NST 160 Lecture 2
How is synthesis of protein stimulated? When is it inhibited? - ANS-Stimulated after a
meal and inhibited during fasting.
What is the primary site for amino acid storage? - ANS-Muscle - specifically skeletal
muscle.
How is a learned avoidance developed? - ANS-Diets with severe amino acid imbalance,
or that are devoid of a single essential amino acid, reduce food intake and produce a
learned avoidance of the imbalanced diet. This is due to sensing of amino acids post
absorption.
What amino acid can humans taste? - ANS-Glutamate (umami)
What does a high protein diet lead to in the short term? - ANS-Suppresses food intake
over the short term because protein is the most satiating macronutrient per calorie.
What can high protein diets promote? - ANS-1. Weight and adiposity loss as a result of
the reduced food intake
2. Maintained fat free mass
3. Increased energy expenditure.
What is postprandial increase in protein synthesis caused by? - ANS-Caused by
sensing of amino acids, NOT concentration of amino acids.
What are the three reasons that explain why the SENSING of amino acids causes
increase in postprandial protein synthesis, and NOT concentration? - ANS-1.
Translational initiation, NOT elongation, is increased by increased amino acid levels.
2. Removal of essential amino acids (like leucine) prevent effects of amino acids on
protein synthesis.
3. Norleucine, which can't be incorporated into protein, can also stimulate protein
synthesis.
What are the two checkpoints in protein synthesis? What is one of them regulated by? -
ANS-1. Emergency break (translational repression) for when something goes wrong
2. Gas pedal (derepression), which is regulated by insulin.
, What is eIF2? What kind of check point is it? - ANS-eukaryotic initiation factor 2:
heterotrimeric GTP binding protein that mediates the binding of methionyl-tRNAi to the
40S ribosomal subunit to form the 43 S pre-initiation complex.
EMERGENCY BREAK
What is step 1 in the initiation pathway? What state would this occur in? - ANS-Occurs
during fed state to increase protein translation.
Step 1: Form the 43S subunit.
What is the 43S subunit composed of? What does it interact with? - ANS-eIF2 + GTP +
Met + 40s
Interacts with cap binding complex
When is eIF2 active? - ANS-When bound to GTP.
What is Step 2 of Initiation? - ANS-43S and CAP binding complex stabilize the mRNA.
What is Step 3 of Initiation? - ANS-43s engages with the start codon. Either translation
occurs, or step 4 occurs.
What is Step 4 of Initiation? - ANS-eIF2-GTP is hydrolyzed to GDP by eIF5
How does eIF5 work? - ANS-eIF5 is a GTPase activator protein (GAP). It
de-phosphorylates eIF2-GTP to become eIF2-GDP, rendering eIF2 inactive.
What is Step 5 of Initiation? - ANS-eIF2B recycles eIF2-GDP back to eIF2-GTP to make
eIF2 active again.
What is eIF2B? - ANS-A guanine nucleotide exchange factor (GEF).
How is the GEF activity of eIF2B inhibited? What is the result of inhibition of eIF2B? -
ANS-Phosphorylation of eIF2-GDP, when bound to eIF2B, inhibits the GEF activity of
eIF2B. This traps eIF2-GDP in its inactive state, because eIF2-GDP can't be turned
back into eIF2-GTP.
3 ways to inhibit initiation - ANS-1. Inhibit eIF2B by phosphorylation of eIF2-GDP.
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