2.1.3 Nucleotides + Nucleic Acids

Question 1

What are nucleic acids?

What are the two types?

Answer 1

Nucleic acids are polymers of nucleotides (monomer).

DNA and RNA - both are polynucleotides.

Question 2

What is the structure of a nucleotide?

Answer 2

Composed of a pentose sugar, phosphate group and nitrogenous base.
On pentose sugar, phosphate group linked to C5 and nitrogenous base linked to C1.

Question 3

Describe the structure of DNA.

Answer 3

Deoxyribose pentose sugar with a hydrogen atom on C2.
Phosphate group on C5
One of four nitrogenous bases on C1: adenine, cytosine, guanine, thymine.

Question 4

Describe the structure of RNA.

Answer 4

Ribose pentose sugar with a hydroxyl group (-OH) on C2.
Phosphate group linked to C5.
Nitrogenous base on C1: adenine, cytosine, guanine, uracil.

Question 5

What are the three types of RNA?

What are their functions?

Answer 5

Messenger RNA (mRNA) - carries copy of gene out of the nucleus to a ribosome for protein synthesis.
Transfer RNA (tRNA) - transports amino acids to ribosomes.
Ribosomal RNA (rRNA) - makes up the ribosomes.

Question 6

What is the difference between a purine base and a pyrimidine base?
Give examples.

Answer 6

Purine bases have a double ring structure (e.g. adenine + guanine).

Pyrimidine bases have a single-ring structure (e.g. cytosine, thymine + uracil).

Question 7

What is a polynucleotide?

Answer 7

A chain of nucleotides bonded together via phosphodiester bonds.

Question 8

What is a phosphodiester bond?

Answer 8

The bond between two nucleotides.

Forms between the sugar of one nucleotide, and the phosphate group of another - makes a sugar-phosphate backbone.

Question 9

Describe the structure of DNA.

Answer 9

• Two antiparallel polynucleotide strands in a double-helix.
• Each DNA nucleotide consist of a deoxyribose sugar, a phosphate group, and one of four bases: adenine, thymine, cytosine, guanine.
• The rungs of the ladder consist of complimentary base pairs (adenine, thymine, cytosine, guanine) joined by hydrogen bonds.
• Covalent bond between pentose sugar and phosphate group.

Question 10

Name the complementary base pairs, and identify how many hydrogen bonds are between them.

Answer 10

Adenine + Thymine = 2 H-bonds

Cytosine + Guanine = 3 H-bonds

Question 11

Why can adenine only bind to thymine, and not cytosine or guanine?

Why is this complementary base pairing important in DNA replication?

Answer 11

Because a purine is only able to bind to a pyrimidine due to the different sizes of each.

Important as DNA can be replicated without error. Also reduces occurrence of mutation.

Question 12

How does the structure of DNA enable it to carry out its functions?

Answer 12

• Two strands - makes it stable.
• Bases located inside sugar-phosphate backbone - so they are protected, and integrity of code is maintained.
• Molecules are long - so can store a lot of genetic information.
• Weak hydrogen bonds - so they can break easily enabling the molecule to unzip for replication and transcription.