Chapter 2 Biological Molecules

Question 1

Benedict’s test for reducing sugars

Answer 1

Equal volume of sample being tested and Benedict’s solution, mixed and heated in a water bath.
- POSTIVE: green, yellow, orange, brick-red ( depending on amount of reducing sugar present )
- NEGATIVE: solution remains blue

Question 2

Iodine test for starch

Answer 2

Using a pipette, add few drops of iodine solution to the sample.
- POSTIVE: sample will turn blue-black
- NEGATIVE: remains orange-brown

Question 3

Emulsion test for lipids

Answer 3

Add equal volume of sample, ethanol and distilled water, shake.
- POSTIVE: forms a white, milky emulsion
- NEGATIVE: remains clear

Question 4

Biuret test for proteins

Answer 4

Equal volume of sample and biuret solution, mix.
- POSTIVE: purple
- NEGATIVE: remains blue

Question 5

Test to identify the presence of
non-reducing sugars

Answer 5

Hydrochloric aid is added to hydrolyse the sugar in the sample in a ratio of 1:2, and heated. Sodium hydroxide is added to make the solution alkaline. Benedict’s test is carried out.
- POSTIVE: green, yellow, orange, brick-red
- NEGATIVE: remains blue

Question 6

Structure of α-glucose and β-glucose

Answer 6

Glucose has molecular formula C6H12O6

• α-glucose: The –OH on carbon 1 is below the ring
• β-glucose: The –OH on carbon 1 is above the ring

Question 7

Define monomer

Answer 7

A simple molecule which is used as a basic building block for the synthesis of a polymer

Question 8

Define polymer

Answer 8

A giant molecule made from many similar repeating subunits joined together in a chain, held together by covalent bonds

Question 9

Define macromolecule

Answer 9

A large molecule formed due to polymerisation

Question 10

Define monosaccharide

Answer 10

A molecule consisting of a single sugar unit with the general formula (CH2O)n

Question 11

Define disaccharide

Answer 11

A sugar molecule consisting of two monosaccharides joined together by a glycosidic bond

Question 12

Define polysaccharide

Answer 12

A polymer whose subunits are monosaccharides joined together by glycosidic bonds

Question 13

Is sucrose a reducing sugar or non-reducing sugar?

Answer 13

Non-reducing sugar

Question 14

Name some reducing sugars

Answer 14

• Glucose
• Fructose
• Maltose

Question 15

Formation of a glycosidic bond

Answer 15

A C-O-C link formed when two monosaccharides undergo condensation reaction, releasing a water molecule.

Question 16

Breakage of a glycosidic bond

Answer 16

• The breakage of a glycosidic bond occurs through hydrolysis
• Acid hydrolysis of sucrose breaks glycosidic bond to retrieve the monomers

Question 17

What are the two components that make up starch?

Answer 17

Amylose and Amylopectin

Question 18

Molecular structure of amylose

Answer 18

• α-1,4 glycosidic bond
• Helical and more compact
• Unbranching

Question 19

Molecular structure of amylopectin

Answer 19

• α-1,4 and 1,6 glycosidic bonds
• Branched

Question 20

Molecular structure of glycogen

Answer 20

Used for storage of energy in animal cells

• α-1,6 glycosidic bonds
• Branched

Question 21

Molecular structure of cellulose

Answer 21

• Found in plant cell walls
• β-1,4 glycosidic bonds
• Alternate Beta glucose molecules are rotated 180° to form bonds
• 60-70 cellulose molecules tightly cross-linked to form bundles called microfibrils
• Microfibrils are held together in bundles called fibres by hydrogen bonds

Question 22

Formation and molecular structure of triglycerides

Answer 22

• Forms by condensation of 3 fatty acids and a glycerol molecule, forming an ester bond

Question 23

Unsaturated fatty acids

Answer 23

C=C bonds

Question 24

Saturated fatty acids

Answer 24

C-C bonds

Question 25

Are triglycerides polar or non-polar?

Answer 25

Non-polar hydrophobic molecules

Question 26

Role of triglycerides

Answer 26

- Act as energy storage compounds - Acts as an insulator - Provides buoyancy

Question 27

Molecular structure of phospholipids

Answer 27

- Hydrophilic head containing a phosphate group and glycerol - Hydrophobic tail containing 2 fatty acids

Question 28

Structure of amino acids

Answer 28

- Amino group, -NH2 - Carboxylic acid, - COOH - R group - An hydrogen atom

Question 29

Formation of peptide bond

Answer 29

C-N link between 2 amino acid molecules , formed by a condensation reaction

Question 30

Breakage of a peptide bond

Answer 30

Hydrolysis

Question 31

Primary structure

Answer 31

The sequence of amino acids in a polypeptide or protein

Question 32

Secondary structure

Answer 32

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

Question 33

α-helix structure

Answer 33

The polypeptide chains twist into a regular spiral and is maintained by hydrogen bonds between the -NH group and CO-group of another amino acid

Question 34

β-pleated sheet structure

Answer 34

A loose, sheet-like structure, formed by hydrogen bonding between parallel polypeptide chains

Question 35

Define tertiary structure

Answer 35

The compact structure of a protein molecule resulting from the 3D coiling of the chain of amino acids - Hydrogen bonds between wide varieties of R-groups - Disulfide bonds between 2 cysteine molecules - Ionic bonds between R-groups containing amine and carboxyl groups - Weak hydrophobic interactions between non-polar R-groups

Question 36

Define quaternary structure

Answer 36

The 3D arrangement of two or more polypeptide, or a polypeptide and a non-protein component

Question 37

Define globular proteins

Answer 37

- A protein whose molecules are folded into a relatively spherical shape - Have physiological roles - Generally soluble

Question 38

Define fibrous proteins

Answer 38

- A protein whose molecules have a relatively long, thin structure - Have structural roles - Generally insoluble

Question 39

Structure of haemoglobin

Answer 39

Example of a globular protein - 4 polypeptide chains - 2 α-globin chains - 2 β-globin chains - Each chain has one haem group containing an iron atom that reversibly binds to an oxygen molecule

Question 40

Importance of iron in the haem group

Answer 40

Iron’s ability to reversibly bind oxygen is crucial for delivering oxygen to tissues and muscles.

Question 41

What is sickle cell anaemia?

Answer 41

A genetic condition caused by faulty coding for haemoglobin, in which polar glutamic acid is substituted by non-polar valine on the surface of the β-chain, making it less soluble

Question 42

Structure of collagen

Answer 42

Example of a fibrous protein - 3 polypeptide chains, coiled in a shape of a stretched-out helix - Held together by hydrogen bonds and covalent bonds - Almost every 3rd amino acids is glycine - Collagen molecules lie side by side linked to each other by covalent cross-links between side chains, forming fibrils - Many fibrils together, forms a fibre

Question 43

Function of collagen

Answer 43

- Flexible - High tensile

Question 44

Why is water a good solvent?

Answer 44

- Because of its polarity. It can form electrostatic interactions with other polar molecules and ions - Its a transport medium and reagent for metabolic and other reactions in the cells of plants and animals

Question 45

Why does water have a high specific heat capacity?

Answer 45

- Due to the hydrogen bonds. Allows water to store more energy for a given temperature rise. Makes water more resistant to changes in temperature - Temperature within organisms remains constant compared to external temperatures, and water bodies also have a slow change in temperature, providing stable aquatic habitats

Question 46

Why does water have high latent heat of vaporisation?

Answer 46

- Due to its high specific heat capacity, hydrogen bonds must be broken before water can be vaporised -Sweating is a good cooling mechanism, however a larger amount of energy can be lost for little amount of water, thus dehydration is prevented