Nucleic Acids

Question 1

How is an ATP molecule formed from its component molecules?

Answer 1

1. Adenine, ribose/pentose, three phosphates
2. Condensation reaction
3. ATP synthase

Question 2

Nucleotide

Answer 2

The monomer that joins together to make the polymer of DNA (a nucleic acid)

Question 3

Condensation reactions

Answer 3

• Condensation reactions join the base, phosphate and sugar to form nucleotide
• Condensation reactions also join each nucleotide together between the phosphate group of one and a carbon of the pentose sugar of the other
• This bond is known as a phosphodiester bond
• The backbone of DNA is made up of the repeated joining of the sugar and the phosphate group of each nucleotide

Question 4

Base and Base Pairs

Answer 4

• There are four bases
• They are held together by hydrogen bonds
• Their structures force the bases to bind together in a specific way this is called specific or complimentary base pairing
• Adenine (A) always binds with Thymine (T)
• Guanine (G) always binds with Cytosine (C)
• Bases are often referred to by their letters and the order of the letters makes up the DNA code

Question 5

DNA double helix

Answer 5

• Double = two strands
• Helix = twisted around each other
• The two phosphate backbone strands are held together by chemicals called ‘bases’

Question 6

RNA

Answer 6

• Contains the bases A,C and G but T is replaced with Uracil (U)
• The sugar is ribose
• Single nucleotide strand
• Two types of different RNA - mRNA and tRNA

Question 7

Differences

Answer 7

Bacterial DNA - short, circular and not associated with proteins
Eukaryotic DNA - long, linear and associated with proteins to form chromosomes

Question 8

How does DNA replicate

Answer 8

• DNA has to replicate itself every time a cell divides so that both cells have identical copies of the entire genome
• Semi Conservative Replication - this is because half of each new double helix is a strand that has come from the double helix of the original DNA molecule
• It has been conserved from the parent cell
• The hydrogen bonds between the bases can be easily broken to allow both strands to be a template and complimentary base pairing
• The correct bases can only pair with each other due to their structure

Question 9

DNA Polymerase

Answer 9

• Each DNA strand has a directional structure due to the ends being either a sugar that’s attached to the 5th carbon or a hydroxyl group attached to the 3’
• Only complementary to the 3’ end of the template strand so it can only move along the template strand and add nucleotides in the 3’ to 5’ direction
• This means the new strand is built 5’ to 3’ because the strands are antiparallel
• While one strand is continuously built the other is built in the other direction in sections as the DNA is unwound
• The DNA polymerase on the opposite template strand has to detach and re-attach so it often moves more slowly