DNA replication + the genetic code (d,e,f)

Question 1

What is DNA replication?

Answer 1

The semi-conservative process of the production of identical copies of DNA molecules

Question 2

How does DNA helicase work?

Answer 2

• separates the 2 strands of DNA
• travels along the DNA backbone, catalysing reactions that break the hydrogen bonds between complementary base pairs as it reaches them

Question 3

How does DNA polymerase work?

Answer 3

• catalyses the formation of phosphodiester bonds between free nucleotides and newly exposed bases on template strand

Question 4

Describe the process of DNA replication?

Answer 4

1. DNA helicase causes the 2 strands to separate
2. Meanwhile, free nucleotides that have been activated are attracted to their complementary bases
3. Once lined up, DNA polymerase joins them together. Remaining unpaired bases continue to attract their complementary nucleotides
4. All nucleotides are joined to form a complete polynucleotide chain using DNA polymerase

Question 5

How is DNA semi-conservative?

Answer 5

• two molecules of DNA are produced, each one consisting of one old strand of DNA and one new strand
• thus it is semi-conservative - half the same - replication

Question 6

How can replication errors occur>

Answer 6

• sequences of bases are not always matched exactly and an incorrect sequence may occur in the newly-copied strand
• errors are random and spontaneous and lead to a change in the sequence of bases = mutation

Question 7

What is the genetic code?

Answer 7

The sequences of bases in DNA are the ‘instructions’ for the sequences of amino acids in the production of proteins. It is universal = all organisms use the same code.

Question 8

What is a triplet code?

Answer 8

Instructions that DNA carries are contained in the sequence of bases along the chain of nucleotides in DNA strands. The code in the base sequence is a simple triplet code = sequence of 3 bases = codon = each codes or an amino acid.

Question 9

What is a gene?

Answer 9

A section of DNA that contains the complete sequence of bases (codons) to code for a protein.

Question 10

How many different codons are possible?

Answer 10

There are 4 different bases so 4³=64 possible

Question 11

How is the code non-overlapping?

Answer 11

There is a single code to signal the start of a sequence ensuring the codons are read ‘in frame’ (e.g. from base 2 rather than 2 or 3).

Question 12

What is the degenerate code?`

Answer 12

Only 20 amino acids regularly occur in biological proteins - a lot more codons than amino acids. Thus many amino acids can be coded for by more than 1 codon.

Question 13

What is a frameshift mutation?

Answer 13

An insertion or deletion of DNA bases that causes the genetic code to be read incorrectly,