biological molecules

Question 1

Answer 1

Question 2

Most of the molecules in living organisms fall into three categories:

Answer 2

carbohydrates, proteins and lipids

Question 3

These all contain..and so are described as … molecules

Answer 3

carbon

organic

Question 4

carbohydrates

Answer 4

Long chains of simple sugars

Glucose is a simple sugar ( a monosaccharide)

When 2 glucose molecules join together maltose is formed (a disaccharide)

When lots of glucose molecules join together starch, glycogen or cellulose are formed (a polysaccharide)

Glycogen, cellulose and starch are all made from glucose molecules

Question 5

Fats

Answer 5

Most fats (lipids) in the body are made up of triglycerides

Their basic unit is one glycerol and three fatty acids

The fatty acids vary in size and structure

Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)

Question 6

Proteins

Answer 6

Long chains of amino acids

There are about 20 different amino acids

They all contain the same basic structure but the ‘R’ group is different for each one

When amino acids are joined together a protein is formed

The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins

Even a small difference in the order of the amino acids results in a different protein being formed

Question 7

Protein Shape

Answer 7

There are thousands of different proteins in the human body and other organisms

Many of these proteins are different shapes and the shape often has an important effect on the function of the protein

For example:

Enzymes have an area in them known as the active site – this is important as this is the place where another molecule fits into the enzyme in order for a reaction to take place

If the shape of the active site does not match the shape of the molecule that fits into it, the reaction will not take place

Every enzyme has a different shaped active site

Antibodies are proteins produced by certain types of white blood cell to attach to antigens on the surface of pathogens

The shape of the antibody must match the shape of the antigen so that it can attach to it and signal it for destruction

The different sequences of amino acids cause the polypeptide chains to fold in different ways and this gives rise to the different shapes of proteins

In this way every protein has a unique 3-D shape that enables it to carry out its function

Question 8

Test for Glucose (a reducing sugar)

Answer 8

Add Benedict’s solution into sample solution in test tube

Heat at 60 – 70 °c in water bath for 5 minutes

Take test tube out of water bath and observe the colour

A positive test will show a colour change from blue to orange or brick red

Testing for glucose using Benedict’s solution

Question 9

Test for Starch

Answer 9

Add drops of iodine solution to the food sample

A positive test will show a colour change from brown to blue-black

Testing for starch using Iodine solution

Question 11

Test for Protein

Answer 11

Add drops of Biuret solution to the food sample

A positive test will show a colour change from blue to violet / purple

Question 12

Test for Fat

Answer 12

Food sample is mixed with 2cm3 of ethanol and shaken

The ethanol is added to an equal volume of cold water

A positive test will show a cloudy emulsion forming

Question 13

Test for vitamin C

Answer 13

Add 1cm3 of DCPIP solution to a test tube

Add a small amount of food sample (as a solution)

A positive test will show the blue colour of the dye disappearing

Question 14

When describing food tests in exam answers, give the …colour of the solution and the colour it changes to for a …

Answer 14

starting

positive result

Question 15

Describing DNA structure

Answer 15

NA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms

It consists of two strands of DNA wound around each other in what is called a double helix

Question 16

The individual units of DNA are called

Answer 16

nucleotides

Question 17

Answer 17

Question 18

bases of DNA

Answer 18

There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)

The bases on each strand pair up with each other, holding the two strands of DNA in the double helix

The bases always pair up in the same way:

Adenine always pairs with Thymine (A-T)

Cytosine always pairs with Guanine (C-G)

Question 19

The phosphate and sugar section of the nucleotides form

Answer 19

the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder

Question 20

It is this sequence of bases that

Answer 20

holds the code for the formation of proteins

Question 21

importance of water

Answer 21

Water is important as a solvent in the following situations within organisms:

Dissolved substances can be easily transported around organisms – eg xylem and phloem of plants and dissolved food molecules in the blood

Digested food molecules are in the alimentary canal but need to be moved to cells all over the body – without water as a solvent this would not be able to happen

Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine

Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells