2.2 Biological Molecules

Question 1

Why does ice have a lower density that water?

Answer 1

There are enough hydrogen bond between the water molecules to form a rigid lattice. There are air spaces between the molecules hence there are Less water molecules per unit area making ice have a lower density than water.

Question 2

Give the 8 properties of water due to hydrogen bonding

Answer 2

• thermal stability due to high shc and slh due to high lattice enthalpy of HB.
• ice less dense that water so floats on bodies of water forming an insulation layer
• evaporation requires a lot of energy making water available as a liquid over a large range of temperatures
• Cohesion
• mass movement
• capillary action
• incompressibility means water can take on large pressures be an efficient transport medium
• ideal transport medium as it’s a very good solvent

Question 3

What are the 2 types of monosaccharides?

Answer 3

Pentose and hexose:

Ribose and deoxyribose = pentose

Hexose=
Alpha glucose HOH

Beta glucose OHH

Question 4

What are the properties of amylose

Answer 4

Alpha glucose subunits
unbranched coiled chain
hydroxyl group on carbon 2 of each subunit hidden inside coil
molecule insoluble hence doesn’t affect water potential of the cell
1,4 glycosidic bonds
Glucose storage molecule

Question 5

What are the properties of amylopectin and glycogen?

Answer 5

• alpha glucose
• 1.4 glycosidic bonds
• branched
• glycogen has 1.6 as well which makes it MORE branched as a storage molecule
• insoluble and compact

Question 6

What are the properties of cellulose? Explain why cellulose in insoluble

Answer 6

• beta glucose
• 1.4 glycosidic bonds
• straight chain
• strong and insoluble as all the hydroxyl groups form hydrogen bonds with other cellulose molecules
• large molecule so doesn’t dissolve hence doesn’t affect water potential of the cell
• 60-70 form microfibril and microfibrils join to form macrofibril

Question 7

What are the bonds found within a triglyceride?

Answer 7

Ester bonds

Question 8

What are the 4 structures of protein?

Answer 8

• 1° = straight chain polypeptide
• 2° = alpha helix or beta pleated sheets (held together by HYDROGRN bonds)
• 3° = Further folding caused by side interactions to form the following bonds:
  •hydrogen bonds between polar R groups
  •ionic bonds between oppositely charged R groups
  •covalent disulphode bridge between sulphur containing R groups (cysteine)
  •hydrophilic R groups twist outwards while hydrophobic twist into centre of molecule
• 4°= more than 2 polypeptide subunits and sometimes a prosthetic group

Question 9

Define globular protein

Answer 9

Highly folded globular shape

Water soluble

Metabolicaly active due to their 3D shape

Shape and activity sensitive to ph and temperature

Question 10

Explain why proteins that are metalbollically active or hormones are globular?

Answer 10

Shape of globular proteins is very specific allowing for specific response.

3D structure gives hormones a binding site for signalling chemicals and enzymes an active site

Temperature can change the shape, varying activity based on the body’s conditions

Question 11

Define fibrous proteins

Answer 11

Regular sequence of AA repeated many times . Usually insoluble and form fibres.

Question 12

Give an example of a globular protein

Answer 12

Any laws which has both a helix and b pleated sheets and a calcium cofactor

Question 13

Give 3 examples of fibrous proteins

Answer 13

Collagen
3 polypeptide chains wrapped around another. Doesn’t stretch easily. Found in tendons and in bones where its hardened by calcium phosphate. Also provides strength in walls of arteries

Keratin
2 PP coiled together
Strong
Hair, hooves, nails, horns, scales or feathers
Water impermeable

Elastin
Made by linking many TROPOELASTIN fibres together
TE coiled like a spring and can stretch and recoil
Used in vessels and lumens like arteries, alveoli and wall of bladder

Question 14

Give the test for proteins

Answer 14

Biuret test
Dissolve in water and add biuret solution
Positive colour change from blue to purple

Question 15

Test for reducing sugars (like glucose)

Answer 15

Benedict’s solution
Dissolve in water and add solution. Heat for 2 mins at 80 - 90°C
Ppt formed and colour change from blue to brick red

Question 16

Test for non reducing sugars (like sucrose)

Answer 16

Benedict’s solution
First test for reducing sugars to ensure none are present. Then dissolve in water and add a few drops of HCl and boil for 2 mins. Neutralise solution with a few drops of NaOH and add Benedict’s and reheat for 2 mins
Ppt forms and solution goes from blue to brick red

Question 17

Test for starch/amylose

Answer 17

Iodine solution
Dissolve in water and add iodine solution
Colour change from deep blue to black

Question 18

Test for Lipids

Answer 18

Emulsion test
Dissolve in alcohol, filter, add water to filtrate
When water added filtrate will turn cloudy or milky

Question 19

How do you make the Benedict’s test quantitative?

Answer 19

By using known concentrations of reducing sugars make a range of colours to make a colour standard. Place in centrifuge for 2 mins to make it precise and leave ppt at bottom of tube and any unused benedicts at the top. The more concentrsted the reducing sugar, the less blue colour will be left. Measure intensity of the blue in a cuvette and colorimeter and measure absorbance of your colour standard. Plot this on an absorbance-concentration graph and when finding concentrations of unknown reducing sugars solutions refer to this graph