Nutrition-Part3
Proteins.
Protein functionality.
Protein in diet.
Macronutrients.
Micronutrients.
Vitamins.
Minerals.
Water.
Health and nutrition.
Proteins.
Proteins are one of the three macro nutrients,
that is essential for the body.
A diet should contain, carbohydrates, fats, and proteins.
The cells in our body, have a finite life time.
The body continuously regenerates, the cells, that the body loses.
Proteins supply the raw materials, to regenerate the components of these cells.
The body synthesises the proteins, that it needs.
The raw materials for this synthesis, is amino acids.
These amino acids are extracted from the proteins, that we eat,
through catabolic biochemical reactions.
Proteins play a critical role in almost every physiological process.
Biochemistry of proteins.
Proteins mainly comprise of carbon, hydrogen, oxygen and nitrogen.
They have small quantities of other substances , like sulphur.
Unlike carbohydrates and fats, proteins have an additional element,
nitrogen, as a component.
All proteins have some amount of nitrogen.
Proteins are large molecules.
They are formed by linking together a large number of sub-units.
These sub-units are amino acids.
Proteins are polymers of amino acids.
Amino acids.
Almost all amino acids have an amino group,
and a carboxyl group, attached to a carbon atom.
The amino group is - N H 2.
The carboxyl group is - C O O H.
The third bond of the carbon atom is attached to a hydrogen atom.
The fourth bond of the carbon atom is attached, to an amino acid, side chain.
We will call this amino acid, side chain, as “R”.
The general formula for an amino acid, can be written as:
R - C H, with one branch of N H 2, with another branch of C O O H.
The side branch “R”, uniquely defines, an amino acid.
Human beings have the same set of 20 different amino acids.
Polypeptides.
The bond formed between an amino, and a carboxyl group,
is called as a peptide bond.
When one amino acid, combines with another amino acid,
one amino acid loses hydrogen and oxygen, or O H, from the C O O H group,
and another amino acid loses hydrogen, from the amino group, N H 2,
resulting in a dipeptide, and one molecule of H 2 O.
The peptide bond, can be represented as a molecular component,
(- C O - N H - ).
A sequence of amino acids linked together by peptide bonds,
is called as a polypeptide.
When less than 50 amino acids, are linked together, the resulting molecule,
is called as a peptide.
When more than 50 amino acids, are linked together, the resulting molecule,
is called a protein.
This is just a convenient convention.
Protein structure.
Two factors determine the structure of the protein, or a peptide.
- The total number of amino acids, in the chain.
- The specific type of amino acid, at each position, in the chain.
The number of combinations, in which protein molecule are built,
are almost infinite.
Let us take an example, of a simple peptide molecule with just 3 amino acids.
Since we can select from 20 different amino acids, and 3 possible positions,
we can have 20 into 20 into 20, equal to 8000 types of peptides.
If we choose to have six amino acids in the chain,
the number of possible peptides is 20 to the power of 6,
equal to 64 million types of peptides.
A typical protein will have more than thousand amino acids,
linked together.
If we extend the arithmetic, to calculate the number of possible proteins,
the resulting number will be so very large, that it is almost infinite.
The body thus using only 20 types of amino acids, can synthesise,
an almost unlimited number of proteins.
The structure of a protein is analogous to a long string of beads.
Each bead represents one of the 20 amino acids.
Another interesting aspect of a protein molecule, is that it can,
curl up and twist into many different types of shapes.
We can try and imagine, a thousand bead chain,
and the number of 3 dimensional shapes, that we can create from it.
These shapes are called conformations.
Different conformations, could result in different behaviour, of the protein.
Now, we can begin to comprehend the fascinating complexity,
from 20 relatively simple amino acids.
Protein metabolism.
The proteins that we eat, are digested with the help of enzymes.
These enzymes are called proteases.
In the stomach proteins are broken down, by an enzyme called pepsin.
In the small intestine, the enzymes trypsin and chymotrypsin, further break it down.
The enzyme carboxypeptidase, finally breaks it down to free amino acids.
