Hepatic Protein Metabolism Flashcards
What is the maim source of protein and the main loss of protein from the body?
What is the main source of protein in a fasting state?
Main source = dietary protein
Main loss = urea
Skeletal muscle
What is a de novo a.a vs an essential a.a.?
De novo a.as can be synthesised from other a.as where as essential a.a can not they must come from the diet.
Conditionally essential = may require an essential a.a to be synthesised from - if not there then they too are now essential
These essential a.as can come from protein already in body, but leads to breaking down of muscle etc
Structure of an a.a?
Draw it
Amino group
Carboxylic acid group
Side chain
Hydrogen
The carbon backbone of the R group and the a.a can be used for ATP or gluconeogensis
What is a dipeptide?
Polypeptide?
Protein?
Dipeptide = 2 a.a joined by a peptide bond
Draw it
Polypeptide tends to refer to a.a < 50
Protein > 50
What does it mean if your nitrogen balance is said to be in balance, positive balance, negative balance?
What can free a.as be used for?
In balance = equal excretion and intake
Positive balance = intake>excretion
Negative balance intake
What is Kwashiorkor?
Condition with adequate calories, inadequate protein.
Inadequate protein — oedema of the belly
A.A metabolism overview once absorbed:
A.a are absorbed in from gut
Travel in the portal circulation to the liver
The liver forms many blood proteins e.g albumin
Some a.a will enter the systemic circulation where they travel to tissues and are used to form specific proteins in those cells
Those not used can be used to from a carbon backbone via the removal of the amino group
How are proteins digested and absorbed?
Dietary protein ingested
In the stomach - pepsin and HCl - denature protein
SI - Chymotrypsin, Trypsin, Aminopeptidase - from A.As and oligosaccharides
Enterocyte peptidases - A.As
These are then absorbed into the blood stream via contra sport with NA+
Na+ AT out of the enterocyte, lower conc of NA= in the neterocyte than in the lumen of the intestine so move down conc grad, moving A.as in at the same time. Then they move Bevis facilitated diffusion into the blood
3 x important hepatic proteins:
Albumin
Coagulation factors
IGF-1
The nitrogenous part of an a.a can be removed and used for:
X 3
DNA Bases
Serotonin
Dopamine
Nitric acid
If excess amino groups removed by urea in urine
What is transamination?
What is an alpha-ketoacid?
Enzyme involved?
Most common?
Moving an amino group from one a.a to an existing alpha ketoacid.
a.a 1 + alpha-ketoacid 2 — alpha-ketoacid 1 + a.a. 2
Reaction catalysed by aminotransferase
An Alpha-ketoacid = an a.a with the amino group removed
Most common = glutamate and alphaketoglutamate
Precursor of alanine, Aspartate, glutamate?
Pyruvate
Oxaloacetate
Glutamate
Why does a protein become degraded? And how?
Ubiquitin a small protein that attaches to a protein. The longer the ubiquitin chain (>4) the stringer the signal for destruction of the protein.
Once the protein has been marked:
Proteasome will breakdown the the protein through the use of hydrolases.
Note the a.a structure determines how easily a protein can be marked by ubiquitin and under degradation. The most important a.a is at the N terminus. Some are stabilising some are destabilising - see notes if need more.
What is the other main method of proteolysis?
Via lysosomes
Can be:
Macroautophagy - non selective
Phagosomes engulf proteins the lysosome fuses and initiates proteolysis
Microautophagy - non selective
Lysosomal membrane engulf proteins
Chaperone-mediated autophagy
Selective
Phagocytosis
Glucose - alanine cycle simplified:
Glucose is used by the skeletal muscles and produces pyruvate
The private can be recycled by a transamination reaction with glutamate to form alanine and alphaketogluterate
Alanine can travel back to the liver
The amino group is removed hence forming pyruvate again. The pyruvate can then be used for gluconeogenisis
Hence utilising carbon backbone and removing excess nitrogen.
