Biological Molecules

Question 1

Food Test- Proteins

Answer 1

Biuret Test:
-Add NaOH to sample
-Add few drops of dilute CuSO4 solution
Positive result: Solution turns mauve

Question 2

Food Test- Starch

Answer 2

Iodine Test:
-Add a few drops of iodine solution to sample
Positive result: Turns blue-black

Question 3

Food Test- Lipids

Answer 3

Emulsion Test:
-Dissolve sample by shaking with ethanol
-Pour solution into water in test tube
Positive result: White emulsion forms

Question 4

Food Test- Reducing Sugars

Answer 4

Benedict’s Test:
-Heat sample with Benedict’s reagent
Positive Result: Orange-red precipitate forms

Question 5

Food Test- Non-Reducing Sugars

Answer 5

Benedict’s Test:
-Check for reducing sugars first
-Hydrolise sample by heating with dilute HCl
-Neutralise by adding sodium hydrogen carbonate
-Test again with Benedict’s reagen
Positive result: Orange-red precipitate formed

Question 6

Define macromolecules

Answer 6

Very large organic molecules

Question 7

Define monomers

Answer 7

Small building blocks in molecules

Question 8

Define polymers

Answer 8

Several monomers joined together

Question 9

What is a condensation reaction?

Answer 9

The process by which 1 monomer joins to another (formation of bonds) and a water molecule is removed

Question 10

What is a hydrolysis reaction?

Answer 10

Water molecules are added in the process of breaking bonds between molecules

Question 11

What is a monosaccharide?

Answer 11

Single sugar, e.g. glucose

Question 12

What is a disaccharide?

Answer 12

Two monosaccharides joined together, e.g. sucrose

Question 13

What is a polysaccharide?

Answer 13

Many monosaccharides joined together to form a very large molecule, e.g. starch

Question 14

What bond forms between two monosaccharides in a condensation reaction?

Answer 14

Glycosidic bond, e.g. maltose from alpha glucose forms 1,4-glysodic bonds.

Question 15

Describe the structure of amylose

Answer 15

• Joined together by alpha glucose monosaccharides
• Coils up in helix
• Bonded by 1,4-glycosidic bonds

Question 16

Describe the structure of amylopectin

Answer 16

• Branched chains of alpha glucose residues

- This is because joined by 1,6 and 1,4-glycosidic bonds`

Question 17

Difference between the structure of starch molecules and cellulose molecules

Answer 17

• Starch is formed from alpha-glucose whereas cellulose if formed from beta-glucose
• The position of H and OH groups on Carbon-1 is inverted
• Starch doesn’t contain fibrils
• Starch doesn’t have H bonds between molecules

Question 18

Name 3 adaptations of starch and explain why they are beneficial

Answer 18

1) Insoluble, so it won’t affect water potential
2) Helical, so it’s compact
3) It’s a large molecule, so it cant leave the cell

Question 19

Describe the structure of glycogen

Answer 19

• Alpha glucose polymer

- Many branches on molecules, so high SA, faster hydrolysis for glucose production

Question 20

What is the purpose of glycogen?

Answer 20

It is a polysaccharide made of excess glucose that is stored in muscles for respiration but mostly in the liver and is continuously broken down to maintain blood sugar levels.

Question 21

Explain how cellulose is adapted to its function

Answer 21

1. Long and straight chains;
2. Become linked together by many hydrogen bonds to form fibrils;
3. Provide strength (to cell wall).

Question 22

Describe the structure of cellulose

Answer 22

• Made of beta glucose
• Every other glucose is upside down
• 1,4-glycosidic bonds
• Chains linked by H bonds
• Formed into strong microfibrils
• Abundant polysaccharide, enzymes can’t hydrolyse

Question 23

Describe the structure of amino acids

Answer 23

• Central C
• Carboxyl group (OH–C=O)
• H atom
• R group
• Amine group (H–N–H)

Question 24

What is the name given for a long chain of amino acids?

Answer 24

Polypeptides

Question 25

What bond forms between two amino acids?

Answer 25

Peptide bonds

Question 26

What is ‘primary structure’ in proteins?

Answer 26

A sequence of amino acids in a polypeptide

Question 27

What is ‘secondary structure’?

Answer 27

Shape polypeptide folds into:

• alpha helix
• beta pleated sheet

Question 28

What is ‘tertiary structure’?

Answer 28

• Secondary structure folded
• -Fibrous [long, thin and insoluble]
• -Globular [spherical, biochemical functions]

Question 29

What bonds do proteins with a tertiary structure contain?

Answer 29

• Hydrogen bonds (btwn R groups, not strong)
• Ionic bonds (btwn + and - amino acids, not strong)
• Disulfide bridges (amino acids with S in R group, strong covalent)
• Hydrophilic and Hydrophobic

Question 30

What is ‘quarternary structure’?

Answer 30

Protein made up from 2 or more polypeptide chain.

Held by same bonds as tertiary structure

Question 31

What bond forms in the condensation reaction between a fatty acid and a glycerol molecule in lipids?

Answer 31

Ester bond.

Question 32

What is the difference between saturated and unsaturated fats?

Answer 32

Saturated fats: no double bonds, solid fats

Unsaturated fats: double bonds, liquids (kinks in chain)

Question 33

What is the name given to molecules made of a glycerol and three fatty acid chains?

Answer 33

Triglyceride

Question 34

What is a phospholipid?

Answer 34

Made up of a glycerol molecule, a phosphate group and two fatty acid chains.
Makes up cell membrane (phospholipid bilayer)
Hydrophilic head and hydrophobic tail

Question 35

What monosaccharides make up maltose?

Answer 35

Two glucose molecules

Question 36

What monosaccharides make up sucrose?

Answer 36

A glucose molecule and a fructose molecule

Question 37

What monosaccharides make up lactose?

Answer 37

A glucose molecule and a galactose molecule

Question 38

Structure of glucose

Answer 38

alpha glucose (l-r excl. carbons)
H, O, H HO, OH
beta glucose
H, O, OH OH, H

Question 39

What forms from a condensation of alpha-glucose?

Answer 39

Glycogen

Question 40

What forms from a condensation of beta-glucose?

Answer 40

Cellulose

Question 41

How many types of amino acids are there?

Answer 41

20