Food and nutrition.
Nutrients.
Metabolism.
Carbohydrates.
Monosaccharides.
Disaccharides.
Polysaccharides.
We eat, a wide variety of food.
There are hundreds of types, of grains, vegetables, fruits, etc,.
There are thousands of types, of dishes available today.
Surprisingly, the body needs, and can use very few types of nutrients.
Regardless of what type of food, or dish we eat, the body extracts,
only the same limited number of nutrients, that it needs.
Cuisine varies from country to country, and region to region.
Taste and preferences, can vary from person to person,
even within a family.
But eventually, all human beings, extract the same nutrients, from food.
The food that we eat, is of no direct use to the body.
The body digests the food that we eat, and extracts the nutrients, that we need.
The digestive system, performs this role of, extracting nutrients from food.
The digestive system, is a vital sub system, of the human body system.
The process of digestion starts in the mouth, and goes on till the intestines.
Most of the digestion, takes place, in the stomach and small intestine.
Digestion involves many steps, of bio chemical reactions.
The organic compounds in the food, is converted into simpler nutrient compounds.
The body synthesises acids and enzymes, to aid digestion.
Complex food, is typically broken down, by digestion,
into simple essential nutrients.
There are thousands of types of biochemical reactions,
which are involved in the processing of nutrients.
Enzymes are chemicals synthesised in the body.
Enzymes catalyse the biochemical reactions.
Enzymes helps in digesting food.
Most of the metabolic processes in the cell, require enzymes.
Sometimes the same end product, can be derived,
from multiple metabolic pathways.
Enzymes also play a role in determining, a specific metabolic pathway.
Though enzymes do not directly participate, in the biochemical reaction,
they play an important role, in the metabolic process.
The digestion system, extracts the essential nutrients,
from the food that we eat.
There are two broad categories of nutrients, that a human body needs:
Macronutrients.
Micronutrients.
Macronutrients, are required in significant quantities by the body.
Macronutrients, provide the energy for metabolism.
This energy is required, just to keep us alive.
Without macronutrients, the body will starve to death.
Macronutrients also provide the bio chemicals, required by the body,
to build the structural elements, required for maintenance and growth.
The living body is in a dynamic state, where cells are dying,
and new cells are being built.
Macronutrients are required to synthesise the components of these cells.
There are three essential macro nutrients that a body needs.
They are:
Carbohydrates.
Proteins.
Fats.
The body also requires water, in significant quantities to function.
Though water is strictly not a nutrient,
it should be considered as an essential ingredient, of food.
Without water, we cannot survive.
Most of the bio chemical reactions, can take place, only with the presence of water.
The body also requires dietary fibre.
Dietary fibre cannot be digested, and converted to nutrients.
It is needed only to aid the process of digestion.
Apart from macro nutrients, the body also needs, very small quantities,
of micronutrients.
Vitamins and minerals, are some of the micro nutrients, that the body needs.
The body synthesises most of the biochemicals that it needs.
The macronutrients are the raw material, for some required biochemicals.
There are certain biochemicals that the body cannot synthesise.
These biochemicals, that the body cannot synthesise,
has to be supplied in the food, for the body.
These nutrients are called as essential nutrients.
Omega fatty acids, and vitamin C, are examples of essential nutrients.
Our body is a fascinatingly, complex biochemical factory.
It would be interesting to note, the body synthesises most of the biochemicals,
that it requires.
The macronutrients, carbohydrates, fats, and proteins,
are only raw materials, to produce the bio chemicals,
that the body ultimately uses.
The macronutrients are broken down into simpler, bio chemical molecules,
through a long series of biochemical reactions.
The body synthesises the required biomolecules,
through a long series of biochemical reactions.
These series of biochemical reactions, are called metabolic pathways.
There are a large number of metabolic pathways, in the human body.
These biochemical reactions, are continuously taking place, in our body.
All these biochemical reactions, when considered together,
is referred to, as the metabolism of the body.
Some of these biochemical reactions, take place, during the process of digestion.
Enzymes play a very important role, in the digestion process.
Enzymes do not directly take part, in the bio chemical reaction.
Enzymes help to catalyse, or speedup the chemical reaction.
Different enzymes, participate in different biochemical reactions.
This synthesis of enzymes, is controlled by hormones.
