Gene Regulation and Mutation Notes and Questions How do mutations affect a cell?

Main Idea Gene expression is regulated by the cell, and mutations can affect this expression. Gene regulation is the ability of an organism to control which genes are transcribed in response to the environment.

Prokaryote Gene Regulation In prokaryotes, an operon often controls the transcription of genes in response to changes in the environment. An operon is a section of DNA that contains the genes for the proteins needed for a specific metabolic pathway.

Eukaryotic Gene Regulation Controlling transcription Transcription factors ensure that a gene is used at the right time and that proteins are made in the right amount. The complex structure of eukaryotic DNA also regulates transcription.

Hox Genes Hox genes are responsible for the general body pattern of most animals.

RNA Interference RNA interference can stop the mRNA from translating its message.

Mutations A permanent change that occurs in a cell’s DNA is called a mutation. Types of Mutations: ▫Point mutations, insertion, deletion

A mutation in DNA changes the amino acid base sequence. A different amino acid or series of amino acids are incorporated into the protein that is made on the ribosome. The result can be a misfunction of the protein. A mutation can affect a single nucleotide or a large segment of DNA.

Types of Mutations – Point Mutations Point mutations (Base-pair substitutions) - a mutation in which one nucleotide base replaces another Point mutations affect only one codon, so they affect only one amino acid in a peptide chain It may or may not have serious effects on an organism. It depends on where the mutation occurs and how it affects the protein for which it codes It can be harmless

Types of Mutations - Insertion Insertion is the addition of one or more bases into a nucleotide sequence This can change many amino acids in the polypeptide chain, thus changing the protein

Types of Mutations - Deletion Deletion – one or more bases is removed from a nucleotide sequence A different amino acid is put into the peptide chain, thus changing the protein

Frameshift Both insertion and deletion result in a frameshift. A frameshift is simply a shift (to the left or right) in the nitrogen bases, resulting in new codons. A frameshift changes the number of bases in a sequence.

Types of Mutations - Chromosomal Point mutations, insertions, and base deletions affect only a single gene or segment of DNA. A chromosomal mutation affects the entire chromosome. Chromosomal mutations change the number of genes in a chromosome or the organization of the chromosome. We will cover more of this with genetics.

Fragile X An example of a mutation is Fragile X. Fragile X syndrome is due to many extra repeated CGG units near the end of the X chromosome, making the lower tip of the X chromosome appear fragile.

Protein Folding and Stability Substitutions can lead to genetic disorders Substitutions can change both the folding and stability of the protein An example is sickle-cell disease

Causes of Mutation Mutations can occur spontaneously. Chemicals and radiation also can damage DNA. High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic. A mutagen is any agent that changes the DNA of an organism.

Body-cell v. Sex-cell Mutation Somatic cell mutations are not passed on to the next generation. Somatic cells are cells in the body that are not sex cells. Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.