University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

358

Pages:

3
Author:

Mariam A. A.

Physical Mutations How does X-Ray act as a mutagen? • • • • • X-ray radiation can alter the nitrogenous base sequence of DNA. X rays form radicals, which then act as a mutagen and form the mutation X-ray has high ionising energy (the shorter wavelength the higher the ionising) allowing it to either ionising DNA directly or ionise the cellular water that is surrounding the DNA which then give rise to reactive radicals that then reacts with DNA. the nitrogenous base sequence of the DNA can be altered resulting in insertion or translocation mutations. Insertion: when one or more extra nitrogenous base is incorporated into the normal DNA sequence. This alters the mRNA codon sequence, and a different amino acid can be specified as a result. - mRNA codon sequence: ✓ Each group of three bases in mRNA forms a codon, and each codon specifies a particular amino acid In mRNA -> each 3 bases -> form a group -> that group is a codon -> each codon forms a specific amino acid GGC do not form the same amino acid as GCG • ✓ The mRNA sequence is thus used as a template to assemble— in order—the chain of amino acids that form a protein Translocation mutation is a type of mutation where chromosomes can swap segments of their DNA sequence, resulting in one chromosome having a segment of another chromosome and vice versa. Draw a mind map summarizing the above information How does ultraviolet radiation act as a mutagen? • • • Ultraviolet radiation can act as a mutagen by causing two adjacent base pairs to form covalent bonds with each other, resulting in a dimer structure. Dimer is when a covalent bond is formed between 2 bases Radicals cannot be formed using ultraviolet radiation as it is lower ionising strength than Xrays (less capable of removing electrons). So, instead, dimers may be produced due to effect of ultraviolet radiation as a result. • • • • • • For example: ultraviolet radiation results in two adjacent thymine bases on the same DNA strand form covalent bonds with each other. sometimes dimers can be formed between base pairs on opposite DNA strands. the DNA double helix structure is distorted at the position of which the dimer is located. The formation of the dimer molecule prevents both of the thymine bases from bonding with adenine bases on the opposite strand as the hydrogen bonds between A=T are weakened This dimer molecule is not replicated by DNA polymerase during DNA replication and thus no nucleotides are paired with the covalently bonded thymine nitrogenous bases. This therefore alters the mRNA sequence that specifies the amino acid sequence of the polypeptide chain used to produce the required protein. This may result in the reduction in the protein’s activity or render it being unable to function completely. However, we do have enzymes that can repair such cross links between adjacent bases.