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EATING WELL
“THE CHEMISTRY OF FOOD”
If you eat a balanced diet,you are already well on the way to good health.
A healthy balanced diet can be a achieved by eating sufficent amounts of each
of the following types of food: carbohydrates, fats, proteins, fibre, vitamins,
minerals and water, ideally in as pleasant form as possible.
Progetto “SCIENCE SPEAKS ENGLISH” Classe 5B a.s. 2007/2008
THE FOOD GUIDE PYRAMID
The Food Guide Pyramid suggest
optimal nutrution guidelines for each
food category, per day, using a
mnemonic graphic of a pyramid with
horizontal dividing lines, to represent
suggested percentages of the daily
diet for each food group.
The Food Groups, according to the
Food Guide Pyramid, are:
-Bread, Cereals, Rice and Pasta
-Vegetable group
-Fruit group
-Milk, Yogurt and Cheese group
-Meat, Poultry, Fish, Dry Beats,
Eggs and Nuts group
CARBOHYDRATES
They contain the elements Crabon, Hdrogen and Oxygen; they are
included in organic compounds because they contain Carbon.
They have general molecular formula Cx(H2O)x.
Carbohydrates are produced from CO2 and H2O during photosynthesis
and are therefore the end products of the process by which plants
capture energy in sunlight.
Carbohydrates, especially starches, provide the bulk of the calories
(4kcal/g) in most diets.
Carbohydrates include:
•Monosaccharides
•Disaccharides
•Polysaccharides
Monosaccharides
Also known as “single” sugars or “simple” sugars, they are soluble and easily digested.
Monosaccharides have the general molecular formula CnH2nOn or Cn(H2O)n.
Ribose (C5H10O5) is the sugar in RNA and deoxyribose (C5H10O4)is the sugar in DNA.
Three common sugars share the same molecular formula: C6H12O6. They are:
Glucose, which is carried around the body in blood and is used by our cells and tissues
as a source of energy;
Galactose, a sugar in the disaccharide lactose;
Fructose, a sugar found in fruits, honey and others.
Ribose
Deoxyribose
Glucose
Galactose
Fructose
Disaccharides
They consist of two monosaccharides linked together: they are turned in monosaccharides
by the digestive system.
The three most common disaccharides are:
•sucrose, or cane sugar = α-glucose + β-fructose
•lactose (the main sugar in milk) = β-galactose + α-glucose
•maltose, a product of starch digestion = α-glucose + α-glucose
Polysaccharides
Monosaccharides may be bonded together to form long chains called polysaccharides.
Polysaccharides are the most abundant compounds in the biosphere. They include:
•Starches (long chains of a- glucose): they are insoluble in water and serve as energy
storage molecules in plants, particularly in seeds, tubers, etc. Rice, bread, wheat, corn
and others are the major sources of starch in the human diet. Before starches can enter
(or leave) cells, they must be digested. The hydrolysis of starch is done by amylase.
amylopectine
amylose
•Glycogen (chains of α-glucose): it is only in animal cell. Animals store extra
carbohydrates in glycogen in the liver and muscles.
•Cellulose ( a long chain of β-glucose): is the main structural component of plant cell
walls and is the most abundant carbohydrate on earth. Cellulose serves as a source of
dietary fibre since humans do not have the intestinal enzymes necessary to digest it.
LIPIDS or FATS
Fats and their compounds are known as lipids.
Amongst the various foods, fats provide the body with maximum
energy (9kcal/g), approximately twice that for an equal amount of
protein or carbohydrates. That is why the human body stores fat as an
energy source. When it needs extra fuel, our body breaks down the fat
and uses the energy.
They are compounds that are generally insoluble in water but soluble
in organic solvents (except for phospholipids).
Major roles of lipids:
They are concentrated source of energy
They are structural component of cell membranes (phospholipids)
They cushion internal organs
They transport fat-soluble vitamins A, D, E and K through the body
They play a role as messengers (hormones)
They make food taste nicer
They contain essential fatty acids, which have a positive effect on the
health of the heart and the immune system
Different kinds of lipids are:
triglycerides
phospholipids
steroids
waxes
Triglycerides
A triglyceride is made up of a molecule known as GLYCEROL which is connected to one,
two, or three FATTY ACIDS, that are long chains of carbon atoms connected to each other.
There are two kinds of triglycerides: saturated and unsaturated.
Unsaturated triglycerides have at least one double bond in one of the fatty acids.
They are usually liquid at room temperature and generally come from vegetable sources.
They are healthier alternatives to saturated fats and can be found in vegetable oils such
as sesame, sunflower, soya and olive; oily fish, such as sardines and salmon, and soft
margarine.
Saturated triglycerides have no double bonds.
They are generally solid at room temperature ans are usually from animal sources.
They can be found in lard, butter, cheese, whole milk, eggs and any thing that contains
these ingredients, such as cakes, chocolate, biscuits, pies and pastries. It is also the
white fat that can be seen on red meat.
The less saturated fat you eat, the better, since a high intake has been linked with an
increased blood level of cholesterol and an increased risk of coronary heart disease.
Steroids - Waxes
Steroids are used in animals in hormones. The basis of
a steroid molecule is a four ring structure, one with five
carbons and three with six carbons in the ring.
Waxes are used to coat and protect things in nature.
Bees make wax.
Plant leaves even have wax on outside. Plants use wax
to stop evaporation of water from their leaves.
