chapter 4 bio nutrients

Chapter 4

Nutrients

Purpose of food

•Provide energy for vital activities of the body.

•Synthesize new protoplasm; for cell growth, repair of worn out parts of the body & cell division

•Maintain health, i.e. to prevent deficiency diseases.

Nutrients in food

Carbohydrates Organic Nutrients

Fats

Proteins

Vitamins

Dietary fibre

Water Inorganic Nutrients

Mineral Salts

WaterMakes up 60% to 70% of body weight.

• Lost in urine, perspiration and breathing.

• If not replaced, body gets dehydrated.

Functions Mode of actionTransport Main part of blood and body fluid

Medium for transport of nutrients

Reactions Solvent for chemical reactionNeeded for digestion

Lubrication Part of the fluid in muscular jointPart of mucus in the alimentary canal

Homeostasis Evaporation of water, cools down the bodyPrevents overheating

Carbohydrates :-Organic compounds made up of the elements carbon, hydrogen and oxygen.

Carbohydrates

Monosaccharides Disaccharides Polysaccharides

(simple sugars) (complex sugars)

starch cellulose glycogen

Eg. Glucose Eg. Maltose

Fructose Lactose

Galactose Sucrose

Functions of carbohydrates

•Source of energy

•Form supporting structures, e.g. cellulose cell walls in plants.

•To be converted to other organic compounds such as amino acids and fats.

•Formation of nucleic acids.

•Synthesize lubricants, eg. Mucus.

•Produce nectar in flowers which attracts insects and allow cross pollination to occur.

Types of sugar:-• Simple sugars or monosaccharides

• Complex sugars or disaccharides

-sucrose (glucose + fructose)

-lactose (glucose + galactose)

-maltose (glucose + glucose)

• polysaccharides

Types of polysaccharides:-• Starch

• Glycogen

• Cellulose

monosaccharides

disaccharides

Condensation

The following equation shows how a maltose molecule can be produced from two glucose molecules.

Condensation

+

C6H12O6 glucose (simple molecule)



Condensation

+

C12H22O11 maltose (larger molecule)




Condensation

H2O water

+

+




The following equation shows how a maltose molecule can be produced from two glucose molecules. In this reaction, a molecule of water is lost. This is called a condensation reaction.

Condensation

Condensation

Definition: A condensation reaction is a chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one molecule of water.

H2O water

+

+




The following equation shows how a maltose molecule can be produced from two glucose molecules. In this reaction, a molecule of water is lost. This is called a condensation reaction.

Hydrolysis

A double sugar can be split into two single sugar molecules by using an organic molecule called an enzyme.

Hydrolysis

C12H22O11 maltose (double sugar)

A double sugar can be split into two single sugar molecules by using an organic molecule called an enzyme. For example, when a solution of maltose is mixed with the enzyme maltase,

maltase (enzyme)

Hydrolysis

+


A double sugar can be split into two single sugar molecules by using an organic molecule called an enzyme. For example, when a solution of maltose is mixed with the enzyme maltase, glucose molecules are produced.

C6H12O6 glucose (single sugar)


maltase (enzyme)

Hydrolysis

H2O water

+

+


A double sugar can be split into two single sugar molecules by using an organic molecule called an enzyme. For example, when a solution of maltose is mixed with the enzyme maltase, glucose molecules are produced. Note that a molecule of water is needed to split up the maltose molecule.



maltase (enzyme)

Hydrolysis

Hydrolysis

Definition: Hydrolysis or a hydrolytic reaction is a reaction in which a water molecule is needed to break up a complex molecule into smaller molecules.

H2O water

+

+


A double sugar can be split into two single sugar molecules by using an organic molecule called an enzyme. For example, when a solution of maltose is mixed with the enzyme maltase, glucose molecules are produced. Note that a molecule of water is needed to split up the maltose molecule.



maltase (enzyme)

Test for reducing sugars Benedict’s solution contains

copper(II) sulphate (blue). When reduced, it forms a brick-red precipitate of copper(I)oxide.

Add 2 cm3 of Benedict’s solution to 2 cm3 of test solution in a test-tube.

Shake the mixture before immersing the test-tube in a beaker of boiling water. Observe any colour changes.

The colour change can range from blue to green to yellow to brick-red or orange-red precipitate.

Test for starch

Add a few drops of iodine solution to the food sample.

