Biological molecules:

Question 1

What is the structure and function of amylose?

Answer 1

Made up of α-glucose

Straight chain

Tends to coil up

Plant storage polysaccharide

Question 2

What is the structure and function of cellulose?

Answer 2

Made up of β-glucose joined by 1,4 bonds in a chain no branches.

Alternate glucose subunits are inverted

Forms straight chains which form fibres with hydrogen bonding between chains

The β-glycosidic bond can only be broken down by a cellulose enzyme, which herbivores have, but humans do not

Forms plant cell walls

Question 3

Function of glucose:

Answer 3

Used in respiration to release energy and cause the formation of ATP

Easily converted into glycogen for storage

Soluble in water, lowers water potential, causes osmotic problems.

Question 4

Function of Amylose:

Answer 4

Insoluble in water so does not affect the water potential of the cell so excellent for storage.

Question 5

Function of cellulose

Answer 5

Hundreds of the polysccharide chains lie side by side forming hydrogen bond cross links with each other- forms a very strong structure

The arrangement of macrofibrils in cell walls:
allows water to move through cell walls, allows water to move in and out of cells easily, prevents cells bursting when turgid and determines how a cell can grow or change shape

Cell walls can be reinforced with other substances to provide extra support, or make the walls waterproof

Question 6

Function of glycogen

Answer 6

Highly branched so it can be hydrolysed into glucose very quickly due to lots of branches for enzymes to attach

Insoluble so does not affect the water potential of the cell

Compact molecule therefore high energy content for its mass

Question 7

Structure of a Triglyceride

Answer 7

Glycerol plus three fatty acids

joined by 3 ester bonds between the fatty acids and the glycerol

Question 8

What is a saturated fatty acid?

Answer 8

In animals the fatty acids are saturated (few or no double bonds) and the triglycerides are more solid

Question 9

What is an unsaturated fatty acid?

Answer 9

In plants the fatty acids are unsaturated (many double bonds) and the triglycerides are oils

Question 10

Structure of a phospholipid

Answer 10

Glycerol plus two fatty acids and a phosphate group, joined by 2 ester bonds

Question 11

What is esterification?

Answer 11

Formation of an ester bond.

Question 12

Functions of a triglyceride

Answer 12

Compact energy store
Insoluble in water
Does not affect cell water potential
Stored as fat providing insulation and protection
Provides buoyancy
Provides waterproofing (on feathers, leaves)
Source of water (from respiration – camel’s humps)
Provides electrical insulation around neurons
Helps in the absorption of fat soluble / A / D / E / K, vitamins

Question 13

Function of a phospholipid

Answer 13

Part hydrophilic (head), part hydrophobic (tail), so ideal basis for cell surface membranes

Phosphate may have carbohydrate attached forming glycolipids involved in cell signalling

Question 14

Structure and function of cholesterol

Answer 14

It’s positioned between the phospholipids and it adds fluidity and stability to the membrane. It maintains the fluidity at low temperatures but also stops it becoming too fluid at high temperatures

Question 15

What is the primary structure of a protein?

Answer 15

The sequence of amino acids found in a protein molecule

Question 16

What is the secondary structure of a protein?

Answer 16

The coiling or folding of parts of a protein molecule (localised folding) due to the formation of hydrogen bonds as the protein is synthesised. The main forms are the α-helix and the β-pleated sheet.

Question 17

What is the tertiary structure of a protein?

Answer 17

The overall three-dimensional structure of a protein molecule. It is the result of interactions between the R groups of different amino acids in parts of the protein molecule such as:
hydrogen bonding between R groups
formation of disulfide bridges between 2 cysteine amino acids
hydrophobic interactions (hydrophobic R groups tend to associate together in the middle of the molecule away from the aqueous environment)
hydrophilic interactions (hydrophilic R groups tend to associate with water molecules in the cell and so become arranged on the outside of the molecule)
ionic interactions occur between R groups with opposite charges

Question 18

What is the quaternary structure of a protein?

Answer 18

Protein structure where a protein consists of more than one polypeptide chain. Haemoglobin has a quaternary structure as it is made up on four polypeptide chains. Not all proteins have a quaternary structure

Question 19

Structure and function of a fibrous protein (collagen):

Answer 19

Fibrous proteins are long strands of polypeptide chains that have cross-linkages due to hydrogen bonds
These proteins have little or no tertiary structure
Due to a large number of hydrophobic R groups, fibrous proteins are insoluble in water
Fibrous proteins have a limited number of amino acids with the sequence usually being highly repetitive
The highly repetitive sequence creates very organised structures that are strong

Question 20

Structure and function of a globular protein (haemoglobin):

Answer 20

Globular proteins are compact, roughly spherical (circular) in shape and soluble in water
Globular proteins form a spherical shape when folding into their tertiary structure because:
their non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings and
their polar hydrophilic R groups orientate themselves on the outside of the protein