Carbohydrates

Question 1

Contain

Answer 1

Only carbon, hydrogen, oxygen

Question 2

General formula

Answer 2

Cx (H2O) y

Question 3

3 groups

Answer 3

Monosaccharides - single sugars eg galactose, fructose, glucose

Disaccharides - two sugars eg maltose, sucrose, lactose

Polysaccharides - many sugars eg starch, cellulose, glycogen

Question 4

Condensation reaction

Answer 4

Two monosaccharides join to from a disaccharides, water is also produced and a glycosidic bond forms

Many monosaccharides join in many condensation reactions to form a polysaccharide

Question 5

Most common monosaccharide

Answer 5

a Glucose - C6H12O6

Question 6

Isomer

Answer 6

Molecule with the same molecular formulae but a different arrangement of atoms

Question 7

Optical isomerism

Answer 7

When the bonds in the molecules can rotate in space to give a different form of the molecule (glucose to B glucose)

B glucose - the hydroxyl group rotates 180 around carbon 1

Question 8

Fructose and galactose formulae + structure

Answer 8

C6H12O6 - makes it a structural isomer of A and B glucose (different arrangement of atoms, same molecular formulae)

Hexose sugars - 6 carbon atoms

Question 9

Monosaccharides use

Answer 9

Make ATP - respiration
Formation of other carbohydrates
Formation of other molecules (DNA & RNA)

Question 10

Properties of monosaccharides

Answer 10

Small, can move across membranes with channel or transport proteins

Soluble in water, easily transportable and diffuse around living organisms to be used as a respiratory substrate

Lower water potential

Reducing sugars

Question 11

Test for reducing sugars

Answer 11

Add Benedicts reagent, heat

Present - red/brown/orange/green
Absent - blue

Question 12

Reducing sugars , quantitative

Answer 12

Use standard solution, a colorimeter and calibration curve

Question 13

Reducing properties come from

Answer 13

The aldehyde or ketone group within the molecule

Question 14

Disaccharides

Answer 14

Maltose, sucrose, lactose

Bond formed when 2 monosaccharides join by a condensation reaction with a glycosidic bond

Question 15

Maltose + formulae

Answer 15

Disaccharides formed by condensation of A glucose & A glucose

C12H22O11 as there are 2x glucose and - water since it is a condensation reaction

Question 16

Sucrose + formulae

Answer 16

disaccharides formed by condensation of A glucose & fructose

C12H22O11 as there are 2x glucose and - water since it is a condensation reaction

Question 17

Lactose + formulae

Answer 17

Disaccharides formed by condensation of A glucose & galactose

C12H22O11 as there are 2x glucose and - water since it is a condensation reaction

Question 18

Use of disaccharides

Answer 18

Make polysaccharides

Hydrolysed to make monosaccharides for respiration

Question 19

Properties of disaccharides

Answer 19

• soluble in water
• need to be hydrolysed before the monosaccharides produced can be transported across membranes
• lower water potential
• maltose + lactose are both reducing sugars
• sucrose is a non-reducing sugar

Question 20

Lactose and maltose and the reducing sugar test

Answer 20

• if you perform benedicts test on lactose or maltose you get a precipitate
• if you add lactase to lactose or maltase to maltose then perform benedicts test you get double the precipitate

Question 21

Non-reducing sugars test sucrose

Answer 21

Sucrose will give a blue colour

Question 22

Test for non-reducing sugars

Answer 22

• add acid, boil
• neutralise
• add benedicts reagent
• heat

Present - red/brown/ orange/ green
Absent - blue

Question 23

Non-reducing sugars, semi-quantitative

Answer 23

Using standard solutions, a colorimeter and a calibration curve

Question 24

Maltose hydrolysed

Answer 24

By maltase which is produced by epithelial cells of the ileum

Question 25

Sucrose hydrolysed

Answer 25

By sucrase which is produced by epithelial cells of the ileum

Question 26

Lactose hydrolysed

Answer 26

By lactase which is produced by epithelial cells of the ileum

Question 27

Polysaccharides

Answer 27

Chains of many monosaccharides joined together by condensation reactions with many glycosidic bonds Three important : starch, cellulose, glycogen

Question 28

Properties of polysaccharides dependent on

Answer 28

- number of monosaccharide molecules in the chain - type of monosaccharide in the chain - how they are joined together (branched or un-branched - overall shape of the molecule

Question 29

Starch

Answer 29

Polymer of A glucose molecules - all atoms lie upwards - found only in plants, storage polysaccharides (acting as a store of glucose) - insoluble and doesn’t affect water potential of the cell or solution - 1-4 and 1-6 glycosidic bonds

Question 30

Describe structure of starch

Answer 30

- large insoluble chains of A-glucose - helix - branched with 1-4 and 1-6 glycosidic bonds - consists of 2 polysaccharides amylose and amylopectin

Question 31

Structure related to function starch

Answer 31

Large and insoluble - doesn’t affect water potential, cannot pass across the cell membrane and move out of the cell Helix - will compress/compact into starch grains which take up less space Branched - more ends so larger surface area for faster hydrolysis by enzymes to release glucose for respiration

Question 32

test for starch

Answer 32

iodine or potassium iodide solution present - blue/black absent - orange/yellow/brown

Question 33

food in the stomach

Answer 33

when food is swallowed the enzyme is denatured by the acid in the stomach or hydrolysed by the endopeptidase, pepsin in the stomach

Question 34

stomach acid pH

Answer 34

1-2

Question 35

glycogen features

Answer 35

- all atoms lie in 1 direction - polymer formed by the condensation of A glucose molecules - found only in animals and fungi and is a storage polysaccharide (acting as a store of glucose) - glycogen is insoluble and doesn't affect water potential of the cell or solution - 1-4, 1-6 glycosidic bonds

Question 36

structure of glycogen

Answer 36

large and insoluble - doesn't affect water potential, cannot move past cell membrane and move out of the cell helix - will compress/compact which takes up less space branched - more ends, larger surface area, for faster hydrolysis by enzymes to release glucose for respiration

Question 37

why is glycogen more branched than starch

Answer 37

only found in animals so the more ends increases surface area for faster hydrolysis of glucose by enzymes for respiration.

Question 38

cellulose features

Answer 38

- polymer formed by condensation of B glucose molecules - found only in plants and is a structural polysaccharide found in plant cell walls - cellulose is insoluble and doesn't affect water potential of the cell or solution - atoms alternate up and down - only 1-4 glycosidic bonds

Question 39

structure of cellulose

Answer 39

long unbranched parallel chains of B-glucose cross-linked by hydrogen bonds to form microfibrils

Question 40

how is cellulose adapted for its role as a structural polysaccharide

Answer 40

long unbranched chains of B-glucose lie parallel (as there are only 1-4 glycosidic bonds) allows hydrogen bonds to form between them so they are cross-linked to microfibrils individual hydrogen bonds are weak however many of them together makes the strong structure that gives them strength and rigidity to the molecule important in cell walls