Water soluble vitamins effectively act as coenzymes. These vitamins participate in chemical reactions after the initial reaction has finished, precipitating additional reactions. They consist largely of hydrogen, carbon and oxygen atoms, which are not stored in the body, but disperse in water and pass through in the form of urine. They have a particular importance in energy metabolism, providing links and regulating reactive factors. e.g. vitamin C’s main function is to provide connective tissue stability and to aid wound healing.
Structurally, proteins resemble carbohydrates and lipids because they contain carbon, oxygen and hydrogen atoms. In the same way that glycogen is formed from simple glucose molecules linked together, the protein molecule is polymerised from its amino acid ‘building block’. Peptide bonds link amino acids to produce a dipeptide, and three amino acids, producing a tripeptide, and so on. A polypeptide contains between fifty and a thousand amino acids. Single cells contain many thousand protein molecules, each with a different configuration: some linear, some complex shapes. ‘The twenty different amino acids required by the body each have a positively charged amine group at one end, and a negatively charged organic acid group at the other end. The amine group has two hydrogen atoms attached to nitrogen (NH2), whereas the organic acid group contains one carbon, two oxygen and one hydrogen atom (COOH). The remainder of the amino acid, referred to as the R group takes on a variety of forms.’ (Exercise Physiology fifth edition, McArdle, Katch and Katch.2001 Maryland, USA.Lippincott Williams & Wilkins). The ‘building blocks’ for synthesising tissue are anabolic reactions – one third of protein is used for anabolism in a child’s growth. Structural proteins, so-called because of their rigid bonds allowing them to form plasma membranes and internal cell material. egg. collagen makes hair, skin, nails, bones, tendons and ligaments, whilst involved to a lesser degree in blood clotting. the most common structural proteins are actin and myosin, which slide together during movement thanks to their linear structure, providing muscle action.
Minerals become part of structures and existing chemicals in the body:
- form bones and teeth (calcium)
- maintain a normal heart rhythm
- regulate cellular metabolism – they become part of enzymes and hormones involved in cellular activity
A lack of minerals in the body disrupts the balance between anabolism and catabolism. They also participate in the synthesis of nutrients i.e. glycogen from glucose, triglycerides from fatty acids and glycerol, and proteins from amino acids.
Water makes up from 40% to 70% of body mass, depending on age, gender and body composition: it constitutes around 70% of muscle weight and about 10% of the mass of fat. ‘The body contains two fluid compartments. The first, intracellular refers to fluid inside the cells. The second, extracellular, includes the fluid that flows within the microscopic spaces between cells. In addition to lymph, saliva, fluid in the eyes, fluid secreted by glands and the digestive tract, fluid that bathes the spinal cord nerves, and fluid excreted from the skin and kidneys.’ (Exercise Physiology fifth edition, McArdle, Katch and Katch.2001 Maryland, USA.Lippincott Williams & Wilkins).
Blood plasma makes up nearly 20% of the extracellular fluid, lost through sweating. Of the body’s total water mass, an average of 62% represents intracellular water.
Water serves as the body’s transport and reactive base; diffusion of gas can only take place across surfaces moistened by water. Nutrients and gases are transported in water solution; waste products in the form of urine and faeces leave the body through water. Water combines with various proteins, lubricating joints and cushioning organs, such as the heart, lungs and eyes. As it cannot be compressed, water gives structure and form to the body, providing for the body’s tissues. Due to its simple structure, lack of rigid bonds and the presence of hydrogen bonds attracting other water molecules together, water has an amazing heat stabilising quality. It absorbs high amounts of heat with minimal changes in temperature. Combined with a high level of vaporisation, water maintains a stable temperature during environmental heat stress and increased internal heat as a result of exercise.
Energy transfer in cells follows a general principal, that is, potential energy dissipating to kinetic energy which produces work resulting from harnessing the potential energy, eventually becoming lower potential energy, which gradually increases, completing the cycle. Carbohydrates, lipids and proteins possess considerable potential energy. The formation of product substances gradually reduces the nutrient’s original potential energy, with a matching increase in kinetic energy. Living cells have the capacity to extract and use chemical energy derived from a compound atomic structure, they also bond atoms and molecules together, increasing the level of potential energy. The energy from sunlight degrades to heat energy when light strikes and is absorbed. Food is an example of a basic store of potential energy. As the food decomposes however, the stores of potential energy decrease to the unusable form of kinetic or heat energy.
