More Biological Molecules AS

Question 1

DNA and RNA are both types of _______ _____

Answer 1

nucleic acid

Question 2

What is the role of DNA?

Answer 2

used to store genetic information

Question 3

What is the role of RNA?

Answer 3

transfer genetic information from the RNA to the ribosomes

Ribosomes read the RNA to make polypeptides in a process called translation

Question 4

Molecules of DNA and RNA are polymers of _______

Answer 4

nucleotides

Question 5

What is a nucleotide composed of?

Answer 5

A pentose sugar
A nitrogen containing organic base
A phosphate group

Question 6

How is a polynucleotide formed?

Answer 6

Nucleotides joined together via a condensation reaction between the phosphate group of one nucleotide and the sugar of another.

This formed a phosphodiester bond

The chain of phosphates and sugars is known as the sugar-phosphate backbone

Question 7

Describe DNA structure

Answer 7

Double helix structure - formed from 2 separate strands of polynucleotides

The two polynucleotide strands are antiparallel - they run in opposite directions.

DNA molecules are really long and coiled up tightly so a lot of genetic information can fit into a small space in the cell nucleus

Question 8

What is DNA nucleotide structure?

Answer 8

Phosphate group, pentose deoxyribose sugar and a nitrogen containing organic base

Base can change
can be either
A, T, C, G

Question 9

What is complimentary base pairing?

Answer 9

Two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base only has one complimentary partner.

A-T
C-G

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

Question 10

DNA vs RNA

Answer 10

• Sugar in RNA is ribose sugar not deoxyribose sugar
• Uracil replaces thymine as a base
• The nucleotides form a single polynucleotide strand not a double one
• RNA strands are much shorter than most DNA polynucleotides

Question 11

Why does DNA replicate?

Answer 11

DNA copies itself before cell division so that each new cell has full amount of DNA. This method is called semiconservative replication because half of the strands in each new DNA molecule are from the original DNA molecule.

Question 12

Explain DNA replication

Answer 12

1. The enzyme DNA helicase breaks down the hydrogen bonds between bases on the two polynucleotide DNA strands. This makes the helix unwind to form 2 single strands.
2. Each original strand acts as a template strand for a new strand. Complimentary base pairing means that free DNA nucleotides are attracted to their complimentary exposed bases on each original template strand
3. Condensation reactions join the nucleotides of the new strand together - catalysed by the enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strand

Question 13

Describe the action of DNA polymerase

Answer 13

During DNA replication the active site of DNA polymerase is only complimentary to the 3’ end of the newly forming DNA strand - so the enzyme can only add nucleotides to the new strand at the 3’ end. This means that the new strand is made in a 5’ to 3’ direction and that DNA polymerase moves down the template strand in 3’ to 5’ direction.

Because the strands in the double helix are anti parallel, the DNA polymerase working on one of the template strands moves in the opposite direction to the DNA polymerase working on the other template strand.

Question 14

Explain Meselson and Stahl’s experiment

Answer 14

Used 2 isotopes of nitrogen

1. Two samples of bacteria were grown, one in a nutrient broth containing light nitrogen and one containing heavy nitrogen. As the bacteria grew and reproduced, they took up the broth to help make nucleotides so nitrogen is becoming a part of the DNA
2. A sample of DNA was taken from each bacteria. The DNA from heavy nitrogen broth settled lower in the centrifuge tube than the lighter nitrogen broth bacteria
3. Then the bacteria grown in heavy nitrogen broth was taken out and put in a broth containing only light nitrogen. The bacteria were left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge
4. If replication was conservative the original heavy DNA would settle at the bottom and new light DNA would settle at the top
5. If replication was semi-conservative, the new bacterial DNA molecules would contain one heavy strand and one light strand. So the DNA would settle between where light and heavy would have settled.
6. The DNA settled in the middle showing the replication is semi conservative

Question 15

Why is energy important?

