1. |
Amino
Acids |
Amino
Acids are organic compounds that contain both:
- an amino group (-NH2)
and
- a carboxyl group (-COOH)
Amino acids are fundamental constituents of all proteins.
Breakdown of the proteins in the body yields amino acids, specifically:
alanine,
arginine,
asparagine,
aspartic acid,
cysteine,
glutamic acid,
glutamine,
glycine,
histidine,
isoleucine,
leucine,
lysine,
methionine,
phenylalanine,
proline,
serine,
threonine,
tryptophan,
tyrosine,
valine.
Some amino acids can be synthesised by the human body but essential amino acids must be obtained from protein in the diet. |
2. |
Bile |
Bile
is a thick alkaline fluid that is secreted by
the liver and stored in
the gall bladder.
It is ejected into the duodenum via the common bile duct. It does not flow continuously but is released at intervals.
Bile may vary in colour (e.g. yellow, green, brown) according to the proportions of bile pigments. Leithin, cholesterol and bile salts are also present in bile.
What it does:
Bile salts help to emulsify fats in the duodenum so that they can be more readily broken-down by pancreatic lipase into fatty acids and glycerol. Bile salts also form compounds with fatty acids. Bile also helps to stimulate peristalsis in the duodenum. |
3. |
Carbohydrates |
There are many different
carbohydrates.
The term carbohydrate refers to any one of a huge
group of compounds that contain the elements carbon
(C), oxygen (O) and hydrogen (H) and have the
general formula Cx(H2O)y.
Examples of carbohydrates include sugars and starch.
Why are they important?
Carbohydrates
are an important source of energy. They are produced
by plants, in which carbohydrates form important
structural and storage materials, e.g. cellulose
and starch, respectively. Carbohydrates are ingested
into the human body as food (incl. sugary drinks).
Carbohydrates are one of the three main parts
of the human diet, the others being fat and protein.
How does the body process, use, and store
carbohydrates?
All carbohydrates ingested
as part of the diet are eventually broken-down
by the body into the simple sugar glucose
- which can participate in energy-generating metabolic
processes. Excess carbohydrates, ingested but
not needed by the body immediately are stored
in the liver and muscles
in the form of glycogen. |
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4. |
Disaccharides |
Disaccharides are carbohydrates that consist of two linked monosaccharide units.
The most common disaccharides include maltose,
lactose and sucrose.
(The -suffix "ose" indicates
that these are sugars.) |
5. |
Enzyme |
Enzymes
are types of proteins
that, in small quantities, increase the rate
of biological reactions without being used-up
in the reactions themselves. That is, enzymes
can act as catalysts (see below).
Enzymes form within living cells
and may act either within the cell or ouside it.
Many enzymes are unstable and are easily de-activated,
e.g. by heat or by other chemicals.
Certain enzymes are essential for normal functioning
and development of the human body. Failure in
the production or activity of even a single enzyme
can lead to serious problems / disorders.
How do enzymes act as catalysts ?
Enzymes act by binding with the substance involved
in the reaction (called the "substrate")
and converting it to another substance (called
the "product" of the reaction).
Particular enzymes catalyse specific reactions.
There are many different enzymes that
assist in many of the huge range of different
biochemical reactions. Even when considering
the specific enzyme that could help with a particular
reaction, understand that each enzyme needs certain
conditions in order to act as a catalyst
with the maximum efficiency possible for it. Such
conditions can include a particular range of:
- temperature(s)
- pH
- presence of specific other enzymes called 'co-enzymes'
- lack of particular inhibitors i.e. substances that reduce or prevent the particular reaction
Names of specific enzymes:
The names of many enzymes end with the suffix
"-ase". They are generally
named according to either the substrate on which
they act (e.g. lactase), or according to the type
of reaction they catalyse (e.g. hydrolase). |
6. |
Fats |
Fats
are substances that contain one or more fatty
acids in the form of triglycerides.
They are also the main form in which energy is
stored in the body as adipose
tissue.
