Cellular Metabolism Flashcards
What are 7 key energy metabolism pathways?
Gluconeogenesis Krebs cycle ETC Beta fat oxidation Photosynthesis Glycolysis Fatty acid synthesis Photosynthesis ( plants)
What is an exergonic pathway?
What controls them?
Give and example
Gluconeogenesis + glycolysis both occur in the cytoplasm
It is an exergonic pathway to avoid a futile cycle ( creating the breaking down via substrate recyling)
Exergonic pathways have a net release of energy/products. Proceed in the forward direction
Specific control points determine which reaction occurs ( glycolysis or gluconeogenesis)
What can affect the rate of a chemical reaction?
Conc of reactants + products Temperature, pH Catalytic activity Conc. of enzyme Rate of translation vs rate of degradation
What are 3 ways that can alter enzyme activity?
- Altering number of available molecules in the cell
- Altering their effective activity
- Changing activity of the existing molecules
How does substrate conc. alter the ROR?
Lower substrate concentrations mean the ROR increases rapidly ( rate is more sensitive at lower conc)
Higher substrate concentrations cause rate to increase more slowly as more enzymes are fully saturated with substrate
What is Km constant?
At what substrate conc. is Km usually achieved?
The concentration of substrate/metabolite at which the enzyme is working at 50% of its maximal capacity
Km is normally achieved at the physiological concentration of the substrate
What are regulatory proteins?
Bind to enzymes and alter their activity
What happens when there is a fall in ATP concentration?
Rapid reduction in the activity of ATP utilising enzymes
Increased AMP formation
What is AMP and why is it more potent?
Allosteric regulator that is much more potent
This is because its concentration is very low before ATP degradation and hence reduction occurs
What is AMPK?
What can lead to its activation?
AMP activated protein kinase, it is a key regulator fat and carbohydrate metabolism
It phosphorylates target proteins
Activated by: Low ATP/High AMP Sympathetic nervous system Exercise Leptin + adiponectin
What is the function of AMPK?
It phosphorylates target proteins away from energy consuming processes
It causes extra hepatic tissues to use fatty acids as a fuel source
Triggers gluconeogenesis in the liver to provide glucose to the brain
Stimulates feeding behaviour in the hypothalamus so we eat more
What is the elasticity coefficient?
Responsiveness of an enzyme to substrate
Substrate concentrations below the Km an increase in the substrate concentration will increase the rate
At substrate concentrations in XS of the Km there is no increase in enzyme velocity( rate)
Describe the process of glycolysis
Glucose broken down
Pyruvate -> acetyl Co enzyme A in mitochondria
Citric acid cycle produces NADH + FADH
Oxidative phosphorylation: ETC produces ATP as an energy source for the cell
What are izozymes?
alternative forms of the same enzyme that exist in different proportions in different tissues
Can have different kinetic properties
How many isozymes of hexokinase are there?
Examples
4
HK1 is expressed in all tissues at variable levels
HK4 is only expressed in the liver and has a high Km so will respond to high concentrations of glucose substrate. This also means it can clear the blood of glucose at high [glucose]
Give an example of how kinetic properties differ between HK1 + HK4
HK1 only responds at a lower glucose concentration
HK4 can respond effectively at higher glucose concentrations as it has a high Km
How is hexokinase 4 activity controlled?
When fructose-6 phosphate concentration is high
Regulatory proteins bind to HK4 drawing it into the nucleus to prevent it phosphorylating glucose
When glucose concentration is high it can be released from the regulatory protein to phosphorylate glucose
What is the function of phosphofructose kinase 1?
Catlayses the conversion of fructose 6-phosphate and ATP to fructose 1,6-bisphosphate and ADP
A commitment step in glycolysis
How is the activitiy of phosphofructokinase 1 regulated?
ATP can kick start glycolysis
Glucose should not be used to produce ATP in glycolysis if large amounts of ATP are already present ( waste of cellular resources)
How does ATP affect the activity of phosphofructokinase 1 ?
Effect of low [ATP]
Effect of high [ATP]
Low ATP -> Low Km
- The enzyme will have a high rate a low concentration of fructose-6 phosphate
High ATP -> High Km
When will glycolysis occur?
High AMP
Low ATP
When will gluconeogenesis occur?
Low AMP
What is the role of Fructose-2,6 bisphosphate?
Regulator of glycolysis and gluconeogenesis
It activates phosphofructokinase and hence glycolysis ( allows for conversion of fructose 6-phosphate and ATP to fructose 1,6-bisphosphate and ADP)
It inhibits fructose 1,6-biphosphatase and hence gluconeogenesis
