Biological Molecules

Question 1

Define the terms:
1. Monomer
2. Polymer
3. Macromolecule
4. Monosaccharide
5. Disaccharide
6. Polysaccharide

Answer 1

1. a simple molecule which is used a building block for the synthesis of a polymer; many monomers are joined together by covalent bonds. Examples are monosaccharides, amino acids and nucleotides.
2. a giant molecule made from many similar repeating subunits (monomers) joined together in a chain. Examples are polysaccharides, proteins and nucleic acids.
3. a large molecule such as a polysaccharide, protein or nucleic acid.
4. a molecule consisting of a single sugar unit and with the general formula (CH2O)n.
5. a sugar molecule consisting of two monosaccharides joined together by a glycosidic bond.
6. a polymer whose subunits are monosaccharides joined together by glycosidic bonds.

Question 2

What are the two major functions of monosaccharides?

Answer 2

The two major functions of monosaccharides are:
1. Source of energy in respiration: They contain many carbon-hydrogen bonds that release energy when broken, which is used to produce ATP.
2. Building blocks for larger molecules: For example, glucose is used to form polysaccharides like starch, glycogen, and cellulose, while ribose is used to make RNA and ATP and deoxyribose is used to make DNA.

Question 3

What are the monosaccharides used to make these disaccharides?
• Maltose
• Sucrose
• Lactose

Answer 3

1. Maltose (a-glucose + a-glucose)
2. Sucrose (a-glucose + b-fructose)
3. Lactose (b-glucose + b-galactose)

Question 4

Why is it important for living organisms to store glucose in an appropriate form?

Answer 4

1. If glucose accumulates, it would dissolve and make the cell contents too concentrated, affecting osmotic properties.
2. Glucose is reactive and would interfere with normal cell chemistry.

Question 5

How do living organisms avoid problems caused by glucose accumulation?

Answer 5

They convert glucose into storage polysaccharides through condensation reactions. These polysaccharides are compact, inert (unreactive), and insoluble.

Question 6

What are the storage polysaccharides in plants and animals?

Answer 6

• Plants: Starch
• Animals: Glycogen

Question 7

How is amylose structured?

Answer 7

• Made by condensation of α-glucose molecules.
• Composed of long, unbranching chains of 1,4 linked glucose molecules.
• Chains are curved and coil into helical structures, making the molecule compact.

Question 8

How is amylopectin structured?

Answer 8

• Composed of shorter chains of 1,4 linked α-glucose molecules.
• Contains 1,6 linkages that form branches extending from the main chain.

Question 9

How is glycogen structured?

Answer 9

• Structurally similar to amylopectin.
• Composed of chains of 1,4 linked α-glucose with 1,6 linkages creating branch points.

Question 10

What is the main difference between amylose and amylopectin?

Answer 10

• Amylose: Long, unbranching chains of 1,4 linked glucose.
• Amylopectin: Shorter chains of 1,4 linked glucose with 1,6 branch points.

Question 11

What is the main structural difference between cellulose and starch/glycogen?

Answer 11

• Cellulose is a polymer of β-glucose.
• Starch and glycogen are polymers of α-glucose.

Question 12

Why is the tensile strength of cellulose important for cells?

Answer 12

• It allows cells to withstand the large pressures caused by osmosis without bursting.
• These pressures make tissues rigid and support the plant.

Question 13

Describe the structure of cellulose.

Answer 13

• polymer of B- glucose
• joined by 1-4 glycosidic bonds and the glucose units are linked at 180 to each other
• unbranched

Question 14

Explain why cellulose is suitable as a component of plant cell walls.

Answer 14

• molecules form fibrils and fibres
• hydrogen bonding between molecules
• gives strength to cell wall to prevent cell bursting
• cellulose molecule is straight chain and allows molecules to lie parallel to each other

Question 15

What makes a fatty acid unsaturated?

Answer 15

A fatty acid is unsaturated if its carbon tail has double bonds between neighboring carbon atoms, meaning it does not have the maximum possible amount of hydrogen.

Question 16

How do double bonds affect the properties of fatty acids and lipids?

Answer 16

Double bonds make fatty acids and lipids melt more easily.

Question 17

What is the difference between animal and plant lipids?

Answer 17

• Animal lipids are often saturated (no double bonds) and occur as fats.
• Plant lipids are often unsaturated (contain double bonds) and occur as oils.

Question 18

What is an ester bond or ester linkage?

Answer 18

It is the chemical link between an acid and an alcohol formed during the reaction that produces an ester.

Question 19

Why are triglycerides insoluble in water?

Answer 19

Triglycerides are insoluble in water because their hydrocarbon tails are non-polar and hydrophobic, meaning they do not mix freely with water molecules.

Question 20

In which type of solvents are triglycerides soluble?

Answer 20

Triglycerides are soluble in organic solvents, such as ethanol.

Question 21

Why are triglycerides excellent energy stores?

Answer 21

They are rich in carbon-hydrogen bonds, which yield more energy on oxidation compared to the same mass of carbohydrates, giving them a higher calorific value.

Question 22

What additional function do triglycerides serve when stored below the skin?

Answer 22

They act as an insulator, reducing heat loss.

Question 23

How do triglycerides act as a metabolic source of water?

Answer 23

When oxidised in respiration, triglycerides are converted to carbon dioxide and water, which can be important in dry habitats.

Question 24

What is the primary structure of a protein?

Answer 24

The particular amino acids contained in the chain, and the sequence in which they are joined, is called the primary structure of the protein.

Question 25

What is the secondary structure of a protein?

Answer 25

The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an a-helix or ß-pleated sheet).

