Biological molecules: Monomers+Carbohydrates

Question 1

Define polymer.

Give three examples.

Answer 1

Molecules formed when many monomers join together through condensation reactions (where a chemical bond forms between two molecules and a water molecule is released) .

-polysaccharides

-proteins

-DNA/RNA

Question 2

Define monomer.

Give three examples.

Answer 2

Monomers are smaller units from which larger molecules are made. E.g.

-monosaccharides(glucose, fructose, galactose)

-nucleotides

-amino acids

Question 3

What happens in a condensation reaction?

Answer 3

a chemical bond forms between two molecules and a water molecule is released.(When showing a condensation reaction ensure to put a water molecule as the product)

Question 4

What happens in a hydrolysis reaction?

Answer 4

A water molecule is used to break the chemical bond between two molecules.

Question 5

What monomers are carbohydrates made from?

Answer 5

Monosaccharides which are the molecules from which larger carbohydrates are made’

Question 6

State four(common) hexose monosaccharides.

Answer 6

-Alpha glucose
-Beta glucose
-Galactose
-Fructose

Question 7

Recall the structures of the two isomers of glucose.

Answer 7

-Alpha glucose (OH group on bottom)
-Beta glucose (OH group on top)

Question 8

A condensation reaction between two monosaccharides forms a….

Answer 8

(1,4or 1,6) glycosidic bond

Question 9

Describe how disaccharides form

Answer 9

A condensation reaction between two monosaccharides forms a glycosidic bond and releases a water molecule

Question 10

Name three disaccharides and their monomers.

Answer 10

A condensation reaction between…+…=
-maltose = alpha glucose + alpha glucose

-sucrose = fructose + alpha glucose

-lactose = glucose and galactose

Question 11

Describe Benedict’s test for reducing sugars

Answer 11

1. Add an equal volume of Benedict’s reagent to a sample.
2. Heat the mixture in an electric water bath at 100℃ for 5 mins.
3. Positive result: colour change from blue to orange & brick-red precipitate forms.

Question 12

Describe the Benedict’s test for non-reducing sugars.

Answer 12

1. Heat sample with Benedict’s reagent and get a negative result.

2.Hydrolyse non-reducing sugar(into its reducing sugar monomers) by heating it with dilute hydrochloric acid then neutralise sample by adding sodium hydrogencarbonate.

3.Proceed with benedict’s test as normal.

Question 13

Examples of reducing sugars.

Answer 13

All monosaccharides and some disaccharides e.g maltose and lactose

Question 14

Example of a non reducing sugar

Answer 14

Sucrose

Question 15

How would you prepare a solution if the sample is solid.

Answer 15

Crush the solid with water then filter out the solid.

Question 16

What should you do to ensure that all the sugar reacts?

Answer 16

Use an excess of benedict’s solution

Question 17

How are the samples heated

Answer 17

Always heated in a boiling water bath (could be electric)

Question 18

How are polysaccharides formed?

Answer 18

Polysaccharides are formed when more than two monosaccharides are joined together by condensation reactions.

Question 19

Name the monomers of the three polysaccharides.

glycogen

starch

cellulose

Answer 19

formed through the condensation of:

-alpha glucose

-alpha glucose

-beta glucose

Question 20

Describe structure and function of glycogen

Answer 20

Mainly a storage polymer (acts as an energy store) of a-glucose in animal cells (but also found in plant cells):

• 1,4 and 1,6 glycosidic bonds
• branched = stored glucose can be released quickly which is important for energy release in animals.
• Insoluble = no osmotic effect and does not diffuse out of cells.
• compact = good for storage

(similar to amylopectin except it has more side branches coming off it)

Question 21

Describe structure and function of starch

Answer 21

Storage polymer of alpha glucose in plants

insoluble=no osmotic effect on cells

large= does not diffuse out of cells

Question 22

Describe a method to test for the presence of starch and state what a positive and negative result will look like.

Answer 22

-Add iodine dissolved in potassium iodide solution to the test sample.
- If starch is present, the sample changes from browny-orange to a dark black blue colour,

Question 23

Describer structure and function of amylose

Answer 23

-Long unbranched chain of alpha glucose
-1,4 glycosidic bonds
-helix structure with intermolecular hydrogen bonds which help hold amylose in its helical structure= compact so good for storage

Question 24

Describe structure and function of amylopectin

Answer 24

-long branched chain of alpha glucose= many terminal ends for hydrolysis into glucose so glucose can be released quickly
-1,4&1,6 glycosidic bonds

Question 25

Describe structure and function of cellulose

Answer 25

Polymer of b-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up). * 1,4 glycosidic bonds * straight chain, unbranched molecule * alternate glucose molecules are rotated 180 degrees. * H-bond crosslinks between parallel strands to form strong fibres called microfibrils =structural support for cells

Question 26

Outline how colourimetry could be used to give qualitive results for the presence of starch and sugars.

Answer 26

-Make standard solutions with known concentrations(record absorbance or %transmission values) -Plot calibration curve absorbance or transmission %(y-axis), concentration(x-axis) -Record absorbance or transmission values of unknown samples. Use calibration curve to read off samples