12.Glycolysis Flashcards
What is glycolysis?
the first step in the breakdown of glucose to extract energy for cellular metabolism
What are the two polymers of glucose?
starch and cellulose
Glucose
- the most important carbohydrate
- primary energy source
- oxidised to GOCOWE - glucose and oxygen to carbon dioxide, water and energy
- cells like erythrocytes, retina, Renal medulla use glucose as their only source of energy
- required for function of the brain
Glycolysis reaction
C6H1206 +O2 → CO2 + H2O + energy
State the two forms of glucose
straight chain and intermediate
What is the difference between alpha-glucose and b-glucose?
alpha- glucose - OH on aldehyde group points down
beta- glucose - OH on aldehyde group points up
What are the 3 stages of metabolism?
- Glycolysis
- Citric acid cycle
- Electron transfer chain
How can glucose be transported in the cell?
- via Na+/glucose symporters in the gut.
2. passive-facilitated diffusion through glucose transporters.
GLUT 1 tissue/characteristics
- brain
- low Km
GLUT 2 tissue/characteristics
- liver/pancreatic B cells
- high Km/ insulin independent
GLUT 3 tissue/characteristics
- brain
- low Km
GLUT 4 tissue/characteristics
- muscle/adipose tissue
- insulin dependent
GLUT 5 tissue/characteristics
- gut
- fructose transport
Describe the action of GLUT 1
- binding of glucose to the outside triggers a conformational change so that the binding site faces inwards
- glucose can be released in the cell
- conformational change regenerates binding site on the outside
Glycolysis reaction (glucose to pyruvate)
Glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 Pyruvate + 2 ATP + 2 H20 + 2 NADH and 2 H+
Stages of Glycolysis
- Energy investing - glucose is trapped and destabilised
- Two 3 carbon molecules are formed
- Generation of ATP
What type of linkage is formed from the reaction between a-glucose and fructose? What product is formed and what is removed?
- a-1,2-glycosidic linkage (sucrose)
- water
What type of linkage is formed from the reaction between a-glucose and b-glucose? What product is formed and what is removed?
- a-1,4-glycosidic linkage (maltose)
- water
What type of linkage is formed from the reaction between b-glucose and b-glucose? What product is formed and what is removed
- b-1,4-glycosidic linkage (cellobiose)
What are the two main cellular requirements in Glycolysis?
- production of ATP
- provision of building blocks for synthetic reactions
What acts as control points In Glycolysis?
enzymes
Hexokinase
Glucose + ATP → Glucose-6-phosphate + ADP + H+
ΔG°= -33.5 KJ mol-1
Phosphofructokinase
Fructose-6-phosphate + ATP → Fructose-1,6- diphosphate + ADP +H+
ΔG°= -22.2 KJ mol-1
Pyruvate kinase
Phosphoenolpyruvate + ADP + H+ → Pyruvate and ATP
ΔG°= -16.7 KJ mol-1
What is the key enzyme in the control of Glycolysis?
phosphofructokinase
Negative modulators
ATP and citrate -early intermediate in citric acid cycle -biosynthetic precursors are abundant Hydrogen -prevents excessive formation
Positive modulators
AMP and fructose-2,6- bisphosphate
What is energy change?
the ATP/AMP ratio
If cell Is fully charged..
all adenyl nucleotides are in the shape of ATP
If cell is discharged..
the cell only contains AMP and Pi
What is AMP and not ATP the positive modulator?
- if ATP is rapidly used up…(ATP → ADP +Pi)
- adenyl kinase can salvage some of the energy in ADP (2 ADP → ATP + AMP)
