3.8 Nucleic acids

Question 1

What are nucleotides?

Answer 1

• The monomers that are used to form nucleic acids.

- Made up of a pentose monosaccharide, a phosphate group and a nitrogenous base.

Question 2

What are nucleic acids?

Answer 2

• Large polymers formed from nucleotides.

- Contain the elements carbon, hydrogen, nitrogen, phosphorus and oxygen.

Question 3

What is an individual nucleotide made of?

Answer 3

• A pentose monosaccharide, containing five carbon atoms
• A phosphate group, an inorganic molecule that is acidic and negatively charged.
• A nitrogenous base: A complex organic molecule containing one or two carbon rings in its structure as well as nitrogen.

Question 4

How are nucleotides linked together to form polypeptides?

Answer 4

By condensation reactions. The phosphate group at the fifth carbon of the pentose sugar of one nucleotide forms a covalent bond with the hydroxyl group at the third carbon of the pentose sugar of an adjacent nucleotide.

Question 5

What are phosphodiester bonds?

Answer 5

Phosphodiester bonds forms a long, strong sugar phosphate ‘backbone’ with a base attached to each sugar. The phosphodiester bonds are broken by hydrolysis, the reverse of condensation, releasing the individual nucleotides.

Question 6

Whar two groups can bases be divided into?

Answer 6

Pyramidines and purines

Question 7

What are pyramidines?

Answer 7

The smaller bases, which contain single carbon ring structures- thymine, and cytosine

Question 8

What are purines?

Answer 8

The larger bases, which contain double carbon rings structures- adenine and guanine

Question 9

What does RNA contain?

Answer 9

• RNA (ribonucleic acid) contains nucleotides with a ribose sugar (5 C sugar/pentose sugar)
• A RNA nucleotide also has a phosphate group and one of four different bases.
• In RNA, uracil (a pyramidine) replaces thymine as a base.
• An RNA molecule is made up of a single polynucleotide chain.

Question 10

How can you phosphorlyate a nucleotide?

Answer 10

You add one or more phosphate groups to it.

Question 11

What is ADP & ATP?

Answer 11

• ADP (adenosine diphosphate) contains the base adenine, the sugar ribose and two phosphate groups.
• ATP (adenosine triphosphate) contains the base adenine, the sugar ribose and three phosphate groups.

Question 12

How does ADP form ATP?

Answer 12

• ATP is synthesised frim ADP and inorganic phosphate, using the energy from an energy releasing reaction.
• The ADP is phosphorylated to form ATP and a phosphate bond is formed.
• Energy is stored in the phosphate bond.
• When this energy is needed by a cell, ATP is broken back down into ADP and an inorganic phosphate.
• Energy is released from the phosphate bond and used by the cell.

Question 13

What types of cell activity requires energy?

Answer 13

• Synthesis : e.g of large molecules such as proteins
• Transport: e.g pumping molecules or ions across cell membranes by active transport.
• Movement: E.g protein fibres in muscle cels that cause muscle contraction

Question 14

What are the properties of ADP?

Answer 14

• Small : Moves easily into, out, within cells.
• Water soluble: Energy requiring processes happen in aqueous solutions.
• Easily regenerated: Can be recharged with energy
• Releases energy in small quantities: Quantities are suitable to most cellular needs, so that energy is not wasted as heat.
• Contains bonds between phosphates with intermediate energy: large enough to be useful for cellular reactions but not so large that energy is wasted as heat.

Question 15

How many hydrogen bonds form between adenine and thymine?

Answer 15

2

Question 16

How many hydrogen bonds form between cytosine and guanine?

Answer 16

3

Question 17

How can you purify DNA using a precipitation reaction?

Answer 17

1) Swill drinking water around mouth for 30 seconds and spit back into plastic cup. (Cheek cells)
2) Pour some of the water into a test tube.
3) Add 1cm^3 of salt solution, 1cm^3 of detergent solution and 1cm^3 of protease solution into the test tube.
4) Invert the test tube three times to mix contents and place it in a water bath for 10 minutes.
5) Hold the test tube at an angle and carefully pour 2cm^3 of ice-cold ethanol down the inside of the test tube.
6) Leave the test tube to stand upright for 5 minutes.
7) Your DNA should become visible in the ethanol layer.

Question 18

structure of DNA

Answer 18

• has one phosphate group
• 4 different types of nitrogenous bases ; adenine, thymine, cytosine and guanine
• has a pentose sugar called deoxyribose

Question 19

describe and explain the role of ATP in the cell

Answer 19

• it releases 30kJ of energy when a
  phosphate is removed by hydrolysis (ATP → ADP + P(i))
• energy released for) metabolism/muscle contraction
• ADP can attach a phosphate (forming ATP) during , respiration / photosynthesis (ATP + H2O → ADP + P(i))
• energy released in ,
  small ‘packets