Lecture 25: Glycolysis and the TCA Cycle Flashcards
(37 cards)
Define Metabolism
the process by which living systems acquire and use free energy in order to carry out their functions
Define Catabolic
the degradation of nutrients to salvage components and gain energy
Define Anabolic
synthesis of biomolecules from simpler components
What principles govern metabolism?
- common evolutionary theory
- laws of thermodynamics
Where does Glycolysis occur?
the cytosol
Where does the TCA cycle occur?
mitochondria
What is the function of glycolysis?
provide energy in the form of ATP
Why is glycolysis useful?
all sugars can ultimately be converted to glucose
In what 2 ways does glucose enter cells?
- Na+-independent facilitated diffusion transport
- ATP-dependent Na+ monosaccharide transport
Describe Na+-independent facilitated
diffusion
- glucose moves down its concentration gradient
- via GLUT 1-14 transporters
- transporters have tissue-specific expression
- eg. GLUT 4 commonly expressed in muscle and adipose tissue (high response to insulin)
Describe ATP-dependent Na+ monosaccharide transport
- co-transport system
- glucose travels against its concentration gradient
- down Na+ concentration gradient
- Na+ gradient created by active transport (using ATP) of Na/K pump
- found in intestinal epithelial cells
What are the two main phases of glycolysis and which reactions do these include?
- energy investment phase (reactions 1-5)
- energy generation phase (reactions 6-10)
Why is the phosphorylation if glucose important?
- phosphorylated sugar molecules cannot cross the cell surface membrane
- phosphorylation of glucose is irreversible
- traps the glucose in the cytosol which commits it to glucolysis
Describe reaction 1 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- phosphorylation of glucose
- glucose -> glucose 6-phosphate
- hexokinase I-III in most tissues
- non-reversible
Why is hexokinase important?
- 1st regulatory enzyme in glycolysis
- it is inhibited by glucose 6-phosphate
- it has a low Km (high affinity for glucose) meaning it can do efficient phosphorylation in low glucose concentrations
- it has a low Vmax meaning it prevents overabundance of glucose 6-phosphate
What is the alternative name for hexokinase IV and where is it found?
- glucokinase
- liver beta cells (parenchymal cells)
Describe reaction 2 of glycolysis, including:
- type of reaction
- reactant and product
- enzyme used
- is it reversible?
- isomerisation
- Glucose 6-Phosphate -> Fructose 6-Phosphate
- phospoglucose isomerase
- reversible
Describe reaction 3 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- phosphorylation of fructose 6-phosphate
- Fructose 6-phosphate -> Fructose 1,6-Bisphosphate
- phosphofructokinase 1
- non-reversible and rate-limiting
Why is phospofructokinase-1 important?
- most important regulatory enzyme and rate-limiting step
- controlled by ATP and fructose 6-phosphate
- high concentrations of ATP inhibit it while high concentrations of AMP activate it (dependent on abundance of energy)
- also inhibited by citrate (favouring glucose synthesis)
Describe reaction 4 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- Cleavage
- Fructose 1,6-Bisphosphate -> Glyceraldehyde 3-Phosphate AND DHAP
- aldolase
- reversible
Describe reaction 5 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- interconversion
- DHAP -> Glyceraldehyde 3-Phosphate
- triose phosphate isomerase
- reversible
Why must reaction 5 of glycolysis occur?
only glyceraldehyde 3-Phosphate can be used in glycolysis
(DHAP is used in triacylglycerol synthesis)
Describe reaction 6 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- redox (oxidation of GAP)
- Glyceraldehyde 3-Phosphate -> 1,3-Bisphospoglycerate
- GAPDH
- reversible
Describe reaction 7 of glycolysis, including:
- reaction type
- reactant and product
- enzyme used
- is it reversible?
- synthesis
- 1,3-bisphosphoglycerate -> 3-Phosphoglycerate
- phosphoglycerate kinase
- reversible (by physiologically reversible enzyme unlike other kinases)
