BIOCHEMISTRY – COLLEGE
OF PHARMACY
Dr. ABDULHUSSIEN
M.K. ALJEBORY
Metabolism:
Every time you swallow
a bite of sandwich or slurp a smoothie, your body works hard to process the
nutrients you ve eaten. Long after the dishes are cleared and the food is
digested, the nutrients you ve taken in become the building blocks and fuel
needed by your body. Your body gets the energy it needs from food through a
process called metabolism.
Metabolism is a
collection of chemical reactions that takes place in the body s cells to
convert the fuel in the food we eat into the energy needed to power everything
we do, from moving to thinking to growing. Specific proteins in the body
control the chemical reactions of metabolism, and each chemical reaction is
coordinated with other body functions. In fact, thousands of metabolic
reactions happen at the same time - all regulated by the body - to keep our
cells healthy and working.
Metabolism is a
constant process that begins when we re conceived and ends when we die. It is a
vital process for all life forms - not just humans. If metabolism stops, a
living thing dies.
Here s an
example of how the process of metabolism works in humans - and it begins with
plants: First, a green plant takes in energy from sunlight. The plant uses this
energy and a molecule called chlorophyll (which gives plants their green color)
to build sugars from water and carbon dioxide. This process is called
photosynthesis, and you probably learned about it in biology class.
When people and
animals eat the plants (or, if they re carnivores, when they eat animals that
have eaten the plants), they take in this energy (in the form of sugar), along
with other vital cell-building chemicals. The body s next step is to break the
sugar down so that the energy released can be distributed to, and used as fuel
by, the body s cells.
After food is
eaten, molecules in the digestive system called enzymes break proteins down
into amino acids, fats into fatty acids, and carbohydrates into simple sugars
(e.g., glucose). In addition to sugar, both amino acids and fatty acids can be
used as energy sources by the body when needed. These compounds are absorbed
into the blood, which transports them to the cells. After they enter the cells,
other enzymes act to speed up or regulate the chemical reactions involved with
"metabolizing" these compounds. During these processes, the energy
from these compounds can be released for use by the body or stored in body
tissues, especially the liver, muscles, and body fat.
In this way, the
process of metabolism is really a balancing act involving two kinds of
activities that go on at the same time - the building up of body tissues and
energy stores and the breaking down of body tissues and energy stores to
generate more fuel for body functions.
Anabolism, or
constructive metabolism, is all about building and storing: It supports the
growth of new cells, the maintenance of body tissues, and the storage of energy
for use in the future. During anabolism, small molecules are changed into
larger, more complex molecules of carbohydrate, protein, and fat.
Catabolism, or
destructive metabolism, is the process that produces the energy required for
all activity in the cells. In this process, cells break down large molecules
(mostly carbohydrates and fats) to release energy. This energy release provides
fuel for anabolism, heats the body, and enables the muscles to contract and the
body to move. As complex chemical units are broken down into more simple
substances, the waste products released in the process of catabolism are
removed from the body through the skin, kidneys, lungs, and intestines.
Several of the
hormones of the endocrine systemare involved in controlling the rate and direction of metabolism. Thyroxin, a
hormone produced and released by the thyroid (pronounced: thigh-royd) gland,
plays a key role in determining how fast or slow the chemical reactions of
metabolism proceed in a person s body.
Another gland,
the pancreas secretes (gives off) hormones that help determine whether the
body s main metabolic activity at a particular time will be anabolic or
catabolic. For example, after eating a meal, usually more anabolic activity
occurs because eating increases the level of glucose - the body s most
important fuel - in the blood. The pancreas senses this increased level of
glucose and releases the hormone insulin, which signals cells to increase their
anabolic activities.
Metabolism is a
complicated chemical process, so it s not surprising that many people think of
it in its simplest sense: as something that influences how easily our bodies
gain or lose weight. That s where calories come in. A calorie is a unit that
measures how much energy a particular food provides to the body. A chocolate
bar has more calories than an apple, so it provides the body with more energy -
and sometimes that can be too much of a good thing. Just as a car stores gas in
the gas tank until it is needed to fuel the engine, the body stores calories -
primarily as fat. If you overfill a car s gas tank, it spills over onto the
pavement. Likewise, if a person eats too many calories, they "spill
over" in the form of excess fat on the body.
Look for
continue in the second lecture. thank you