So, what starts as a protein in the diet, ends up as free amino acids,
in the small intestine.
These amino acids are absorbed, into the blood stream, from the small intestine.
Proteins can be catabolized to produce energy.
Proteins are not the preferred source, for the body, to produce energy.
Only a small percentage of proteins, is used by the body, to produce energy.
The body prefers carbohydrates, and fats to produce energy.
One gram of protein typically, can give 4 kilo calories of energy.
When required, the body can use protein as a source of energy.
The body prefers to synthesise different proteins that it needs,
from the proteins, that we eat, and digest.
But it has metabolic pathways through which amino acids can be converted,
to energy.
The intermediate molecule that are produced, are keto acid.
A keto acid has the general formula, R - C O - C O O H.
These keto acids enter the Krebs cycle, or the glycolytic pathway to produce energy.
All three macro nutrients, share these metabolic pathways, to produce energy.
When a amino acid is broken down, in the presence of a coenzyme,
the resulting product is a Keto acid, and ammonia.
The chemical reaction can be written as :
Amino acid + H 2 O + coenzyme,
results in R- C O - C O O H + N H 3 + coenzyme - 2, H .
The ammonia is carried in the blood stream to the liver.
In the liver it combines with carbon dioxide to produce urea.
Urea is excreted by the kidneys, in urine.
Protein biosynthesis.
The body synthesises all the proteins, that it needs,
from the 20 basic amino acids.
The proteins that we eat, are broken down to amino acids.
Some amino acids, can be synthesised by the body.
The remaining amino acids, have to be supplied, from our food.
Protein biosynthesis, is the most important reason, to have protein in the diet.
DNA which is present in every cell, controls the process of protein biosynthesis.
DNA uses RNA to achieve this functionality.
RNA provides a unique template, for each type of protein, that it wants to synthesise.
As we discussed this could be any of the large number of types of proteins,
that the body needs.
The largest known proteins, are called ’Titins’.
Titins proteins have more than 27000 amino acids, linked together.
The proteins that the cell generates, determines what type of cell it will be,
in different organs of the body.
Protein biosynthesis, is a crucial part of the metabolism of life.
Though protein molecules, are large and complex,
the basic building blocks of proteins, are relatively simple.
Proteins are built up, from 4 basic building block molecules, called nucleotides.
These 4 building blocks, have the code, A, U, C and G.
”A” stands for Adenine.
”U” stands for Uracil.
”C” stands for Cytosine.
”G” stands for Guanine.
An amino acid comprises of 3, of these nucleotides.
The combination of these 3 nucleotides, are called as Codons.
Of the possible combinations, 20 combinations,
or codons are present in human beings.
These are the 20 amino acids, that we discussed.
DNA is the master architect, which designs these proteins.
RNA are templates, and messenger molecules, which contain the codons.
The Ribosomes are a large and complex molecular machine,
found in all living cells.
It is the site for protein synthesis in the cell.
It receives the messenger RNA molecule, which contains the codon for an amino acid.
It links together, a long chain of amino acids.
This process of synthesising proteins, from RNA messenger cells,
is called translation.
A protein that results from this, can be represented, by a series of characters.
Each building block or a codon, will have 3 of these characters.
A protein with thousand amino acids, will have 3000 characters,
a 3 character amino acid, at a time.
The complexity of life, is about building complex structures,
with simple building blocks.
Incidentally the master architect, the DNA, shares 3 of the basic nucleotides,
with proteins.
DNA has the nucleotides, A, C and G.
Instead of U, it has a nucleotide, called Thymine, with a code ’T’.
So, DNA is a long chain of nucleotides,
with the codes A, T, C and G.
DNA has the genetic code, to build all the proteins and bio molecules,
that it synthesises, which is required for life.
Scientists have recently succeeded, in sequencing the genetic code, of human beings.
We can expect many exciting discoveries, in bio science, in the coming years.
Protein functionality.
Proteins perform, an amazing number of functions, within the cell,
and in the human body.
Each unique protein, performs a unique function.
Within the cell, there are large variety of proteins.
