Final Study Guide (Nutri Sci Exam 2)

Amino acids are named for containing what?

Nitrogen (amino group)

Structure of an amino acid

NH₂ (amino), COOH (carboxylic acid), R (side chain)

Essential amino acids must come from

Diet

Non-essential amino acids can be

Made by the body

Conditionally essential amino acids

Needed in diet under stress/illness (e.g., cysteine from methionine)

Cysteine is made from

Methionine

Tyrosine is made from

Phenylalanine

PKU (phenylketonuria) affects which pathway?

Tyrosine synthesis from phenylalanine

Transamination does what?

Transfers NH₂ group between amino acids and keto acids

Deamination removes what?

NH₂ group → produces ammonia (toxic)

Where is ammonia converted to urea?

Liver

Urea is excreted by

Kidneys

Protein turnover =

Protein synthesis + protein breakdown

Nitrogen balance equation

Protein intake (g) / 6.25 - urinary urea N - (0.25 × urinary urea N) - 2 g

Positive nitrogen balance occurs in

Pregnancy, growth, muscle gain

Negative nitrogen balance occurs in

Fasting, illness, stress

Peptide bond formation is

Condensation (removes H₂O)

Peptide bond breaking is

Hydrolysis (adds H₂O)

Primary protein structure

Sequence of amino acids

Secondary structure

Alpha helices and beta sheets (H-bonds)

Tertiary structure

3D folding of polypeptide (R-group interactions)

Quaternary structure

Multiple polypeptide subunits (e.g., hemoglobin)

Denaturation affects which structures?

Secondary, tertiary, quaternary (NOT primary)

Protein digestion requires

Denaturation (unfolding) by acid/enzymes