Monomers, Polymers And Carbohydrates

Question 1

Define Monomer. Give Examples

Answer 1

Smaller units that join to form larger molecules.
E.g., Monosaccharides (glucose, fructose, galactose), nucleotides, amino acids

Question 2

Define Polymer. Give some examples

Answer 2

Molecules formed when many monomers join together.
E.g., Polysaccharides, DNA/RNA, Protein

Question 3

What happens in a condensation reaction?

Answer 3

For 2 monosaccharides, a new chemical bond has formed between 2 molecules (glycosidic bond.)
It is the chemical process in which 2 molecules combine to form a more complex one with the elimination of a simple substance, usually water. Examples are polysaccharides and polypeptides.

Question 4

What happens in a hydrolysis reaction?

Answer 4

It is the breaking of large molecules to smaller ones by the addition of water.

Question 5

What is a monosaccharide? Give some examples.

Answer 5

Monomers from which larger carbohydrates are made from. Examples of hexose Monosaccharides are glucose, fructose and galactose. They all follow the C6H12O6 formula.

Question 6

The type of bond formed when Monosaccharides react.

Answer 6

(1,6, or 1,4) Glycosidic bond. They are chemical bonds that link ring-shaped sugar molecules to other molecules.

Question 7

Describe 3 Disaccharides and describe how they have formed.

Answer 7

Lactose: alpha Glucose and Beta Galactose
Maltose: x2 Alpha Glucose
Sucrose; Alpha Glucose and Beta Fructose

Question 8

Describe 2 main functions of Monosaccharides:

Answer 8

Energy source for fuelling cell metabolism e.g., respiration.
Structural units for disaccharides and monosaccharides.

Question 9

Information on Lactose

Answer 9

Lactose is found in milk and the enzyme is lactase. Naturally occurs in small intestines of mammals.

Question 10

Information on Maltose.

Answer 10

Uses enzyme maltose. Naturally occurs in small intestines of mammals and germinating seeds.

Question 11

Information on Sucrose.

Answer 11

Table sugar from plants as sugar cane. Sucrase. Found in small intestines of mammals.

Question 12

Test for Reducing Sugars

Answer 12

1. Add 2cm3 of food sample into a test tube (if not in liquid form, grind it up in water.)
2. Add equal volumes of Benedict’s reagent.
3. If present, it turns brick-red. Spectrum of colour depends on the amount of sugar (green if small amount.)

Question 13

Test for Starch

Answer 13

1. Add 2cm3 of sample into a test tube/ 2 drops into a depression on a spotting tile.
2. Add 2 drops of Iodine solution and shake.
3. If present, blue-black colouration.

Question 14

Test for Non-reducing sugars.

Answer 14

1. Add 2cm3 of sample into a testable.
2. Add dilute HCl (2cm3) and place test tube in a gently boiling water bath (80 degrees) for 5 minutes - HCl hydrolyse the glycosidic bond.
3. Add equal amounts of Sodium hydroxide to neutralise acid
4. Add 2cm3 of Benedict’s reagent and gently heat mixture for 5 minutes.
5. If present, would turn brick red.

Question 15

Give examples of Reducing Sugars

Answer 15

-all monosaccharides
-Maltose and Lactose (2 examples of disaccharides.)

Question 16

Give examples of Non-reducing sugars

Answer 16

• Sucrose
  -Polysaccharides

Question 17

What is a reducing sugar?

Answer 17

A sugar that can donate electrons to another chemical or reduce another chemical.

Question 18

What is a non-reducing sugar?

Answer 18

Sugars that do not possess the ability to donate electrons, hence they cannot be oxidised.

Question 19

What does quantitive mean?

Answer 19

Tells us the amount of substance present.

Question 20

What does qualitative mean?

Answer 20

Tells us if a substance is either present or not.

Question 21

Outline how colorimetry can be used to give qualities results for the presence of sugar and starch.

Answer 21

Using machine, we can plot a calibration curve, with absorbance and concentration, which we can use to read off the concentration.

Question 22

Function of Starch

Answer 22

Energy storage in plants

Question 23

Structure of Starch

Answer 23

-Found in plants, in small grains
- formed through the condensation reaction between alpha glucose with glycosidic bonds.
-made up of amylose and amylopectin

Question 24

Structure and function of Amylose

Answer 24

-makes up 20% of starch.
- made up of (1,4) glycosidic bonds - makes it compact as it is linear, so can then coil up into a helical structure, so lots can be stored in a small amount of space.
-

Question 25

Structure and function of Amylopectin

Answer 25

• makes up 80% of starch.
  -contains (1,4) and (1,6) glycosidic bonds - (1,6) branches every 20 monomers.
  -Branched so enzymes can easily break it down for respiration

Question 26

Structure and function of starch

Answer 26

• large so does not diffuse out of cells.
  -insoluble - having no osmotic effect, and not affecting water potential of a cell

Question 27

Structure and function of glycogen

Answer 27

• found in animal cels (e.g., liver and muscles.)
  -Energy source and storage in animal cells
• Extremely branched (contains 1,4 and 1,6 glycosidic bonds).
  -1,6 every 10 monomers - more terminal ends to be hydrolysed quickly
  -Insoluble - does not affect water potential of cell
• Compact - large amount stored as highly branched so can pack more glucose units together.

Question 28

Structure and function of cellulose

Answer 28

• structural component in plant cell walls (strong and permeable to protect from bursting and keeping turgid.)
• Beta glucose - (1,4 ) bonds inverted every other one by 180 degrees to create unbranded linear chains
• Lots of straight chains (microfibrils packed together with hydrogen bonds between hydroxyl group) form cellulose fibrils.
• Lots of straight chains and hydrogen bonds make cellulose strong
  -H bond crossings between parallel strands from microfibrils - height tensile strength.