Metabolism Flashcards
What is metabolism?
All the chemical reactions in the body –> costs energy
What is anabolism?
Reactions that synthesise new (larger) molecules from smaller precursors. These need energy
What is canabolism?
Refers to reactions that break down larger molecules into smaller ones, usually to release energy
What are the absorptive and post-absorptive phases of metabolism?
- Dealing with a meal
- Maintaining homeostasis between meals
What is the fasting phase of metabolism?
Dealing with the challenge of longer periods without food
What is the intense exercise phase of metabolism?
Responding to dramatic increases in demand
What is the acute time scale of metabolism?
Minute to minute regulation of plasma glucose
What is the longer time scale of metabolism?
- Maintenance of adequate stores
- Turnover of proteins and cells
- Growth
- Reproduction
How is ATP involved in high energy reactions (e.g. glycolysis and oxidative phosphorylation)?
High energy reactions can stick a third phosphate onto ADP to form ATP.
Cells can then get that back by hydrolysing the ATP, to drive other reactions.
What do muscles contain as a short-term energy store?
Phosphocreatine
ADP + PCr –> ATP + Creatine
Creatine kinase catalyses this reaction
What do most cells convert ADP to?
ATP and AMP
ADP + ADP –> ATP + AMP
Adenylate kinase catalyses this
What is AMP a marker of?
A low-energy state
What is glycolysis?
Produces two molecules of ATP through the conversion of glucose into pyruvate, water, and NADH in the absence of oxygen.
Glycolysis is a series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates
Does glycolysis require oxygen?
No
How many ATPs get used by when preparing glucose for glycolysis?
2 but get 4 back (2 from each 1,3 DPG)
If we can handle the pyruvate aerobically, how many molecules of ATP can we get?
We get 36 more per glucose (18 per pyruvate)
What are we left with at the end of glycolysis?
2 ATP, 2 NADH, 2 pyruvate molecules
If If oxygen is available, the pyruvate can be broken down (oxidised) all the way to carbon dioxide in cellular respiration, making many molecules of ATP
How is CoA generated?
- By oxidative decarboxylation of pyruvate from glycolysis, which occurs in mitochondrial matrix
- By oxidation of long-chain fatty acids
- By oxidative degradation of certain amino acids.
Acetyl-CoA then enters in the TCA cycle where it is oxidised for energy production.
What can we make from TCA intermediates?
Fatty acids and amino acids
What is glucose only made from?
Pyruvate, and so from amino acids
Why are carbohydrates relatively inefficient as an energy store?
They bind a lot of water, making them bulky
How is glucose stored?
Glucose can be stored as polymers, mainly glycogen, in liver and muscle: this provides a rapid but relatively short-lived energy store.
Liver, but not muscle, can release glucose derived from glycogen into the circulation.
Why do fats provide a very dense energy store?
Because they don’t bind much water, and contain little oxygen.
It takes longer to re-release the energy, and it can’t be synthesised back into glucose.
What do many tissues use fatty acids as?
Their main source of energy.
What can the liver convert fatty acids into during starvation?
Ketone bodies
What are proteins mainly stored as?
Not ideal as source of energy
Mainly stored as functional proteins, so catabolism impairs cellular function.
What does the liver convert most amino acids into?
Glucose (gluconeogenesis)
What do muscle cells contain a lot of? What can it convert this to?
Protein
Can convert it to alanine and glutamine, which can be exported for gluconeogenesis.
Why are erythrocytes unable to carry out aerobic metabolism?
Lack mitochondria
Where do erythrocytes get all their energy from? Where do the waste products go?
Anaerobic glycolysis (inefficient)
“Waste” pyruvate and lactate can go back to the liver for gluconeogenesis.
Do erythrocytes have a high metabolic demand?
No
Does brain tissue have mitochondria?
No
Does brain tissue have a high metabolic demand?
Yes
What does the blood brain barrier limit?
What foodstuffs can get across.
Under normal conditions, what does the brain depend on?
The brain depends on a fairly steady plasma glucose concentration: sudden falls below about 3 mM can lead to unconsciousness and death
During fasting for several days, ketone bodies come to be an important foodstuff.
What are adipocytes?
A cell specialised for the storage of fat, found in connective tissue.