Nucleotides and Nucleic acids

Question 1

Draw, and label, the basic structure of a nucleotide.

Answer 1

Phosphate + pentose sugar + nitrogenous base.

They all contain the elements hydrogen, phosphorous, oxygen and nitrogen.

Question 2

Draw a nucleotide showing the structure of the pentose sugar and where the phosphate group and
nitrogenous base attach using the standard system for numbering the carbons in the sugar.

Answer 2

The phosphate group attaches to the 5’ (prime) carbon. The nitrogenous base attaches the 1’ (prime) carbon.

Question 3

State the two main types of nucleic acid.

Answer 3

Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).

Question 4

Draw a table to show the similarities and differences between the nucleotides of DNA and RNA.

Answer 4

1) Pentose Sugar: RNA = ribose, DNA = Deoxyribose
2) Purines (two rings): RNA and DNA = adenine and guamine
3) Pyrimidine (one ring): RNA = cytosine and uracil, DNA = thymine and cytosine

Question 5

Draw the structures of ribose and deoxyribose and identify the difference between the two pentose
sugars.

Answer 5

Deoxyribose - there is an H below the 2’ carbon

Ribose - there is an -OH group below the 2’ carbon

Question 6

List the full names of the 5 possible nitrogenous bases in nucleic acids.

Answer 6

Adenine (purine) , thymine (pyrimidine), guanine (purine), cytosine (pyrimidine) and uracil (pyrimidine).

Question 7

Name the two types of nitrogenous base.

Answer 7

The two types are purine and pyrimidine.

Question 8

Outline the structure of the two types of nitrogenous base.

Answer 8

Purines:
Larger bases which contain a double carbon ring structure.
Pyrimidines:
Smaller bases which contain a single carbon ring structure.

Question 9

Define the term monomer.

Answer 9

An individual molecule that makes up a polymer.

Question 10

Define the term polymer.

Answer 10

A long chain molecule composed of bonded multiple individual monomers in a repeating pattern.

Question 11

Define the term nucleic acid.

Answer 11

Large polymers formed from nucleotides. They contain carbon, hydrogen, nitrogen, phosphorous and oxygen.

Question 12

Define the terms polynucleotide.

Answer 12

A molecule made up of lots of nucleotides joined together in a long chain.

Question 13

Define the term nucleotide.

Answer 13

The monomers used to form nucleic acids, made up of a pentose monosaccharide, a phosphate group and a nitrogenous base.

Question 14

Define the term phosphodiester bond.

Answer 14

Covalent bonds formed between the phosphate group of one nucleotide and the hydroxyl group of another.

Question 15

Draw and label a diagram to show how nucleotides can link together to form polynucleotides (including
the production of water).

Answer 15

The phosphate group of the second nucleotide bonds to the hydroxyl group of the 3’ carbon of the pentose sugar in the first nucleotide to form a phosphodiester bond. This releases a water molecule.
This forms a long, strong sugar phosphate backbone.

Question 16

State the name of the reaction that joins nucleotides to other nucleotides and the name of the reaction
that breaks phosphodiester bonds.

Answer 16

Joining: condensation reaction
Breaking: hydrolysis reaction

Question 17

State 3 main types of activity for which cells require energy.

Answer 17

• Anabolic reactions such as the synthesis of large molecules (fats, polysaccharides, polypeptides ect)
• Movement e.g. protein fibres in muscle cells that cause muscle contractions.
• The transportation of ions and molecules across the membrane.

Question 18

Draw and label a diagram of ATP. (Adenosine triphosphate)

Answer 18

Three phosphate groups bonded to 5’ carbon of a ribose sugar. The nitrogenous base adenine is bonded 1’ carbon.

Question 19

Draw and label a diagram of ADP.

Answer 19

Two phosphate groups, the base adenine and ribose sugar. Bonding all in the same place.

Question 20

List 2 similarities and 2 differences between the structure of ATP and DNA and RNA nucleotides

Answer 20

• RNA and ATP both have a ribose sugar, but DNA has deoxyribose
• DNA and RNA both have 1 phosphate group but ATP has 3
• They all have only one nitrogenous base.

Question 21

Draw a reaction to show how energy is released from ATP to provide energy for cellular activities.

Answer 21

Energy is stored in the phosphate bond, when energy is needed ATP is broken down to ADP and inorganic phosphate. Energy is released from the phosphate bond and used by the cell.

Question 22

Draw a diagram to show the interconversion of ATP and ADP, the names of the types of reactions
involved, where energy is released and the role of respiration.

Answer 22

Hydrolysis where ADP, P and energy is produced from ATP and H2O. Energy is released for use by cells.
Condensation where ATP and water is produced from ADP and P. This is when energy is supplied from respiration.

Question 23

State 5 properties of ATP and explain why each makes it ideally suited to function as an energy transfer
molecule.

Answer 23

1) Small so it moves easily into, out of and within cells.
2) Water soluable - energy requiring processes happen in aqueous environments.
3) Contains bonds between phosphates with intermediate energy large enough to be useful for cellular reactions but not so large that energy is wasted.
4) Releases energy in small quantities - quantities are suitable to most cellular needs so energy isn’t wasted as heat.
5) Easily regenerated- can be recharged with energy.

Question 24

. Define the term phosphorylation.

Answer 24

The addition of phosphate group to a molecule.

Question 25

Draw and label a diagram of the structure of DNA.

Answer 25

DNA is composed of two polynucleotide strands joined together by hydrogen bonding in a double helix shape.
The two polynucleotides are anti-parallel, this means they run in opposite directions.

Question 26

Define the term complementary base pairing.

Answer 26

Specific hydrogen bonding between nucleic acid bases. So A-T/U and C-G.

Question 27

Define the term sugar-phosphate backbone.

Answer 27

The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. This backbone is composed of alternating sugar and phosphate groups.

Question 28

Define the term anti-parallel.

Answer 28

Two molecules that are side by side but are arranged so that they run in opposite directions.

Question 29

State the complementary base pairing rules, name the bond that holds them together, and state the
number of bonds that hold each pair together.

Answer 29

A small pyrimidine base will always bind to a purine base. Adenine-Thymine/Uracil (2 hydrogen bonds hold them together), Cytosine-Guanine (3 hydrogen bonds).

Question 30

Explain why a DNA molecule has equal amounts of adenine and thymine and equal amounts of
cytosine and guanine

Answer 30

They always pair up together so you can’t have one without the other.

Question 31

Describe how purines and pyrimidines are arranged in the complementary base pairing rules.

Answer 31

One pyrimidine always binds to a purine - this maintains a constant distance between the DNA backbones.

Question 32

Describe the significance of the double stranded, complementary base paired nature of DNA for its
function.

Answer 32

• Complementary base pairing allows it replicate easily
• It is long so it can store a lot of information
• It is coiled into a double helix, so it can store a lot of info in a small space.
• It is a very stable molecule due to it’s double helix shape and sugar phosphate backbone.

Question 33

Describe the significance of the sequence of bases in a DNA strand for its function.

Answer 33

• The sequence of bases allows it to carry coded information for protein synthesis.

Question 34

Describe, and explain the importance of the steps in the isolation and purification of DNA by
precipitation.

Answer 34

1) Grind sample - breaks cell wall
2) Mix with detergent - breaks cell membrane, releasing cell contents into solution.
3) Add salt - breaks hydrogen bonds between the DNA and the water molecules.
4) Add protease enzymes - breaks proteins associated with DNA in nuclei.
5) Add layer of alcohol on top of sample - causes DNA to precipitate out of solution.
6) White strands will form - this DNA between the sample and the layer of the alcohol.