Most of the digestive enzymes, are synthesised in the pancreas.
Digestive enzymes break down, more complex molecules, into simpler molecules.
Carbohydrates have organic chemicals, like polysaccharides.
The digestive enzyme glycoside hydrolase, breaks down polysaccharides,
into simpler monosaccharides.
The digestive enzyme proteases, breaks down proteins, into simpler amino acids.
The body has an interesting self regulating mechanism,
to control the intake of food.
Hormones are signalling molecules.
The body generates, the grehlin hormone, when it needs food.
This is like a hunger hormone.
When we feel hungry, we feel like eating food.
When the body feels, that it has had enough food,
it generates another hormone, called Leptin.
This makes us feel full, or satiated, which signals us to stop eating.
The hormone signals are received, by the hypothalamus in the brain.
The hypothalamus regulates the appetite, to achieve energy homeostasis.
This self regulating process, in normal conditions,
helps us consume, the right amount of food.
Our body comprises of billions of cells.
A large number of metabolic processes, take place within the cell.
We can broadly classify these metabolic processes as:
Catabolism.
Anabolism.
Nutrients contain bio chemical energy.
In catabolic processes, large complex molecules, of nutrients, are broken down,
into simpler and smaller molecules, releasing energy in the process.
Oxygen is the most common, oxidising agent, in this process.
The oxygen we breathe in, is carried in the haemoglobin molecules,
in the blood stream.
The blood stream also transports, the nutrients, derived from digestion of food.
Cells absorbs nutrients, and oxygen.
The nutrients and the oxygen, react to release energy.
An example of a catabolic reaction, is the break down of glucose, to release energy.
Glucose is the simplest of sugars.
It is a monosaccharide.
It has the molecular formula C6, H12, O6.
C6, H12, O6, +, 6O2, =, 6CO2, + 6H2O, + energy.
This is sufficient energy to create about 38 ATP molecules.
CO2 is a waste product, which is expelled from the cell.
The released energy, from the reaction is harvested.
The citric acid cycle, plays a key role in cellular respiration.
The citric acid cycle, is also known as the Krebs cycle.
In this cycle, acetates are derived from, carbohydrates,
fats and proteins.
Citric acid is a weak organic acid.
Citric acid is naturally found in citrus fruits, like lemon.
It has the molecular formula, C6, H8, O7.
The citric acid cycle, is a series of bio chemical reactions,
which oxidises the acetates, derived from the nutrients.
This series of bio chemical reactions,
starting from carbohydrates, fats, and proteins,
results in producing energy.
This energy is stored, in a molecule called ATP.
The citric acid cycle, is not only present in human metabolism,
but is present in some of the earliest cellular metabolisms,
in the evolution of life.
Catabolic processes are exergonic, which releases energy.
The released energy needs to be stored.
Adenosine triphosphate, ATP, is a bio chemical molecule.
ATP has a nitrogen containing adenine base,
a five carbon sugar molecule called ribose,
and three phosphate groups.
ATP acts like a battery, for energy storage, and release.
The exergonic energy released from catabolic processes, is stored,
in adenosine triphosphate, or ATP, in cells.
The energy released, is stored by converting adenosine diphosphate,
or ADP, into ATP.
The process of converting biochemical energy, from nutrients,
and storing it in ATP, is also referred to as cellular respiration.
Energy management with in a cell, happens in the mitochondria.
The mitochondria is an organelle, within the cell.
Mitochondria is called as the power house, of the cell.
Most of the ATP, is generated in the mitochondria.
The type and number of mitochondria,
varies depending on the tissue type.
Active muscle cells have more mitochondria.
Liver cells also contain a large number of mitochondria,
because of the high metabolic activity, that occurs in the liver.
The mitochondria is a distinct organelle, which has it’s own DNA.
Interestingly, the DNA in our mitochondria, bears a strong resemblance,
to the DNA present in bacteria.
Anabolism is the biochemical process, of bio synthesising,
complex molecules from simple molecules.
Anabolic processes are endergonic, which absorbs energy.
Muscle activity is also endergonic, which consumes energy.
Energy is required for these processes.
The required energy is retrieved, from the energy stored, in ATP molecules.
The anabolic process typically involves multiple steps.
Catabolism results in, producing simple molecules.
