•BIOCHEMISTRY
– 3rd CLASS 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
system are involved in controlling the rate and
direction of metabolism. Thyroxine, 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.
•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
Look for
continue in the second lecture. thank you
.