Metabolic Stores Flashcards by Hannah Mathias

Q

What is metabolism ?

A

Mechanisms which couple the demand for energy (which is constant), with the fuel supply (which is intermittent)

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Q

Describe absorptive/fed state

A

Nutrients are plentiful - fuels broken down and excess stored (anabolism)

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Q

What is the aim of the absorptive/fed state ?

A

To store nutrients in mobilizable form, for times of need.

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Q

Function of insulin

A

Promotes :

Glucose uptake
Fatty acid synthesis
Protein synthesis

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Q

Describe post-absorptive / fasting state

A

Storage molecules broken down for energy (catabolism) - biosynthesis slows down

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Q

What is the aim of the post absorptive / fed state ?

A

To provide metabolites for cellular respiration and ATP synthesis.

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Q

What is the primary aim / goal of the post absorptive state ?

Blood glucose levels

A

TO maintain blood glucose levels within homeostatic range of 70-110 mg/dl or 4-7 mmol/L

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Q

Describe interconversion of fuels

A

Metabolic storage molecules are interconvertible as their pathways are linked by key intermediates.

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Q

What effector organs control the release/interconversion of fuels ?

A

Liver
Adipose
Muscle

Mobilisation of glucose, triglycerides and amino acids

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Q

Where does blood glucose come from in the post absorptive state ?

A

Glycogenolysis
Gluconeogenesis

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Q

Where does glucogenesis occur ?

A

Occurs mainly in the liver

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Q

Describe glycogenolysis

Liver and Muscle

A

Liver glycogen (around 100g) –> enough for about 3-5 hours activity.

Mucle glycogen is only utilised within muscle

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Q

What is glycogenolysis ?

A

Breaks down glycogen to release glucose
Stimulated by low blood glucose

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Q

What is gluconeogenesis ?

A

Formation of glucose from non-carbohydrate molecules.

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Q

Describe gluconeogenesis

A

Lipolysis of fatty acids to generate glycerol, which generates glucose.

Catabolism of muscle protein - deamination of amino acids –> glucose

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Q

What does it mean when blood glucose levels are :

<53 mg/dL and <3 mmol/L

A

Severe Hypoglycaemia
Metabolic Consequences

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Q

What does it mean when blood glucose levels are :

<70 mg/dL and <3.9 mmol/L

A

Hypoglycaemia

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Q

What does it mean when blood glucose levels are :

<125 mg/dL and <7 mmol/L

A

Normal

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Q

What does it mean when blood glucose levels are :

<200 mg/dL and <10 mmol/L

A

High

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Q

What does it mean when blood glucose levels are :

> 200mg/dL and >10 mmol/L

A

High-Metabolic Consequences

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Q

What is glycogen ?

A

A branched polysaccharide storage molecule for glucose.

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Q

Where are the main glycogen storage reservoirs ?

A

Liver and Skeletal muscle atrophy the main glycogen reservoirs.

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Q

Function of the liver

A

Maintains blood glucose levels

Enough glycogen for 3-5 hours of moderate exercise or 12 hours overnight fast

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Q

Function of muscle (in relation to glycogen)

A

Stores glycogen for muscle contraction - channeled into glycolysis

(not released in the bloodstream)

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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