The proteins in a particular cell type, is called a proteome.
The study of interactions between specific proteins, is the key to understand,
the important cellular functions.
Ultimately, this is what determines the cell type.
Proteins also perform a wide variety of extra cellular functions.
This is the reason, we can say, that proteins, are the molecular machines of the body.
To get an idea of what proteins can do, we will discuss a few examples.
Most structural proteins, are fibrous proteins.
When proteins bind together, they form fibrils, which have structural functionality.
Collagen is a structural protein, found in most connected tissues in the body.
It is the most abundant protein, in our body.
Collagen is present in tendons, ligaments, and skin.
It is also present in the eye cornea, cartilage, bones and blood vessels.
The cytoskeleton is the intra cellular matrix,
that supports the cell shape, and functions.
The cytoskeleton comprises of proteins.
Mechanical forces, are generated by motor proteins.
They generate the forces, in contracting muscles.
Keratin found in hard filamentous structures, such as hair and nails,
is also a structural protein.
Enzymes are used to catalyse bio chemical reactions.
Each enzyme catalyses one type of bio chemical reaction.
Each enzyme is a particular type of protein.
There are about 4000 known bio chemical reactions,
which are catalysed by protein enzymes.
Enzymes can play a dramatic role, in a bio chemical reaction.
A reaction which take years, can be accelerated by enzymes,
to take place in seconds.
Though the enzymes, may not directly participate in the reaction,
it can be considered as important as the bio chemicals themselves.
Enzymes are also involved,
in DNA replication, repair and transcription.
Many signalling mechanisms are also carried out by proteins.
Hormones are signalling molecules.
They travel in the blood circulatory system, and carry messages,
to distant organs.
Insulin is an example of a protein, which acts as a signalling molecule.
It regulates the metabolism of carbohydrates and fats.
It stimulates the absorption of glucose, from the blood stream.
It also stimulates the synthesis and storage of fat.
Membrane proteins, act as receptors, in cell membranes.
They bind with signalling molecules, and induce a bio chemical reaction.
Many drugs are targeted, to act on membrane proteins.
Membrane proteins can also act as selective gate keepers, in the cell membrane.
They allow specific molecules, to come in, and go out of cells.
Oxygen, carbon dioxide, glucose, sodium, potassium etc.
which travel across membranes, are regulated by membrane proteins.
Antibodies are proteins, which function in the immune system.
Antibodies bind to antigens, or foreign substances, like harmful bacteria,
and target them for destruction.
Ligand transport proteins, bind to certain molecules,
and transport them, in the body.
The protein haemoglobin, transports oxygen, in the blood stream,
from the lungs to all parts of the body.
Protein in diet.
Proteins can be found in many food substances, that we eat.
Some examples, of food items that are rich in protein are :
Pulses, soybeans, lentils, rajma, white beans, green gram, bengal gram,
kabuli chana, cow peas, lima beans, toor dal, almonds, brazil nuts, cashews,
pumpkin seeds, sesame seeds, sunflower seeds, milk, eggs, meat and fish.
We need to include a healthy proportion, of proteins in our diet.
All the proteins that we require, are available in plant based foods.
As we discussed, proteins are the molecular engine, of the body.
The proteins that we eat, is not the proteins, that the body actually uses.
The body synthesises, all the proteins, that it requires.
However, we need to provide the raw materials to synthesise,
the proteins, the body requires.
This raw material is provided, by the proteins that we eat.
The proteins that we consume, is broken down into amino acids,
by the digestive system.
Using amino acids, the body synthesises the wide variety of proteins,
that it requires.
Macronutrients.
Carbohydrates, fats, and proteins, are the macro nutrients,
that the body requires.
We need to consume relatively larger amounts, of macro nutrients.
We need energy to survive.
The energy requirements, of a person varies from person to person.
Age, body size, and physical activity, are some of the factors,
that determine the energy requirements of a person.
Growing children, and adolescents, require more energy.
Physically active persons, require more energy.
Conversely sedentary persons, require less energy.
It is a good principle, to eat that much food,
which provides the energy that we require.
