Biological Molecule

Question 1

Structural characteristics of starch

Answer 1

• compact
• helical
• insoluble, doesn’t affect water potential
• large, cannot leave cell
• 1-4 1-6 glycosidic bond

Question 2

Structural characteristics of cellulose

Answer 2

• long straight chains
• 1-4 glycosidic bond
• beta glucose
• flip 180
• form microfibrils
• H bonds hold chains together= strength

Question 3

Structural characteristics of glycogen

Answer 3

• 1-4 1-6 glycosidic bond
• made up of alpha glucose
• highly branched ( more than starch) and coiled chains

Question 4

methods used to measure quantity of reducing sugar

Answer 4

• use colorimeter and calibration curve
• (without using colorimeter) filter and dry precipitate, find mass or weight comparison

Question 5

5 roles of lipids

Answer 5

• make up cell membrane, e.g. phospholipid contribute to flexibility of membrane and transfer of lipid soluble substance across them
• soucrce of energy
• waterproofing
• insulation
• protection

Question 6

Lipids role of waterproofing

Answer 6

insoluble, plants and insects have waxy lipid cuticle that conserves water. Mammals produce oil secretion from the sebaceous glands in skin

Question 7

Lipids role as source of energy

Answer 7

• when oxidised, lipids provide more than twice the energy as carbohydrates and release valuable water

Question 8

Lipids role of insulation

Answer 8

• fats are slow conductors of heat help retain body heat.

Question 9

Lipids role of protection

Answer 9

• often store around delicate organs like kidney

Question 10

Structure of lipids

Answer 10

• made of CHO, greater ratio of H:O of 2:1and long hydrocarbon chains (R group)
• not polymers because no repeating units, not a continuous chain

Question 11

Saturated fatty acid

Answer 11

• only with single C-C bond
• typically more reactive
• solid at room temperature
• typically unhealthy fats

Question 12

Unsaturated fatty acid

Answer 12

• with one or more double C=C bond
• one double bond is mono unsatured
• two or more double bond is polyunsaturated
• liquid in room temp, typically healthier oils

Question 13

Triglycerides structure to functions

Answer 13

• low mass to energy ratio so a good storage molecules because a lot of energy can store in a small volume
• it is large, non polar molecules, insoluble so doesn’t affect osmotic balance or water potential
• high ratio of H to O atoms, it release water when oxidised, provide a source of water

Question 14

Phospholipids structure

Answer 14

• 1/3 fatty acid replaced by a phosphate molecule
• it has a hydrophilic head and hydrophobic tail
• It is a polar molecule

Question 15

Phospholipids structure to properties

Answer 15

• in aqueous environment, it form a bilayer within cell surface membranes. So a hydrophobic barrier is formed between inside and outside of a cell
• hydrophilic head help to hold the surface of cell surface membranes
• allow to form glycolipids by combining carbohydrate within cell surface membranes. Glycolipids are important in cell recognition

Question 16

Test for lipids

Answer 16

• add 5cm3 ethanol in a 2cm3 sample, shake gently to let them dissolve. And water and shake again.
• a cloudy white emulsion indicates the presence of lipids

Question 17

Why is ethanol test results in cloudy white? 🤍

Answer 17

Because lipids is being finely dispersed in the water to form emulsion. Light will be refracted when passing through from oil droplets to water droplets, making it appear cloudy

Question 18

Four groups attached with a central carbon atom

Answer 18

• amino group NH2
• hydrogen atom
• carboxyl group COOH
• R group( variety of different chemical groups, each amino acid has different R group)

Question 19

How is dipeptide formed?

Answer 19

• condensation reaction of two amino acids with the form of peptide bonds
• the water is made of OH in the carboxyl group of one and H in the amino group of the other

Question 20

Primary structure of a polypeptide

Answer 20

• the sequence of amino acids of a polypeptide chain forms the primary structure of a protein
• the sequence is determined by DNA, and it determines the ultimate shape and function of the protein
• change in shapes will change the function of the protein

Question 21

Secondary structure of protein

Answer 21

• the H in NH is positive and O of the C=O is negative so they readily form a weak hydrogen bonds , caused the long peptide bond to twist into 3D coil, α- helix shape or β pleated sheet
• hydrogen bonds are easy to break

Question 22

Tertiary structure of protein

Answer 22

• α- helix structure can be twisted and fold even more to give complex 3D shape
• it is maintained by disulfide bridges, ionic bonds and more hydrogen bonds
• this allows protein to be distinctive and can be recognised by other molecules

Question 23

Properties of different bonds form in protein

Answer 23

Disulfide bridges- very strong, not sure easy to break
Ionic bonds- formed between carboxyl and amino group, not involved in forming peptide bonds. Weaker than disulfide bridges, can easily break by change in PH
Hydrogen bonds- easily broken

Question 24

Quaternary structure of proteins

Answer 24

• few polypeptide chains link together
• sometimes non protein components are added e.g. iron of haem group to make haemoglobin

Question 25

Structure of haemoglobin

Answer 25

- example of globular proteins - 2 alpha polypeptide chains 2 beta polypeptide chains 4 harm group

Question 26

Biuret test

Answer 26

- for protein - biuret made of sodium hydroxide and very dilute copper(II) sulphate - from pale blue to lilac purple

Question 27

Functions of proteins

Answer 27

- enzymes -antibodies, destroy invading cells and bacteria - transport proteins, transport materials across the body - structural proteins- gives structure for the body

Question 28

E.g. How does cellulose give cotton strength to make cloth ?

Answer 28

- has long, straight unbranded chains - group together to form microfibrils - hydrogen bonds holding chains together

Question 29

E.g. What is the benefit of mitochondria having small width comparing to its length ?

Answer 29

- short diffusion pathway= faster diffusion - large SA to volume ratio

Question 30

E.g. name of the different structures of alpha and beta glucose ?

Answer 30

Isomer

Question 31

E.g How does colorimeter identify the amount of sugar content ?

Answer 31

- higher absorption = more sugar - lower transmission = more sugar

Question 32

E.g. one advantage of different % of cholesterol in red blood cells compared with cells lining the ileum (1)

Answer 32

M1 red blood cells free in blood, not supported by other cells so cholesterol helps maintain shape of RBC

Question 33

E.g. explain why starch has spiral shape is important to its function ? (1)

Answer 33

- compact so can store a lot of energy in small area

Question 34

E.g. describe how saturated fatty acid differs in molecular structure from unsaturated ? (2)

Answer 34

M1 saturated F.A has single C-C bond unlike unsaturated with double bond M2 it is saturated with hydrogen