Carbohydrates

Question 1

What is a organic molecule?

Answer 1

A molecule containing carbon and hydrogen

Question 2

Describe hydrolysis

Answer 2

the breaking down of polymers into monomers by the addition of water and the breaking of a covalent bond.

Question 3

Describe condensation

Answer 3

the joining of monomers into polymers by the removal of a water molecule to form a covalent bond

Question 4

What is the general formula for a monosaccaride?

Answer 4

(CH2O)n

Question 5

Are monosaccarides polar, if so explain why?

Answer 5

Yes, because they contain OH groups so they are polar and can dissolve in water.

Question 6

What is an isomer?

Answer 6

Isomers are molecules with the same chemical formula but different structure e.g. glucose and fructose.

Question 7

Give an example of a triose (C3H6O6)

Answer 7

Glyceraldehyde triose phosphate - used in photosynthesis and respiration

Question 8

Give an example of a pentose (C5H10O5)

Answer 8

ribulose 1,5 biphosphate - used in photosynthesis. Ribose. Deoxyribose - DNA

Question 9

Give an example of a hexose (C6H12O6)

Answer 9

glucose - transport sugar. Fructose - found in plants. Galactose - milk sugar.

Question 10

What are the two isomers of glucose and describe the difference between them.

Answer 10

Alpha and Beta glucose. The location of of the OH group bonded to carbon-1. On alpha-glucose the OH group sits below the ring, while beta has the OH group above the ring. (ngl easier just to look at a picture)

Question 11

What bonds form between monomers of carbohydrates?

Answer 11

Glycosidic

Question 12

Describe the disaccaride maltose.

Answer 12

Maltose is 2 alpha glucoses forming a 1,4 glycosidic bond. Reducing sugar

Question 13

Draw the complete structure of a alpha glucose - and explain how the carbons are numbered.

Answer 13

ngl I would add a photo here but since we need brainscape pro it aint happening but just make sure u can do dat.

Question 14

Describe sucrose and its function.

Answer 14

alpha glucose and fructose. Non-reducing sugar.

Found in plant phloem.

Question 15

Describe lactose and its function

Answer 15

beta glucose and galactose. Reducing sugar. Milk sugar. 1,4 glycosidic bonds where monomers are flipped with respect to each other.

Question 16

Describe the test for reducing sugars.

Answer 16

Benedicts test.

1. Place sample in clean test tube.
2. Add equal volume of Benedicts solution (CuSO4) (Blue) with pippette.
3. Heat solution at 100’C in water bath for 3 minutes.

Question 17

Describe positive result of Benedicts test for reducing sugars.

Answer 17

Depending on the concentration of reducing sugars the results are Blue(none), Green(trace), yellow, orange, brick-red(high) precipitate.

Question 18

Explain the chemistry of the results.

Answer 18

Reducing sugars oxidise (donate electrons) so when they are put into a solution with Cu2+ they form C+ ions which bond to form Cu2O - a brick-red precipitate.

Question 19

Test for non-reducing sugars e.g. sucrose

Answer 19

1. Add 1 mol. HCl to sample in test tube and swirl.
2. Heat at 100’C for 5 minutes in water bath
3. Neutralise solution by adding NaHCO3
4. Carry out Benedicts test

Question 20

Describe reagent test for reducing sugars and give a use.

Answer 20

1. Dip testing strip into sample
2. Compare colour change to calibration card
   Used to test urine samples for diabetes

Question 21

Describe test using a colorimeter

Answer 21

place sample in colorimeter and record the absorbance of red light. More light absorbed the lower the concentration of reducing sugars. disclaimer: i dont rly get this colorimeter stuff so u might want to check yrself - soz.

Question 22

Describe test for starch.

Answer 22

1. Add sample to clean test tube
2. Add potassium iodide solution and swirl
3. If starch is present solution will change from yellow brown to blue black

Question 23

Explain why starch turns blue black when tested with iodine

Answer 23

The iodine molecules enter the helix of amylose - blocking light travelling through

Question 24

Describe the structure of amylose and give properties

Answer 24

• alpha glucose
• 1,4 glycosidic bonds
• coils to form helix by intramolecular hydrogen bonds
• makes up 20% of starch
• Mr around 50,000 and composed of 300 monomers

Question 25

Describe the structure of amylopectin and give properties

Answer 25

- alpha glucose - 1,4 and every around 24 monomers a 1,6 glycosidc bond - branches highly - Mr and no. of monomers is 500,000 and 3000

Question 26

Describe the structure and properties of glycogen

Answer 26

- alpha glucose - 1,4 and frequent 1,6 glycosidic bond (more than amylopectin) - animal storage carbohydrate, particularly cells with high metabolic activity e.g. muscle cells - very highly branched

Question 27

Explain why starch (particularly amylopectin) and glycogen make good energy storage.

Answer 27

- Very compact; high energy density, due to branches - Insoluble in water; doesn't effect water potential of cells or cause osmotic swell - Glycogen and amylopectin are both highly branched which means enzymes can hydrolyse to release glucose monomers for respiration quickly

Question 28

Why do animals use glycogen as a energy storage carbohydrate?

Answer 28

Glycogen is more branched so it can more quickly release energy which is important as animals are more metabolically active as they perform high energy functions such as movement.

Question 29

What is the structure of cellulose?

Answer 29

- Beta glucose - 1,4 glycosidic bonds - It is a straight and linear chain that does not coil due to alternating monomers are flipped respective of each other - chains of cellulose lie parallel to each other and form hydrogen bonds.

Question 30

Give properties of cellulose and explain why.

Answer 30

- High tensile due to strong covalent glycosidic bonds and lots of hydrogen bonds. - around 80 chains join together to form microfibrils which run in lots of directions for support. - Plants use it as support as they don't have skeletons - They are fully permeable however can be mixed with substances to make them impermeable - e.g. cutin, suberin and lignin - cellulose fibres stop plant cells bursting when turgid, this turgidity give cell support and strength

Question 31

Give two other examples of polysaccharides.

Answer 31

- Chitin: cell wall of fungi and exokeletion of arthropods. | - Mucopoly