KIN 211
Metabolism
Metabolism
The sum total of all chemical reactions
that go on in the living cells.
 Energy Metabolism-the reactions by
which the body obtains energy from
food.

Two Categories of Metabolism

Metabolism is usually divided into two
categories.
– Catabolism
– Anabolism
Anabolism


Anabolism- when small molecules are used
to build larger compounds.
Examples:
– Glucose to Glycogen
– Glycerol and Fatty Acids to Triglycerides
– Amino Acids to Proteins
–
Refer to Figure 7-2.
Catabolism

Breaking down of compounds to release
energy.
– Examples:
 Glycogen to Glucose to Energy
 Triglycerides to Glycerol and Fatty
Acids to Energy
 Protein to Amino Acids to Energy
ATP (Adenosine Triphosphate)

body uses a high energy compound in which
to trap energy released from glucose,
glycerol, fatty acids, and amino acids.

The body converts chemical energy of food
to the chemical energy of ATP at about 50%
efficiency.
Helpers in Metabolic Reactions


Enzymes and co-enzymes are used as coworkers in metabolic reactions.
Several B vitamins act as co-enzymes in the
process of energy metabolism.
Following Digestion and Absorption of
Nutrients


After the body has broken down the energy
units and absorbed into the bloodstream,
these energy nutrients can be used to fuel
the body with energy.
The body turns to carbohydrates and fats
primarily to provide the energy needs, while
protein is used for building body compounds.
Carbohydrate Metabolism

The first pathway glucose takes in order to
yield energy is called Glycolysis:
The 6 carbon glucose is
converted into other
6 carbon compounds
and eventually is split in half.
The results is
two three-carbon
compounds called pyruvate.
–
Glycolosis
 Is
reversable, anaerobic, and
occurs in the cytosole of the cells.
Fate of Pyruvate

Pyruvate may enter either an anaerobic or
aerobic pathway:
–
–
–
Anaerobic: energy is needed quickly (in the absence
of sufficient oxygen), pyruvate is converted to lactate.
In high intensity work, the body uses lactate to
provide energy.
Lactate is eventually transported from the muscles to
the liver. The liver then uses it to produce glucose,
which can be returned to the muscle. This process if
called the Cori Cycle.
Fate of Pyruvate

Aerobic:
–
–
–
If the cells need energy and enough oxygen is
available, pyruvate then enters the mitochondria
of the cells.
The three-carbon pyruvate drops off a carbon
group (COOH), leaving a two-carbon compound.
The two-carbon compound combines with a
molecule of CoA, resulting in Acetyl CoA.

Refer to Figure 7-7.
Pyruvate to Acetyl CoA
 This
step is irreversable.
 Acetyl CoA has two main functions:
Making Fats(when ATP’s are in
abundance)
– Generate ATP(When the body needs
ATP, the acetyl CoA proceeds to the
TCA cycle.
–
TCA Cycle




Tricarboxylic Acid Cycle
Occurs in the Mitochondria of the Cells
Oxaloacetate- a 4-carbon compound,
carbohydrate intermediate.
Oxaloacetate can be made from either
pyruvate (from glucose) or amino acids, but
cannot be made from fat.
Fate of Oxaloacetate


As oxaloacetate enters the TCA cycle, it
picks up Acetyl CoA, then drops off a carbon,
then another. (These carbons mix with
oxygen, form carbon dioxide and are
breathed out) and then goes back to get
another acetyl CoA.
When the acetyl CoA breaks down to carbon
dioxide, hydrogen atoms are removed, and
each turn of the TCA cycle releases 8
electrons.
Coenzymes: B Vitamins and The
Electron Transport Chain


The coenzymes then pick up the hydrogen
atoms and their electrons and transfer them to
the electron transport chain.
Electron Transport Chain- a series of proteins
that serve as electron carriers.
Results of The Electron Transport
Chain



Oxygen combines with hydrogen and forms
water
Energy is trapped in the high energy bonds
of ATP: ATP then enters the cyroplasm of the
cells and is used for energy.
Refer to Fiber 7-19
Where Fat and Amino Acids Enter the
Energy Metabolism Pathway
Refer
to Figure 7-21
Feasting and Fasting

In a state of feasting when we eat too
much, the body will allow fat formation,
whether the calories come from
carbohydrates, protein or fat.
Excess Carbohydrates



Carbohydrates are first converted into
glycogen, which has limited space.
Excess glucose is then converted into fat.
Excess glucose can then contribute to
obesity.
Excess Fat
 Excess
fat moves efficiently into
the body’s fat stores, contributing
to obesity.
Excess Protein



Remember that the body cannot grow extra
muscles simply by eating extra protein.
When a person eats too much protein, the
body will first replace daily losses. The
remaining protein is deaminated and the
remaining carbons are made into fatty acids,
then stored at triglycerides in the adipose
tissues.
Excess protein builds fat in the body.
Fasting
 During
fasting at some point,
carbohydrates, protein and fat
is all used as energy.
Fast Begins



The body will turn to glucose from the stored
glycogen.
Cells of the nervous system and red blood cells
need glucose for energy.
Red Blood cells do not contain a mitochondria
(Where energy is extracted from fatty acids,
ketone bodies, or oxidative phosphorylation).
What happens to Protein?




Remember that the brain and red blood cells require
glucose for energy.
Fatty Acids cannot be made into glucose, while
amino acids that yield pyruvate can be used to make
glucose.
The breakdown of body protein is an expensive way
to make glucose, and in the first days of the fast the
body will use protein to make about 90 percent of the
needed glucose.
The muscles begin to atrophy quickly and continued
fasting will eventually result in death.
Fats and Ketosis


The body will eventually find a way to use fat
to fuel the brain in an emergency fasting
state.
The body will begin to combine fragments of
acetyl CoA (from fatty acids) to produce
ketone bodies.
Ketosis



Ketone body production continues to rise,
until they are meeting most of energy needs
of the nervous system.
Many areas of the brain will continue to rely
on glucose to function. The body will still turn
to body proteins to make this glucose.
Elevated ketones results in an increase of
the PH of the blood, making it very acidic.
The End