Starting from these simple molecules, like monosaccharides and amnio acids,
more complex molecules like polysaccharides, proteins,
lipids and nucleic acids, are bio synthesised.
The synthesised molecules are required to perform, a wide variety of functions.
Cell structure, cell components are some of the examples,
where synthesised molecules, by anabolism is used.
Metabolism is the total of all catabolic, and anabolic, reactions, in the body.
Metabolism is a continuous process, in the body.
Even when there is no physical activity, metabolism of living, is always present.
This is called as the basal metabolic rate.
Every living individual has a basic metabolic rate, or BMR.
The basic metabolic rate can vary from person to person.
Food is thus essential, just to derive energy, for sustaining life.
The energy content of nutrients can be measured in kilo joules.
Another popular unit of measuring energy is the calorie.
The calorie is the amount of energy, required to raise the temperature,
of one gram of water, by one degree centigrade.
1 kilo calorie is popularly referred to as a food or nutritional Calorie.
The food Calorie is spelt with a capital C.
One food Calorie, is equal to 1000 calories,
which is equal to 4.2 kilo joules.
Interestingly about 70% of the energy we consume,
is for the basal life processes, within the organs of the body.
10% of the energy goes for thermogenesis,
which results in heat generation.
Only 20% of the body’s energy expenditure goes for muscular activity.
Of course, this could vary, from person to person, depending on life style.
Powering the human body, is roughly equivalent to,
the energy consumed by a 80 watt bulb.
There are thousands of biochemical reactions, taking place continuously,
in the various organs, tissues, and cells in the body.
All these reactions are interrelated to each other.
For the harmonious functioning of the body, all these reactions,
have to be coordinated.
In an orchestra, all the instrument players, have to be coordinated,
to create harmonious music.
In a sense, the metabolism of the body, is like a huge orchestra,
all working harmoniously together, in a well regulated symbiotic way.
The body uses signalling mechanisms, to coordinate its metabolism.
Hormones are biochemical modules, synthesised in the body.
Hormones act as chemical signalling molecules.
The endocrine glands in the endocrine system, produces the signalling hormones.
The endocrine system, itself is controlled by the brain.
This is what enables, many of the metabolic processes to act,
like a coordinated orchestra.
Most of the signalling mechanisms, act in pairs.
One signalling hormone, will stimulate a metabolic process.
Another signalling hormone, will inhibit the same metabolic process.
For example, one hormone, called Insulin,
would encourage the synthesis of glycogen.
Another hormone, called glucagon, will inhibit the synthesis of glycogen.
By dynamically increasing, or decreasing the appropriate signalling hormones,
the body is able to effectively coordinate and control,
all the metabolic processes.
This control process, works like a thermostat, in a fridge.
When the temperature goes up, the thermostat, will initiate a cooling process.
When the temperature comes down, the thermostat,
will stop the cooling process.
This is a simple example, of a homeostatic process.
The body, of course, contains many more variables.
Coordinating and controlling, all these variables,
is called as homeostasis.
A healthy body will typically be in a state of homeostatic balance.
There is an interesting relationship between plants,
and animals like human beings.
Plants harvest the sun’s energy, through photosynthesis, to produce and store food.
Human beings consume plant food, to derive energy.
So, in a sense, we indirectly harvest, the sun’s energy, via plants.
There is a symbiotic relationship, between plants and human beings.
We need plants, for our survival.
Plants provide all macro nutrients, like carbohydrates, proteins, and fats.
Plants also provide all the micro nutrients, like vitamins and minerals.
Carbohydrates are one of the most basic macro nutrients,
required by the body.
Carbohydrates are nothing but compounds of carbon and water.
The basic elements, in a carbohydrate are:
Carbon.
Hydrogen.
Oxygen.
Typical carbohydrates have the molecular formula,
C subscript m, H2O subscript n.
”m”, stands for the number of carbon atoms.
”n”, stands for the number of H2O or water molecules.
Glucose has the molecular formula, C subscript 6, H2O subscript 6.
It can also be written as C6, H12, O6.
Carbohydrates are present in all types of food.
In particular, food grains, vegetables, and fruits provide,
the bulk of the carbohydrates, that our body needs.
A healthy diet needs to have, a healthy proportion of carbohydrates.
