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