Dietary Protein Breakdown

- primarily in proteosomes and lysosomes
- catabolism of cellular protein
- Reasons
- Regulation through turnover
- Quality control: errors, mistranslated, misfolded
> Chaperons make an attempt at correction, but lysosome and proteasomes degrade

- Source of amino acids: fuel and anabolic metabolites
> Use proteins for fuel and anabolic reactions

- Can also use proteins as anabolic precursors
- Some N-terminal sequences can affect protein longevity
- Serine is long (>20 hours), aspartate very short (< 3 minutes)
- PEST sequence has short halflife
> Proline (P), Glutamate (E), Serine (S), Threonine (T)
> May be sites for phosphorylation that allows its recognition by ubiquitination machinery 
- Make sure we degrade the right protein at the right time
STEPS
- Ubiquitination
- Transamination


Endogenous protein breakdown

Michigan State University

Proteins are macromolecules that are composed of subunits called amino acids When the number of amino acids linked together becomes very large, or when multiple polypeptides are used as building subunits,

Proteins

Enzymes are proteins that function as biological catalysts, meaning they can increase the rate of a reaction without being consumed.  

Enzymes

Protein Degradation

Amino acids make up every protein. There are 20 total amino acids each with a unique side-chain group. Some additional amino acids are listed, but only 20 are coded from DNA directly. These side-chains allow for chemical interactions like sulfide bonds, hydrogen bonds, and ionic bonds. Amino acids are further divided by being non-polar, polar, and charged. They link together with a peptide bond making a string of amino acids a polypeptide. Finally, each amino acids is assigned a name, a three-letter symbol and a one-letter symbol. 


Amino Acids are involved in many systems and issues with its breakdown can cause diseases: 
- In the liver: major site of urea production in the urea cycle
- Alpha-keto acids can deliver amino groups to the liver 
- Ammonium is toxic: lethargy, headache, vomiting, seizures, death
- Seen in compromised liver


Amino Acids

- Defense protein are also known as immunoglobins (Ig) 
- Antibodies are produced by the B lymphocytes which are in the bone marrow cells. 
- Involved in humoral immunity (fluid). 
- Structurally diverse proteins

Defense Proteins (Antibodies)

An amino acid is an organic molecule in which a hydrogen atom, a carboxyl group, and an amino group (–NH2) are all bonded to the same alpha carbon with the side chain at the end. They can form peptide bonds. Some amino acid groups can be specifiedby the number of amino acids designated such as ooligopeptideswhich can join up to 20 amino acids and polypeptides which can join up to 50 amino acids. 

Amino Acids 

The size (length) and specific amino acid sequence of a protein are major determinants of its shape, and the shape of a protein is critical to its function. Protein structure is categorized in terms of four levels:
- Primary Structure
- Secondary Structure
- Tertiary Structure
- Quaternary Structure

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