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38 Cards in this Set

  • Front
  • Back

When two daughter cells are genetically identical to the original cell what does this mean?

The daughter cells contain DNA with a base sequence identical to the original parent cell.

In order for DNA to replicate what must happen first?

The double helix strand must unwind and then separate into two strands.

For the the DNA strand to unwind and separate what must happen?

The hydrogen bonds between the complimentary base pairs must first be broken.

What will free nucleotides do?

Pair with their complimentary bases, which have been exposed as the strands separate.

What forms between the new nucleotides that join onto their complimentary base pairs once the strands have opened up?

Hydrogen bonds.

Once the new nucleotides have joined to their complimentary base pairs and hydrogen bonds have formed between the bases what happens next?

The new nucleotides join to their adjacent nucleotides with phosphodiester bonds.

What does the term semi-conservative replication mean?

Two new molecules of DNA are produced from the replication, each one consisting of one old strand of DNA and one new strand.

What is DNA replication controlled by?


Which enzyme carries out the process of unwinding and separating of the two strands of the DNA double helix?

DNA helicase.

What does the DNA helicase do?

What can this be seen as?

It travels along the DNA backbone, catalysing the reactions that break the hydrogen bonds between complimentary base pairs as it reaches them.

This can be seen as the strand 'unzipping'.

Free nucleotides pair with the newly exposed bases on the template strands during the 'unzipping process'. A second enzyme catalyses the formation of phosphodiester bonds between these nucleotides , what is this enzyme?

DNA polymerase.

How does DNA polymerase always move along the template strand?

In the same direction.

Which end is the only end of which DNA polymerase can bind to and so what direction do they go in?

It can only bind to the 3' (OH) end so travels in the direction of 3' to 5'.

Why does DNA polymerase have to replicate each of the template strands in opposite directions?

Because DNA only unwinds and unzips in one direction.

Which of the template strands can be continuously replicated as the strands unzip?

The strand that is unzipped from the 3' end.

As the strand that is unzipped from the 3' end can be continuously replicated what name is it given and what does it undergo?

It is called the leading strand and undergoes continuous replication.

The strand being unzipped from the 5' end means that DNA polymerase has to wait until what?

Until a section of the strand has been unzipped and then work back along the strand.

The strand unzipped from the 5' end has DNA being produced in sections. What are these section called?

Okozaki fragments.

The strand which undergoes discontinuous replication is known as what?

The lagging strand.

Sequencing of bases are not always matched properly, and an incorrect sequence may occur in the newly-copied strand. These errors occur randomly and spontaneously and lead to a change in the sequence of bases. What is this known as?

A mutation.

What is the genetic code?

DNA carries the instructions needed to synthesise the different proteins needed by organisms - proteins are made up of a sequence of amino acids - folded into complex structures - so DNA must code for the sequence of amino acids.

Where are the instructions that DNA carries contained?

In the sequence of bases along the chain of nucleotides that make up the two strands of DNA.

The code in the base sequences is what?

Triplet code.

What is a triplet code?

A sequence of three bases called a codon.

What does a codon do?

Codes for an amino acid.

What is a codon?

A sequence of three bases.

What is a gene?

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

The genetic code is universal - all organisms use the same code, but what is different?

The sequence of bases coding for each individual protein.

How many different bases are there?


If there are four bases, how many different base triples or codons are possible?

What does this include?

64 (4 cubed - 4x4x)

This includes the start codon.

What is the function of a start codon?

It signals the start of a sequence that codes for a protein.

If the start codon is in the middle of the gene, what amino acid does it code for?


How many stop codons are there?


Do stop codons code for any amino acids?


What is the function of stop codons?

To signal the end of the sequence.

What ensure that the genetic code is non-overlapping?

By having a single codon to signal the start of a sequence it is ensured that the codons (bases) are read in frame, which means the DNA base sequence is read from base 1, not 2 or three.

Why are there a lot more codons than amino acids?

There are only 20 different amino acids that regularly occur in biological proteins.

Why is the genetic code known as degenerate?

There are a lot more codons than amino acids, therefore many amino acids can be coded for by more than one codon.