Biological molecules 2018

DNA

A DNA molecule looks like a twisted ladder, with two long strands parallel to one another with bases in between forming cross links; we call this shape a double helix.

There are four types of bases, we give them letters A, T, C and G.Base A always pairs with T while base C always pairs with G. The sequence of these bases codes for the sequence of amino acids that make up proteins, different sequences code for different characteristics.

Carbohydrate molecules contain: C, H, O

H:O is 2:1 like in water molecule

Made up of smaller molecules : sugars or monosaccharides.

e.g. glucose, fructose … we call them simple sugars

Two sugars bonded together are called disaccharides e.g. maltose, lactose, sucrose.

Many sugars bonded together make a polysaccharide

e.g. starch, cellulose, glycogen.

Carbohydrates are a source of energy to our bodies.

Carbohydrates

Plant cells for storage

Plant cell wallsFor support

Animal cells for storage

Starch granules in cells

Food rich in carbohydrates

We use Iodine solution (I2/KI), which is a yellowish

brown solution that turns to a blue-black colourwhen it reacts with starch

To test for starch

We use Benedict’s solution to test for reducing sugars. It is a Blue solution, when a reducing sugar is mixed with Benedict’s solution and boiled it forms a precipitate that is green, yellow, orange or brick red.

To test for reducing sugars

Protein molecules contain elements: C,H,O,N (S,P)

Proteins are made of smaller molecules called amino acids.

Two amino acids bonded together are called dipeptides.

Many amino acids bonded together make a polypeptide.

Proteins are needed to make:

1. Enzymes

2. Haemoglobin

3. Muscles fibers

4. Hair and nails (Keratin)

5. Cell membranes of cells

6. As a source of energy during starvation.

Proteins

Food rich in protein

We use NaOH and CuSO4

(Biuret solution) that has a pale blue colour, when it reacts with proteins it changes its colour to lilac, or purple or mauve.

To test for proteins

Fat molecules contain elements: C,H,O

Each fat molecule contains one glycerol and three fatty acids

Fats are needed to:

1. Make cell membranes of cells

2. Good energy storage

3. Act as a heat insulator under the skin

4. Protect some organs

Fats

Foods rich in fat

Add Ethanol to the sample

then shake vigorously to dissolve the fat, then add water. A milky/cloudy appearance is formed.

To test for fats

There are many vitamins known to us by now, we will

study vitamin C and vitamin D as examples.

Vitamin C, the first discovered vitamin, is needed by the body to make an important protein called collagen that toughens the skin, walls of blood vessels and bones.

Lack of vitamin C causes inability to form collagen fibres which gives strength to blood vessels and skin.

Deficiency symptoms: bleeding gums, skin ulcers.

Deficiency disease: scurvy

Vitamins

Citrus fruits

Bell peppers

Dark leafy vegetables

Tomatoes, guava

Broccoli, grapes

Foods rich in vit. C

Use DCPIP a blue stain that becomes colourless

when reduced.

To compare the amount of ascorbic acid (vit. C) we

can count the number of drops (or …) needed to change the blue DCPIP into colourless.

To test for Vitamin C

Your body must have vitamin D to

absorb calcium and promote bone growth. Too little vitamin D results in soft bones in children (rickets) and fragile bones in adults (osteoporosis).

Vitamin D

Fish especially fish oil

Milk and milk products

Egg yolk

Mushrooms

Our skin can make vit. D when exposed to sunlight

Vitamin D