Met 1: Glycolysis Flashcards
What two pathways make glucose?
Gluconeogenesis and glycogenolysis
Describe glucose transport into the cell
Insulin-sensitive tissues (muscle, fat): use GLUT4, which is stored in vesicles and fuses with membrane in response to insulin
Glucose-sensitive tissues (liver, beta-cell, brain): use GLUT2, which is always in cell membrane
Why does glucose need a transporter to get into the cell?
Because it’s large and polar - can’t just diffuse across
Which tissues take up glucose in response to insulin?
Which tissues take up glucose always?
In response to insulin: fat, muscle
Always: brain, liver, beta cells
Name the start and end products of glycolysis
Glucose -> pyruvate
Why is glucose -> G6P a key regulatory step?
Because G6P is highly charged and thus stuck inside the cell.
What enzymes converts glucose to G6P?
Hexokinase and glucokinase
Compare hexokinase and glucokinase.
What is the effect of this difference?
-
Hexokinase: high affinity (low Km), low Vmax
- present in skeletal muscle and adipose
- more active at low glucose conc.
-
Glucokinase: low affinity (high Km), high Vmax
- present in liver and beta cells
- more active at high glucose conc.
This difference directs glucose into skeletal muscle and adipose tissues at low concentrations (b/c only hexokinase has high affinity and will trap the minimal glucose that is present inside the cell)
Insulin causes _______ of enzymes, whereas glucagon causes _______ of enzymes.
Insulin causes DEphosphorylation of enzymes.
Glucagon causes phosphorylation of enzymes.
Glycolysis occurs in _____ tissues, within the cell’s _______, and during a ______ state.
Glycolysis occurs in all tissues, within the cell’s cytoplasm, and during a fed state.
What is the second key enzyme in glycolysis?
What does it do?
Phosphofructokinase-1.
It converts F6P into F16BP.
How do ATP, AMP, and citrate affect PFK-1?
- PFK-1 is a glycolysis enzyme (upregulate it during FED state)
- ATP (high energy) and citrate (TCA intermediate) will inhibit PFK-1
- AMP (low energy) will upregulate PFK-1
Describe regulation of PFK-1 by F26BP
- PFK-1 is a glycolysis enzyme
- Should be active during fed state (high insulin)
- F26BP activates PFK-1 (turns on glycolysis)
- High insulin will dephosphorylate enzymes
- So, insulin dephosphorylates the enzyme that produces F26BP
- This must activate the enzyme
- F26BP is produced by PFK-2
Describe regulation of pyruvate kinase
- Pyruvate kinase is a glycolysis enzyme (converts PEP to pyruvate)
- Insulin tends to dephosphorylate enzymes
- We want glycolysis to be active during high insulin states
- So, dephosphorylation of pyruvate kinase activates it
What hormones upregulate glycolysis?
What hormones downregulate glycolysis?
Upregulate: insulin
Downregulate: epi, glucagon