Carbohydrates can be broadly classified as:
Monosaccharides.
Disaccharides.
Polysaccharides.
Carbohydrates contain the energy required for human metabolism.
1 gram of carbohydrate, provides about 4 kilo calories,
or food calories, of energy.
Monosaccharides and disaccharides, are also known as sugars.
Sugars as we know, is sweet to taste.
Monosaccharides are the most important source for energy,
for the human body.
They are also the building blocks, for more complex molecules,
like polysaccharides.
The most common monosaccharide, in human metabolism, is glucose.
It has the molecular formula, C6, H12, O6.
The other important monosaccharides are:
Fructose.
Galactose.
Fructose and galactose, are isomers of glucose.
Isomers have the same molecular formula,
but have different molecular structure.
Isomers do not necessarily share similar properties.
Glucose, fructose and galactose are sweet tasting sugars.
The most ubiquitous, and important source of energy,
in biology is glucose.
Most forms of life, from bacteria to human beings,
use glucose for energy.
Human bodies digest carbohydrates, and break it down to monosaccharides,
like glucose.
This can happen in a number of biochemical processes.
In cellular respiration, glucose is oxidised and broken down further,
to provide energy, and the by-products, carbon dioxide and water.
C6, H12, O6, +, 6O2, =, 6CO2, + 6H2O, + energy.
Glucose can be considered, as the fuel for life.
Fructose is an isomer of glucose.
Fructose is naturally found in fruits, vegetables and honey.
Fructose is the sweetest, of all naturally occurring sugars.
Fructose is normally metabolised, mostly in the liver.
Glucose, however is metabolised, in most of the human cells,
including brain cells.
Galactose is a component of lactose.
Lactose naturally occurs in milk.
Lactose is the combination of the monosaccharide galactose,
and the monosaccharide glucose.
Glycolysis is the metabolic pathway, which converts glucose,
into usable energy.
Glucose is converted into pyruvate, with the molecular formula CH3, CO, COO, minus,
and a hydrogen ion, H +.
The free energy released in this process,
is used to form the high energy compounds ATP and NADH.
Two joined monosaccharides, are called as disaccharides.
The general molecular formula, for a disaccharide, is C12, H22, O11.
Sucrose and Lactose, are the common examples, of disaccharides.
Monosaccharides and disaccharides are commonly referred to, as sugars.
Sucrose is the combination of the monosaccharides,
where one molecule of glucose is covalently linked to one molecule of fructose.
It has the molecular formula, C12, H22, O11.
The digestive system breaks down, sucrose into glucose and fructose.
Glucose and fructose is directly absorbed, into the blood stream.
Sucrose is also called as table sugar.
It is a popular additive to food and drinks,
for palatability and taste enhancement.
Over consumption of sucrose, is linked to adverse health effects,
including obesity.
Sucrose is added to many readymade refined food products,
to enhance taste.
When large amounts of refined food, with high percentages of sucrose,
are consumed, beneficial nutrients can be displaced from the diet.
This can lead to chronic disease.
Sucrose provides a quick source of energy.
It causes a rapid rise in blood glucose level.
This can cause problems, for people suffering from defective glucose metabolism,
like in persons with diabetes.
Lactose is a disaccharide.
Lactose is found in milk.
It is a combination of the monosaccharides, glucose and galactose.
In early human evolution, only infants could digest lactose.
When the infants grew up, they lost the ability to digest lactose.
This is called lactose intolerance.
When human beings domesticated animals like cows and goats,
they started harvesting the milk from these animals.
Over a period of time, many humans evolved, the ability to digest lactose,
as adults.
Milk has now become an important source of food.
A significant percentage of adult human beings,
continue to be lactose intolerant.
Polysaccharides are long chains of monosaccharides.
They are called polymers, in general.
Starch, glycogen, and cellulose are examples of polysaccharides.
Since most bio chemical polysaccharides,
are polymers of 6 carbon monosaccharides,
the general molecular formula for polysaccharides can be written as,
(C6, H10, O5,) “n”.
The C6, H10, O5, monosaccharide component, repeats, “n” times.
Typically “n” is a very large number.
Polysaccharides are an important class of biological polymers.
They play two important roles in living organisms:
They act as a storage mechanism for energy.
They act as bio structural elements.
