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3.5 Transcription and Translation
Terms in this set (5)
3.5.1 Compare the structure of RNA and DNA
1. The number of strands.
* DNA has two strands forming a double helix.
* RNA has one strand.
2. The type of sugar.
* DNA has a deoxyribose.
* RNA has a Ribose.
3. The Nucleotides.
* DNA has A,C,G,T
* RNA has A,C,G,U, (Uracil replaces Thymine)
3.5.2 Outline DNA transcription in terms of the formation of the RNA strand complimentary to the DNA strand by RNA polymerase.
RNA polymerase is the enzyme used in transcription;
The DNA double helix uncoils and the two strands separate;
Free RNA nucleotides (A, C, G, U) are assembling using one of the two DNA strands as the template;
The RNA nucleotides are linked up to form a strand of RNA;
The mRNA separates from the DNA
The DNA double helix reforms.
3.5.3 Describe the genetic code in terms of codons composed of triplets and bases.
The genetic code is a triplet code.
3 bases code for one amino acid.
A group of three bases is called a codon.
3.5.4 Explain the process of translation, leading to peptide linkage of bases
The two subunits of a ribosome binds onto the mRNA.
The mRNA is made of codon, keeping in mind that one codon codes for one amino acid (aa).
Transfer RNA (tRNA) are present in large numbers around the ribosomes.
Each tRNA has an anticodon (triplet base like codon) and carries the aa matching to this anticodon.
tRNA bind to the ribosome.
2 tRNA can bin at once.
Binding of tRNA with anticodon complementary
to codon on mRNA
Codon and anticodon will be linked together by H bonds.
The 2 aa carried by tRNA are bonded together by a peptide (protein) linkage.
The tRNA who brought the first aa will detach.
The ribosome moves along the mRNA to the next codon.
Another tRNA carrying an aa binds.
So far, we have a chain of 3 aa.
This will be repeated until a polypeptide (protein) is formed.
3.5.5 Discuss the relationship between one gene and one polypeptide.
One gene is transcribed and translated to produce one polypeptide.
Some proteins are composed of a number of polypeptides and in this theory each polypeptide has its own gene.
e.g. haemoglobin is composed of 4 polypeptides (2 of each type) and there is a gene for each type of polypeptide.
This theory, like so many in biology has exceptions;
Some genes code for types of RNA which do not produce polypeptides.
Some genes control the expression of other genes.
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