Biochemistry Flashcards
(2) enzymes that in glycolysis that are INACTIVE when phosphorylated. (So when NOT phosphorylated, they are active.)
pyruvate kinase & PFK-2
Name 1 enzyme that Insulin stimulates and (3) enzymes that it inhibits
stimulates Glucokinase (glycolysis)
Inhibits: pyruvate carboxylase, PEP carboxykinase, and glucose-6-phosphatase (gluconeogenesis)
What does phosphorylation do to glycogen synthase?
Inactivates it. Glycogen synthase is active when it is NOT phosphorylated. So in fed state, we do not have phosphorylation so that glycogen synthase is active. [REMEMBER: Fast = Phosphorylate]
What does phosphorylation do to glycogen phosphorylase? Function of this enzyme?
Activates it. [Fast = phosphorylation]
Glycogen phosphorylase starts at the end of a glycogen chain and cleaves the alpha-1,4 bond, which releases Glucose-1-phosphate. Does this by adding Pi to the bond.
When is glycogen phosphorylase stopped from doing its job?
When there are 4 residues left = steric hindrance. Glycogen phosphorylase goes along cleaving alpha-1,4 bonds until there are about 4 glycosyls on the branch left (before reaching little black ball). *Then debrancher enzyme kicks in.
What are the 2 activities of the debrancher enzyme in glycogen breakdown?
Transferase and Glucosidas:
1) Transferase: transfers 3 of 4 remaining glycosyl residues left on a branch (after glycogen phosphorylase is stopped); and
2) Glucosidase: cleaves the one glycosyl residue remaining at the alpha-1,6 branvch (black ball)
What is yield for each branch of glycogen breakdown?
For every branch, initially yield:
1 Glucose + 7-9 Glucose-1-Phosphate
(Glucose-1-P will later be converted to Glucose-6-P and then glucose-6-phosphatase in the liver will convert it to glucose)
What (2) molecules inhibit glycogen phosphorylase in BOTH the liver and the muscle? What additional (1) inhibits it only in the liver? Why?
Glucose-6-P and ATP inhibit glycogen phosphorylase in both the liver and muscle.
Glucose inhibits this enzyme in the liver, but not the muscle. B/c there is no glucose-6-phosphatase in the muscle, so the muscle keeps it glucose.
What (2) substances stimulate glycogen phosphorylase in the muscle? Where do they come from?
Ca++ and AMP. Come from muscle contraction. So in a working muscle.
What 2 enzymes does Fast Phosphorylate refer to?
phosphorylation of glycogen phosphorylase stimulates its activity. And phosphorylation of glycogen synthase inhibits its activity. So in fasting, you want to BREAKDOWN glycogen.
Role of Ca++ in glycogen degradation during muscle contraction
Ca released from SR and binds to the calmodulin subunit of Glycogen Phosphorylase Kinase b, which is the inactive form and converts it to Glycogen Phosphorylase Kinase A (active form, “A” = active). Then this enzyme can phosphorylate Glycogen phosphorylase b (inactive) to its active form, Glycogen phosphorylase a, leading to glycogen degradation.
How does insulin suppress the glycogen degradation process?
Insulin stimulates the enzyme Protein Phosphatase-1. This enzyme keeps Glycogen Phosphorylase Kinase in its inactive “b” form, so that it can NOT go on to active/phosphorylate Glycogen Phosphorylase.
How do glucagon (liver) and epinephrine (muscle and liver) inactive glycogen synthase?
Both molecules binding to their receptor will stimulate protein kinase A (PKA). PKA directly phosphorylates Glycogen Synthase, converting it from its active “a” state to it’s inactive “b” state. Thus, inhibiting the synthesis of glycogen.
If the amount of protein in the diet exceeds that needed to maintain normal amino acid pools, what happens to the excess amino acids?
They are stripped down to their carbon skeleton, which can be used to synthesize fat for storage. And their nitrogens are excreted as urea.
Positive nitrogen balance. Examples of people in this state
The amount of nitrogen entering the body is greater than that being excreted. This happens if someone is building tissue, particularly muscle. E.g. body builders, pregnant women, growing children, and person healing from severe tissue loss.
Negative nitrogen balance. Examples of people in this state
When more nitrogen is being excreted from the body than entering the body. Ex = people with net tissue loss (trauma or infection) or person with inadequate protein intake.
Which amino acid is required in the human diet even though human have the ability to synthesize it? Who requires this amino acid the most?
Arginine. It can be made in the human body as part of the urea cycle. Some of this arginine can be diverted from the urea cycle for other uses, but not enough to support rapid growth. Arginine is especially important for growing children and of reduced importance for adults.
Name 10 essential amino acids.
I = Isoleucine L = Leucine H = Histadine V = Valine K = Lysine M = Methionine T = Threonine W = Tryptophan R = Arginine F = Phenylalanine
In FED state, name (2) fates of amino acids taken up into tissues and Km of both
Protein synthesis and catabolism for energy. The Km of enzymes that do protein synthesis is low relative to enzymes that do catabolic rxns. Thus, at low [ ], amino acids are preferentially used for protein synthesis. As [ ] rise, protein synthesis rxns are saturated and more and more amino acids get siphoned off to catabolic pathways.
Important role of amino acids during the FASTING state. What’s the primary amino acid used here? What happens once it reaches the liver?
In fasting state, Amino acids provide carbon skeletons to the liver to use in gluconeogenesis to maintain blood glucose levels. Alanine is primary amino acid transported from the muscle to the liver for gluconeogenesis. Once in the liver, Alanine is converted to pyruvate, the 3-carbon precursor for gluconeogenesis.
Which vitamin is a precursor for the coenzyme used by all transaminase enzymes? Name the coenzyme.
Pyridoxine (Vitamin B6). Pyridoxine is converted to pyridoxal phosphate, which is the coenzyme used in ALL transaminase rxns.
(3) uses for dietary amino acids
1) Protein synthesis
2) energy
3) synthesis of other molecules, e.g. neurotransmitters, hormones, purines/pyrimidines, melanin, etc
