Energy Flashcards
Give 4 processes for which energy is required?
Synthesis of new molecules
Establishing ion gradients
Mechanical work
Keeping warm
What is catabolism?
The breakdown of complex molecules to release energy or carry out mechanical work
What is anabolism?
The synthesis of new molecules from less complex components
What are catabolic processes important for in the body?
Catabolic processes degrade components of our diet such as carbohydrates and fats and generate heat, CO2 and the precursors for anabolic processes
What are anabolic processes involved in in the body?
Growth, movement and repair
What are the 4 major oxidative pathways?
Glycolysis
Citric acid cycle
Electron transport coupled to oxidative phosphorylation
Fatty acid oxidation
What is the simplest description of glycolysis?
The conversion of glucose (6C) to pyruvate (3C)
How is glycolysis regulated?
By enzymes catalysing irreversible reactions. The enzyme activity can be regulated by reversible binding of allosteric factors, covalent modification and transcription
What’s the most important control point in glycolysis?
Phosphofructokinase (PFK).
High concentrations of ATP inhibit PFK by lowering the affinity for fructose-6-phosphate. PFK is also inhibited by low pH. Inhibition of PFK leads to inhibition of hexokinase
What regulates hexoinase?
G6P concentration
As G6P accumulates in a cell, hexokinase activity decreases
What regulates PFK?
ATP, citrate and H+.
How does ATP regulate PFK activity?
High ATP content in a cell down regulates PFK activity. This is an allosteric regulation
How does AMP regulate PFK?
AMP positively regulates PFK activity
What’s the function of PFK?
PFK catalyses the formation of fructose-1,6-bisphosphate and ADP from fructose-6-phosphate and ATP
What’s the function of hexokinase?
Hexokinase phosphorylates glucose to glucose-6-phosphate
How can galactose be used in glycolysis?
Galactose can be converted to glucose-6-phosphate in 4 steps. First, galactokinase converts galactose to galactose-1-phosphate. Galactose-1-phosphate then acquires a uridyl group from uridine diphosphate glucose in a reaction catalysed by galactose-1-phosphate uridyl transferase, to form UDP-galactose and glucose-1-phosphate. UDP-glucose is then reformed from UDP-galactose via UDP-galactose 4-epimerase. Glucose-1-phosphate is then isomerised to glucose-6-phosphate by phosphoglucomutase
How can fructose be used in glycolysis?
Fructose can be phosphorylated to fructose-6-phosphate by fructokinase, to then be phosphorylated to fructose-1,6,-bisphosphate and eventually form pyruvate.
Why is AMP a better indicator of energy state than ADP?
ATP can be made from ADP by adenylate kinase. 2ADP gives ATP + AMP, so production of ATP from ADP will also produce AMP, making AMP a signal for low energy state
Why will glycolysis have to stop after extended periods of exercise?
A muscle cell’s NAD stores will get depleted
How do muscle cells get around depleted NAD stores?
Muscle cells produce lactate from the pyruvate formed in glycolysis
What’s the problem with lactate production as a solution to depletion of NAD stores?
Lactate is acidic and inhibits glycolysis at the level of phosphofructokinase.
How is the problem of lactate acidity overcome?
There’s a cycle where lactate is secreted into circulation and transported back to the liver to allow the metabolism in skeletal muscle to continue. Pyruvate can also be converted to acetyl CoA
How does the liver regulate PFK?
PFK is regulated by ATP in the same way as in muscle. Low pH isn’t a problem as the liver doesn’t normally produce lactate.
What inhibits glycolysis in the liver?
Citrate. High levels of citrate indicate the precursors of biosynthesis are abundant
