Chemicals of life

Overview

All cells are made up of a variety of substances some of which organic while others are inorganic. Water forms the largest component and is also a medium for all reactions in the cell. The other substance includes acids, bases, salts, vitamins, carbohydrates, lipids, and proteins. There are enzymes and nucleic acids which perform a variety of functions.

Water

This is the most abundant compound, typically making up of 60-95% the fresh mass of an organism.

Uses of water

• It makes up structures of an organism
• It is a solvent
• It is a reagent in the hydrolysis
• Provide support for aquatic organism
• It is a medium of fertilization through which gametes swim.
• Medium for the removal of waste products
• Temperature control
• Hearing and balance as endolymph 

Uses of water to the plants

• Aid seed dispersal
• Provide support to herbaceous plants
• Breaks up the testa of seed during germination
• Reagent in photosynthesis
• Loss of water through the leaves cools the plant.
• Medium of fertilization

Uses of water to the animals

• A medium of transport
• Evaporation cools the animal
• Lubricates joints, eyes, lungs
• A constituent of protecting fluids such as tears, mucus.

Carbohydrates

Carbohydrates are food substances with a general formula (CH₂O)_n where n is a natural number. They are energy giving foods.

Classification

• Monosaccharides e.g. glucose, galactose, and fructose

Sources: honey, fruits

Properties

• They are sweet
• Are soluble in water
• They reduce blue copper II ions to red precipitates in an alkaline medium.

Testing for reducing sugars

When boiled with Benedict’s or Fehling’s solutions the color changes from blue to green to yellow to oranges ppt.

• Disaccharides

They are made of two simple sugars as shown in the table below

.

Disaccharides	Composition	Source
Maltose	glucose + glucose	malt
Lactose	Glucose + galactose	milk
Sucrose	Glucose + fructose	Sugar cane Sugar beets
Cellobiose	Glucose + glucose	wood

Testing for non-reducing sugars

1. When boiled with Benedict’s solution or Fehling’s’ solution, the color remains blue.

• When boiled with HCl, the solution cooled, neutralized by NaOH, boiled Benedict’s or Fehling’s solution, the color changes from green to yellow to orange.

HCl hydrolyzes non-reducing sugars

NaOH neutralizes the excess acid because Benedict’s or Fehling’s solution does not work in acidic medium.

Polysaccharide (CH₂O)n

These are made of very many monosaccharides per unit molecule e.g. starch and cellulose

Testing for starch

It changes the color of iodine black or blue.

Functions of carbohydrates

1. Glucose, galactose, and fructose are oxidized to release energy in the body
   1. Glyceraldehyde is an intermediate molecule in photosynthesis.
   1. Ribose is a component nucleotide.
   1. Sucrose is a form in which carbohydrates are transported in plants
   1. Lactose is a source of energy in milk
   1. Storage of energy (starch in plants, glycogen in animals, inulin is some plants like Dahlia)
   1. Formation of cellular structures (cellulose in plant cell walls, chitin is

Lipids

Lipids are made of fats and oils. Fats are solids at room temperature while oils are liquids at room temperature

Uses of lipids

Structural functions

• Makeup cell membrane
• Protection: lipids are constituents of the waxy cuticle of plants and insects
• Lipids are water repellant thus prevent water loss from or entry into an animal skin
• Their spongy nature protects delicate organs as shock absorbers.
• Being bad conductors, they reduce water loss from the body when deposited beneath the skin for insulation
• Storage; they are better storage compounds than carbohydrates due to high calories value, due to high hydrogen content, they are light, insoluble in water, compact to fit in a small volume, and are easily used when required.

Physiological functions

• Source of metabolic water
• Store fat-soluble vitamins (ADEK)
• Source of metabolic water
• Raw materials for hormones

Testing for lipids

1. They form a translucent mark on the paper that does not disappear when the paper is dried on a flame.
2. Emulsion test

When 2cm³ of fats or oil are dissolved in 2cm³ of absolute ethanol followed by water, a white cloudy suspension is formed.

• Sudan III

When a few drops of Sudan III are added to a mixture of 2cm3 of water and 2 cm3 of oil and shaken, a red-stained oil layer separates out.

Advantage of storing fats over carbohydrate

• Has high energy content than carbohydrates
  • It is lighter
  • It is compact and requires less space
  • It is a raw material for hormones
  • Insoluble in water that they have low osmotic value

Proteins

These are classified into two groups

• Structural proteins: insoluble proteins that makeup body structures like bones and muscles. Fibrinogen is a soluble structure protein used in blood clotting.
• Globular proteins are soluble proteins such as enzymes, antibodies, hormones, and so on.

Composition of proteins

The basic unit of proteins is amino acids

There are about 22 different amino acids in the body of which isoleucine, leucine, methionine, phenylamine, proline, threonine, and valine cannot be synthesized in the human body and they are referred to as essential amino acids.

Uses of proteins

• Makeup structures, e.g., collagen make up connective tissues.
• Makeup enzymes such as catalyze and amylase.
• Are constituent of hormone such as insulin
• Are constituents of antibodies that protect the body from foreign particles.
• Makeup muscles such as myosin and actin
• They are storage food e.g. egg white
• Constitute toxins such as snake venom for protection.

Testing for proteins

1. They coagulate on heating
2. They coagulate on the addition of Melon’s reagent and on heating they form a pink precipitate.
3. They form a purple color when mixed with an equal  amount of NaOH followed by 3 drops of copper sulphate solution.

Vitamins

Specific objects

The learner should be able to:

1. State the type of vitamins i.e., water-soluble and fat-soluble; essential and nonessential.
   1. State the importance of vitamins in organism
   1. Test for vitamin C.
   1. Demonstrate the effect of over boiling vegetables
   1. Demonstrate the effects of storage on the quality of fresh food.

Vitamins are complex organic compounds present in very small quantities in natural food which are essential for good healthy body and maintains its normal metabolic activities. Some vitamins are fat-soluble (ADEK) while others are not.

                Vitamin C / ascorbic acid

Sources: citrus fruits, green vegetables, potatoes, tomatoes, etc.

The function of vitamin C

Concerned with the metabolism of connective tissues and the production of strong skin.

Deficient disease: anemia and scurvy: the germs bleed, wounds fail to heal.

Testing for Vitamin C

It decolorizes DCPIP.     

Other vitamins and their deficient diseases

Vitamin
A	Night blindness
K	Delayed clotting
E	Reduced fertility in rats

Functions of vitamins

• protect the body against diseases
• formation of a coenzyme that facilitates enzyme reactions
• blood clotting
• components of visual pigment

For questions and answers download PDF

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Compiled by Dr. Bbosa Science