Chapter 17.5 Gene expression and Mutations

RNA’s Versatility RNA can perform a wide range of functions because of 3 properties: 1. RNA can hydrogen bond with other nucleic acid molecules 2. It can assume a 3-D shape by forming hydrogen bonds between bases 3. It has functional groups that allow it to act as a catalyst RNA’s versatility may also be the reason many viruses utilize RNA instead of DNA Table 17.1 section 5 p. 327

Point Mutations Where did eukaryotes and prokaryotes get the genes that encode the huge diversity of proteins they synthesize? The ultimate source of new genes has been the mutation of preexisting genes

Point Mutations Point mutation- chemical changes in just one base pair of a gene If point mutation occurs in a gamete or cell that becomes a gamete, it may be transmitted to offspring and to future generations If adversity is great enough to effect the phenotype of organism it is referred to as a genetic disorder or hereditary disease EX: sickle cell disease

Point mutation example

Types of Point Mutations Base pair substitutions – replacement of one nucleotide and its partner for another pair *silent mutations- may have no effect on coding or amino acid. *missense mutations – still code for an amino acid, but not a needed one at a critical point of polypeptide formation *nonsense mutations – code for a stop sequence that will prematurely terminate translation and likely lead to nonfunctional proteins.

Base Pair Substitution

Types of Point Mutations Insertions and deletions – are additions or losses of nucleotide pairs in a gene Frameshift mutation – alteration of the reading frame of the genetic message from the insertion or deletion of a nucleotide - improperly groups codons downstream - unless at the end, will likely produce a nonfunctional protein

Frameshift Mutations

Mutagens Mutagens – physical or chemical agents that interact with DNA that cause mutations 1.Radiation is physical mutagen 2. Chemical mutagens- a. base analogs that are similar to DNA bases but will pair incorrectly during replication b. mutagens that insert themselves in DNA during replication and distort the double helix c. mutagens cause changes to bases’ pairing properties