Biological Molecules B

Question 1

Base pairing

Answer 1

A-T
Two hydrogen bonds
C-G
Three hydrogen bonds

The quantities of AT and CG are always the same but the ratio of AT CG varies from species to species

Question 2

What is DNA?

Answer 2

The material responsible for passing genetic information from cell to cell and generation to generation

Question 3

DNA structure

Answer 3

The double helix has anti-parallel structure
The uprights of the phosphate and deoxyribose wind around one another
They form the structural backbone of the DNA molecule
DNA is a polynucleotide chain

Question 4

Why is DNA a stable molecule?

Answer 4

The phosphodiester back bone protects the more chemically reactive bases inside the double helix

As there are 3 H bonds between CG the more CG pairings the more stable

Question 5

Ribonucleic structure

Answer 5

Polymer made up of nucleotides (polynucleotides)
Single stranded and shorter than DNA
Pentose sugar is ribose no deoxyribose
And thymine is switched out for uracil

Question 6

How is DNA adapted to its function

Answer 6

Stable structure allowing it to pass generations without significant change
The two strands are joined by H bonds allowing them to separate during replication and protein synthesis
A large molecule so can carry a lot of genetic information
Helical structure protects genetic information to some extent from chemical and physical forces
Base pairing allows DNA to replicate and transfer information as mRNA

Question 7

Semi conservative replication

Answer 7

DNA helicase causes the double helix to unwinds as it breaks hydrogen bonds between complementary base pairs
Each exposed polynucleotide strand acts as a template
DNA polymerase joins free floating nucleotides which align due to specific base pairing
Nucleotides are joined together in a condensation reaction catalysed by DNA polymerase
Phosphodiester/hydrogen bonds reform

Question 8

Four requirements for semi conservative replication

Answer 8

The four nucleotides each with their bases

DNA polymerase

A source of chemical energy

Both strands of the DNA molecule to act as a template strand for the attachment of nucleotides

Question 9

ATP to ADP

Answer 9

A hydrolysis reaction
Catalyzed by ATP hydrolase (ATPase)

Question 10

How does ATP store energy

Answer 10

The bonds between the phosphate groups are unstable so have a low Ea
This means they’re easily broken
When broken they release energy
It is a immediate source of energy - it’s not a good long term store because of its instability

Question 11

Why is ATP a better energy source than glucose?

Answer 11

Each ATP molecule releases less energy than a glucose molecule which is released in smaller, more manageable amounts
The hydrolysis of ATP to ADP is a single reaction that releases immediate energy whether the breakdown of glucose is a long series of reactions and the energy release takes longer

Question 12

Structure of ATP

Answer 12

Adenosine triphosphate
Chain of 3 phosphate groups
Ribose sugar which has a 5 carbon ring structure (pentose sugar) that acts as a backbone
Adenine - a nitrogen containing organic base

Question 13

How is ATP adapted to its function?

Answer 13

It can’t move through the cell membrane
Phosphorylation

Question 14

Roles of ATP

Answer 14

Movement
Metabolic processes
Active transport
Secretion
Activation of molecules

Question 15

ADP + Pi to ATP

Answer 15

A condensation reaction
ATP synthase
It can occur in 3 ways -
Photophosphorylation
Oxidative phosphorylation
Substrate level phosphorylation

Question 16

Evidence for semi-conservative replication

Answer 16

Two isotopes of nitrogen
Heavy (15)
Light (14)
Two samples of bacteria were grown, one in each nutrient broth
The bacteria took up nitrogen as they grew to make new nucleotides for new DNA
A sample was taken from each and spun in a centrifuge
The isotope 15 was heavier so settled lower down the tube
Both were then grown in heavy nitrogen broth and then light
They were left for one round of DNA replication and then taken out and spun in a centrifuge
If replication was conservative the original heavy DBA would still be together and settle at the top
If replication is semi-conservative the new DNA molecules would contain one strand of the heavy and one of the light so the DNA would settle between

Question 17

What is an inorganic ion?

Answer 17

An ion is an atom/atoms with an electric charge
A cation is a positive charge
An anion is a negative charge
They don’t contain carbon (though there are some exceptions to this
They’re found in solution - cytoplasm and bodily fluids

Question 18

The role of important ions in the body

Answer 18

Fe2+ temporarily binds to the oxygen in haemoglobin and becomes Fe3+ until the oxygen is released

pH is determined by the concentration of H+ ions. The more H+ ions, the lower the pH and the more acidic the environment. This is important to enzyme controlled reactions

Na+ ions help transport glucose and amino acids across membranes by co-transport

PO4 3- ions store energy in ATP and allow nucleotides to form polynucleotides in RNA and DNA

Question 19

Water as a metabolite

Answer 19

Many metabolic reactions involve hydrolysis and condensation

Question 20

Water has a high latent heat of vapourisation

Answer 20

It takes a lot of heat energy to break the hydrogen bonds so has a high latent heat of vapourisation - a lot of energy is used up when water evaporates
This is useful for organisms because it means they can use water loss through evaporation to cool down without loosing too much (sweating)
Cooling effect through evaporation

Question 21

Water as a buffer to temperature changes

Answer 21

The hydrogen bonds between water molecules can absorb a lot of energy
This means water has a high specific heat capacity (takes a lot of energy to heat up)
This is useful for organisms as it mean water doesn’t experience rapid temperature changes and helps them maintain a constant internal body temperature

Question 22

Water is a good solvent

Answer 22

A lot of substances in metabolic reactions are ionic
Because water is polar the positive end of the water molecule will be attracted to the negative ion and vice versa
This means ions will dissolve in water
Also allows transport of substances

Question 23

Cohesion between water molecules

Answer 23

Cohesion is the attraction between molecules of the same type
Water molecules are very cohesive because they’re polar
Can support columns of water in plants
Strong cohesion also results in a high surface tension when it comes in contact with air. This is why sweat forms droplets which evaporates from the skin. It’s also the reason why some insects can ‘walk’ on the surface of water