Metabolism Flashcards
What is anabolism?
Reactions that synthesise new (larger) molecules from smaller precursors. These need energy.
What is catabolism?
Reactions that break down larger molecules into smaller ones, usually to release energy.
What is metabolism?
All the chemical reactions in the body. Because of the second law of thermodynamics, this costs energy.
What are the 4 phases of metabolism?
Absorptive: dealing with a meal
Post-absorptive: maintaining homeostasis between meals
Fasting: dealing with the challenge of longer periods without food
Intense exercise: responding to dramatic increases in demand
What does muscle also contain as a very short term energy store?
phosphocreatine
What does adenylate kinase do?
Turns 2 ADPs into an ATP and an AMP
What is AMP a marker of?
AMP is a marker of a low-energy state, and regulates a number of metabolic enzymes allosterically.
Can acetyl CoA be made from amino acids or fatty acids?
Both, to power the TCA cycle.
What can you use TCA intermediates to make?
fatty acids and amino acids.
Are carbohydrates an efficient energy store?
Carbohydrates bind a lot of water, making them bulky and relatively inefficient as an energy store.
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.
Can glucose be released from muscle?
Liver, but not muscle, can release glucose derived from glycogen into the circulation.
Are fats a good energy store?
Fats provide a very dense energy store, because they don’t bind much water, and contain little oxygen.
What can the liver do to fatty acids during starvation?
The liver can convert fatty acids into ketone bodies during starvation.
Is protein a good store of energy?
Not ideal as a source of energy, as mainly stored as functional proteins, so catabolism impairs cellular function.
But, the liver can convert (most) amino acids to glucose (gluconeogenesis).
How do erythrocytes get energy?
Erythrocytes lack mitochondria, so they are unable to carry out aerobic metabolism.
In some ways, that’s quite good, since their main job is to carry oxygen, and not to use it up…
…but it does mean that they have to get all their energy from anaerobic glycolysis, which is pretty inefficient.
Fortunately, they don’t have high metabolic demands,and “waste” pyruvate and lactate can go back to the liver for gluconeogenesis.
Plasma glucose concentration below what value can lead to unconsciousness and death?
Under normal conditions, the brain depends on a fairly steady plasma glucose concentration: sudden falls below about 3 mM can lead to unconsciousness and death.
Uptake of glucose in adipocytes is sensitive to what?
Insulin-sensitive uptake of glucose, and glucagon-sensitive release of FFA and glycerol.
What happens in adipocytes when glucose levels fall?
As glucose levels fall, adipocytes metabolise triglyceride to release FFA and glycerol.
Describe metabolism in the liver
First “port of call” for foodstuffs absorbed from the gut. Insulin-sensitive uptake, and glucagon-sensitive release, of glucose.
During periods of high glucose, converts glucose to glycogen.
As glucose levels fall, metabolises glycogen to release glucose.
Gluconeogenesis using lactate, glycerol, amino acids
Ketone body production from Acetyl CoA
Describe metabolism in cardiac muscle
Highly aerobic tissue: up to 40% mitochondria, and abundant myoglobin. Fatigue in cardiac muscle is bad news…
Main energy source is fatty acids, but can also use lactate or ketone bodies.
Glucose uptake is insulin-sensitive.
Describe type 1 skeletal muscle metabolism
Rather like cardiac muscle: highly aerobic
Adapted to prolonged, relatively modest, activity: for example, postural muscles
Main energy source is fatty acids.
Why is skeletal muscle type 2b white?
Few mitochondria, and little or no myoglobin (hence white)
What kind of metabolism does skeletal muscle type 2b rely on?
Rely mainly on anaerobic glycolysis, with glucose coming from their glycogen store.
Describe metabolism of skeletal muscle type 2a
Intermediate between Type 1 and Type 2b. Contain some mitochondria, and myoglobin. Will maintain aerobic metabolism as much as possible.
Phosphocreatine and glycogen provide a good store of energy.
Adrenalin (or insulin) allow glucose uptake.
At lower exercise levels, fatty acids are the main energy source.
During fasting, release amino acids for gluconeogenesis
Why is just keeping plasma glucose high a bad idea?
That’s what happens in diabetes mellitus…
Osmotic effects
Glucose lost in the urine, wasting energy and causing polyuria.
Glycation of proteins, and later cross-linking
- microvascular and macrovascular disease - peripheral neuropathy - low-grade inflammatory effects