Question 26

What can break the hydrogen bonds in α-helix and β-pleated sheet structures?

Answer 26

High temperatures and pH changes can easily break these hydrogen bonds.

Question 27

What is the tertiary structure of a protein?

Answer 27

The compact structure of a protein molecule resulting from the three-dimensional coiling of the chain of amino acids.

Question 28

What are the four types of bond that help to keep folded molecules in their precise shapes.

Answer 28

• Hydrogen bonds - can form between R groups. • Disulphide bonds - form between cysteine molecules. They are strong covalent bonds. They can be broken by reducing agents. • Ionic bonds - form between ionised amino groups and ionised carboxylic acid groups. They can be broken by pH changes. • Weak hydrophobic interactions - occur between non-polar R groups. Although the interactions are weak, the groups tend to stay together because they are repelled by the watery environment around them.

Question 29

What is the quaternary structure of a protein?

Answer 29

The three dimensional arrangement of two or more polypeptides.

Question 30

What type of protein is haemoglobin, and is it soluble in water?

Answer 30

Haemoglobin is a globular protein and is soluble in water.

Question 31

How many polypeptide chains make up haemoglobin, and what is this structural level called?

Answer 31

Haemoglobin is made up of four polypeptide chains, giving it a quaternary structure.

Question 32

What are the two types of globin that make up haemoglobin and how are the polypeptide chains arranged?

Answer 32

The two types of globin are alpha-globin (α-globin) and beta-globin (β-globin) and contains two α-globin chains (α chains) and two β-globin chains (β chains).

Question 33

What is the shape of the haemoglobin molecule, and how are the R groups arranged?

Answer 33

Haemoglobin is nearly spherical. The hydrophobic R groups point inward, while the hydrophilic R groups point outward.

Question 34

Why are hydrophobic and hydrophilic R groups important in haemoglobin?

Answer 34

Hydrophobic R groups help maintain haemoglobin’s three-dimensional shape, while hydrophilic R groups on the surface maintain its solubility.

Question 35

What genetic condition results from a change in an amino acid in the β-globin chain, and what amino acid substitution occurs?

Answer 35

Sickle cell anaemia results from the substitution of valine (non-polar) for glutamic acid (polar) in the β-globin chain.

Question 36

How does the amino acid substitution in sickle cell anaemia affect haemoglobin?

Answer 36

The substitution reduces the solubility of haemoglobin, leading to the symptoms of sickle cell anaemia.

Question 37

What is a prosthetic group, and which prosthetic group is found in haemoglobin?

Answer 37

A prosthetic group is a non-amino acid component that is a permanent part of a protein. Each polypeptide chain in haemoglobin contains a haem group as its prosthetic group.

Question 38

Describe the structure of a cellulose molecule and a cellulose microfibril.

Answer 38

Cellulose molecule • B-glucose joined by 1,4 glycosidic bonds • adjacent monomers rotated through 180° • straight chain Cellulose microfibril • parallel molecules of cellulose • hydrogen bonds, between molecules • staggered starts and ends

Question 39

Describe the structure of a collagen molecule.

Answer 39

• three polypeptide chains form triple helix • hydrogen bonds hold the three polypeptides together • the three polypeptides are tightly wound • every third amino acid in the polypeptide chain is glycine • glycine is found on the inside of each polypeptide

Question 40

Compare fibrous and globular proteins. 

Answer 40

Fibrous - 3 polypeptides - haem is absent - insoluble in water - provides high tensile strength - structural protein Globular - 4 polypeptides - haem is present - soluble in water - oxygen transport - functional protein Similarities - polymers - proteins - have quaternary structure - biological molecules 

Question 41

Compare phospholipids and triglycerides. 

Answer 41

Phospholipids - partially soluble - 2 fatty acid chains - 2 ester linkage - polar - has a phosphate head Triglycerides - insoluble - 3 fatty acid chains - 3 ester linkage - non-polar - doesn’t have a phosphate head Similarities - both are fats/lipids - both are biological molecules - both have fatty acid chains that are hydrophobic - both have hydrophobic and hydrophilic parts - both can be saturated and unsaturated - both have glycerol molecules and ester linkage 

Question 42

Explain why water is important as a solvent.

Answer 42

Water is an excellent solvent because its molecules are attracted to ions and polar molecules, allowing them to dissolve and move freely. This is essential for biochemical reactions, as most processes in living organisms occur in solution. Water’s ability to dissolve substances also makes it an effective transport medium in blood, lymph, xylem, and phloem. In contrast, non-polar molecules like lipids are insoluble in water and tend to be pushed together, which plays a crucial role in protein folding and membrane stability. This property helps maintain cell structure and function in living organisms.

Question 43

Explain the importance of water having a high specific heat capacity.

Answer 43

Water has a high specific heat capacity due to hydrogen bonding, which requires extra energy to break before molecules can move freely. This means water absorbs and stores more heat without large temperature changes. Biologically, this is important because it helps maintain stable temperatures in cells and organisms, ensuring consistent biochemical reaction rates. It also makes large bodies of water like lakes and oceans more resistant to temperature fluctuations, creating stable habitats for aquatic life.

Question 44

Explain the importance of water having a high latent heat of vaporisation.

Answer 44

Water has a high latent heat of vaporization because hydrogen bonds must be broken for molecules to escape as gas, requiring large amounts of energy. This is biologically important as it allows organisms to cool down through evaporation, such as sweating, panting, or transpiration in plants, while minimizing water loss and dehydration risk. Additionally, the high energy loss required for freezing helps protect aquatic organisms and prevents freezing in living organisms with high water content.