Answer 15

Plants need energy for things like active transport, DNA replication, cell division and protein synthesis

Animals need energy for things like active transport(e.g. absorb glucose from the ileum epithelium into the bloodstream), DNA replication, cell division and protein synthesis

Question 16

Describe the structure of ATP

Answer 16

Nucleotide base adenine combined with a ribose sugar and three phosphate groups

Once made, ATP diffuses to the part of the cell that needs energy

The energy in ATP is stored in high energy bonds between the phosphate groups

Question 17

What happens to ATP when energy is needed in a cell?

Answer 17

ATP is broken down into ADP + Pi by a hydrolysis reaction

A phosphate bond is broken and energy is released. The reaction is catalysed by the enzyme ATP hydrolase

Question 18

ATP hydrolysis can be ‘_______” to other energy requiring reactions in a cell- this means that energy released can be used directly to make the _______ reaction happen, rather than being lost as heat

Answer 18

coupled

Question 19

The release inorganic phosphate can also be put to use - it can be added to another compound - this is known as ___________ , this often makes the compound more reactive

Answer 19

phosphorylation

Question 20

How is ATP resynthesised?

Answer 20

Condensation reaction between ADP and Pi

Happens during respiration and photosynthesis and is catalysed by the enzyme ATP synthase

Question 21

What is the importance of water?

Answer 21

• Water is a metabolite in loads of important metabolic reactions including condensation and hydrolysis
• Water is a solvent - most metabolic reactions so water is essential
• Water helps with temperature control because it has a high latent heat of vaporisation and high SHC
• Water molecules are very cohesive which helps water transport in plants as well as transport in other organisms

Question 22

Explain the structure of water

Answer 22

Water is polar as has slight - and slight + on different sides

Hydrogen bonds form between water molecules because the slightly negative charged oxygen atoms attract the slight positive hydrogen atoms.

Question 23

Explain how water is an important metabolite

Answer 23

Many metabolic reactions involve condensation or hydrolysis for example amino acids joined to make polypeptides by condensation, energy from ATP is released through hydrolysis

Question 24

Explain how water is a good solvent

Answer 24

Because water is polar, the slightly positively charged end of a water molecule will be attracted to the negative ion, and the slightly negatively charged end of a water molecule will be attracted to the slightly positively charged molecule. This means that ions will get surrounded in water molecules so there will be dissolved.

This means that living organisms can take up useful substances dissolved in water and these dissolved substances can be transported around the body.

Question 25

Explain how water has a high latent heat of vaporisation

Answer 25

Water evaporates when the hydrogen bonds are broken. It takes a lot of energy to do this so a lot of energy is used up when water evaporates. This means water has a high latent heat of vaporisation.

This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water.

Question 26

Explain how water can buffer (resist) changes in temperature

Answer 26

Hydrogen bonds give water a high specific heat capacity. When the water is heated, a lot of the heat energy is used to break the hydrogen bonds between water molecules so there is less heat energy to increase the temperature of the water.

This is useful for living organisms because it means that water doesn’t experience rapid temperature water changes - making water a good habitat as the organisms remain at a fairly stable temperature.

Question 27

Explain how water is very cohesive

Answer 27

Cohesion is the attraction between molecules of the same type. Water molecules are very cohesive because they are polar. Strong cohesion helps water flow to help substances to be transported. Strong cohesion also means that water has a high surface tension when it comes into contact with air.

Question 28

An ion with a positive charge is called a ______

Answer 28

cation

Question 29

An ion with a negative charge is called an ______

Answer 29

anion

Question 30

What are inorganic ions and what are their uses?

Answer 30

Inorganic ion = doesn’t contain carbon (few exception). There are inorganic ions in solution in the cytoplasm of cells and in the body fluids in organisms.

Iron ions in haemoglobin
Fe2+ binds to the oxygen in haemoglobin. When oxygen is bound, Fe2+ become Fe3+ until oxygen is released

Hydrogen ions
More H+ present the lower the pH so more acidic

Sodium ions
A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions = co-transport

Phosphate ions
When a phosphate ion is attached to another molecule, it is known as a phosphate group. It is the bonds between phosphate groups that store energy in ATP. The phosphate groups in DNA and RNA allow nucleotides to join up to form the polynucleotides.