Biological Molecules

Question 1

What type of bonding occurs in water molecules and how does it arise

Answer 1

Hydrogen bonds form between water molecules.
Water is a polar molecule. The oxygen is electronegative so attracts the shared pair of electrons making the oxygen δ– and the hydrogens δ+.
Opposite charges attract and a hydrogen bond is formed between loan pair of electrons on oxygen and the hydrogen of another water molecule.

Question 2

What are some properties of water

Answer 2

High specific heat capacity
High latent heat of vaporisation
Ice is less dense then water
Solvent, medium 
Cohesion, adhesion 
Surface tension

Question 3

Explain waters high specific heat capacity

Answer 3

A large amount of energy is required to increase waters temperature by a degree
Therefore water can act as a stable environment or be involved in reactions acting as a buffer

Question 4

Explain waters high latent heat of vaporisation

Answer 4

A large amount of energy is required to evaporate water. This is due to the strong hydrogen bonds between water molecules.
As a result water can act as a coolant as it removes a lot of heat when it evaporates
This is why dogs pant and some animals put saliva on their armpits

Question 5

Why is ice being less dense then water

Answer 5

Ice is less dense then water so it floats. It can act as an insulting layer so animals don’t freeze underneath
It can also provide a habitat on top of the ice

Question 6

How can water at as a solvent

Answer 6

Being a polar molecule it can dissolve a range of charged substances and transport them around the body and elsewhere
For example oxygen can dissolve in water making it accessible to aquatic life
Opposite charges surround and seprarate ionic compounds into their ions

Question 7

Explain waters cohesive (surface tension as well) and adhesive nature

Answer 7

Water molecules are attracted to each other so can provide surface tension. This can be a habitat for species like pond skaters

Water molecules also get attracted to for example the walls in the xylem. This is called adhesion and provides a long continuous column of water that can be transported up the plant.

Question 8

What is a monomer and a polymer

Answer 8

Monomer single unit eg nucleotides

Polymer multiple repeating units of monomers eg nucleic acids

Question 9

What is a condensation and a hydrolysis reaction

Answer 9

Condensation - Two substances combine forming a bond and a by product of water
Hydrolysis - Adding water to a substance to break a bond

Question 10

What atoms do carbohydrates consist of how do you test for it

Answer 10

C H O

Question 11

What type of sugar is glucose

Answer 11

Hexose monosaccharide

Question 12

What are the two types of glucose what are the structural differences

Answer 12

α-glucose
β-glucose

With alpha glucose on Carbon 1 the hydrogen atom is above the hydroxyl group
With beta glucose on Carbon 1 the hydroxyl group is above the hydrogen atom

Question 13

What are the two types of pentose sugars that can be present in DNA and RNA

Answer 13

Deoxyribose and Ribose

Question 14

How are disaccharides formed what is the bond called

Answer 14

2 monosaccharides join together and a glyosidic bond is formed between Carbon 1 and Carbon 4 (alpha 1,4 glycosidic bond) and molecule of water is released

Question 15

What is disaccharides are Lactose, Sucrose and Maltose formed from
How do you test for these

Answer 15

Lactose - Glucose and Galactose
Sucrose - Glucose and Sucrose
Maltose - 2 Glucose

Reducing sugars - Add benedict’s reagent blue to brick red if positive

Non reducing sugars - Add dilute HCL and NaOH and boil and perform testing for reducing sugars as normal. Sucrose is an example

Question 16

What is Starch comprised of in plants how can you test for this

Answer 16

Amylose - Contains alpha 1,4 glycosidic bonds it is a chained molecule but can coil up to make it compact

Amylopectin - contains alpha 1,4 and alpha 1,6 glycosidic bonds. This makes the molecule more branched. This is useful as there’s more ends for the enzymes to break down to release energy

To test for this add iodine orange to black is positive

Question 17

What is glycogen comprised of how does this compare to mainly amlyopecitin in starch

Answer 17

Similar structure to amylopectin, it contains 1,4 and 1,6 alpha glyosidic bonds, however it contains more 1,6 making it more branched.
This is as mammals typically have a higher metabolic so demands are much higher. Glycogen needs to be broken down much quicker as a result

Question 18

Why is glucose stored as starch and glycogen inside cells

Answer 18

It’s insoluble so doesn’t affect osmotic potential and is compact so more energy dense

Question 19

Describe the structure of glucose

Answer 19

Long and unchained due to the beta 1,4 glycosidic bonds. Being beta glucose to form the bonds every other glucose is flipped 180 degrees so a straight chain is formed.