Too much food, or too little food is not good for health.
The average energy requirement of a person,
is about 2000 kilocalories per day.
Most of this energy, can be derived from the carbohydrates,
and fats, that we eat.
Carbohydrates provide about 4 kilocalories of energy, per gram.
Fats provide about 9 kilocalories of energy, per gram.
Body is likely to use most of the proteins, to build cellular components and cells,
for growth and regeneration.
Micronutrients.
Apart from macronutrients, the body needs some micronutrients.
These micronutrients are required in very minuscule quantities.
The requirement for micronutrients, will be typically measured in,
milligrams or micrograms.
The important micronutrients are :
Vitamins.
Minerals.
Cofactors.
Enzymes act as a catalyst, for biochemical reactions.
Enzymes are recycled by the body.
A small amount of enzymes, are sufficient,
to enable a large amount, of bio chemical reactions.
Many enzymes are inactive, in the absence of other substances.
These substances are called as “cofactors”.
The cofactors are also recycled.
Only minuscule amounts, of cofactors, are required by the body.
In some cases the cofactors are trace minerals, like :
Magnesium, iron, zinc, copper etc.
In some cases, the cofactor is an organic molecule.
Such cofactors are called coenzymes.
Coenzymes help to remove some molecule, from an organic molecule,
and add it to another organic molecule.
For example, it might help an enzyme, to remove 2 hydrogen atoms,
from biomolecule R1, and add it to another biomolecule R2.
At the end of the process, the coenzyme remains intact.
Only minuscule amounts of coenzymes, are required,
to maintain the enzymatic reactions, in which they participate.
Coenzymes are derived, from a special class of nutrients, called vitamins.
Vitamins.
Vitamins are organic compounds, which cannot be synthesised by the body.
They are required to be supplied, as part of the diet.
Vitamins play a important role in the biochemistry of metabolism.
For example, many coenzymes are derived from vitamins.
Vitamins, though required only in minuscule quantities,
are still essential to be provided, in the diet.
Fortunately all the vitamins, are present,
in most naturally occurring food items.
When vitamins were first discovered, their molecular structure was not known.
They were named by english alphabets, like A,B,C, etc.
We will briefly discuss some important vitamins, required by the body.
Vitamins can be broadly classified as:
Fat soluble vitamins.
Water soluble vitamins.
Water soluble vitamins, are typically coenzymes.
Vitamin A, D, E and K are fat soluble vitamins.
Vitamin B and C are water soluble vitamins.
Vitamin A.
Vitamin A, is a fat soluble vitamin.
Vitamin A is required by the immune system.
It is also required for good vision.
Some natural sources of vitamin A are :
Carrot, Sweet potato, Pumpkin, spinach, tomatoes, mango, apricots, etc.,
Vitamin D.
Vitamin D acts as a regulator for mineral metabolism.
It aids in the intestinal absorption of calcium, iron, magnesium, phosphate, and zinc.
Vitamin D is synthesised, in the skin, in the presence of sunlight.
Vitamin E.
Vitamin E acts as an antioxidant.
Some natural sources of Vitamin E are:
Olive oil, safflower oil, sunflower oil, mango, almonds, peanuts, sweet potato, etc.
Vitamin K.
Vitamin K is used in the synthesis, of some proteins.
It is also required for blood coagulation.
It protects bones, from fracture.
Some natural sources of vitamin K are:
Spinach, green peas, asparagus, carrots, etc.,
Vitamin B.
Vitamin B, is actually a class of vitamins.
There are 8 types of vitamin B.
They are named as B1, B2, B3, B5, B6, B7, B9, B12.
Together they are called as B complex.
Some examples of the functionality, that B complex vitamins,
help to achieve are:
Production of RNA and DNA.
Nerve functions.
Metabolism of carbohydrates.
Metabolism of glucose.
Metabolism of lipids.
Metabolism of proteins.
Catabolism of fatty acids.
Citric acid cycle.
Synthesis of amino acids.
Synthesis of fatty acids.
Synthesis of cholesterol.
Synthesis of hormones.
