3.1.2 carbohydrates

Question 1

what is a monosaccharide?

Answer 1

+ the monomers from which larger carbohydrates are made
+ simple sweet-tasting sugar
general formula ( CH2O)n
+ n can be anywhere from 3-7
+ glucose, galactose and fructose are common

Question 2

what happens in a condensation reaction between 2 monosaccharides?

Answer 2

+ a glycosidic bond is formed

Question 3

how are disassachrides formed?

Answer 3

+ by the condensation of two monosaccharides

Question 4

what is maltose?

Answer 4

+ a disaccharide formed by condensation of two glucose molecules

Question 5

what is sucrose?

Answer 5

+ a disaccharide formed by condensation of a glucose molecule and a fructose molecule

Question 6

what is lactose?

Answer 6

+ a disaccharide formed by condensation of a glusoce molecule and a galactose molecule

Question 7

what are the two isomers of glucose?

Answer 7

+ alpha-glucose
+ beta-glucose

Question 8

how are polysaccharides formed?

Answer 8

+ by the condensation of many glucose units

Question 9

how is glycogen and starch formed?

Answer 9

+ by the condensation of alpha-glucose

Question 10

how is cellulose formed?

Answer 10

+ by the condensation of beta-glucose

Question 11

What are carbohydrates?

Answer 11

+ contains only C,H,O atoms
+ carbon atoms form bonds with each other allowing for long chains to be formed
+ can be used as a backbone for other atoms to join in order to form other molecules
+ in all organisms the function is it act as an easily accessible source of energy
+ in plants, carbs also have a structural role

Question 12

Formula of a triose sugar?

Answer 12

C3H6O3

Question 13

Formula of tetrose sugar?

Answer 13

C4H8O4

Question 14

Formula of pentose sugar?

Answer 14

C5H10O5

Question 15

Formula of hexose sugar?

Answer 15

C6H12O6

Question 16

Formula of heptose sugar?

Answer 16

C7H14O7

Question 17

What is an isomer?

Answer 17

+ same molecular formula but different structure (their atoms are arranged to give them slightly different properties)

Question 18

What is the test for starch?

Answer 18

+ add iodine solution
+ blue/black precipitate forms if

Question 19

What is a reducing sugar?

Answer 19

+ a sugar that can donate electrons (or hydrogen) to other chemicals

Question 20

What is Benedict’s Reagent?

Answer 20

+ an alkaline copper (II) sulphate solution

Question 21

How do you test for reducing sugars?

Answer 21

1. Test tube with food sample dissolved in water
2. Add an equal volume of Benedict’s Reagent
3. Heat the mixture in gently boiling water

Question 22

How are disaccharides formed?

Answer 22

+ two alpha-glucose molecules C1 and C4 meet
+ hydroxyl group (OH) from C1 and C4 react
+ a condensation reaction occurs so water is removed- so there will be less oxygen and hydrogen
+ the bond formed is caused an alpha-1,4 glycosidic linkage

Question 23

How to test for non-reducing sugars?

Answer 23

1. add liquid food sample to a test tube
2. add 1cm^3 of hydrochloric acid (hydrolyses the disaccharide)
3. place in a beaker of water and boil for approx. one minute
4. allow the test tube to cool
5. add sodium hydrogencarbonate to neutralize the acid
6. carry out Benedict’s test as for reducing sugars
7. non-reducing sugar present = brick red precipitate

Question 24

what are polysaccharides?

Answer 24

+ formed by combinations of many monosaccharides molecules
+ they are joined by glycosidic bonds that were formed by condensation reactions (many bonds present within polysaccharides)
+ they are insoluble as they are large, making them highly suited for storage

Question 25

What is starch?

Answer 25

+ polysaccharide found in the form of small grains in plants
+ large amounts found in seeds and storage organs
+ major energy source
+ formed from many alpha-glucose monomer units linked via glycosidic bonds

Question 26

What is the structure of starch?

Answer 26

+ large - can’t diffuse out of cells easily (good for storage)
+ can be hydrolysed easily - good for storage in small spaces
+ starch is insoluble - water is not drawn into cells by osmosis so doesn’t affect water potential
+ tightly coiled and compact - good for storage in small spaces
+ OH groups point inwards and form H-bonds with neighbouring molecules

Question 27

What is glycogen?

Answer 27

+ found in animals and bacteria
+ formed from many monomers of alpha-glucose
+ has shorter chains and more branches
+ mainly stored in the muscles and the liver
+ however, isn’t the main long term storage in animals - constantly using it for source of glucose (energy)

Question 28

What is the structure of glycogen?

Answer 28

+ same as starch except for…
+ more highly branched - more ends available for enzymes to breakdown - more rapidly broken down to glucose - more glucose available for respiration

Question 29

What is cellulose?

Answer 29

+ formed from beta-glucose
+ the glucose molecules are orientated in a way that makes the OH groups stick outwards in opposite directions
+ these can form hydrogen bonds with neighbouring chains
+ forms straight and unbranched chains
+ chains run parallel to each other allowing for hydrogen bonds to form cross-linkages
+ overall high numbers of hydrogen bonds - provide considerable strength to cellulose

Question 30

What is the structure of cellulose?

Answer 30

+ long straight, unbranched chains- provides rigidity which is required to provide support to a plant cell
+ cross-linked chains held together by hydrogen bonds - provides even further strength to the cell wall
+ arranged into fibrils which contain microfibrils- provides EVEN further strength to the cell wall

Question 31

What is the function of cellulose?

Answer 31

+ stops the cell wall from bursting under osmotic pressure
+ this is because it exerts inward pressure that stops the influx of water
+ this means that the cells stay turgid and rigid, helping to maximise the SA of plants for photosynthesis

Question 32

Cellulose in animals?

Answer 32

+ the beta-glycosidic bond cannot be broken by amylase, but requires a specific cellulose enzyme