Metabolism Flashcards
What are the 3 irreversible steps of glycolysis? Name the enzymes used.
Steps 1, 3 and 10
1) Glucose –> Glucose 6-Phosphate
Hexokinase and glucokinase
3) Fructose 6-phosphate –> Fructose 1,6 BP
PFK
10) PEP –> Pyruvate
Pyruvate Kinase
How would you overcome the irreversible steps of glycolysis in gluconeogenesis? State the reactions.
10) Pyruvate –> PEP
PEP carboxykinase
3) F-1,6-BP –> F 6-P
F-1,6-BPase
1) G-6P –> Glucose
G-6Pase
Why does lactate build up in anaerobic respiration?
NADH + H+ + pyruvate –> NAD+ + lactate
Enzyme - LDH
What is lactose made up of?
Galactose + glucose
What is galactosaemia? What is the rare and common forms of it? What is the result of galactosaemia? How is it treated?
Inability to convert galactose to glucose.
Rare - Lack of galactokinase
Common - Lack of transferase
Results in galactose –> Galactitol via Aldose reductase. Depletes NADPH
NADPH prevents cross linking of proteins in eye, results in cataracts.
Treatment is to avoid lactose.
What does the pentose phosphate pathway produce? What enzyme is necessary?
Produces NADPH and C5 sugars for nucleic acid synthesis.
Needs G-6-P DHase
Give 2 examples of uncouplers
Dinitrophenol and dinitrocresol
How is TAG stored in adipose tissue and how does this system ensure that fatty acids are released in times of low serum glucose?
TAGs constantly being converted from TAG to FAs and back.
Conversion back to TAG requires extracellular glucose to enter cell and reform TAG.
Lack of glucose in ECF results in FA reslease from cell.
How is fat broken down for energy in the mitochondria?
FA links to CoA and taken into matrix using carnitine shuttle.
Oxidative reaction cycles produce FADH2 and NADH. Lose 2 Carbons for every cycle.
Describe the steps in glycogen synthesis
- Glucose –> G-6-P via glucokinase
- G-6-P –> G-1-P via phosphoglucomutase
- G-1-P + UTP –> UDP-Glucose
- Glycogen + UDP-glucose –> Glycogen + UDP via glycogen synthase.
Describe the steps for glycogen breakdown.
- Glycogen –> G-1-P via glycogen phosphorylase
- G-1-P –> G-6-P –> glycolysis
What is phenylketonuria? What enzyme is deficient? What is its pattern of inheritance?
Inability to convert phenylalanine to tyrosine which is needed to create dopamine. Phenylketones excreted in urine
Phenylalanine hydroxylase
Autosomal recessive
What is homocysteinuria? What enzyme is deficient? What is its pattern of inheritance?
Inability to convert homocysteine to cystathionine, which goes on to make cysteine. Results in connective tissue defects.
CBS
Autosomal recessive.
How do statins function?
Inhibit HMG-CoA reductase which synthesises cholesterol
What happens in an overdose of paracetemol?
Drug spills over from phase 2 into phase 1 of drug metabolism.
Results in generation of NAPQI intermediates which exhausts glutathione reserves and leaves hepatocytes open to ROS.
How is alcohol metabolised?
1) Alcohol –> acetaldehyde via Alcohol DHase
2) Acetaldehyde –> Acetate via Aldehyde DHase
How is cortisol secretion controlled?
HPA axis