There are six main types of energy used and produced in various metabolic pathways:
- chemical – energy trapped inside a cell usually within the mitochondria
-
heat – a reaction that produces heat is usually the result of a series of other reactions, i.e. potential kinetic heat
- potential – the storage form of energy in cells that is ready to be used e.g. triglycerides in adipocytes
- kinetic- movement produced through the transfer of one energy form to another e.g. muscles contracting and relaxing
- light – usually the end to a chain of reactions that produces light, that is usually derived from chemical and/or kinetic energy
-
mechanical – the energy used in processes such as running, a by-product of chemical/potential energy. The movement of the muscle provides the runner’s mechanical energy. It is, in this way, similar to kinetic energy e.g. chemical energy kinetic/mechanical energy in the process of glycolysis, the Krebs Cycle and the electron transport chain.
Metabolism
In very simple terms, your metabolism is the rate at which your individual body burns up
energy. Metabolism varies from person to person. You may have a faster metabolism than
normal, for a person of your size, or a slower one.
Catabolism: Catabolism is the general name given to those steps in metabolism where
complex organic compounds are broken down into simpler compounds, for example the
taking glucose and breaking it down into carbon dioxide and water.
Anabolism: Anabolism is the general name for those steps in metabolism in which simple
compounds are used to make more complex compounds, for example taking amino acids and
combining them together to make proteins.
Basal Metabolic Rate (BMR)
Your BMR is the rate at which you use up energy when at rest - e.g. when you are sleeping or
just lying in bed. The more you weigh the higher your BMR will be. The metabolic rate of
very fat women is 25% higher than that of thin women.
- BMR is much greater in childhood than in adulthood. After the age of about 20, it
drops about 2 per cent, per decade.
- People whose bodies contain a higher proportion of muscle to fat, tend to have a
higher BMR than those with lower muscular proportions - all other things being equal.
As a very rough guide, the average person's BMR is about half a calorie per pound of body
weight, per hour. So, if you weigh 140 pounds you will use up approximately 70 calories an
hour or 1680 calories per day doing nothing.
There are several different methods of calculating a persons BMR, the most recognised and
widely used is the Harris-Benedict formula;
H = height in cm
W = weight in kg
A = age in years
For adult males BMR = 88.362 + (4.799 x H) + (13.397 x W) – (5.677 x A)
For adult females BMR = 447.593 + (3.098 x H) + (9.247 x W) – (4.330 x A)
My own personal BMR is:
88.362 + (4.799 x 177) + (13.397 x 86) – (5.677 x 20) = 1976.387 cal
(1) The higher your BMR, the easier it is to lose weight
All other things being equal, the more energy your body needs in order to tick over, the more
food you can eat without gaining weight - or, the less reduction in food you need to make in
order to lose weight. A high BMR tends to make dieting and weight loss easier.
(2) Your BMR decreases when you go on a diet which has fewer calories than your
normal diet
In response to fewer calories, the body lowers its BMR because it thinks there is a famine. It
therefore 'slows down' in order to conserve energy.
(3) Your BMR increases in response to increased physical activity
Not only do we use up calories doing exercise but the increased BMR continues even after we
have done our exercise, often for several hours. The amount of increase varies from person to
person but even a modest increase should counteract the body's tendency to decrease BMR
when we cut calories.
(4) Exercise is the ONLY effective way to increase your BMR
Many diets claim to increase metabolic rate through special fat-burning exercises or fat-
burning foods. The truth is, your metabolic rate falls if you start dieting and start to shed
excess pounds. You may be able to reduce the extent of the fall by increased exercise but
there is no evidence whatsoever that your metabolic rate will be higher than it was before you
dieted.
(5) Obesity is not caused by a slow BMR
Except in the rare cases of serious metabolic illness it is not possible to blame your
metabolism for obesity. Your metabolism certainly has an effect on how much you weigh but
the main reasons lie elsewhere.
ATP (Adenosine Tri-Phosphate)
Without ATP, life as we understand it could not exist. It is a perfectly-designed, intricate
molecule that serves a critical role in providing the proper size energy packet for scores of
thousands of classes of reactions that occur in all forms of life. Even viruses rely on an ATP
molecule identical to that used in humans. The ATP energy system is quick, highly efficient,
produces a rapid turnover of ATP, and can rapidly respond to energy demand changes.
