MUTATIONS Chapter 17

Mutation: Effects of changes to the genetic information of a cell or virus. Responsible for huge diversity of genes Source of new genes It can be large scale mutation-chromosomal rearrangement that can affect long segments of DNA or small scale mutation/point mutation-changes in a single nucleotide pair of a gene.

Point mutation: Occurs in a gamete or cell that give rise to a gamete. Can be passed on to offsprings If it has an adverse effect on the phenotype (appearance) of an organism, the mutant condition is referred to as genetic disorder or hereditary disease. Ex: sickle cell disease- mutation of a single nucleotide pair that encodes beta globin of hemoglobin, resulting in having Valine instead of Glutamic acid.

Types of Point mutation: Single nucleotide pair substitution: -replacement of one nucleotide and its partner with another pair of nucleotides. Subtypes of Point mutation: 1.Silent mutation-no observable effects on the phenotype. 2.Missense mutation-changes in one amino acid to another; may have little effect on the protein. 3.Nonsense mutation-point mutation that can change into a stop codon; causes translation to be prematurely terminated; shorter polypeptide and can lead to nonfunctional proteins.

Deletion and Insertion: Additions or losses of nucleotide pair in a gene. Bad effect on the resulting protein. Alters the reading frame of the genetic message Subtype: 1. Frameshift mutation-number of nucleotides inserted or deleted in multiples of 3; downstream deletion or insertion; improperly grouped resulting in extensive missense; protein is certainly nonfunctional.

Mutagens: Spontaneous mutation-incorrect base will be used as a template in the next round of replication Mutagens are physical and chemical agents that interact with DNA and causes mutation. Herman Muller in 1920 discovered that xray causes mutation in Drosophilia (fruit flies). He also discovered that high energy radiation and UV can cause disruptive thymine dimers in DNA.

Comparing Gene Expression in Bacteria, Archaea and Eukarya Bacterial and eukaryotic RNA polymerase are different Single archaeal RNA polymerase resembles the eukaryotic ones Archaea and eukaryotes uses set of transcription factors. Transcription is terminated differently in bacteria and eukaryotes. Archaeal ribosomes are the same size as bacterial ribosomes.

The most important differences between bacteria and eukaryotes with regard to gene expression arise from the bacterial cell’s lack of compartmental organization. What is a gene? A gene is a region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule. Gene is precisely regulated!