Structure and replication of DNA

Question 1

What is the genetic code?

Answer 1

The sequence of bases on DNA.

Question 2

When does DNA replication occur?

Answer 2

Prior to cell division

Question 3

What does DNA replication require?

Answer 3

• ATP
• DNA nucleotides
• Enzymes

Question 4

Describe the structure of DNA

Answer 4

• DNA has a double stranded helix structure and consists of 2 long chains of subunits called nucleotides.
• Nucleotides consist of deoxyribose sugar, a nitrogenous base and a phosphate.
• The four nitrogenous bases are Adenine, Thymine, Guanine and Cytosine.
• Adenine pairs with Thymine
  Guanine pairs with Cytosine.
• nucleotides make up the phosphate -sugar backbone.
• There are hydrogen bonds between the bases, they are weak.
• The strands run in opposite directions so have an antiparallel structure.
• the phosphate is the 5’ and the deoxyribose sugar is the 3’.

Question 5

What is the enzyme that replicates DNA?

Answer 5

DNA polymerase.

Question 6

What is required for DNA polymerase to start replication?

Answer 6

A primer

Question 7

What is a primer?

Answer 7

its a short strand of nucleotides.

Question 8

What is the process of DNA replication?

Answer 8

1. DNA is unwound and the hydrogen bonds between the bases are broken which forms two template strands.
2. Primer attaches to a short sequence on the DNA allowing the primer to bind
3. DNA polymerase will add nucleotides using the complementary base pairing rule to the deoxyribose 3’ of the new strand which is forming.

Question 9

How does the leading strand replicate?

Answer 9

DNA polymerase works in a 5’ to 3’ direction. DNA polymerase can only add nucleotides to the 3’ end of the growing strand. This means the strand is replicated continuously.

Question 10

How does the lagging strand replicate?

Answer 10

DNA polymerase can only add to the 3’ end, the opposite end has to be replicated in fragments. it requires the use of many primers and the fragments produced are joined together by the enzyme ligase.

Question 11

What does PCR do?

Answer 11

It amplifies the DNA using complimentary primers for specific target sequences.

Question 12

What are the stages of PCR?

Answer 12

1. DNA is heated to between 92 and 98 to break the hydrogen bonds between bases and separate the two strands.
2. The DNA is then cooled to between 50 and 65 to allow the primers to bind to the target sequences.
3. It is then heated to between 70 and 80 for heat tolerant DNA polymerase to replicate the region of DNA.

Question 13

What are some practical applications of PCR?

Answer 13

• Solve crimes
• settle paternity suits
• diagnose genetic disorders