Metabolic Stores Flashcards
What is metabolism ?
Mechanisms which couple the demand for energy (which is constant), with the fuel supply (which is intermittent)
Describe absorptive/fed state
Nutrients are plentiful - fuels broken down and excess stored (anabolism)
What is the aim of the absorptive/fed state ?
To store nutrients in mobilizable form, for times of need.
Function of insulin
Promotes :
- Glucose uptake
- Fatty acid synthesis
- Protein synthesis
Describe post-absorptive / fasting state
Storage molecules broken down for energy (catabolism) - biosynthesis slows down
What is the aim of the post absorptive / fed state ?
To provide metabolites for cellular respiration and ATP synthesis.
What is the primary aim / goal of the post absorptive state ?
Blood glucose levels
TO maintain blood glucose levels within homeostatic range of 70-110 mg/dl or 4-7 mmol/L
Describe interconversion of fuels
Metabolic storage molecules are interconvertible as their pathways are linked by key intermediates.
What effector organs control the release/interconversion of fuels ?
Liver
Adipose
Muscle
Mobilisation of glucose, triglycerides and amino acids
Where does blood glucose come from in the post absorptive state ?
Glycogenolysis
Gluconeogenesis
Where does glucogenesis occur ?
Occurs mainly in the liver
Describe glycogenolysis
Liver and Muscle
Liver glycogen (around 100g) –> enough for about 3-5 hours activity.
Mucle glycogen is only utilised within muscle
What is glycogenolysis ?
Breaks down glycogen to release glucose
Stimulated by low blood glucose
What is gluconeogenesis ?
Formation of glucose from non-carbohydrate molecules.
Describe gluconeogenesis
Lipolysis of fatty acids to generate glycerol, which generates glucose.
Catabolism of muscle protein - deamination of amino acids –> glucose
What does it mean when blood glucose levels are :
<53 mg/dL and <3 mmol/L
Severe Hypoglycaemia
Metabolic Consequences
What does it mean when blood glucose levels are :
<70 mg/dL and <3.9 mmol/L
Hypoglycaemia
What does it mean when blood glucose levels are :
<125 mg/dL and <7 mmol/L
Normal
What does it mean when blood glucose levels are :
<200 mg/dL and <10 mmol/L
High
What does it mean when blood glucose levels are :
> 200mg/dL and >10 mmol/L
High-Metabolic Consequences
What is glycogen ?
A branched polysaccharide storage molecule for glucose.
Where are the main glycogen storage reservoirs ?
Liver and Skeletal muscle atrophy the main glycogen reservoirs.
Function of the liver
Maintains blood glucose levels
Enough glycogen for 3-5 hours of moderate exercise or 12 hours overnight fast
Function of muscle (in relation to glycogen)
Stores glycogen for muscle contraction - channeled into glycolysis
(not released in the bloodstream)
What promotes glycogenesis ?
Insulin
What promotes glycogenolysis ?
Promoted by glucagon, adrenalin, cortisol and growth hormone.
IN muscle, there are no glucagon receptors and so responds mainly to adrenalin.
What enzymes are involved in glycogenesis ?
Glucose residues formed by alpha1,4-glycoside linkages
Branching occurs via alpha1,6-glycosidic linkages
What enzymes are involved in glycogenolysis ?
Glycogen phosphorylase - alpha1,4 linkages
De-branching enzyme : alpha1,6, linkages
Describe glycogenolysis in the liver
Glycogen –> G-1-P –> G-6-P –> Glucose
Released into the bloodstream (Glut2), for uptake by all cells, but especially brain and RBCs.
Describe glycogenolysis in muscle
No G-6-Pase enzyme, G-6-P enters glycolysis
State other sources of energy other than glycogen
Lipids are the major form in which energy is stored.
Triglycerides can produced 6 times as much energy as glycogen.
Describe glucogenesis
Formation of glucose from non-carbohydrate sources :
Glycerol from triglycerides
Glucogenic amino acids (alanine & glutamine)
Lactate
What is the importance of glucogenesis ?
Crucial for survival : i.e. tissues whose primary source of energy is glucose
- Brain
- RBCs
- Renal Medulla
- Lens
Where does glucogenesis mainly take place ?