PROTEINS
Proteins are needed regularly by the body for
growth, and also for the repair and
replacement of cells; what’s more, proteins
play many important functions in our body. The
main sources of dietary proteins are meat, fish,
eggs, milk, cheese, pulses, etc.
Proteins contain Carbon, Hydrogen, Oxygen,
Nitrogen and sometimes sulphur. Proteins
consist of smaller units called amino-acids,
which link together to form chains.
Some amino-acid are created by our body, but
those called essential amino-acids must come
from our diet.
Although all animal and plant cells contain
some protein, the amount and the quality of
the proteins varies a lot.
The functions of proteins
Proteins are truly the physical basis of life, since every function in the
living cell depends on them:
the structure of cells and tissues is largely made of protein
the catalysis of all biochemical reactions is done by enzymes, which are
proteins
the transport of materials in body fluids depends on proteins
proteins are important in motion and locomotion of cells and organisms
the receptors for hormones and other signalling molecules are proteins
proteins, such as antibodies, play an important role in defending our
body
Structrures of the body formed from proteins
Hair and nails are made of keratins which are long
protein chains containing a high percentage (15-17 %)
of the amino-acid cysteine.
Collagen is the most common protein in the body and
comprises approximately 20-30% of all body proteins.
It is found in tendons, ligaments, and many tissues
that serve structural or mechanical functions.
Collagen consists of amino-acid sequences that coil
into a triple helical structure to form very strong fibres.
Tooth enamel and bones consist of protein matrix
(mostly collagen) with dispersed crystals of minerals
such as phosphate of calcium.
Muscle tissue consists of approximately 65% actin and
myosin, which are the contractile proteins that enable
muscle movement.
ENZYMES
Enzymes are sometimes called biological catalysts because they speed up
reactions, and only small amounts are required.
Digestive enzymes speed up the breakdown of complex food substances into simpler
subunits. The breakdown of food in digestion is actually caused by water chemically
splitting the complex food molecules, a process called hydrolysis. Digestive enzymes
do not break down foods into the elements they are made of, and they do not release
any energy from the food. This happens when the simpler food substances are
respired in the individual cells.
Enzymes names usually end in the letters –ase, as in amylase, protease and lipase.
The enzyme amylase is in the saliva, and is released as soon as we put food into our
mouths. Amylase digests starch molecules (long chains), cutting them up into the
shorter molecules of maltose. Another group of enzymes breaks disaccharides down,
turning them into simple sugars. Protease digests proteins cutting them up into
smaller chains of amino-acids and eventually into individual amino-acids; lipase
digests lipids (it cuts triglycerides up into fatty acid molecules and glycerol).
maltase
maltose
sucrase
amylase
starch
glucose + glucose
maltose
sucrose
glucose + fructose
lactase
lactose
galactose + glucose
There are two main types of enzymes. Digestive enzymes are extra-cellular
enzymes: they control reactions that take place outside cells. Those enzymes
which control reactions inside cells are called intracellular enzymes.
Enzymes intervene in chemical reactions by locking onto one of the reactants
and speeding up the reaction. The chemical which the enzymes locks onto is
called the substrate, and enzyme has a kind of chemical sensor, called
active site, which helps it to recognise the substrate. Just like a key fits into a
specific lock, each enzyme has its own specific substrate. Once the reaction
is completed and the required product has been produced, the enzyme
releases itself and moves on to the next reaction.
VITAMINS
Vitamins are organic substances found in plants and animals. Most of them
can not be made by our body, so they must be taken from our diet.
Nutritionists have divided vitamins into two groups: fat-soluble and watersoluble.
The fat-soluble vitamins - A, D, E and K - are transported through the body
by fat. They can also be stored in fat and liver cells for a limited period of time.
The water-soluble vitamins - B and C – are absorbed by and and trasported
through our body in water. They need to be eaten every day, as they can not
be stored for any length of time.
A fat-soluble vitamin:
The vitamin D helps our body absorb calcium,
needed to ensure strong bones and teeth.
The most important source is the sun, but it’s also
found in tiny amounts in dairy products, cod liver oil
and oily fish.
A water-soluble vitamin:
The vitamin C helps our body produce
collagen and absorb iron.
We can found it in a wide variety of
vegetables and fruit, including spinach,
broccoli, tomatoes, strawberries, citrus
fruit and potatoes.
MINERALS
Minerals have an important role to play in our good health.
They are inorganic substances, since they are found in the rocks and soil.
Vegetables absorbe mineral goodness as they grow, while animals digest it
through their diet.
Like vitamins, minerals can also be divided into two groups: those that are
needed in minute quantities and those that are needed in larger quantities.
The latter are the major minerals and include calcium, magnesium,
sodium, potassium and phosphorus.
The former are called trace minerals; this group include iron, zinc, iodine,
selenium and copper.
The importance of calcium
Calcium is a mineral that strengthens bones and
teeth and makes sure that everything runs smoothly
with muscles and nerves.
It’s especially important for growth because it can
continue to add to the strength of our bones until
you reach the age of 30-45, when peak bone mass
is reached. After this point, as a natural part of the
ageing process, your bones lose their density and
grow weaker. If people have not had enough
calcium in their diet prior to this, there is an
increased risk that bones will not be strong enough
to cope with any weakening, which can result in
osteoporosis.
Health professionals estimate that one in three
women and one in ten men suffer from
osteoporosis, and there is concern that the diets of
teenage girls and young women, in particular, are
not high enough in calcium.