Protein
Synthesis
Two Processes
Transcription
DNA (nucleus) ® mRNA (cytoplasm)
Translation (Ribosomes in the
Endoplasmic reticulum)
mRNA ® protein AA sequence
mRNA is divided into 3 base pairs (codon)
that code for a specific AA.
tRNA carries specific AA to Ribosomes for protein
synthesis & recognizes specific codons on mRNA.
MRNA + tRNA-AA1 + tRNA-AA2 + tRNA-AA3 =
AA1-AA2-AA3
4 ATP needed to add one AA to chain (work)
Turnover = constant protein turnover and it is energy demanding (4
ATP) This is part of the maintenance energy requirement.
AA availability - Protein synthesis stops if a specific AA is not available
when the ribosome needs it.
¶ All AA have to be available
for protein synthesis to occur, it will not skip a missing AA. Maximum protein
synthesis occurs when all Essential AA are at or above requirement
Limiting AA concept
Deficiency
of on essential AA stops the entire process!!
Amino
Acid Metabolism
Catabolism
1) Constant
body turnover (75% reused for protein synthesis; 5% catbolized)
2) AA in
excess of requirements
3) non-limiting
AA are catabolized
4) AA for
energy production ~20% of daily energy requirement (normal)
Deamination - removal
of amino group as amonia
Transamination - Transfer of amino group from a compound to another
