Metabolism Overview Flashcards
What is catabolism?
Metabolic breakdown of complex substances into smaller products
(Food –> building blocks + energy + heat)
What is anabolism?
Energy-requiring transformation of simpler substances into more complex ones
Why are substances broken down step-wise rather than all in one go?
Step-wise releases small, usable packages of energy
Each step has a smaller activation energy (all in one go = lots of energy wasted as heat and high Ea)
Why are forward and reverse pathways not direct opposites of each other?
Allows separate regulation
Prevents ‘futile cycle’
What is another term for activated carrier molecules?
Cofactors
Coenzymes
Why is energy stored at each step of an energetically favourable reaction?
To be used in energetically unfavourable reactions
What bonds in ATP are broken to release energy?
Phosphoanhydride
What properties make ATP suitable for energy storage in humans?
Chemically stable at physiological pH (6-9)
Structural features can be recognised by specific proteins, enzymes, etc
Hydrolysis releases energy
What does ΔG mean?
Change in free energy
What does it mean when ΔG is negative?
Energy released
What is the ΔG of ATP hydrolysis?
-31 to -50kJ/mol
Why is ATP hydrolysis energetically favourable?
Relieves electrostatic repulsion between phosphate groups (unstable molecule)
Released phosphate ion is resonance stabilised (electron delocalisation)
Increase in entropy
How much energy is release when ATP is hydrolysed to AMP + PPi?
Almost twice as much as ATP to ADP hydrolysis
As PPi spontaneously breaks down into two Pi
What is PPi called?
Pyrophosphate
Give some of the functions of ATP
Cell motility and muscle contraction
Active transport
Metabolic control by regulating enzyme activity
Activate/phosphorylate molecules
What UTP used for?
Synthesis of complex sugars
What is GTP used for?
Protein synthesis (translation)
Microtubule elongation
Which activated energy carriers carry electrons and protons?
NAD(H)
NADP(H)
FAD(H2)
What does acetyl coenzyme A carry?
Acetyl
Which activated energy carrier carries a carboxyl group?
Carboxylated biotin
What activated energy carrier carries a methyl group?
S-adenosylmethionine
What activated energy carrier carries a glucose?
Uridine diphosphate glucose (UDP-glucose)
What does NAD stand for?
Nicotinamide adenine dinucleotide
What are the main differences between NAD+ and NADP+?
NADP+ has a phosphate group
NADP+ replaces NAD+ in anabolic reactions
What happens molecularly when NAD+ is reduced?
Nicotinamide group accepts one H and an electron (leaving a spare proton)
What does FAD stand for?
Flavin adenine dinucleotide
What happens molecularly when FAD is reduced?
Flavin group accepts two H (added to nitrogens)
Originally neutral so no spare protons
What type of bonds does coenzyme A form with carboxylic acids?
Thioester
How do we write the structure of coenzyme A?
CoA-SH
What are the three main stages of catabolism of sugars, fats and amino acids?
Conversion to acetyl unit
Krebs/TCA cycle
Oxidative phosphorylation
What is pyruvate converted to in anaerobic respiration?
Lactate/lactic acid
What is the structure of pyruvate?
-OOC–CO–CH3
What enzyme catalyses anaerobic respiration?
Lactate dehydrogenase
What is the purpose of anaerobic respiration?
Regenerate NAD+ so glycolysis can continue
By what process is glucose converted to the acetyl unit?
Glycolysis
By what process is a fatty acid converted to the acetyl unit?
Beta oxidation
How is an amino acid converted to the acetyl unit?
Transamination
How can regulation of metabolic pathways be achieved?
Changes in amount of enzyme (gene expression)
Changes in enzyme activity
How can enzyme activity be altered?
Allosteric regulation/binding of allosteric regulators
Phosphorylation and dephosphorylation
What kind of alteration to enzyme activity is instantaneous and local?
Allosteric regulation
