Glycolysis Flashcards
What is glycolysis?
- Key pathway in preparing glucose ( and other CHO) for oxidative degradation
- Glycolysis - sugar splitting
What is the fate of glucose in the blood?
- Blood glucose transported into cells (e.g. Glut2 and Glut4 – enhanced by insulin), lowering blood concentrations
- Fate within the cell:
- Glycolysis( catabolism)
- Glycogen ( anabolism)
- Fat ( anabolism)
What is the aim of glycolysis
One molecule of glucose is converted into two molecules of pyruvate
What is the fate of pyruvate?
- In aerobic conditions, pyruvate enters the citric acid cycle
- In anaerobic conditions, lactate is formed from pyruvate (fermentation)
What stages can glycolysis be split into?
- Investment
- Cleavage
- Energy harvest
What is step one and two of the glycolysis pathway
STEP ONE :
- Phosphorylation of glucose at carbon 6
- Requires ATP - investment stage
- Increases free energy state and locks glucose inside the cell ( maintains glucose gradient)
STEP TWO
- Conversion of glucose6-P to fructose 6-P
- G-6-P ring structure opens to enable isomerisation and subsequent ring closure F-6-P
What is step 3 glycolysis
STEP THREE:
Phosphorylation of Fructose-6-Phosphate (F-6-P) at Carbon 1
Enzyme: Phosphofructokinase-1 (PFK-1)
Requires ATP (another investment of energy)
Converts Fructose-6-Phosphate (F-6-P) → Fructose-1,6-Bisphosphate (F-1,6-BP)
Regulatory step: PFK-1 is a key regulatory enzyme in glycolysis, influenced by ATP, AMP, and citrate levels
two molecules of G3
What is step 4 of glycolysis
STEP FOUR:
Cleavage of Fructose-1,6-Bisphosphate (F-1,6-BP) into Two 3-Carbon Molecules
Enzyme: Aldolase
Splits F-1,6-BP → Dihydroxyacetone phosphate (DHAP) + Glyceraldehyde-3-phosphate (G3P)
DHAP is quickly converted into G3P by triose phosphate isomerase, so the pathway continues with
What is step 5 of glycolysis
STEP FIVE:
Isomerization of Dihydroxyacetone Phosphate (DHAP) into Glyceraldehyde-3-Phosphate (G3P)
Enzyme: Triose Phosphate Isomerase (TPI)
What is step 6 of glycolysis
STEP SIX:
Oxidation and Phosphorylation of Glyceraldehyde-3-Phosphate (G3P)
reaction:
G3P + NAD⁺ + Pi → 1,3-Bisphosphoglycerate (1,3-BPG) + NADH + H⁺
Key points:
First oxidation step in glycolysis
Produces NADH, which carries electrons for later ATP production in oxidative phosphorylation
Inorganic phosphate is added
What is step 7 of glycolysis
First formation of ATP (energy harvest)
- The newly formed high-energy phosphate bond used to synthesise ATP and 3-phosphoglycerate (3PG)
1,3-Bisphosphoglycerate (1,3-BPG) + ADP → 3-Phosphoglycerate (3-PG) + ATP
What is step 8 of glycolysis
3Phosphoglycerate converted to 2Phosphoglycerate – essential preparation for next energy harvest step
What is step 9 of glycolysis?
2Phosphoglycerate dehydration to form phosphoenolpyruvate (PEP) – converts low-energy phosphate ester bond of 2PG into high-energy intermediate phosphate bond
What is step 10 of glycolysis
- hydrolysis of Phosphoenolypyruvate high-energy bond generates ATP and pyruvate (physiological irreversible reaction)
- E.g. of substrate-level phosphorylation
Describe the energy yield of glycolysis
4 ATP (generated) – 2 ATP (invested) = Net 2 ATP
Explain the fate of pyruvate in aerobic conditions
- Pyruvate is transported into the mitochondrial matrix & converted to Acetyl-CoA in aerobic condition
- Acetyl-CoA feeds into the citric acid cycle
- NADH + H+ oxidised to replenish NAD+ via the electron transport chain
- When cellular energy levels (ATP) in excess, Acetyl-CoA used for synthesis of fatty acids
What happens to glycolysis in anaerobic conditions?
- For glycolysis to continue in anaerobic conditions NAD must be replenished
- When ATP demand is high and O2 depleted, homolactic fermentation regenerates NAD+
- Reversible reaction which enables glycolysis to continue for short amounts of time
- Build up of lactate causes muscle cramps and limits activity
- Slow/fast twitch myofibre composition determine rate of muscle fatigue
Describe Lactate dehydrogenease
- Composed of 2 different types of subunit: Heart (H) or Muscle (M)
- 5 isozymes – tissue specific expression
- The isozymes have different properties, specialised for the tissues they are expressed in
- LDH1
- LDH2
- LDH3
- LDH4
- LDH5
How is lactase dehydrogenase used in diagnosis
- Differing Properties and tissue locations
- Damage to specific tissues releases cell contents into circulation
- Changes in serum levels – aid disease diagnosis
How is glycolysis regulated?
- Key enzymes
- High [ATP] inhibit enzyme activity
- Intermediate substrates (e.g. fructose-6-P) stimulate PFK activity
- High [citric acid] inhibits
- Low pH inhibits
- Hormones
What are the regulatory enzymes
Hexokinase; Phosphofructokinase pyruvate kinase
What inhibits phosphofructokinase?
High ATP inhibits PFK, it allostericically binds
What activates phosphofructokinase
High AMP
What inhibits Hexokinase
Glucose-6-P
What inhibits pyruvate kinase?
High ATP
What activate pyruvate kinase?
Fructose-1,6-Bisphosphate (FBP)
