose isomerase
Reaction mechanism for phosphoglucose isomerase?
Ring opening , followed by isomerization and ring closure. The active site residues are thought to be lys and His -Glu .
what is Fructose - 6-phosphate converted into in the third reaction of glycolysis?
Fructose 1, 6 - bisphosphate
What is the enzyme in the third reaction of glycolysis?
phosphofructokinase (PFK)
Which of the first three reactions in glycolysis need ATP inout?
the first and the third
What happens in the first step?
- Irreversible and proceeds with a large decrease in free energy.