The colour changes from brown to blue-black

Enzyme hydrolysis of starch

part of a starch molecule

amylase amylase amylasestarch is first broken down by amylase



maltose molecules

amylase amylase amylase

amylase enzymes break bonds, releasing maltose



maltose molecules


maltose molecules cannot be broken down by amylase

amylase amylase amylaseamylase



maltose molecules

maltase maltase maltase maltase


maltose molecules are broken down by maltase




maltose molecules

glucose molecules

further bond-breaking by maltase enzymes releases glucose

maltase maltase maltase maltase


FatsOrganic compounds made up of the elements carbon, hydrogen and oxygen, but contain lesser oxygen in proportion to hydrogen.

Functions of fats:-• As an efficient source and storage of energy.

• As an insulating material, especially beneath the skin, prevent excess heat loss.

• As a solvent for fat-soluble vitamins and many other vital substances. E.g. sex hormones.

• As a constituent of protoplasm.

• As a mean to restrict water loss from the surface of the skin.

Hydrolysis of fats

Fats can be broken down into simpler compounds by hydrolysis.

fat molecule

H O

H - C - O - C - R

=_

==

__ O

H - C - O - C - R

H

O

H - C - O - C - R

_

Hydrolysis of fats

Fats can be broken down into simpler compounds by hydrolysis. This involves the addition of water molecules (hydrolysis),

three water molecules

fat molecule

+

H O

H - C - O - C - R

=_

==

__ O

H - C - O - C - R

H

O

H - C - O - C - R

_

H2O

H2O

H2O

Hydrolysis of fats

Fats can be broken down into simpler compounds by hydrolysis. This involves the addition of water molecules (hydrolysis) and occurs readily with an enzyme or a catalyst.

catalyst


fat molecule

+

H O

H - C - O - C - R

=_

==

__ O

H - C - O - C - R

H

O

H - C - O - C - R

_

H2O

H2O

H2O

Hydrolysis of fats

Hydrolysis of fats

Fatty acids and glycerol are the products of fat hydrolysis.

Fats can be broken down into simpler compounds by hydrolysis. This involves the addition of water molecules (hydrolysis) and occurs readily with an enzyme or a catalyst.

catalyst

glycerol three fatty acid molecules


fat molecule

++

H O

H - C - O - C - R

=_

==

__ O

H - C - O - C - R

H

O

H - C - O - C - R

_

H2O

H2O

H2O

H

H - C - OH

__

_

H - C - OH

H

H - C - OH_

O

HO - C - R

==

= O

HO - C - R

O

HO - C - R

Test for fats

Add 2 cm3 of ethanol to a drop of food sample in a test tube.

Add 2 cm3 of water to the mixture. Shake the mixture.

A cloudy white emulsion is formed.

Proteins Complex organic substances containing carbon, hydrogen, oxygen and nitrogen. Sulphur and phosphorus often present.

Functions of protein:-• Essential for the synthesis of protoplasm, for growth and repair of worn-out body cells.

• Used for the synthesis of enzymes and some hormones.

• Used in the formation of anti-bodies to combat diseases.

• A source of energy.

Test for proteins

Add 2cm3 of Biuret solution to the food sample.

Shake well and allow the mixture to stand for 5 mins.

The colour change from blue to violet.

Protein Formation and Denaturation

amino acidsAmino acids are the building blocks of proteins.


polypeptides

amino acidsAmino acids link up to form polypeptides or peptones.


polypeptides

amino acidsThe bond formed between two amino acids is strong and is called a peptide bond. Peptide bonds are formed in a condensation reaction. peptide bond


polypeptides

amino acids

longer chain of amino acids

Polypeptides in turn may be linked up to form an even longer chain of amino acids.


polypeptides

amino acids


protein

The coils are held in place by weak bonds. weak bonds


polypeptides

amino acids


protein

A protein molecule is made up of one or more long chains of amino acids folded together. The chains are coiled or folded to give the protein a three-dimensional shape.


protein

weak bonds

These weak bonds are easily broken by heat and chemicals such as acids and alkalis.



protein


When these bonds are broken, the protein loses its three-dimensional shape. We say the protein has been denatured. Denaturation usually involves a loss of function of the protein.

weak bonds broken

denaturation

Why Must Proteins Be Broken Down in the Body?

protein molecule

pore on membrane

cell surface membrane

An animal cannot directly absorb the proteins it takes in because protein molecules are too large to pass through living cell surface membranes.


protein molecule

pore on membrane


An animal cannot directly absorb the proteins it takes in because protein molecules are too large to pass through living cell surface membranes.

