Flashcards in Nitrogen Metabolism Deck (36):
General concepts in this section?
-Breaking down amino acids for energy
How can we store carbohydrates?
Glycogen in our liver
How do we store fat?
How do we store amino acids?
What two ways do we get protein?
2. Protein turnover (breakdown pre-existing proteins)
What is the average half-life of a protein?
What are enzymes that break down proteins in our digestive system called?
Proteases / peptide protease / proteases
What's an example of a protease that we talked about?
How does protein in our cells get broken down (what's the process called)?
Where do proteins tagged by ubiquitin go?
Peptide bonds broken inside proteosome
What two major things are amino acids used for?
1. Build new proteins
2. Broken down for energy
What are essential amino acids?
Can't be synthesized by precursors (so need them in our diet)
How will proteins eventually be stored if needed?
Stored as fat - go into citric acid cycle, turned into adipose tissue
Why does nitrogen need to be removed in amino acid catabolism?
What is transamination?
Move NH3 to a-ketoacids to make amino acids
How you make nonessential amino acids from essential
How many metabolic intermediates are there when you remove the amino group of an amino acid?
7 intermediates: all 7 can turn into different stuff
>pyruvate, acetyl-CoA, and intermediates in the citric acid cycle
What is the precursor to purines?
What is the precursor to pyrimidines?
Carbanoyl phosphate (also involved in urea cycle)
What is the basic structure of the proteosome?
Two regulatory subunits on the top/bottom
Catalytic subunit in the middle
What do the regulatory subunits of the proteosome do?
Only allow polyubiquitinated proteins through
What does the catalytic subunit of the proteosome do?
Cleaves protein into 7-9 amino acid polypeptides
Spits out all the chains + ubiquitin
What happens to amino acid chains after they're spit out by the proteosome?
Split up into individual amino acids by cytosolic proteases
What is ubiquitin?
It's a protein that marks other proteins for degredation
Inactive by itself until activated
What first activates ubiquitin?
E1 - ubiquitin activating enzyme- (phosphorylation)
Prepare ubiquitin to get attached to a protein
What happens after ubiquitin is phosphorylated by E1?
Transferred to E2 (ubiquitin-conjugating enzyme)
What is E2 complexed with?
E3 (ubiquitin protein ligase)
What does the E2-E3 complex do to ubiquitin?
Attach ubiquitin to a protein ready to be degraded
How does a protein 'know' when it's ready to be degraded?
There are markers on the hydrophobic core of the protein; when a protein starts to unfold due to age, those markers get exposed and the E2-E3 complex can bind
What amino acid is ubiquitin added at?
A lysine residue, ALWAYS
When does polyubiquitination happen?
How many ubiquitins are necessary?
Added one at a time after the first ubiquitin is added
Need at least 4 ubiquitins to get into the proteosome
What happens once an amino group is removed from amino acid?
Left with a carbon skeleton
R group removed by an enzyme specific to that amino acid
Goes into citric acid cycle as a metabolic intermediate
What are glucogenic amino acids?
Amino acids that can eventually be turned into glucose
What are ketogenic amino acids?
Get turned into ketone bodies / Acetyl-CoA
What happens to excess ammonia after amino acid breakdown?
Transported to liver
After liver, excretion as urea from urea cycle
What's the general idea of the urea cycle?
Remove ammonia from amino acids, get urine out. Carbanoyl phosphate involved in the beginning step