The discovery of the structure of DNA immediately suggested a method of copying the genetic material to Watson and Crick in 1953. This topic looks at these methods, DNA replication making an exact copy of the genetic material as well as Transcription and translation in the expression of a gene to make a protein.
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Revision summary list for topic 2.7 DNA Replication
- DNA replication
- Complementary base pairing leads to the semi-conservative replication of DNA.
- The enzyme helicase unwinds the double helix and breaks hydrogen bonds which hold the two DNA strands together.
- DNA polymerase (generalised name) links DNA nucleotides together to form a new strand DNA,using the pre-existing strand as a template.
- Transcription is the synthesis of mRNA by RNA polymerase using the DNA base sequence as a template
- Translation is the synthesis of polypeptides on ribosomes.
- The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
- Three bases of mRNA is called a codon and corresponds to one amino acid in the polypeptide.
- Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.
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Review questions
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DNA replication is known as semi-conservative. Which it the best explanation of this term?
The process of replication produces a new DNA double helix. One of the strands is from the original DNA molecule which was copied. The new strand is built from nucleotides.
This is semi-conservative replication .
Complementary base pairing occurs in DNA replication.
Which base(s) pair with Guanine (G) ?
DNA replication builds DNA so T pairs with A
Transcription builds mRNA so U pairs with A
What is the role of RNA polymerase?
RNA polymerase synthesises mRNA during transcription.
What is the name of the molecules which binds to each mRNA codon in translation?
Three bases of mRNA make a single codon which pairs with a tRNA molecule carrying an amino acid.
The three bases of tRNA which bind to the mRNA are called an anti-codon.
Which process in the list below occurs on ribosomes?
Translation occurs on ribosomes which are not found in the nucleus, they are in the cytoplasm, and on the rER membranes.
Whichi enzyme unwinds DNA and breaks the hydrogen bonds between the strands?
Helicase is the enzyme which unwinds the DNA and breaks the hydrogen bonds holding the two DNA strands together.
What is the name of the process shown in the diagram below.
As the nucleotides being added are RNA nucleotides making mRNA, it is transcription.
The enzyme which does this is called RNA polymerase
Which enzymes are responsible for DNA replication?
DNA polymerase builds a DNA polymer, and unwinds the DNA and separates the strands so that each can be used as a template.
What is the process which takes place on ribosomes?
The synthesis of polypeptides (translation) takes place on ribosomes and involves mRNA molecules and tRNA.
How many nucleotide bases is there in a mRNA codon or a tRNA anti-codon?
Each codon has three mRNA nucleotide bases.
anticodons have the same number of RNA bases on a tRNA molecule..
Revision fun activity
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