These protein molecules must be broken down by enzymes during digestion.


Digestion is a series of hydrolytic reactions.


polypeptides

protein


The proteins are first hydrolysed into short polypeptides (or peptones).

hydrolysis (digestion)


polypeptides

amino acids

protein


The proteins are first hydrolysed into short polypeptides (or peptones).

Polypeptides are in turn hydrolysed into amino acids.




protein molecule

amino acids

pore on membrane


Amino acids are simpler and much smaller molecules than proteins. They are soluble in water and are small enough to diffuse through living membranes. Hence, they can be easily absorbed into an animal’s body.

Figure 4.16 Proteins are too large to diffuse through cell surface membranes, whereas amino acids are small enough to pass through.


polypeptides

amino acids

protein

When amino acids enter the body cells, they are linked up again to form the protein needed by the animal.


The Chemicals of Life (Concept Map)

Carbohydrates

NUTRIENTS

may beFunctions of water In animals, water: • is a medium for chemical reactions to occur; • transports digested food products, excretory products, and hormones from one part of the body to another; • is an essential part of protoplasm, lubricants, digestive juices and blood; • is essential for hydrolysis; and • helps to control body temperature.

Monosaccharides (single sugars), e.g. glucose, fructose and galactose

In plants, water: • is essential for photosynthesis; • is needed to keep plant cells turgid; • transports mineral salts from the roots to the leaves; and • transports food substances from the leaves to other parts of the plants.

WaterFats

Organic compounds made up of carbon, hydrogen and oxygen but they contain much less oxygen in proportion to hydrogen.

Organic compounds made up of carbon, hydrogen and oxygen in a ratio of 1 : 2 : 1.

Organic compounds made up of carbon, hydrogen, oxygen and nitrogen. Sulphur may also be present.

Inorganic nutrient. Water does not contain carbon.

Proteins

Disaccharides (double sugars), e.g. maltose, lactose and sucrose

Polysaccharides (complex carbohydrates) made up of many monosaccharides

e.g.

Starch

Glycogen

Cellulose • forms the cell walls in plants; and • cannot be digested by mammals, but is used as fibre in their diet.

Identification Test for reducing sugars: A reducing sugar gives a brick-red precipitate when boiled with Benedict’s solution. Sucrose is a non-reducing sugar.

• serves as the main form of storage for carbohydrates in green plants; and • gives a blue-black colour with iodine (test for starch).

• serves as the main form of storage for carbohydrates in animals and fungi.

Basic units Fats are hydrolysed to form fatty acids and glycerol.

Identification Test for fats: A cloudy white emulsion is formed in the ethanol emulsion test.

Basic units Proteins consist of amino acids linked together by peptide bonds.

Identification Test for proteins: Proteins give a violet colouration with Biuret reagent.

amino acids

polypeptides

proteins

Organic compounds.

•Required in small amounts.

• Vitamins B and C are water soluble. (cannot be stored in the body)

• Vitamins A, D, E and K are fat soluble. (can be stored in the body and not required to be consumed daily)

Vitamins Sources Function Deficiency

C FruitsPotatoesGreen Vegetables

Healthy skinStrong GumsAids in iron absorption

ScurvyBleeding gumsLoose teeth

D Fish liverFish oilDairy products

Aids in calcium absorptionBuilds teeth and bonesMaintains teeth and bones

RicketsLeads to bowlegs

Vitamins

Minerals • Inorganic, chemical elements

• Regulate body processes

• Not stored in the body (except Fe)

• Is quickly used and lost

• Body needs – calcium, phosphorus, magnesium, iodine, iron and zinc

Minerals Sources Functions Deficiency

Calcium CheeseMilkOysterGreen Vegetables

Blood clottingMuscle contractionDevelopment of strong bones

Soft bonesOsteoporosisRickets

Iron EggLegumeGreen Vegetables

Forms haemoglobinTransport oxygen

AnemiaFatigue

Fibre • Consists of carbohydrates. (mainly cellulose and lignin)

• Not digested by the human beings.

• Prevents constipation.

Sources Functions

FruitsVegetablesWholemeal breadCereals

Stimulates peristalsis.Absorbs water, making wastes softer.

Energy value of food

•Different organic food substances have different energy values.

Energy value of:-Energy value of:-

- carbohydrates is - carbohydrates is 16kJ/g16kJ/g

- proteins is 17kJ/g- proteins is 17kJ/g- fats is 38kJ/g- fats is 38kJ/g

chapter 4 bio nutrients

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