The Catabolism of Glucose (Glycolysis) Flashcards
Revision (33 cards)
What is the definition of metabolism?
All chemical reactions that maintain the living state of cells and organisms.
What types of reactions does metabolism consist of?
Anabolic and Catabolic reactions.
What are anabolic reactions?
Assimilation of molecules and complex structures from the building blocks of life.
Requires energy.
What are catabolic reactions?
Breakdown of molecules to obtain the anabolic “building blocks” of life and substrates for energy.
Breakdown of molecules to yield energy.
Where does out energy come from?
Ultimately, all our energy comes from the sun.
Plants synthesise macromolecules, using sunlight as energy.
Catabolic pathways oxidise macromolecules, thereby creating ATP.
ATP can be used to drive biosynthetic reactions.
Why is glucose the most important carbohydrate?
More than half of all organic carbon is in three polysaccharides:
Starch and cellulose, both used in plants. And glycogen (glucose in a polymer source) used in animals.
Why is glucose considered our primary energy source?
Oxidised to CO2 and H2O.
What cell types require glucose as an energy source?
Erythrocytes Retina Renal Medulla Brain (the brain accounts of about 20% of the oxygen requirement in a resting person although it represents only about 2% of the body weight). All cancer cells
What is the structure of glucose?
Glucose has 6 carbons and you will very rarely find it in a straight chain, More likely you will find glucose forming a hexagon shape.
What determines if a polysaccharide can be used in the body?
Alpha and beta bonds determine whether a polysaccharide can be used in the body.
What are the different fates of glucose?
Storage
-Glycogen
- Starch
- Sucrose
- Conversion to lipids
Oxidation through Aerobic glycolysis
- Pyruvate, efficient ATP production by oxidative metabolism.
Fermentation by Anaerobic Glycolysis
- Lactate, rapid inefficient ATP production
Oxidation through the Pentose Phosphate Pathway
- Ribose-5-Phosphate, precursor for nucleotide synthesis and DNA repair, essential for growth
What are the Intracellular stages of metabolism?
Stage 1 is essentially eating the food.
Stage 2 is Acetyl-CoA production.
Stage 3 Acetyl-CoA oxidation
Electron transfer and oxidative phosphorylation
How is glucose transported into cells?
Via NA+/glucose symporters
Via passive facilitated diffusion glucose transporters
- GLUT 1, Brain, Low KM (M is subscript)
- GLUT 2, Liver, High KM, insulin independent, Beta-cells
- GLUT 3, Brian, Low KM
- GLUT4, Muscle, Insulin-dependent, Adipose tissue
- GLUT 5, Gut, Fructose transport
(The brain works at low glucose concentration so that even at low glucose concentration, it will carry on working and tell you to eat.
The liver works at high KM, to convert it into insulin and store it.)
What is KM (M is subscript)?
The concentration at which you reach half the maximum.
How does GLUT 1 carry out it’s role as a glucose transporter?
Binding of glucose to the outside triggers a conformational change.
Binding site faces inwards.
Glucose can be released in the inside.
Conformational change regenerates the binding site on the outside.
What is glycolysis?
He initial pathway for the conversion of glucose to pyruvate.
(glucose + 2ADP + 2Pi + 2NAD+) -> (2pyruvate + 4ATP + 2H2O + 2NADH +2H+)
Once glucose is inside the cells it’s converted into pyruvate.
What is the process of glycolysis?
In the 1st step glucose is destabilised and so activated by giving it phosphates. Which converts it into fructose-1,6-bisphosphate.
This is less stable than glucose and can easily be broken down into 2 triose phosphates.
These can then be further metabolised to create 2 pyruvate, 4 ATP and 2NADH + 2H+.
What are the 3 stages of glycolysis?
Stage 1: glucose is trapped and destabilised.
Stage 2: 2 interconvertible 3-carbon molecules are formed.
Stage 3: generation of ATP.
What is the difference in symmetry between glucose and fructose?
Fructose has 2 carbons that sit above the plane and glucose has 1. Therefore fructose is more symmetrical.
Fructose has 2 phosphates however so is less stable.
What are the 2 major cellular needs of glycolysis?
Production of ATP.
Provision of building blocks for synthetic reactions.
What are the 3 control points of glycolysis?
The control points occur where enzymes are catalysing irreversible reactions.
1. Hexokinase - substrate entry
2. Phosphofructokinase - rate of flow
3. Pyruvate Kinase - Product exit.
(The middle step is regulated because it converts fructose 6 into fructose-1 because the latter is unstable so it makes sense to not covert something stable back into something unstable unless it is going to be used).
(Each step is regulated by numerous molecules)
(If the system is backed up and not flowing quickly, you et an accumulation of glucose-6-phosphate).
What are the irreversible/controlled reactions in glycoysis
Hexokinase
glucose + ATP -> glucose 6-phosphate + ADP + H+
DeltaG = -33.5 kJ mole-1
Phosphofructokinase
fructose6-phosphate + ATP -> fuctose1,6-bisphosphate + ADP + H+
DeltaG = -22.2 kJ mole-1
Pyruvate kinase
phosphoenolpyruvate + ADP + H+ -> pyruvate + ATP
DeltaG = -16.7 kJ mole-1
These 3 reactions are regulated because they are irreversible reactions. Enzymes that control reactions with large free energies make good control points.
What is phosphofructokinase?
Key enzyme controlling rate of substrate movement along glycolytic pathway.
fructose6-phosphate + ATP -> fructose1,6-bisphosphate + ADP + H+
What effect do AMP and fructose2,6-bisphosphate have?
Will increase glycolysis if energy is needed.