Synthesis of antibodies.
Production of blood cells.
Vitamin C.
Vitamin C, acts as a cofactor in many enzymatic reactions.
It also acts as an antioxidant.
Antioxidants protects cells from free radicals, or excessive oxidation.
Improves absorption of iron.
Some good sources for vitamin C, are :
Citrus fruits like lemon, orange, etc.
Strawberries, papaya, tomatoes, potatoes, cauliflower.
Leafy greens such as lettuce, spinach, etc.
This list of functions, are only illustrative of the wide variety, of functions,
that vitamins help to perform.
Vitamins are essential for a healthy metabolism.
Vitamins can be found in plenty, in natural foods.
If we include vegetables and fruits, in our diet,
we can get all the vitamins required, in sufficient quantity.
Only a minuscule amount of vitamins, is used by the body.
Excess water soluble vitamins, are excreted via urine.
Excess fat soluble vitamins, are stored along with fat.
Excess stored vitamins, can be potentially toxic.
More vitamins, than required, does not result in better health.
Vitamin supplements, are required only when there is a known deficiency,
identified by a doctor.
Minerals.
Minerals are essential chemical elements, that the body requires.
Earlier these chemical elements were called as essential minerals.
This popular terminology, is still used.
Minerals act as cofactors, in biochemical reactions.
They are recycled, by the body.
The body requires only minuscule quantities, of these minerals.
There are 7 mineral elements, which are required, in minuscule amounts, by the body.
They are:
Calcium, phosphorus, potassium, sulphur, sodium, chlorine, and magnesium.
About 13 other elements are required in trace quantities, in the body.
They are:
Iron, iodine, copper, zinc, manganese, cobalt, chromium, selenium, molybdenum,
fluorine, tin, silicon, and vanadium.
Minerals are mostly dissolved in the intracellular, and extracellular fluids, in the body.
Some minerals act as ionic electrolytes.
Ion gradients, across cell membranes maintain, osmotic pressure and pH.
They play a role, in the exchange of electrolytes, between the extra cellular fluid,
and the cytosol, or the cellular fluid.
Electrolytes enter and leave, through proteins in the cell membrane,
called ion channels.
Ions are required for nerve and muscle functions.
The solid matrix of bone tissue, mainly contains calcium and potassium.
Many enzymes are inactive in the absence, of cofactors.
Some of these cofactors are minerals.
Minerals like magnesium, iron, zinc and copper, bind to enzymes,
and activate it.
A few minerals, like sodium and chlorine, are absorbed by the body,
as inorganic chemicals, like sodium chloride, or table salt.
Most of the minerals, have to be, a part of organic molecules,
to enable them, to be absorbed, by the body.
Plants naturally absorb, minerals from the soil.
The roots of the plant absorb, mineral elements from the soil,
and include them, in the organic compounds, they synthesise.
These organic compounds can be found in the stem,
leaves, seeds, flowers, fruits, etc., of the plant.
Eating plant food is the best way,
human beings can absorb these minerals.
Some examples of food, rich in minerals are :
Tomatoes, bananas, potatoes, spinach, turmeric, milk, green leafy vegetables,
cinnamon, oats, soybeans, ginger, cumin, cloves, asparagus, yogurt, garlic, barley,
strawberries, onions, carrots, etc.
Water.
Most of our body comprises of water.
Most of the biochemical reactions, in the body takes place, in the presence of water.
We can say that the metabolism of life, is dependent on water.
Though water is not used to produce energy,
water should be considered, as an essential nutrient.
Along with food, we need to consume water, to live.
Health and nutrition.
Consuming the right amount of food, and the right type of food,
can play a very significant role, in maintaining good health.
We need to have a balanced diet, which has good carbohydrates, fats, and proteins.
Diet should also include food, rich in vitamins, and minerals.
Fortunately, all this is available in naturally occurring foods.
The more natural the food is, the better it is.
It is a healthy practice to eat fresh vegetables and fruits.
Industrial food, is now widely available.
These foods are required to have labels, which list the major nutrients.
This enables us to choose the right food.