Biochem Lecture 26: Nitrogen Metabolism

Amino Acid Catabolism: Step 1

remove α-NH₃ group

Amino Acid Catabolism: Step 2

remaining carbon skeleton is metabolized

• gluconeognesis

  or

• TCA cycle

Reaction: α-amino acid + α-ketoglutarate → ____

glutamate (NH₃⁺) + α-keto acid

Reaction: Glutamate → deamination = ____

NH₄⁺

ALT

alanine aminotransferase

AST

aspartate aminotransferase

what happens to nitrogen in our body?

we excrete them

what is the purpose of the urea cycle?

to detoxify and excrete NH₄⁺

where does the urea cycle occur?

in the liver

what happens if the urea cycle is defective?

the liver gets damaged

Why is amino acid anabolism important?

we need all 20 amino acids in order to make protein. Our bodies can make amino acids but some we can’t make so we get them from food.

What are the essential (the amino acids we can’t make) amino acids?

PVT TIM HaLL

p - phenylalanine

v - valine

t - tryptophan

t - threonine

i - isoleucine

m - methionine

h - histidine

a (conditional essential) - arginine

l - leucine

l - lysine

essential

histidine

essential

isoleucine

essential

leucine

essential

lysine

essential

methionine

essential

phenylalanine

essential

threonine

essential

tryptophan

essential

valine

conditionally essential

arginine

what is negative nitrogen balance?

when you are missing an essential amino acid in your diet so your body increases protein degradation

• Outcome: you excrete more nitrogen than what you are taking in

  • More OUT (-) than IN (-)

nucleoside

nitrogen containing ring + ribose

nucleotide

nitrogen containing ring + ribose + phosphate

nitrogenous bases

purines and pyrimidines

what is the structure of a purine

2 rings

what is the structure of a pyrimidine

1 ring

purine

adenine

purine

guanine

how do you remember purines

Pure As Gold

pyrimidine

cytosine

pyrimidine

thymine

what are the ways for nucleotide biosynthesis

salvage pathways and de novo synthesis

salvage pathways

recycle bases and nucleosides from nucleic acid degradation

de novo synthesis

make nucleotides from scratch

pyrimidine biosynthesis

1. build base

2. add sugars

purine biosynthesis

1. start with sugar

2. build base

deoxynucleotide synthesis

deoxyribose + -CH₃ → TMP