Biological Molecules

Question 1

What is the test for a reducing sugar?

Answer 1

Benedict solution
Add 2cm^3 sample to a test tube
Add Benedict reagent
Insoluable brick red ppt forms in presense of reducing sugars

Question 2

State the difference between the two isomers of glucose

Answer 2

Alpha glucose has both hydroxy groups on the bottom

Beta glucose has hydroxy groups above and below

Question 3

Glucose + glucose =

Answer 3

Maltose

Question 4

Glucose + fructose =

Answer 4

Sucrose

Question 5

Glucose + galactose =

Answer 5

Lactose

Question 6

When a c_______ reaction occurs between two monosaccharides occurs a __________ bond is fromed

Answer 6

Condensation glycosidic

Question 7

How would you test for a non reducing sugar?

Answer 7

Add Benedict solution
Nvc 
Hydrolyse with HCl 
Neutralise with NaHCO3 
Re do Benedict should go brick red 
You have shown the solution is a sugar as it has reduced benedicts, but in its original form not a reducing one

Question 8

How is benedicts solution semi quantitative, what experimental technique could you do to work out a sugar concentration from this value

Answer 8

Greater concentration of reducing sugar means stronger red ppt
Calorimetry curve, known concentration in colorimeter and plot graph, compare unknown samples colour with Benedict solution

Question 9

What is the test for starch?

Answer 9

Add potassium iodide

Yellow to black/blue

Question 10

Describe the structure if starch, where is it found

Answer 10

Plants
Alpha glucose
Condensation to branched or unbranched chains, form tight coils so is very compact

Question 11

Why is starch a good store of energy?

Answer 11

Insoluable therefore no effect on osmosis
Large therefore wont leave the cell
Compact so large amounts of energy stored
Branched ends allow many ends to be reacted on

Question 12

Describe glycogens structure relative to starch

Answer 12

Still alpha glucose

But shorter more branched chains

Question 13

What is the significant differnece between starch and cellulose? Describe the structure os cellulose

Answer 13

Beta glucose
Straight unbranched chains
Pack together tightly
Hydrogen bonding between chains
Forms microfibrils
Microfibrils group to form fibres

Question 14

What is the role of cellulose?

Answer 14

Provides the cell walls of plants with ridgidity

Maintianing a turgid state, prevents cell bursting when lost of water enters

Question 15

Describe the structure of a triglycerides

Why are the good energy stores ?

Answer 15

3 fatty acids and a glycerol
Condensation reaction to form ester bonds, fatty acids can be saturated or unsaturated
Good storage as high amount of C-H bonds with lots of energy. Also a low mass to energy ratio
Insoluble so no effect on osmosis
Release water when oxidised

Question 16

Describe the structure of a phospholipid and explain why this relates to its structure

Answer 16

Fatty acid replaced with a phosphate
Hydrophilic phosphate head and hydrophobic fatty acid tails
Forms a bi layer in aqueous conditions form cell membranes

Question 17

What is the test for lipids?

Answer 17

Add 5cm3 of ethanol to 2cm3 sample

Cloudy white emulsion forms

Question 18

What bond is formed beween protein monomers?

Answer 18

Peptide

Question 19

Describe the structure of a protein

Answer 19

Primary is amino acid sequence
Secondary is the hydrogen bonding between monomers twisting into alpha helix or beta pleated sheet
Tertiary is disulphide bridges and ionic bonds causing further twisting
Quaternary is the IMF’s between peptide chains

Question 20

What is the chemical test for proteins?

Answer 20

Biuret test
Add NaOH
Add copper sulphate
Purple colour if peptide bonds present