3.9 DNA replication

Question 1

What is DNA replication?

Answer 1

The semi-conservation process of the production of identical copies of DNA molecules.

Question 2

What is semi-conservation replication?

Answer 2

DNA replication results in one old strand and one new strand present in each daughter DNA molecule.

Question 3

What enzymes are present in this process?

Answer 3

1) DNA helicase- carries out the unwinding and separating of the two strands of the DNA double helix.
2) DNA polymerase- catalyses the formation of phosphodiester bonds between these nucleotides.

Question 4

What is the process of semi-conservative replication?

Answer 4

1) DNA helicase breaks the hydrogen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands.
2) Each original single strand acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing- A with T and C with G.
3) The nucleotides of the new strand are joined together by the enzyme DNA polymerase. This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand. The strands twist to form a double helix.
4) Each new DNA molecule contains one strand from the original DNA molecule and one new strand.

Question 5

What is a mutation?

Answer 5

• A mutation is a change in the sequence of bases

- This can be caused by a random error where the sequence of bases are not matched exactly.

Question 6

What is the genetic code?

Answer 6

The sequence of bases in DNA are instructions for the sequences of amino acids in the production of proteins.

Question 7

What is the triplet code?

Answer 7

The code in the base sequences.

Question 8

What is a codon?

Answer 8

A three base sequence of DNA or RNA that codes for an amino acid.

Question 9

What is a gene?

Answer 9

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

Question 10

How is DNA copied into RNA?

Answer 10

1) DNA molecules are found in the nucleus of the cell, but the organelles that make proteins (ribosomes) are found in the cytoplasm.
2) DNA is too large to move out of the nucleus, so a section is copied into mRNA. This process is called transcription.
3) The mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein. This process is called translation.

Question 11

What is messenger RNA (mRNA)?

Answer 11

• Made in the nucleus.
• Three adjacent bases are called a codon.
• It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s going to make a protein during translation.

Question 12

What is transfer RNA (tRNA)?

Answer 12

• Found in the cytoplasm.
• It has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon.
• It carries the amino acids that are used to make proteins to the ribosomes during translation.

Question 13

What is ribosomal RNA?

Answer 13

• It forms the two subunits in a ribosome.
• The ribosome moves along with the mRNA strand during protein synthesis. The rRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids.

Question 14

What does non-overlapping mean?

Answer 14

The genetic code is non-overlapping- the adjacent codons do not overlap. A nonoverlapping code means that the same letter is not used for two different codons

Question 15

What does degenerate mean?

Answer 15

There are more possible combinations of triplets than there are amino acids. So, the same amino acid is coded by more than one base triplet.

Question 16

What are start & stop codons?

Answer 16

• The triplets that tell the cell when to start and stop the production of proteins.
• They are found at the beginning and end of the gene.

Question 17

What does universal mean?

Answer 17

• The genetic code is universal.

- The same specific base triplets code for the same amino acids in all living things.

Question 18

First stage of protein synthesis: Transcription

Answer 18

1) DNA helicase unwinds and unzips the section of DNA containing the gene by breaking hydrogen bonds between complementary bases
2) Free RNA nucleotides will base pair with complementary bases exposed on antisense strand (adenine and uracil , guanine and cytosine).
3) RNA polymerase joins up RNA nucleotides by forming phosphodiester bonds, making mRNA
4) mRNA is small enough to leave through nuclear pore to travel to ribosomes on the RER for translation

Question 19

Second stage of protein synthesis: Translation

Answer 19

1) mRNA binds to a ribosome
2) tRNA molecule, with complementary anticodon and specific amino acid binds to mRNA’s codon
3) A second tRNA molecule binds to the next complementary codon in the same way
4) First amino acid binds to second amino acid through peptide bond by peptide transferase
6) This process continues, producing a chain of linked amino acids (a polypeptide chain), until there’s a stop codon on the mRNA molecule.
7) The polypeptide chain moves away from the ribosome and translation is complete.