Biological molecules

Question 1

What is a hydrolysis reaction?
What is a condensation reaction?

Answer 1

Breaking down with water - hydrolysis
Removing a water molecule, forms a glycosidic bond- condensation

Question 2

Describe the structure of glycogen and explain why it is a suitable molecule for storage.

Answer 2

Glycogen has a branched structure meaning it can be rapidly hydrolysed for use.
Glycogen is insoluble because it has strong glycocidic bonds making it suitable for storing energy. Glycogen is also compact meaning lots of it can be stored in a small place in a cell.

Question 3

Properties of amylose

Answer 3

-Insoluble in cold water
-No branching, not easily digested
-Helical shape allows it to be compact but not easily breakable
- Has 1-4 glycosidic bonds only

Question 4

properties of amylopectin

Answer 4

-Insoluble in hot and water

-Branching means it is easily accessible, can be rapidly hydrolysed and has lots of terminal glucose molecules can be broken off

-Glucose molecules can be readily added to branches making it an excellent storage molecule.

• Has 1-6 and 1-4 glycosidic bond

Question 5

properties of starch

Answer 5

• Polysaccharide formed in plants
• Made up of alpha glucose
• Amylopectin is branched
• Amylose is a polymer that isn’t branched
• Starch contains 1-4 and 1-6 glycosidic bonds

Question 6

Distinguish between the structures of each of the following pairs of carbohydrate molecules:

(i) Monosaccharides and disaccharides

(ii) Amylose and amylopectin

Answer 6

(i) monosaccharides are made from one simple sugar whereas disaccharides are made of 2 simple sugars and disaccharides have a glycosidic bond

(ii) Amylose isn’t branched. However amylopectin is branched meaning it can be rapidly hydrolysed. Amylose is a coiled helix shape. Amylopectin has 1-6 glycosidic bonds and 1-4 glycosidic bonds but amylose only has 1-4 glycosidic bonds.

Question 7

Explain two ways in which the structure of amylose and glycogen make them suitable for energy storage

Answer 7

• Both amylose and glycogen are insoluble meaning there is no osmotic effect
• Both amylose and glycogen are compact meaning lots of them can be stored in a small space in a cell.

Question 8

Explain how the structure and properties of starch are related to its function as a storage molecule.

Answer 8

-Amylopectin is branched meaning it can be rapidly hydrolysed and easily broken down.
-Amylose is coiled making starch compact so more can be stored in the cell.
-Starch contains glucose required for respiration.

Question 9

Properties of water

Answer 9

-Uneven sharing of electrons, more electrons held by oxygen and less being held by hydrogen in a covalent bond
-Slightly opposite charges means all the water molecules pull on eachother due to attraction
-Molecules at the top get drawn in and are pulled closer together creating a membrane like layer at the top creating surface tension.

Question 10

Explain how the properties of water molecules result in surface tension (3 marks)

Answer 10

Water molecules are cohesive. They are attracted to eachother because they are dipole therefore they pull in on eachother. The top layer of water molecules are drawn in on eachother which creates a membrane like layer at the top, creating surface tension.

Question 11

Explain the difference between saturated and unsaturated lipids

Answer 11

Unsaturated - Contain carbon-carbon double bonds. Found in plants
Saturated - Dont contain any carbon-carbon bonds

Question 12

Explain the structure of triglycerides

Answer 12

1 glycerol and 3 fatty acids joined by an ester bond.
non polar hydrophobic molecules
Joined through a condensation reaction

Question 13

Explain why water is a good solvent (2)

Answer 13

-Description of water as a {polar / dipole / dipolar} molecule (1)
-Water surrounds (polar) molecules allowing them to dissolve (1)

Question 14

Describe how glucose enters muscle cells through the cell membrane (2)

Answer 14

-Carrier proteins (located in membrane) (1)
-(glucose enters by) facilitated diffusion (1)

Question 15

Describe the formation of glycogen from glucose (2)

Answer 15

-Joining together in condensation reactions (1)
-Forming {1,4 and 1,6} glycosidic bonds (1)

Question 16

Describe how the structure of glycogen is related to its function as a storage molecule (2)

Answer 16

-Branched molecule for more rapid hydrolysis (1)
-Compact so more can be stored (1)

Question 17

Explain how the properties of water make it an ideal transport medium (3)

Answer 17

-Water is a solvent (1)
-Because water molecules surround { polar molecules / ions } / hydrogen bonds form between water molecules and solute molecules (1)
-Water is liquid so has the ability to flow (1)

Question 18

Starch is composed of amylose and amylopectin.

Which of the following terms is the correct description of amylose? (1)

A disaccharide
B monosaccharide
C polysaccharide
D trisaccharide

Answer 18

c - polysaccharide

Question 19

Starch can be broken down by a … (1)
A condensation reaction involving ester bonds
B condensation reaction involving glycosidic bonds
C hydrolysis reaction involving ester bonds
D hydrolysis reaction involving glycosidic bonds

Answer 19

D - hydrolysis reaction involving glycosidic bonds

Question 20

Give one structural difference between amylose and amylopectin (1)

Answer 20

-Amylose is {unbranched / has only 1,4 glycosidic bonds}

OR

Amylopectin {is branched / has (1,4 and) 1,6 glycosidic bonds}

Question 21

Explain how the structures of amylopectin and glycogen make them suitable for storing energy (3)

Answer 21

-Branched therefore can be rapidly hydrolysed (to release glucose) (1)
-Compact so more (energy / glucose) can be stored (1)
-Insoluble therefore does not affect osmosis (1)
-Molecules too large to diffuse across cell surface membrane (1)

Question 22

State the type of reaction where two monosaccharides join to form a
disaccharide molecule (1)

Answer 22

Glycosidic bond

Question 23

Which of the following bonds joins two monosaccharides to form a disaccharide molecule? (1)
A ester
B glycosidic
C hydrogen
D peptide

Answer 23

B - Glycosidic bond

Question 24

Name the two monosaccharides that are produced when sucrose is broken down.

Answer 24

Glucose and Fructose

Question 25

Name the two monosaccharides that are produced when lactose is broken down.

Answer 25

Glucose and Galactose

Question 26

Name the two monosaccharides that are produced when maltose is broken down.

Answer 26

Glucose and Glucose

Question 27

Compare and contrast the structure of a disaccharide with glycogen (4)

Answer 27

Similarities

• Both contain glycosidic bonds (1)
• Both contain glucose (1)

Differences
* Glycogen contains 1,4 and 1,6-glycosidic bonds whereas disaccharides only contain one type of glycosidic bond (1)
* Glycogen only contains glucose whereas disaccharides
can contain glucose and other monosaccharides (1)