Biological Molecules (CARBOHYDRATES)

Question 1

Define a monomer

Answer 1

monomers are smaller, repeating units which can create larger molecules

Question 2

Give some examples of monomers

Answer 2

amino acids, glucose, nucleotides, monosaccharides

Question 3

Define a polymer

Answer 3

molecules from a large number of monomers joined together

Question 4

Give some examples of polymers

Answer 4

proteins, cellulose, starch, glycogen

Question 5

Define a condensation reaction

Answer 5

A reaction which joins 2 molecules (monomers) together with the formation of a chemical bond and the elimination of a water molecule

Question 6

What is the opposite of a condensation reaction

Answer 6

A hydrolysis reaction - breaks a chemical bond between 2 molecules and involves the use of a water molecule

Question 7

What are monosaccharides

Answer 7

Monosaccharides are the monomers from which larger carbohydrates are made (monomers specific to carbohydrates)

Question 8

Give 3 monosaccharides

Answer 8

Glucose
Fructose
Galactose

Question 9

How are disaccharides formed

Answer 9

By the condensation of 2 monosaccharides which forms a glycosidic bond

Question 10

Give the 3 disaccharides

Answer 10

Maltose
Sucrose
Lactose

Question 11

How is maltose formed

Answer 11

Glucose + glucose

Question 12

How is sucrose formed

Answer 12

Glucose + fructose

Question 13

How is lactose formed

Answer 13

Glucose + galactose

Question 14

What are the 2 isomers of glucose

Answer 14

alpha (α) & beta (β) glucose

Question 15

What is the difference in structure between alpha glucose and beta glucose

Answer 15

In alpha glucose, carbon 1 has the H at the top and OH at the bottom whereas the H is at the bottom and OH is at the top in beta glucose

REMEMBER TO ADD THE OXYGEN FOR BOTH

Question 16

What glycosidic bond does maltose form

Answer 16

A 1 -4 glycosidic bond

Question 17

How are polysaccharides formed

Answer 17

Polysaccharides are formed by the condensation of many glucose monomers

Question 18

Give three polysaccharides

Answer 18

starch
glycogen
cellulose

Question 19

what monomer is starch formed from

Answer 19

alpha glucose - amylose and amylopectin

Question 20

Compare structure of amylose and amylopectin

Answer 20

amylose is an unbranched chain of alpha glucose that only has 1-4 glycosidic bonds which gives it a tight, coiled helix structure. This is due to the hydrogen bonding within amylose. Whereas amylopectin has 1-4 and 1-6 glycosidic bonds which gives it a branched structure

Question 21

Where is starch found

Answer 21

Only in plant cells (eg: in chloroplasts)

Question 22

what is the function of starch

Answer 22

It is an insoluble store of glucose

Question 23

What are the properties of starch that make it suited to its function

Answer 23

It is insoluble - doesn’t affect water potential of cell so it doesn’t cause water to enter cell by osmosis which would make the cell turgid.

Helical structure = coiled structure → makes it compact = can fit more into a small space (= good for storage)

The branched structure increases surface area (ends) for rapid hydrolysis back to alpha glucose so glucose is easily released for respiration

Question 24

what monomer is glycogen formed from

Answer 24

alpha glucose
( Glycogen is a polymer of alpha glucose)

Question 25

where is glycogen found

Answer 25

in muscle and liver cells

Question 26

what is the function of glycogen

Answer 26

stores excess glucose in muscle and liver cells

Question 27

How is glycogen’s structure related to its function

Answer 27

Glycogen has a similar structure to amylopectin, except it has a lot more branches due to more 1 - 6 glycosidic bonds, Loads of branches means glucose can be quickly and easily released in respiration → important for energy releases in animals It is insoluble and so doesn’t draw water in by osmosis. or affect water potential It is compact, making it good for storage

Question 28

Despite both starch and glycogen being branched molecules, why is glycogen more branched

Answer 28

Glycogen is found in animals and humans - they are more metabolically active than plants - branched structure means glycogen can hydrolysed to alpha glucose and be used in respiration

Question 29

What monomer is cellulose formed from

Answer 29

Beta glucose

Question 30

where is cellulose found

Answer 30

In cell wall of plant cells

Question 31

What is the function of cellulose

Answer 31

Cellulose provides structural strength and support to plant cells

Question 32

Describe the structure of cellulose

Answer 32

only contains 1-4 glycosidic bonds which creates long straight chains. These long straight chains lie parallel to each other and are held together by many hydrogen bonds.

Question 33

What do chains of cellulose molecules form

Answer 33

Microfibrils which eventually form fibres

Question 34

How is cellulose’s structure related to its function

Answer 34

Every other beta glucose molecule is flipped 180 degrees (inverted) so hydrogen bonds can form between cellulose chains. Individual hydrogen bonds are weak but due to the large number of them, collectively they provide strength

Question 35

What is a reducing sugar

Answer 35

Sugars that can donate electrons to another chemical e.g. Benedict’s reagent

Question 36

Describe the test for reducing sugars

Answer 36

1) Mix equal volumes of test sample and benedicts reagent 2) Heat in water bath at 80 degrees celsius Positive test result shows solution turn from blue to brick red (brick red means a stronger concentration of reducing sugar present)

Question 37

Describe the test for non reducing sugars

Answer 37

1) Do the reducing sugar test. If negative and benidicts remains blue: 2) Add hydrochloric acid 3) Boil in water bath for 2 mins (short period of time) 4) Add sodium hydroxide (an alkali) for neutralisation 5) Add benedicts reagent 6) Heat in water bath Positive test result shows solution change to a brick red colour

Question 38

What’s a more accurate way of comparing the amount of reducing sugar in different solutions than colour change

Answer 38

Filter solution, dry precipitate and weigh it

Question 39

Why is hydrochloric acid added in the test for non reducing sugar

Answer 39

To provide hydrolysis and break the non-reducing sugar (disaccharide) into monosaccharides

Question 40

Give the name of a non reducing sugar

Answer 40

Sucrose

Question 41

Describe the test for starch

Answer 41

1) Mix iodine/potassium iodide with test solution 2) Positive test result shows solution goes from browny orange to a blue/black colour