Carbohydrates

Question 1

What elements make up carbohydrates

Answer 1

Carbon, hydrogen and oxygen

Question 2

Examples of disaccharides

Answer 2

Maltose, lactose, sucrose

Question 3

What is an isomer

Answer 3

Same molecular formula, different arrangement of atoms

Question 4

Isomers of glucose and the structural difference

Answer 4

Alpha and beta
The hydroxyl group is below for a and above b

Question 5

What is the test for reducing sugars

Answer 5

Benedict’s test: add 2cm3 of sample with equal volume of Benedict’s reagent (copper sulfate) and heat between 70 and 90 for 5 minutes. Goes from blue to brick red (copper oxide) if reducing sugar is present

Question 6

What colour does benedicts reagent go when reducing sugars are present and why

Answer 6

From blue to red as they contain a group that reduces the cu 2+ ions to cu+ when heated in an alkaline solution

Question 7

All monosaccharides are reducing sugars, true or false

Answer 7

True

Question 8

How is a glycosidic bond formed in disaccharides

Answer 8

Water taken away to form oxygen bridge known as a 1-4 glycosidic bond

Question 9

Test for non reducing sugar and why

Answer 9

Boil 2cm3 of sample with 2cm3 dilute hydrochloric acid for 5 mins to hydrolyse disaccharides into monosaccharides
Then neutralise with sodium hydrogen carbonate ( benedicts doesn’t work in acidic)
Then do normal Benedicts test if red it was non reducing

Question 10

What is the test for starch

Answer 10

Add iodine in potassium iodide, if changed to blue black then starch is present

Question 11

Detail the formation of starch

Answer 11

Polysaccharide mainoy of the polysaccharide amylose. Condensation between many alpha glucose. Monomers, water released to from 1-4 glycosidic bonds. Chains can be branched or unbranched and unbranched is wound into a tight coil. Amylose is tightly coiled/compact insoluble polysaccharide and amylopectin is a branched polysaccharide.

Question 12

Why is starch suited to its function

Answer 12

-Helicle shape of coiled starch makes for a compact polysaccharide (fits many subunits/lots of energy into small space) and coiled by hydrogen bonds in the chain
- insoluble so water isn’t drawn into cells by osmosis/ W.p not affected
-Large so doesn’t diffuse out of cells
-When hydrolysed forms a glucose for respiration to make ATP
It is a storage polysaccharide for energy

Question 13

In what organisms is glycogen found

Answer 13

Animals and bacteria

Question 14

What’s the structure of glycogen

Answer 14

Short chains and highly branched, made of alpha glucose

Question 15

Where is glycogen found

Answer 15

Granules in muscles and the liver

Question 16

How is glycogens structure suited for its function

Answer 16

-function in carb storage
insoluble so doesn’t draw water into cells
-insoluble so can’t diffuse out of cells
-Compact (much in small space)
-Highly branched so enzymes can break down ends into monomers fro respiration

Question 17

Detail the formation of cellulose

Answer 17

Polymer of B glucose, condensation reaction between monomers forming 1-4 glycosidic bonds, every second B glucose rotates 180, forms straight unbranched chains that run parallel with hydrogen bonds to from micro fibrils. Many microfibrils combine to form macro fibres which combine to cellusolose

Question 18

Where is cellulose found

Answer 18

Cell walls

Question 19

How are hydrogen bonds made in cellulose

Answer 19

Adjacent molecules are rotated 180 which allow H bonds between OH groups

Question 20

How is the structure of cellulose suited to its function

Answer 20

-many hydrogen bonds add strength
- long unbranched chains made of b glucose
- fibres and micrfibrils add strength
It is a fibrous polysaccharide that is tensile and can withstand osmotic forces when cells absorb water by zo and become turgid, spaced allow material to pass through freely to the CSM/provides rigidity to cell wall and stops cells bursting by exerting inward pressure (cells turgid to max SA for photosynthesis)

Question 21

List some common monosaccharides

Answer 21

Glucose( hexose C6H12O6), galactose and fructose

Question 22

What is maltose

Answer 22

A disaccharide formed from the condensation of two glucose molecules

Question 23

What is sucrose

Answer 23

A disaccharide formed by the condensation of one glucose and one fructose

Question 24

What is lactose

Answer 24

A disaccharide formed by the condensation of a glucose and a galactose

Question 25

What bond joins monosaccharides

Answer 25

Glycosidic (mainly 1-4)

Question 26

Draw out alpha and beta glucose

Answer 26

Do it