Metabolic Stores Flashcards
What is metabolism?
Mechanisms which couple the demand for energy with the fuel supply
What does insulin promote?
- glucose uptake
- Fatty acid synthesis
- Protein synthesis
What is the absorptive/fed state?
nutrients are plentiful - fuels broken down and excess stored the aim is to store nutrients in mobilizable form for times of need
What is the postabsorptive/ fasting state?
Storage molecules broken down for energy; the aim is to provide metabolites for cellular respiration synthesis and maintain blood glucose levels within homeostatic range
What effector organs control interconversion?
- Liver
- Adipose
- Muscle
Where does blood glucose come from in the postabsorptive state?
Glycogenolysis:
Liver glycogen ~100g (enough for ~3 – 5 hours activity)
Muscle glycogen (only utilised within muscle)
Gluconeogenesis (formation of glucose from noncarbohydrate molecules):
What is glycogen and where is it stored?
A branched polysaccharide storage molecule for glucose
Liver and skeletal muscle are the main glycogen reservoirs
How does the liver store glycogen?
maintains blood glucose levels
Enough glycogen for 3 – 5 hours moderate exercise, or
12 hours overnight fast
How does the muscle store glycogen?
stores glycogen for muscle contraction only
Describe glycogenesis
promoted by insulin
Glucose → G-6-P → G-1-P → Glycogen
Glucose residues formed by α1,4-glycosidic linkages
Branching occurs via α1,6-glycosidic linkages
Describe glycogenolysis
promoted by glucagon, adrenalin, cortisol and growth hormone
In muscle, no glucagon receptors – responds mainly to adrenalin
Two enzymes required:
Glycogen phosphorylase - α1,4 linkages
Debranching enzyme – α1,6 linkages
What breaks down glycogen in the muscle
No G-6-Pase enzyme, G-6-P enters glycolysis
What fuel sources can be mobilised?
1) Glucose
2) Triglycerides
3) Amino acids
What promotes glycogenesis?
Insulin
How does glycogenesis occur?
Glucose to G-6-P to G-1-P to Glycogen
How are glucose residues formed?
Glucose residues are formed by α 1,4 glycosidic linkage
How long do glycogen stores last?
Glycogen stores last about 3-5 hours
What are lipid?
Major form in which energy is stored
How much more energy can triglycerides produce than glycogen
triglycerides (triacylglycerols) can produce about 6 times as much energy as glycogen
What substances can be used in gluconeogenesis?
1) Glycerol from triglycerides
2) Glucogenic amino acids (alanine and glutamine)
3) Lactate
What tissues have glucose as their primary source of energy?
1) Brain
2) Red blood cells
3) Renal medulla
4) Lens
Where does gluconeogenesis occur?
Gluconeogenesis takes place mainly in the liver
It can also take place in the kidneys in prolonged fasting
What enzymes are required for gluconeogenesis?
1) Pyruvate carboxylase (mitochondria)
2) Phosphoenol pyruvate carboxykinase (mitochondria + cytosol)
3) Glucose-6-Phosphatase (ER
What lipolysis?
Lipolysis is fat breakdown into glycerol and fatty acids (reverse of lipogenesis)
What happens to glycerol after lipolysis?
1) Glycerol
* Glycerol feeds into gluconeogenesis, but can also be utilised by most cells
* It can be converted into glyceraldehyde-3-phosphate (glycolysis intermediate), which can enter into glycolysis, which results in 15 ATP generated aerobically
What happens to fatty acids after lipolysis?
Fatty acids
* Fatty acids undergo β-oxidation
* They are broken down into Acetic acid (2C) and fused to coenzyme A to form Acetyl CoA
* This process reduces FAD and NAD+, which can then be fe into the ETC
* Acetyl CoA can then enter the citric acid cycle
What need to happen for ketone bodies to be formed?
Ketone bodies are formed when carbohydrate intake is inadequate and beta-oxidation product Acetyl CoA is in excess
What is the limiting factor in the citric acid cycle when glucose is low
When glucose is low, oxaloacetate is the limiting factor in the citric acid cycle, as it is converted to pyruvate on gluconeogenesis
What is converted into ketone bodies and what bodies does it form?
Acetyl CoA is converted to ketone bodies in the liver:
1) Acetoacetate
2) 3-hydroxybuterate
3) Acetone
What happens with ketone bodies in diabetes?
In diabetes, acetoacetate is produced faster than it is metabolised
This results in ketone bodies accumulating in the blood (potential acidosis) and fruity smell of acetone on the breath
What must happen with excess protein?
Excess protein cannot be stored, so amino acids are oxidised for energy or converted to fat
What is transamination?
the process by which some amino acids can be converted to keto acids
What 2 things can happen to modified keto-acids after transamination?
1) generate pyruvate or keto-acid intermediates for the citric acid cycle
2) be converted to glucose via gluconeogenesis
What is deamination?
Deamination is the removal of an amine group (NH2) prior to oxidation or storage
What is the difference between a keto acid and ketone body?
A keto acid is an intermediate of the citric acid cycle
Ketone body is a degradation stage of fatty acid oxidation
What does hepatic portal vein system ensure?
That the liver has ready access to absorbed nutrients
What are 2 major roles of the liver?
The liver is the major metabolism centre orchestrating interconversion of CHO, proteins, fats and lactate
It also maintains blood glucose levels
What 3 things does resting muscle use as fuel
1) Fatty acids
2) Glucose
3) Ketone bodies