ATP-ADP cycle:
The ATP-ADP cycle, shown here involved the harvesting of chemical energy by breaking
down complex organic molecules into simpler molecules, using the energy from this process
to join a phosphate group to an ADP molecule to make ATP. The resulting phosphate bond
between the second and third phosphate of the ATP has a small amount of net energy which
can be released to do work.
The Function of ATP
The ATP is used for many cell functions including transport work moving substances across
cell membranes. It is also used for mechanical work, supplying the energy needed for muscle
contraction. It supplies energy not only to heart muscle (for blood circulation) and skeletal
muscle (such as for body movement). A major role of ATP is in chemical work, supplying the
needed energy to synthesise the multi-thousands of types of macromolecules that the cell
needs to exist.
ATP is also used as an on-off switch both to control chemical reactions and to send messages.
The shape of the protein chains that produce the building blocks and other structures used in
life is mostly determined by weak chemical bonds that are easily broken and remade. These
chains can shorten, lengthen, and change shape in response to the input or withdrawal of
energy. The changes in the chains alter the shape of the protein and can also alter its function
or cause it to become either active or inactive.
The ATP molecule can bond to one part of a protein molecule, causing another part of the
same molecule to slide or move slightly which causes it to change its conformation,
inactivating the molecule. Subsequent removal of ATP causes the protein to return to its
original shape, and so it is again functional. The cycle can be repeated until the molecule is
recycled, effectively serving as an on and off switch. Both adding a phosphorus and removing
a phosphorus from a protein can serve as either an on or an off switch.
How is ATP Produced?
ATP is manufactured as a result of several cell processes including fermentation, respiration
and photosynthesis. Most commonly the cells use ADP as a precursor molecule and then add
a phosphorus to it. This can occur either in the soluble portion of the cytoplasm (cytosol) or in
special energy-producing structures called mitochondria. Charging ADP to form ATP in the
mitochondria is called chemiosmotic phosphorylation. This process occurs in specially
constructed chambers located in the mitochondrion’s inner membranes.
The mitochondrion itself functions to produce an electrical chemical gradient - like a battery –
by accumulating hydrogen ions in the space between the inner and outer membrane. This
energy comes from the estimated 10,000 enzyme chains in the membranous sacks on the
mitochondrial walls. Most of the food energy is produced by the electron transport chain.
Oxidation of the cells in the Krebs cycle causes an electron build-up that is used to push H+
ions outward across the inner mitochondrial membrane.
As the charge builds up, it provides an electrical potential that releases its energy by causing a
flow of hydrogen ions across the inner membrane into the inner chamber. The energy causes
an enzyme to be attached to ADP which catalyses the addition of a third phosphorus to form
ATP. In the human body the energy comes from food which is converted to pyruvate and then
to acetyl coenzyme A (acetyl CoA). Acetyl CoA then enters the Krebs cycle which releases
energy that results in the conversion of ADP back into ATP.
The more protons there are in an area, the more they repel each other. When the repulsion
reaches a certain level, the hydrogen’s ions are forced out of a revolving-door-like structure
mounted on the inner mitochondria membrane called ATP synthase complexes. This enzyme
functions to reattach the phosphates to the ADP molecules, again forming ATP.
The ATP synthase revolving door resembles a molecular water wheel that harnesses the flow
of hydrogen ions in order to build ATP molecules. Each revolution of the wheel requires the
energy of about nine hydrogen ions returning into the mitochondrial inner chamber. Located
on the ATP synthase are three active sites, each of which converts ADP to ATP with every
turn of the wheel. Under maximum conditions, the ATP synthase wheel turns at a rate of up to
200 revolutions per second, producing 600 ATPs during that second.
ATP is used in conjunction with enzymes to cause certain molecules to bond together. The
correct molecule first arrives in the active site of the enzyme along with an ATP molecule.
The enzyme then catalyses the transfer of one of the ATP phosphates to the molecule,
transferring to that molecule the energy stored in the ATP molecule. Next a second molecule
arrives nearby at a second active site on the enzyme. The phosphate is then transferred to it,
providing the energy needed to bond the two molecules now attached to the enzyme. Once
they are bonded, the new molecule is released.
Bibliography
Feur, I (2000) Energy and its systems, Kluwer, NY USA
McArdle,W, Katch,F and Katch,V (2001) Exercise Physiology 5th edition, Lippincott, Williams and Wilkins, Maryland USA
Stanley, S (1993) Biochemistry 2nd edition, MacDonald and Janes, NY USA
Webliography
http:connection.lww.com