Gene Regulation and Structure Grade 10 Biology Spring 2011

 Describe how the lac operon is turned on and off  Summarize the role of transcription factors in regulating eukaryotic gene expression  Describe how eukaryotic genes are organized  Evaluate three ways that point mutations can alter genetic material

 Prokaryotes have about 2,000 genes  Humans have about 30,000 genes  Not all of genes are transcribed and translated at the same time  So as not to waste energy and materials  Both are able to regulate gene expression depending on cell’s needs

 E. Coli  Prokaryote  Gene regulation well undestood- lac operon gene

 E. Coli is in the intestinal tract  Lactose from milk enters and becomes available to E. Coli  E. Coli (bacteria) can absorb lactose and break it down for energy  Recognizing, consuming, and breaking down lactose, into glucose and galactose, requires 3 different enzymes on 3 different genes

 3 lactose metabolizing genes are located next to each other  Controlled by the same promoter site  On-off switch  “turns on” (transcribes and then translates) the 3 genes when lactose is present  “turns off” genes when lactose is not available

 Operator:  Piece of DNA that overlaps promoter site and serves as on-off switch  Able to control RNA polymerase’s access to 3 lactose metabolizing genes  Promoter:  Area in which RNA polymerase binds and allows the genes to be transcribed  Repressor protein:  Protein that binds to an operator and physically blocks RNA polymerase from binding to promoter site  Stops transcription of genes in operon

 Operon:  A group of genes that code for the enzymes involved in the same function, their promoter site, and the operator that controls them all  Lac Operon:  Operon that controls the metabolism of lactose

 Repressor protein turns the operon off  Repressor protein binds to the operator and blocks RNA polymerase from binding to the promoter site  Blocking of RNA polymerase stops the transcription of genes in the operon

 Lactose binds to repressor protein and changes repressor proteins shape  Change of shape causes repressor protein to fall off of the operator  Now the RNA polymerase is free to bind to the promoter (no longer blocked)  RNA polymerase can transcribe the genes that code for the lactose metabolizing enzymes

 By producing the enzymes only when the nutrient is available, the bacterium (E. coli) saves energy

 Lets watch a video to review the lac operon!

 Contain more DNA than prokaryotes  Must continually turn genes on and off  Operons are not common in eukaryotes  Instead, genes with related functions are often scattered on different chromosomes

 Because there is a nuclear envelope that physically separates transcription from translation more opportunities for gene regulation

 Gene regulation can occur:  Before transcription  During transcription  After transcription  And after mRNA leaves the nucleus or after translation, when protein is functional

 Most gene regulation in eukaryotes controls the onset of transcription  When RNA polymerase binds to a gene  Use regulatory proteins- called transcription factors  But many more proteins involved and more complex

 Transcription factors:  Help arrange RNA polymerases in the correct position on the promoter  Gene can be influenced by many different transcription factors

 Enhancer: sequence of DNA that can be bound by a transcription factor  Located thousands of nucleotide bases away from promoter  Loop in DNA may bring enhancer and its attached transcription factor (activator) into contact with the transcription factors and RNA polymerase at the promoter

 In eukaryotes many genes are interrupted by introns  Introns: long segments of nucleotides that have no coding information  Exons: portions of a gene that are translated (expressed) into proteins

 After gene is transcribed, introns in mRNA are cut out by splicosomes  Splicosomes: complex assemblies of RNA and protein  Exons that remain are “stitched” back together by slicosome to form a smaller mRNA molecule  mRNA is then translated

 Each exon encodes part of protein  By having introns and exons cells can occasionally shuffle exons to make new genes  Play an evolutionary role  Thousands of proteins that occur seem to have arisen from a few thousand exons  Some genes exist in multiple copies

 Mutation: change in the DNA of a gene  Rare  Mutations in gametes can be passed on to offspring, those in body cells (somatic cells) cannot

 Gene Rearrangements: mutations that move an entire gene to a new location  Disrupt genes function, gene is exposed to new regulatory conditions  Ex. You move to France and can’t speak French

 Two types of Gene Rearrangements: 1. Tranposition: genes are carried by moving transposons 2. Chromosomal Rearrangement: portions of the chromosome containing a gene may be rearranged during meiosis

 Gene Alterations: mutations that change a gene  Usually result in the placement of the wrong amino acid during protein assembly  Usually disrupts protein’s function

 Three types of Gene Alterations: 1. Point Mutations: single nucleotide changes 2. Insertion Mutation: sizable length of DNA is inserted into a gene Often result when mobile segments of DNA (transposons) move randomly from one position to another on a chromosome 3. Deletion Mutation: segments of gene are lost Often during meiosis

Point Mutation Insertion Mutation Deletion Mutation

 Genetic message is read as a series of triplet nucleotide  Insertions and deletions can upset the triplet groupings  Ex. Delete the C from this sentence, keep letters in triplets  THE CAT ATE  THE ATA TE  meaningless

 Frameshift Mutation: mutation that causes gene to be read in the wrong 3-nucleotide sequence

 THo THo

 Activity Modeling Introns and Exons (p. 218)  Procedure:  Place a 15-20cm strip of masking tape on your desk. Tape represents a gene.  Use 2 colours to write the words APPROPRIATLY JOINED on the tape exactly as shown. Space the letters so that they take up the entire length of the tape. The segments in one colour represent introns; those in the other colour represent exons.  Lift the tape. Working from left to right, cut apart the groups of letters written in the same colour. Stick the pieces of tape to your desk, making two strips according to colour and joining the pieces in their original order.

 Activity Modeling Introns and Exons (p. 218)  Analysis  Determine from the resulting two strips which strip is made of introns and which is made of exons  Predict what might happen to a protein if an intron were not removed