SEHS Topic 3.2Carbohydrate and Fat Metabolism

Outline metabolism, anabolism, aerobic catabolism and anaerobic catabolism

• Metabolism – all of the biochemical reactcions that occur within an organism, including anabolic and catabolic reactions

• Anabolism – Energy requiring reactions reactions whereby small molecules are built up into larger ones

• Catabolism – Chemical reactions that break down complex organic compounds into simpler ones, with the net release of energy

Aerobic vs. anaerobic catabolism

• Aerobic – the breakdown of glucose in the presence of oxygen.

• Anaerobic – the breakdown of glucose WITHOUT oxygen being present in the reaction pathway

State what glycogen is and its major storage sites

• Glycogen is a carbohydrate. • Specifically it is a polysaccharide• It is a polymer of the monomer glucose– Translation: it is a large molecule made up of many

smaller, identical molecules

Cont’d

• Main storage sites in the body:

State the major sites of triglyceride storage in the body.

Explain the role of insulin in the formation of glycogen and the accumulation of body fat

• Insulin is a hormone released from the pancreas.• It tells the cells to do the following:• Absorb glucose, fatty acids and amino acids from

the bloodstream and into cells• Stop breaking down glycogen into glucose; fats into

fatty acids and glycerol; and proteins into amino acids

• (i.e. it stops most catabolic reactions)

Cont’d• Insulin also starts building glycogen from

glucose; fats (triglycerides) from glycerol and fatty acids; and proteins from amino acids (stimulates anabolic reactions)

• The activity of lipoprotein lipases depends upon the levels of insulin in the body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive.

• .

Cont’d

• The fatty acids are then absorbed from the blood into fat cells, muscle cells and liver cells.

• In these cells, under stimulation by insulin, fatty acids are made into fat molecules and stored as fat droplets

Not meant to be a ppt slide, but contains interesting info. Read it!

• It is also possible for fat cells to take up glucose and amino acids, which have been absorbed into the bloodstream after a meal, and convert those into fat molecules. The conversion of carbohydrates or protein into fat is 10 times less efficient than simply storing fat in a fat cell, but the body can do it. If you have 100 extra calories in fat (about 11 grams) floating in your bloodstream, fat cells can store it using only 2.5 calories of energy. On the other hand, if you have 100 extra calories in glucose (about 25 grams) floating in your bloodstream, it takes 23 calories of energy to convert the glucose into fat and then store it. Given a choice, a fat cell will grab the fat and store it rather than the carbohydrates because fat is so much easier to store.

Outline glycogenolysis (i.e. how glygogen is converted into free glucose molecules)• In glycogenolysis, glycogen stored in the liver and

muscles, is converted first to glucose-1-phosphate and then into glucose-6-phosphate. Two hormones which control glycogenolysis are a peptide, glucagon from the pancreas and epinephrine from the adrenal glands.

Cont’d • Glucagon is released from the pancreas in response

to low blood glucose.• epinephrine is released in response to a threat or

stress. • Both hormones act upon enzymes to stimulate

glycogen phosphorylase to begin glycogenolysis and inhibit glycogen synthetase (to stop glycogenesis).

Cont’d

• Glycogen is a highly branched polymeric structure containing glucose as the basic monomer.

• First individual glucose molecules are hydrolyzed from the chain, followed by the addition of a phosphate group at C-1.

• In the next step the phosphate is moved to the C-6 position to give glucose 6-phosphate, a cross road compound.

Cont’d

• Glucose-6-phosphate is the first step of the glycolysis pathway if glycogen is the carbohydrate source and further energy is needed.

• If energy is not immediately needed, the glucose-6-phosphate is converted to glucose for distribution in the blood to various cells such as brain cells.

Outline lipolysis• When glycogen stores are not available in the cells, fat

(triacylglycerol) is cleaved to provide 3 fatty acid chains and 1 glycerol molecule in a process known as lipolysis.

• Lipolysis creates acetyl CoA molecules which can then enter the Krebs Cycle.

Outline the effects of glucagon and adrenaline during fasting and exercise

• During fasting:• Levels of glucagon and adrenaline (epinephrine)

both increase• Glugacon causes release of glucose from glycogen

stores in the liver and skeletal muscle • (NOTE: skeletal muscle stores are only useful to the

muscles they are stored in. Once suppllies are depleted in your biceps, reserves from the triceps can not be funneled to other muscles)

Cont’d

• Additionally, both of these hormones are lipolysis inducers – mobilizing fat stores from the body’s adipose tissues for breakdown into useful energy

Explain the role of insulin and muscle contraction on glucose uptake during exercise

• What is the consequence of exercise on your body’s skeletal muscle?

• Increased O2 demands• Increased energy demands (ATP)

• How is it rectified?• Increased insulin release causes what response by

the muscle cells?

Cont’d

• Increased muscle contraction leads to increased muscular perfusion

• perfusion is the process of delivering blood to a capillary bed in the biological tissue.

• More blood delivered to a capillary bed during exercise = more content of that blood (glucose, O2…etc) delivered to the cells that need it most

Explain the role of insulin and muscle contraction on glucose uptake during exercise