Plants use photosynthesis to produce glucose from carbon dioxide.
Glucose is water soluble.
This property is very useful, when energy has to be extracted from glucose.
When energy has to be stored, plants prefer to store it as starch.
When they need energy, they extract glucose from the starch.
Starch is a long chain polymer of monosaccharides.
It is a more efficient way to store energy.
Starch is relatively a more dense, store of energy.
Also starch is not water soluble.
These properties make starch, as the preferred way for storage by plants.
Plants store starch in tubers, buds, fruits, and seeds.
Human beings harvest the starch, stored by plants,
and use it as a food source.
Starch is the most common carbohydrate, in human food.
Many staple foods contain starch.
Cereals like rice, wheat, maize, etc. containing starch,
is the major source of food, world wide.
Starch is a mixture of amylose, and amylopectin.
Amylose is a linear chain, of several hundred glucose molecules.
Amylopectin, is a branched molecule, with several thousand glucose units.
Typically the units are linked together, in what is called as glycosidic bonds.
During the process of digestion, these bonds are broken,
and glucose is extracted from starch.
Some other examples of starchy foods are, arrowroot, banana, barley, oats,
millet, sorghum, potatoes, yam, beans, peas etc.
Many pre-prepared food like bread, noodles, pasta, cereals, also contain starch.
Raw starch is difficult to digest.
Only after human beings started using fire to cook,
did food grains, become a staple source for food.
We use the enzymes called amylases, to digest starch, into the constituent sugars.
Human saliva, is rich in amylase.
The pancreas also secretes, this enzyme.
Starch is also used for some non food purposes.
It is used, as an adhesive, in the manufacture of paper.
It is also used as a stiffening agent, for clothes.
Glycogen is a multi branched polysaccharide.
It is the equivalent for starch, for animals and human beings.
Glycogen like starch, is insoluble in water.
Glycogen is a means of storage of energy, in human beings.
It is a good energy resource, which can be quickly and conveniently,
converted to glucose, to provide energy.
The liver is the main organ, which metabolises glucose, into glycogen.
The liver is the main storage area, for glycogen.
The liver converts glycogen to glucose, when required.
Glycogen thus acts like a bio chemical battery, for storing energy.
When we eat a meal, comprising of carbohydrates,
the meal is digested, and glucose is harvested.
This glucose enters the blood stream.
When the blood glucose level rises, the pancreas secretes insulin.
Insulin is a hormone, which acts as a messenger signal.
When insulin levels are higher, the liver synthesises, excess glucose into glycogen.
It, does this by forming long chains of glucose units.
The process of synthesising glycogen, is called glycogenesis.
The glycogenic process, is endergonic, and consumes energy.
When the body uses the glucose, the blood glucose level starts to fall.
When blood glucose level falls, insulin secretion decreases.
This causes the liver to stop synthesising glycogen.
Glucagon is another hormone, which acts as a counter signal to insulin.
Glucagon signals that the body needs energy.
Glucagon is secreted in the pancreas, and released into the blood stream.
In the liver, glucagon stimulates the breakdown of glycogen,
to produce glucose, which provides energy to the body.
This process of breaking down glycogen into glucose,
is called as glycogenolysis.
The glycogen stored in the liver, can provide glucose and energy,
to all the cells in the body.
A small amount of glycogen, is present in muscle cells.
It serves as an immediate source of energy needs, of the muscle cell.
This glycogen serves only the energy needs, of the cell it is present in.
It, does not share it’s energy with other cells.
The glycogen present in the liver, on the other hand, supplies energy to all the cells.
Some of the complex carbohydrates, found in plant food,
are not digestible, by human beings.
However they are an important part of the human diet.
They are called dietary fibre.
Dietary fibre can be of two types.
Soluble dietary fibre.
Insoluble dietary fibre.
Dietary fibre influences, how other nutrients are absorbed by the body.
For example, soluble fibre attenuates the absorption of sugar,
normalises blood lipid levels,
and helps in lowering cholesterol.
Insoluble fibre, absorbs water, and helps mechanical movement,
by bulking the food, we eat.
The digestive system is host to billions of bacterial cells.
These cells are beneficial to the body.
These gut bacteria play an important role in the digestive process.
Fibre serves as a source of food for the gut bacteria.