Fats are one of the 3 main parts of the human diet - the others being carbohydrates
and proteins.
Uses and effects of fats:
A healthy diet
should include sufficient essential fatty acids
for the efficient absorption of fat-soluble vitamins
via the intestines. Fats in the body itself provide
several important functions including insulation
beneath the skin (in the subcutaneous tissue)
and around organs such as the kidneys. However,
excessive deposition of fat in the body can lead
to obesity and its many consequences and risks. |
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7. |
Fatty Acids |
Fatty Acids are the basic constituents (parts) of
many important lipids (fats), including e.g. triglycerides.
In terms of their chemistry, fatty acids are organic
acids that have long straight hydrocarbon chains
and an even number of carbon atoms.
In the same way as amino
acids, some fatty acids can be synthesized
(formed) in the body but others, called "essential
fatty acids" must be obtained from
the diet, i.e. ingested within foodstuffs - including
beverages.
Examples of fatty acids include:
- palmitic acid,
- oleic acid,
- stearic acid.
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8. |
Glycerol
(also known as
'glycerin') |
Glycerol
is a clear, viscous (meaning very thick e.g.
flows more like treacle than like water -
but note that the term "viscous" conveys
no information about colour or transparency) liquid
that can be produced by hydrolysis of fats and
mixed oils, e.g. as a by-product in the manufacture
of soap.
What does it do:
Glycerol has various
uses, such as an emollient
in some skin products, as a sweetening agent in
some pharmaceutical products, and as a laxative
(e.g. in the form of suppositories). The
use of glycerol for its laxative effects is relevant
to the digestive system. |
9. |
Insulin |
Insulin is a protein hormone
produced by the beta cells in the islets of Langerhans
within the pancreas.
Secretion of insulin is stimulated by a high concentration
of sugar in the blood.
What it does:
Insulin is important for
regulating the amount of sugar (glucose) in the
blood. Lack of sufficient insulin causes diabetes
mellitus - in which excessive amounts of sugar
are present in both the blood and urine.
Diabetes mellitus can be treated with injections
of insulin. |
10. |
Monosaccharides |
Monosaccharides
are simple sugars that have the general chemical
formula (CH2O)n.
Monosaccharides can have between 3 and 9 carbon
atoms but the most common ones have 5 or 6.
How monosaccharides are described:
Monosaccharides are classified according to the
number of carbon atoms they have:
- trioses have 3 carbon atoms,
- tetroses have 4 carbon atoms,
- pentoses have 5 carbon atoms,
- hexoses have 6 carbon atoms.
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11. |
Peptones |
Peptones are large protein fragments that result from the action of enzymes on proteins in the initial stages of breaking-up proteins. |
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12. |
Peristalsis |
Peristalsis
is a wave-like movement (motion) that progresses
along some of the hollow tubes of the body that
have circular and longitudinal muscles, such as
the intestines. Peristalsis happens involuntarily
and is induced by distension of the walls of the
tube.
What it does:
Immediately behind the distension
the circular muscle contracts. In front of the
distension the circular muscle relaxes and the
longitudinal muscle contracts - which pushes forward
the contents of the tube. |
13. |
Polypeptides |
Polypeptides
are substances whose molecules consist of three
or more amino
acids linked together by peptide bonds. (Note
that the prefix "poly-" indicates "many",
implying a structure consisting of multiple units
attached together.)
An example of a polypeptide is a protein
because all protein molecules are polypeptides. |
14. |
Proteins |
Proteins
are a category of compounds formed from the elements
carbon (C), hydrogen (H), Oxygen (O) and Nitrogen,
and in some cases also Sulphur (S) and Phosphorus
(P). There are many different protein molecules. They have complex structures formed by one or
more chains of linked amino
acids.
Why are proteins important?
Protein is one of the three main parts of the
human diet - the others being fat and carbohydrates.
Proteins are essential as chemical "building-blocks"
within the body because they form the material
structures of many tissues, muscles and organs.
Proteins are also important because of their roles
regulating bodily functions, enzymes and hormones. |
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