The liver (and kidneys in prolonged fasting)
What is lipogenesis ?
Formation of fat
How is most fat stored ?
Stored as triglycerides = triacylglycerols
How are triglycerides formed ?
Glycerol molecule undergoes condensation with 3 fatty acids.
Describe lipids (fatty acids)
Hydrocarbon chain, usually 14-24 carbon atoms - most common FAs 16-18 carbons
What are triglycerides ?
Esters formed by the reaction of an alcohol and organic acid
Describe lipolysis
Fat breakdown into glycerol and fatty acids
REVERSE of Lipogenesis
Where does lipolysis occur ?
Fatty acids and glycerol are released from adipose tissue and metabolised mainly by the liver.
What happens to the glycerol produced from lipolysis ?
Glycerol feed into gluconeogenesis but can also be utilised by most cells -
converted into glyceraldehyde-3-phosphate -> glycolysis
(1/2 glucose = 15ATP aerobically)
What happens to the fatty acids produced from lipolysis ?
Undergo beta oxidation
Describe beta oxidation
Fatty acids are broken down into 2-carbon acetic acid and fused to coenzyme A –> acetyl-CoA
FAD and NAD+ are reduced and feed into the electron transport chain
Acetyl CoA –> Citric Acid Cycle
Describe the production of ketone bodies
When carbohydrate intake is inadequate and beta-oxidation product : acetyl-CoA is in XS (for citric acid cycle metabolism), ketone bodies are formed.
What is the limiting factor in gluconeogenesis ?
Oxaloacetate îs the limiting factor when glucose low, as converted to pyruvate in gluconeogenesis.
Where are ketone bodies formed ?
Acetyl-CoA converted to ketone bodies in the liver :
- Acetoacetate
- 3-hydroxybutyrate
- Acetone
Describe the role of ketone bodies in diabetes
In diabetes acetoacetate is produced faster than metabolised.
Ketone bodes accumulate in blood (potential acidosis) and fruity smell of acetone on breath.
Describe protein metabolism
Excess protein cannot be stored
Amino acids are oxidised for energy OR converted to fat.
What is transamination ?
Process by which come amino acids can be converted to keto acids
What is deamination ?
Removal of an amine group (NH2) prior to oxidation or storage.
Give an example of transamination
Amine group is transferred to keto-glutamate = glutamic acid
Modified keto acids generate pyruvate or keto acid intermediates fr the citric acid cycle
OR
Converted to glucose (gluconeogeneis)
Explain the need for deamination and transamination of amino acids in cellular metabolism
Excess protein cannot be stored
Amino Acids are oxidised for energy or converted to fat
State the function of the hepatic portal system
HPS ensures liver has ready access to absorbed nutrients
Major metabolism centre, orchestrating interconversion of CHO, proteins&fats, plus lactate.
Maintains blood glucose levels
State the function of the brain
60% of all glucose is used by the brain (around 120g per day)
No stores of glycogen or glucose
Can use ketone bodies in starvation
State muscle (metabolic stores)
Resting muscle uses fatty acids as fuel, also glucose and ketone bodies
Large glycogen reserves 3/4 of body stores
Simple definition of glycolysis
Converts glucose to pyruvic acid
Simple definition of glycogenesis
Polymerises glucose to form glycogen
Simple definition of glycogenolysis
Hydrolyses glycogen to glucose monomers
Simple definition of gluconeogenesis
Forms glucose from noncarbohydrate precursors
What is formed during aerobic respiration when electrons are passed down the electron transport chain ?
Water
What is the net gain of ATP from the full oxidation of 2 molecules of glucose ?
60
Which mechanism generates the energy for creating the electrochemical gradient between the mitochondria matrix and inner membrane ?
Oxidation and reduction of cytochrome complexes
What is the process of generating glucose from glycogen called ?
Glycogenolysis
Which effector organ is primarily involved in gluconeogenesis ?
Liver
Which intermediate is a rate limiting factor of the citric acid cycle ?
Oxaloacetate (keto acid)
Metabolism
The sum of anabolic and catabolic reactions within the cells