Cellulose chains can form cross links and hydrogen bonds between fibrils. This gives cellulose HIGH TENSILE STRENGTH. It’s also insoluble

Question 20

What atoms to lipids consist of

Answer 20

CHO(P)

P is present in phospholipids

Question 21

Give some properties of lipids

Answer 21

Energy storage due to many C-H bonds 
Structural component - phospholipid bilayer and glycolipids
Electrical insulator - myelin sheath
Buoyancy
Waterproofing

Question 22

What are the components of triglycerides what are the bonds formed

Answer 22

One glycerol and 3 hydrophobic fatty acids tails

3 ester bonds are formed releasing 3 molecules of water

Question 23

What is the difference between a saturated and an unsaturated triglyceride

Answer 23

Saturated - Contains no double bonds usually solid (fats) and room temp

Unsaturated - Kinked due to double bonds so less intermolecular forces between hydrogen
bonds. Usually liquid (oils) at room temperature. Has a lower melting point as
a result

Question 24

Why do camels store fat in their humps

Answer 24

Triglycerides are rich in energy and when required can be broken down in aerobic reparation also releasing water which is useful for animals in dry conditions

Question 25

Describe the structure of a phospholipid

Answer 25

1 phosphate group which is hydrophilic
2 fatty acids tails that are hydrophobic
Forms phospholipid bilayer only lipid soluble can pass through
Increased fluidity if tails are kinked

Question 26

How do you test for lipids

Answer 26

Emulsion/Precipitation

Add ethanol to your sample and shake then pour into water and a milky white ppt should be visible

Question 27

What atoms does proteins consist of

Answer 27

CHON(S)

S if the amino acid cysteine is present

Question 28

What is the general structure of an amino acid

Answer 28

R
|
H2N—–C—-COOH
|
H

Question 29

What bond is formed between 2 peptides

Answer 29

Peptide bond is formed water is released

Question 30

What are the 4 structures of proteins

Answer 30

Primary - Sequence of amino acids
Secondary - Alpha helix and beta pleated sheet influenced by hydrogen bonds
Tertiary - 3D structure influenced by disulphide bridges , hydrophobic interactions and ionic
bonds
Quaternary - Multiple polypeptide chains

Question 31

What is a globular protein give some examples

Answer 31

3D spherical in shape and is soluble tend to have functional features

Examples include enzymes, antibodies, hormones and haemoglobin

Haemoglobin has a quaternary structure and is a conjugated protein as it contains a prosthetic group called haem (Fe2+ )which is non protein

It’s soluble as it has hydrophilic r groups on the outside

Question 32

What is a fibrous protein give some examples

Answer 32

Long unchained usually unreactive and insoluble in water tend to have structural features
Hydrophobic r groups on the outside

Examples included collagen, keratin and elastin

Collagen - 3 polypeptide chains wound around each other, every 3rd aa is glycine
forms crosslinks between fibrils giving it HIGH TENSILE STRENTH in walls of arteries

Keratin - 2 polypeptide chains protects delicate parts of the body

Elastin - Can stretch and recoil. Found in walls of alveoli

Question 33

How can you make the benedict’s test more quantitative

Answer 33

Use benedict’s reagent can be subjective

Use colorimeter
Plot a calibration curve with known concentrations or prepare using a serial dilution
To calibrate your colorimeter use a blank (distilled water)
Use a red filter
Pour sample in a cuvette and place in colorimeter to obtain absorbance
Read across from your graph (absorbance against concentration ) to identify the concentration