Carbohydrates

Question 1

All carbohydrates are either…

Answer 1

Monosaccharides disaccharides or polysaccharides

Question 2

Monosaccharides are

Answer 2

Simple sugars with a general formula of (CH2O)n where n can be 3 to 7

Question 3

Glucose

Answer 3

Is an important monosaccharide
It has a general formula of C6H12O6
It’s the main way in which carbohydrates are transported around the body

Question 4

Two types of glucose

Answer 4

Alpha glucose and beta glucose

The only difference in their structure is that the OH is above carbon one in beta glucose rather below it

Question 5

Fructose

Answer 5

Very soluble and is sweeter than galactose

It’s the main sugar found in fruits and nectar

Question 6

Galactose

Answer 6

Not as soluble

Has and important role in the production of glycolipids and glycoproteins

Question 7

Ribose

Answer 7

Structural isomer of rna

Has a H and OH group at carbon 2

Question 8

Deoxyribose

Answer 8

Structural isomer if dna has two H atoms at carbon two

Question 9

Disaccharides are

Answer 9

‘Double sugars’ they are formed when two monosaccharides are joined by a glycosdic bond by a condensation reaction

Question 10

Maltose

Answer 10

(Malt sugar) is formed by two glucose molecules held together by an alpha 1-4 glycosidic bond

Question 11

Sucrose

Answer 11

(Table sugar) formed together by a glucose and fructose molecule held together by an alpha 1-4 glycosidic bond

Question 12

Lactose

Answer 12

(Milk sugar) formed by a glucose and galactose molecule held together by an alpha 1-4 glycosidic bond

Question 13

Testing for monosaccharides and disaccharides: reducing sugars

Answer 13

Using the Benedicts test
This is when Benedicts solution is added to a food sample in a water bath
The colour will change depending on amount of reducing sugars from the lowest to highest being green, yellow,orange,brick red

Question 14

Test for non reducing sugars (mono and do saccharides)

Answer 14

Eg sucrose
There is no direct test so we must hydrolise it by adding hydrochloric acid then neutralising it
You can then do the Benedicts test

Question 15

What are polysaccharides

Answer 15

Polymers containing many monosaccharides linked by glycosidic bonds and formed by a condensation reaction
They can be used as energy stores or structural components in cells

Question 16

Starch is

Answer 16

A polysaccharide made of many alpha glucose molecules
Has two structural units: amylose and amylopectin
It is insoluble compact and easily hydrolised to release energy

Question 17

Amylose

Answer 17

Structural unit of starch
Contains glucose molecules joined by alpha 1-4 glycosidic bonds only
Has unbranded chains forming a compact helical structure which is held together by hydrogen bonds

Question 18

Isomer is

Answer 18

The same molecule of something but a different arrangement

Question 19

Amylopectin

Answer 19

Also contains 1-4 alpha glycosidic bonds

But it also has many more 1-6 glycosidic bonds creating a highly branched structure

Question 20

Glycogen is

Answer 20

How carbohydrates are stored in animals and is stored as granules
Has a similar structure to amylopectin containing many alpha 1-6 bonds
It is less dense and more soluble indicating high metabolic requirements in animals

Question 21

Cellulose is

Answer 21

A polysaccharide made of beta glucose molecules in a 1-4 glycosidic bond
It’s the main part of a plants cell wall
Hydrogen bonds give it great tensile strength
Every other glucose molecule is rotated 180 degrees so that the hydroxyl groups are adjacent to each other resulting in long unbranched chains
It’s strong structure prevents plant cells from bursting

Question 22

Testing for polysaccharides (starch)

Answer 22

Iodine test
Few drops of iodine dissolved in potassium iodide solution to sample
If starch is present it will turn blue black colour
The colour changes due to the iodine molecules fitting through the gaps in the helical structure of amylose
This forms a poly iodide starch complex

Question 23

Many alpha glucose molecules create

Answer 23

A helical structure (eg amylose)

Question 24

Many beta glucose molecules create

Answer 24

A straight line (eg cellulose)

Question 25

Give two reasons why poly a glucose polysaccharides are more suitable for energy strong compounds in cells

Answer 25

They are made of glucose which can be respired
Forms a compact shape which can be stored in cells
Too large to diffuse out of cells

Question 26

Monomers

Answer 26

Monomers are the smaller units from which larger molecules are made

Question 27

Polymers

Answer 27

Molecules made from a large number of monomers joined together

Question 28

Condensation reactions

Answer 28

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

Question 29

Monomer of protein

Answer 29

Amino acids