17. Proteins Flashcards
What are amino acids used for?
- Protein synthesis
- Synthesis of nitrogen containing metabolites
- Making glucose/glycogen
- Making fatty acids, ketone bodies (storage)
- Energy (ATP)
Identify 4 signs/symptoms of protein malnutrition.
- Poor growth - need protein for new tissue
- Susceptibility to infection - cant produce enough immunoglobins
- Changes in hair/skin colour - lack of melanin
- Poor skin condition
- Poor nutrient absorption - cant replace epithelial cells when they die
- Abdominal bloating - accumulation of fat in liver + fluid build up
- Lower limb oedema - lack of albumin leads to low water potential
To use the carbon skeleton of an amino acid, the amino group must be removed and the nitrogen excreted.
Why cant the amine group simply be released as ammonia?
Ammonia is very toxic - levels in the blood must be kept low.
Where does the disposal of ammonia mainly occur?
Liver
(urea excreted by kidneys)
explains why liver disease is a common cause of hyperammonaemia
Outline the 3 steps of removing the amino group from an amino acid and disposing it, including the enzymes needed.
- Transamination - transfer the amino group from an amino acid to alpha-ketoglutarate to form glutamate.
Enzyme = transaminase
Pyridoxal phosphate is required for this step.
(occurs in most tissues to safely transfer the ammonia to the liver) - Deamination - release ammonia from glutamate
Enzyme = glutamate dehydrogenase
(in liver) - Urea synthesis - urea cycle
Pyridoxal phosphate is the active form of vitamin B6.
What does a lack of vitamin B6 lead to?
- Anaemia - lack of haem
- neurological problems - lack neurotransmitters + lipid synthesis
- Poor growth, immune responses, skin lesions - lack of protein synthesis
What is the control step in urea synthesis?
ammonia + bicarbonate -> carbamoyl phosphate
Enzyme = carbamoyl phosphate synthase 1
The urea cycle is deactivated by high levels of amino acids.
True or False?
FALSE
activated by high levels of amino acids.
The urea cycle occurs in the mitochondria.
True or False?
FALSE
only the first 2 steps, the rest takes place in the cytosol (urea released here).
How does uric acid differ from urea and what can excessive levels lead to?
Uric acid is derived from purine nucleotides (adenine, guanine (DNA, RNA)) rather than protein.
Hyperuricaemia (excess uric acid in blood) leads to urate crystals being deposited in the kidney (kidney stones) and in the joints (gout).
Which of these metabolic pathways can the carbon skeletons of amino acids NOT be fed into? Krebs cycle Fatty acid + ketone synthesis Glycolysis Glucose synthesis
Glycolysis
All amino acids can be made into glucose.
True or False?
FALSE
lysine + leucine are only ketogenic.
Gluconeogenesis is vital for maintaining blood glucose levels during fasting/exercise.
Where does this process mainly take place and what precursors are used?
Mainly in cytosol of liver + kidneys.
- keto acids - derived from amino acids
- lactate - anaerobic glycolysis
- glycerol
What are the control steps for gluconeogenesis + their enzymes?
1. pyruvate > phosphoenolpyruvate pyruvate carboxylase 2. fructose 1,6 bisphosphate > fructose 6 phosphate fructose 1,6 bisphosphatase 3. glucose 6 phosphate > glucose glucose 6 phosphatase
(basically the reversal of glycolysis, but different enzymes are used so that glucose isn’t cycled up and down continuously for no reason)
Gluconeogenesis + glycolysis are described as being reciprocally regulated.
What does this refer to?
↑ glucose / ↓ energy = glycolysis
↓ glucose / ↑ energy = gluconeogenesis
