Second lecture – continue
The number of
calories a person burns in a day is affected by how much that person exercises,
the amount of fat and muscle in his or her body, and the person s basal
metabolic rate. The basal metabolic rate, or BMR, is a measure of the rate at
which a person s body "burns" energy, in the form of calories, while
at rest. The BMR can play a role in a person s tendency to gain weight. For
example, a person with a low BMR (who therefore burns fewer calories while at
rest or sleeping) will tend to gain more pounds of body fat over time, compared
with a similar-sized person with an average BMR who eats the same amount of
food and gets the same amount of exercise.
What factors
influence a person s BMR? To a certain extent, a person s basal metabolic rate
is inherited - passed on through the genes a person gets from his or her
parents. Sometimes health problems can affect a person s BMR. But people can
actually change their BMR in certain ways. For example, exercising more will
not only cause a person to burn more calories directly from the extra activity
itself, but becoming more physically fit will increase BMR as well. BMR is also
influenced by body composition - people with more muscle and less fat generally
have higher BMRs.
Things That Can Go Wrong With
Metabolism:
v In
a broad sense, a metabolic disorder is any disease that is caused by an
abnormal chemical reaction in the body s cells. Most disorders of metabolism
involve either abnormal levels of enzymes of hormones or problems with the
functioning of those enzymes or hormones. When the metabolism of body chemicals
is blocked or defective, it can cause a buildup of toxic substances in the body
or a deficiency of substances needed for normal body function, either of which
can lead to serious symptoms.
v Some
metabolic diseases are inherited. These conditions are called inborn errors of
metabolism. When babies are born, they re tested for many of these metabolic
diseases in a newborn screening test. Many of these inborn errors of metabolism
can lead to serious complications or even death if they re not controlled with
diet or medication from an early age.
Examples of metabolic disorders and
conditions include:
G6PD deficiency:
ü Glucose-6-phosphate
dehydrogenase, or G6PD, is just one of the many enzymes that play a role in
cell metabolism. G6PD is produced by red blood cells and helps the body
metabolize carbohydrates. Without enough normal G6PD to help red blood cells
handle certain harmful substances, red blood cells can be damaged or destroyed,
leading to a condition known as hemolytic anemia. In a process called hemolysis
red blood cells are destroyed prematurely, and the bone marrow (the soft,
spongy part of the bone that produces new blood cells) may not be able to keep
up with the body s need to produce more new red blood cells. Kids with G6PD
deficiency may be pale and tired and have a rapid heartbeat and breathing. They
may also have an enlarged spleen or jaundice - a yellowing of the skin and
eyes. G6PD deficiency is usually treated by discontinuing medications or
treating the illness or infection causing the stress on the red blood cells.
How humans (and other animals) do it?.
Humans are
heterotrophs. We are totally dependent on ingested preformed organic molecules
to meet all our energy needs. We are also dependent on preformed organic
molecules as the building blocks to meet our anabolic needs.
Ingestion:
taking food within the body (although as the figure shows, it is still
topologically in the external world, not the internal).
Digestion.
The enzyme-catalyzed hydrolysisof
– polysaccharides
(e.g., starch)
to sugars.
– proteins to
amino acids .
– fatsto fatty acids and glycerol.
– nucleic acids tonucleotides.
Absorption into
the body and transport to the cells.