Flashcards in Overview of Protein Biochemistry Deck (12)
Different types of categorization of amino acids
- R group properties
- Essential vs. Non-Essential
- Biochemical pathways
R group properties of amino acids
- Acidic vs. basic
- Polar vs. Nonpolar
- Chemical constituents of R groups
- Sulfur containing amino acids
- Amino acids with nitrogen in the side chain
- Branched chain amino acids
- Aromatic amino acids
Categories of amino acids based on body’s ability to synthesize them
- Essential → cannot be synthesized by the body, so must be obtained from the diet.
- Non-essential → are synthesized from other amino acids.
- Conditionally essential → can be made by the body, but the capacity for their synthesis is limited. In states of high consumption, deficiency may develop.
Biochemical pathway definitions of amino acids
- Glucogenic → these amino acids can be used as substrates for gluconeogenesis.
- Ketogenic → when broken down, these amino acids generate acetyl CoA, and cannot participate in gluconeogenesis.
- produce ATP through the TCA cycle OR
- used in ketone synthesis, similar to the fate of Acetyl CoA derived from β oxidation.
Characteristics of protein breakdown @ gut
- gut consumed protein is broken down by a group of peptidases
- peptidases activated @ gut lumen
- Once activated, peptidases are specific different types of peptide bonds
- categorized by the type of bond that they cleave.
- Peptidases work sequentially to break down long peptide chains into their component amino acids which are then absorbed and enter the circulation.
Protein breakdown @ tissues
- two intracellular pathways for protein degradation that will be discussed:
- Ubquination which targets proteins for degradation in the proteasome and is ATP dependent
- Degradation in lysosomes which is ATP independent
- The resulting AAs are then used in the synthesis of new proteins.
Generation of ammonia from amino acids
- amino acid donates an NH2 group to an α-ketoglutarate==> L-glutamate + keto acid.
- enzyme = aminotransferase
- aminotransferases are specific for different amino acids
- glutamate can then released accepted nitrogen as NH3 ==> regenerates the ketoglutarate.
- NH3 (toxic) ==> urea synthesis ==> leave body
Characteristics of Urea Cycle
- urea cycle occurs in the liver
- Glutamate, NH3, and aspartate enter the urea cycle
- ammonia from transamination reactions is ==> carbamoyl phosphate
- catalyzed by carbamoyl phosphate synthase 1 = key regulated step in protein catabolism
- The nitrogen from the carbamoyl phosphate enters the urea cycle, and ultimately is combined with an NH3 from aspartate to form urea which contains 2 nitrogen atoms.
- Urea then leaves the body in urine
Overall rxn that leads to urea production
- AA + α ketoglutarate (via aminotransferase) ↔
- Glutamate + α keto acid
- → NH3 → Urea cycle
- → Urea
Characteristics of sulfur-containing amino acids
- Sulfur containing → Cysteine and Methionine
- Form disulfide bridges in protein
- S-adenosylmethionine is an important energy source in several reactions and a precursor for cysteine, which is important in wound healing, vascular disease, and folate and B12 metabolism
- Glutathione contains cysteine and is an important buffer and protects against reactive O2 species
Characteristics of branched chain amino acids
- require specific enzymes for their breakdown
- deficiencies in these enzymes ==> maple syrup urine disease
Characteristics of aromatic amino acids
- used as precursors for a number of important products:
- niacin (B3)
- norepinephrine, epinephrine
- thyroid hormone