Overview of Protein Biochemistry Flashcards Preview

DEMS: Unit IIb > Overview of Protein Biochemistry > Flashcards

Flashcards in Overview of Protein Biochemistry Deck (12)
Loading flashcards...

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
  1. ammonia from transamination reactions is ==> carbamoyl phosphate 
    1. catalyzed by carbamoyl phosphate synthase 1 = key regulated step in protein catabolism
  2. 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.
  3. 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:
    • serotonin
    • niacin (B3)
    • dopamine
    • norepinephrine, epinephrine
    • tetrahydrobiopterin
    • thyroid hormone