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Structure of proteins, what elements does it contain and of what amino acids?
C, H, O, and N
Carbon = acid group
Hydrogen = n/a
Nitrogen group = amine
*side chain, "R" portion determines protein name
Amino Acids (AA) characteristics: essential, nonessential, and conditionally essential AA.
Give info. on each of the (3)
Essential: (9) Must be taken in via food (i.e. body cannot produce)
Non-essential: (11) Body can produce so consumption of these isn't necessary
Conditionally ess. AA: Essential during infancy, disease or trauma
What is the synthesis of non ess. AA?
What is its function?
- Transamination: Transfer of an amine group (Nitrogen) to a carbon skeleton to form a new amino acid.
What is the synthesis of Non ess. AA and AA Degradation?
Degradation: AA losing an amine group (N)
Amine group is incorporated into urea in the liver.
-->Urea then is excreted in urine via the kidney.
Complete & Incomplete proteins. What are they? And what are complementary proteins?
Complete: adequate amount of all the essential AA (animal protein except gelatin)
Incomplete: Inadequate amounts of the ess. AA (plant proteins except soy)
Complementary: Combining plant proteins to compensate for limiting AAs (red bean & rice, adding legumes to grains)
What type of bond links amino acids to form proteins? What proteins do they form? (4)
- 1) Dipeptides (2 AA)
- 2) Tripeptides (3 AA)
- 3) Oligopeptides (4-10 AA)
- 4) Polypeptides (>10 AA)
What is Transcription and Translation?
Transcription: forming mRNA from DNA
Translation: converting mRNA to protein (step 4)
Summary of protein synthesis; 4 steps, with the 4th step having 4 substeps.
- 1) DNA unwinds allowing enzymes access.
- 2) Transcription (DNA-->mRNA)
- 3) mRNA is processed and goes to the cytosol.
- 4a) Ribosomes recognize start date.
- 4b) Transfer RNA (tRNA) carries AAs to ribosomes when needed.
- 4c) Protein is made by added 1 AA at a time
- 4d) Protein is finally released from ribosome.
Primary: Sequence of chain of AA
Secondary: Due to H or S bonds between AA.
Tertiary: Occurs from additonal folding and determines protein function.
Quaternary: Occurs when multiple proteins join together.
Denaturation & Turnover of protein. What are they?
Denaturation: Altering protein's tertiary structure (3-d structure).
Acid, alkaline, heat, enzymes & agitation can all cause denaturation.
Protein turnover: Constant state of synthesis, breakdown, rebuilding and repair.
Protein turnover is generally high.
Sources of protein. In the US and worldwide, what percentage is supplied by meat, poultry, fish, milk & milk products, legumes & nuts?
70% in the US.
Worldwide, 35% comes from animals.
Evaluation of food proteins are valued by what two concepts?
- Biological Value: measure of how effecient dietary protein is converted to body tissue protein.
- BV = N retained / N absorbed x 100
Protein Efficiency Ratio (PER): measure of weight gain in lab animals.
PER = weight gain (g) / protein consumed
Evaluation of food protein (cont'd). Define the Chemical Score and the Protein Digestibility Corrected AA Score.
Chemical Score: compares ess. AA composition to reference protein (egg white)
CS = mg of limiting AA per g protein / mg of limiting AA per g of reference protein.
PDCAAS: Chemical Score x digestibility
*MOST WIDELY USED METHOD
DV considers the PDCAAS
Protein RDA (recommended daily avg)
Do most americans consume a good excess of their protein requirements?
Nitrogen balance: positive, equilibrium, and negative nitrogen balance.
Explain the intake/excretion of nitrogen for each.
Pos: N intake down, while N excretion is high.
Equi: balances = healthy adult meeting protein & energy needs.
Neg: N intake up, while N excretion is low.
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