Dna and Base Substitution Mutation Essay

Submitted By ellennnkh
Words: 549
Pages: 3

Chromosomes, genes, alleles and mutations
4.1.1 State that eukaryote chromosomes are made of DNA and proteins.
Eukaryotic chromosomes consist of DNA wrapped around histone proteins
This forms the basic structure of the nucleosome, which is packed together to form chromatin (in a 'beads on a string' arrangement)
Chromatin will supercoil and condense during prophase to form chromosomes that can be visualised under a light microscope
Prokaryotic DNA is not wrapped around proteins and is thus considered to be 'naked'
4.1.2 Define gene, allele and genome.
Gene: a heritable factor that controls a specific characteristic.
Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.
Genome: the whole of the genetic information of an organism.
4.1.3 Define gene mutation.
Gene mutation: a change to the base sequence of a gene.
4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia.
Sickle cell anaemia is a genetic disease that affects red blood cells in the body. It is due to a mutation on the Hb gene which codes for a polypeptide of 146 amino acids which is part of haemoglobin (haemoglobin is an important protein component in red blood cells). In sickle cell anaemia the codon GAG found in the normal Hb gene is mutated to GTG. This is called a base substitution mutation as adenine (A) is replaced by thymine (T). This means that when the mutated gene is transcribed, a codon in the messenger RNA will be different. Instead of the normal codon GAG, the messenger RNA will contain the codon GUG. This in turn will result in a mistake during translation. In a healthy individual the codon GAG on the messenger RNA matches with the anticodon CUC on the transfer RNA carrying the amino acid glutamic acid. However, if the mutated gene is present then GUG on the messenger RNA matches with the anticodon CAC on the transfer RNA which carries the amino acid valine. So the base substitution mutation has caused glutamic acid to be replaced by…