M3c L31

Question 1

Describe nitrogen balance in mammals

Answer 1

Intake vs excretion of nitrogen
Positive during growth; more uptake than excretion
negative when unwell; less uptake than excretion

Question 2

Outline the urea cycle and its metabolic importance

Answer 2

ammonia and bicarbonate is turned into carbamoyl phosphate, it goes into the urea cycle as citrulline after combining with ornithine, it then goes through the cycle and leaves as urea

Question 3

Outline transamination and glutamate dehydrogenase reactions and explain their importance in metabolism of amino acids

Answer 3

transaminase moves a keto acid from where there is not enough and puts it glutamate, making it alpha-ketoglutarate, converted into reducing equivalents and used for energy production

Question 4

Explain the difference between ketogenic and glucogenic amino acids and describe their entry points into metabolic pathways

Answer 4

ketogenic amino acids contribute to A-CoA, cannot contribute to glucose synthesis
entry point is a-coa, succinate, fumarate
glucogenic amino acids contribute to glucose synthesis
entry point is pyruvate

Question 5

Explain why amino acids can be used as an energy source and describe points of entry into the pathways that result in the synthesis of ATP

Answer 5

because of what they contribute to

Question 6

Distinguish between non-essential, essential and conditionally essential amino acids

Answer 6

essential: cannot be synthesized from metabolites in enough quantities in the body, need to be provided by diet
non-essential: can be synthesized from metabolites
conditionally essential amino acids: Cysteine and tyrosine can be formed from methionine and phenylalanine

Question 7

Outline the situations that result in either positive or negative nitrogen balance

Answer 7

positive balance:
Animals consume more nitrogen than excreted
Increase in body weight
negative balance
Starvation due to lack of food
Poor absorption of nutrients in elderly
Protein malnutrition
disease and trauma
Lack of essential amino acids
Vegetarian or vegan diets

Question 8

what amino acids are ketogenic only

Answer 8

leucine and lysine

Question 9

Briefly describe the metabolic connections between carbohydrate, fatty acid and amino acid metabolism