3.8- Nucleic Acids

Question 1

What are nucleic acids?

Answer 1

Large polymers formed from many nucleotides (the monomers) linked together in a chain.

• contain the elements: carbon, hydrogen, oxygen, nitrogen and phosphorus.
• two types: DNA and RNA.

Question 2

What is the role of DNA and RNA?

Answer 2

Storage and transfer of genetic information and the synthesis of polypeptides (proteins). They are the basis for hereditary.

Question 3

What is a nucleotide made up of?

Answer 3

Three components:

1. Pentose (5 carbon atoms) monosaccharide.
2. Phosphate group. (Acidic and negatively charged inorganic molecule)
3. Nitrogenous base. (complex organic molecule containing one or two carbon rings in its structure as well as nitrogen).

Question 4

Explain the formation of a polynucleotide.

Answer 4

Nucleotides are linked together by condensation reactions.

• the phosphate group at the 5th carbon of the pentose sugar of one nucleotide forms a covalent bond with the hydroxyl (OH) group at the 3rd carbon of the pentose sugar of an adjacent nucleotide.
• these bonds = phosphodiester bonds.
• this forms a long, strong sugar phosphate backbone with a base attached to each sugar.

Question 5

How can phosphodiester bonds be broken?

Answer 5

By hydrolysis, releasing the individual nucleotides.

Question 6

Explain the structure of DNA.

Answer 6

The sugar and phosphate group is always the same.
Sugar = deoxyribose (has one fewer oxygen atom than ribose).

Base can vary- each nucleotide has one of four bases:
-thymine (T)
-cytosine (C)
- adenine (A)
- guanine (G)
therefore there are 4 different DNA nucleotides

Question 7

What are the two types of bases? (DNA)

Answer 7

Pyrimidines- smaller bases, which contain single ring structures. Thymine and cytosine.

Purines- larger bases, contain double ring structures. Adenine and guanine.

Question 8

Explain the DNA double helix.

Answer 8

DNA is made up of two strands of polynucleotides coiled into a helix.

• the two strands are held together by hydrogen bonds between the bases.
• each strand has a phosphate group (5’) at one end and a hydroxyl group (3’) at the other.
• the two parallel strands are arranged so they run in opposite directions (anti parallel).

Question 9

Explain complimentary base pairing.

Answer 9

Adenine and thymine are able to form 2 hydrogen bonds and always join with each other.
Cytosine and guanine form 3 hydrogen bonds and therefore only bind to each other.

• these rules mean a small pyrimidine base always bings to a larger purine base and this maintains a constant distance between the DNA backbones.
• also means that DNA always gas equal amounts of A and T and equal amounts of C and G.

Question 10

What is RNA?

Answer 10

Ribonucleic acid plays an essential role in the transfer of genetic information from DNA to proteins that make up the enzymes and tissue in body.
-DNA is too large to leave the nucleus so the section of the DNA molecule corresponding to a single gene is transcribed to mRNA which is much shorter.

Question 11

How are the nucleotides of RNA different to those of DNA?

Answer 11

In RNA pentose sugar= ribose.
-thymine base is replaced by uracil (U)
-uracil is a pyrimidine that forms 2 hydrogen bonds with adenine.
Therefore base pairing rules still apply.

After protein synthesis the RNA molecules are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released+reused.