Biological Molecules

Question 1

name three examples of monomers found in carbohydrates

Answer 1

glucose, fructose, galactose

Question 2

what is maltose made of

Answer 2

alpha glucose + alpha glucose

Question 3

What types of molecules are reducing sugars?

Answer 3

All monosaccharides and some disaccharides

Question 4

how does cellulose differ from starch

Answer 4

cellulose: beta glucose, bonds form above and below, hydrogen bonding between straight chains which are branched. Starch: made from alpha glucose, arranged in a helix shape, unbranched

Question 5

test for starch

Answer 5

add iodine solution: starch = orange to blue/black

Question 6

how does alpha glucose differ from beta glucose (structure

Answer 6

the H and OH groups on c1 are switched (OH on bottom for alpha glucose)

Question 7

test for presence of reducing sugars

Answer 7

benedicts solution + heat = red solution

Question 8

test for non reducing sugars:

Answer 8

add HCl (hydrolyses bonds) + HEAT + sodium hydrogen carbonate (neutralizes acid) and then carry out regular test with benedicts solution.

Question 9

How do the features of cellulose relate to it’s function?

Answer 9

Straight chains of Beta glucose form many hydrogen bonds between them forming microfibrils which provide collective strength for its role as structural support for plant cells.
Cellulose is also insoluble.

Question 10

Describe the structure of a triglyceride and explain how it forms.

Answer 10

Three fatty acids joined to a glycerol molecule by condensation reactions to form ester bonds.

Question 11

What’s the difference between a saturated, monounsaturated and polyunsaturated fatty acids?

Answer 11

Saturated fatty acids contain only single bonds between carbons
monounsaturated fatty acids contain one double bond between two of the carbons in the chain
polyunsaturated fatty acids contain more than one double bond between carbons in the chain

Question 12

What are the important properties of triglycerides?

Answer 12

They contain lots of energy making it good for storage

Insoluble so they don’t affect water potential

Question 13

How could you test for the presence of lipids?

Answer 13

Shake the sample with ethanol, add to water. A milky emulsion indicates that lipids are present.

Question 14

How does a dipeptide form?

Answer 14

A peptide bond forms directly between the N of the amine group of one amino acid and the C of the carboxyl group of another amino acid, with the loss of H from the amine group and OH from the carboxyl group to form water in a condensation reaction.

Question 15

What is meant by the term ‘secondary structure’?

Answer 15

Formation of hydrogen bonds between amine and carboxyl groups of amino acids within the polypeptide chain to form either alpha helix or beta pleated sheet.

Question 16

What is meant by the term ‘tertiary structure’?

Answer 16

Folding of the polypeptide chain by the formation of hydrogen bonds, ionic bonds and disulphide bridges between R groups of amino acids to give the chain a 3D shape.

Question 17

What is meant by the term ‘quaternary structure’?

Answer 17

Some proteins consist of more than one polypeptide and some are associated with non-protein prosthetic groups to make them functional.

Question 18

How could you test for the presence of proteins?

Answer 18

Biuret test – add sodium hydroxide followed by copper II sulphate solution. The presence of protein will cause a colour change from blue to purple.

Question 19

Describe the induced fit model

Answer 19

The active site changes shape and moulds around the substrate to become complementary as they bind. changing shape of the active site holds them close together, reducing any repulsion between them.

Question 20

Why is the rate of an enzyme catalysed reaction slower when the pH is lower than the optimum?

Answer 20

The presence of H+ ions when the pH is low disrupts some of the ionic and hydrogen bonds in the enzymes active site causing it to change shape and denature.

Question 21

How do competitive inhibitors reduce enzyme activity?

Answer 21

Competitive inhibitors bind to the active site of an enzyme, preventing the substrate from binding.

Question 22

How can the effect of competitive inhibitors be reduced?

Answer 22

Increasing the concentration of substrate increases the chance of substrate binding to active sites.

Question 23

How do non-competitive inhibitors reduce enzyme activity?

Answer 23

Non-competitive inhibitors bind to a region on the enzyme other than the active site. This disrupts the tertiary structure causing the enzyme and therefore the active site to change shape.