Lecture 27: EXTRACTING ENERGY FROM FUEL MOLECULES Flashcards
What is the major energy intermediate of the cell?
ATP
What are phosphate bonds?
High energy (storing lots of energy)
What does the delta G of a reaction tell us about?
The relative abundance of the substrates and products, also the energy stored in the chemical bonds of the products and substrates
What does it mean when delta G is less than 0?
The reaction is spontaneous, energy is released, it is energetically favourable (A has more energy than B)
What does it mean when delta G is 0?
The reaction is at equilibrium, no change in the energy
What does it mean when delta G is more than 0?
The reaction is not spontaneous, energy is required, energetically unfavourable
What is the delta G for ATP hydrolysis?
-30 kJ/mol (energetically favourable)
What is the delta G for ATP synthesis?
30 kJ/mol (energetically unfavourable)
What does delta G o’ mean?
Gibbs free energy under standard conditions at pH of 7
How can a reaction with a positive delta G be made to occur?
By coupling it with a reaction that has a negative delta g so that the overall delta g is negative and the reaction is spontaneous
What may unfavourable reactions be coupled to?
ATP hydrolysis
What is an example of a reaction coupled to ATP hydrolysis?
The hexokinase reaction (glucose + phosphate»_space;> glucose-6-phosphate + water) has delta G of 14 kJ/mol and is coupled to ATP hydrolysis to become spontaneous
What are the key reactions?
Those involving ADP and ATP, redox reactions
What is involved in redox reactions?
Fuel molecules get oxidised so something must be reduced and provide the oxidising power (NAD and FAD coenzymes)
What is the oxidised molecule in a redox reaction?
The reducing agent (provides reducing power)
What is the reduced molecule in a redox reaction?
The oxidising agent (provides the oxidising power)
How are the reactions which oxidise fuel molecules described?
As energetically favourable (release energy)
How does oxidation of fuel molecules occur?
‘stepwise’ so that all of the energy can be captured for ATP production and not just released as heat
What do biological redox reactions often involve?
The transfer of hydrogen atoms (includes an electron)
What is hydrogen referred to as?
The reducing equivalent
What are the enzymes which catalyse redox reactions often called?
Dehydrogenases
What are coenzymes a subclass of?
Cofactors
What are coenzymes?
Small organic molecules often derived from vitamins
What is the concentration of coenzymes in a cell?
Low
What also couples to ATP?
Glucokinase reaction
What do coenzymes act as?
Carriers
How do coenzymes exist?
In two forms
What is NAD?
Nicotinamide adenine dinucleotide
What is NAD derived from?
Niacin (vitamin B3)
What does NAD do?
Accepts hydrogen and electrons in metabolic pathways (glycolysis, fatty acid oxidation, citric acid cycle)
What does NAD undergo?
2 electron reduction
What does NAD carry?
2 electrons and 1 H+
What is the oxidised form of NAD?
NAD+
What is the reduced form of NAD?
NADH
What is FAD?
Flavin adenine dinucleotide
What is FAD derived from?
Riboflavin (Vitamin B2)
What does FAD do?
Accepts hydrogen in pathways (fatty acid oxidation, citric acid cycle)
How are flavin coenzymes found?
Tightly bound to the proteins with which they interact (flavoproteins)
How is NAD found?
Soluble
What does FAD undergo?
2 electron reduction
What does FAD carry?
2 electrons and 2 H+
What is the oxidised form of FAD?
FAD
What is the reduced form of FAD?
FADH2
What is coenzyme A derived from?
Pantothenic acid (vitamin B5)
What is CoA a carrier of?
Not electrons so isn’t reduced or oxidised. It carries an acyl group
What are the two forms of CoA?
Free CoA: CoASH
Acyl group attached: Acyl-CoA(AcCoA)
