Bio 160 Unit 4-1

1. Bio 160Unit 4-1 Week Four- Lecture One

2. Control of Gene Regulation • Proteins turn genes on or off • Being “turned on” means being actively transcribed by mRNA and translated to the protein • Gene expression is the process of moving from a genotype to a phenotype • Main control is done by controlling transcription • Gene sequence determines where transcription can begin

3. Gene regulation in prokaryotes • Operon a cluster of genes that have related functions and begin with a promoter and an operator • Promoter- a stretch of nucleotides that create a site where RNA polymerase, the transcription enzyme, can attach and initiate transcription • Operator- a section of nucleotides just after the promoter complete with receptor sites, that will determine if RNA polymerase can attach to the promoter or not

4. Repressor proteins will bind to the operator section of a gene if there is none of the sugar needing to be broken down present, preventing RNA polymerase from binding and transcribing more of the coded enzyme • The repressor protein is coded for by a regulatory gene that sits just in front of the promoter section • It is continually expressed so the cell always has repressor molecules • If the sugar needing to be broke down is present, it will bind with the repressor protein, changing its shape and not allowing it to bind with the operator sequence • If there is no repressor protein, RNA polymerase will allow transcription of the gene for the enzyme needed to break down sugar

5. Kinds of operons • Lac operon controls the processor for breaking down lactose sugar • Lac operon is active alone- meaning the repressor acts only when it is not in the presence of lactose • trp operon controls the process of producing tryptophan • It is the an inactive operon, meaning that when outside tryptophan is around, it will bind to the repressor thereby allowing the repressor to bind to the operator, preventing the tryptophan gene being turned on • Activator operons use a specific activator protein that binds to DNA, turning operons on • These facilitate RNA polymerase binding

6. Eukaryote gene regulation is extremely complex • Cells contain a complete set of genetic information but only express certain parts of it • Cells become specialized in structure and function due to cell differentiation • Gene regulation leads to cell differentiation. Some cells actually retain all of their genetic potential allowing for forms of cloning and regeneration of body parts • Cells differentiate, then express their genes in patterns • DNA packing in chromosomes helps regulate gene expression

7. Coiled and folded DNA in eukaryotes packs around small proteins called histones • Double helix not affected by packing • Helix coils up tight and loops around 8 histone molecules. This creates a “bead” called a nucleosome • At the next level, the beaded string is wrapped into a tight helical fiber • The fiber coils into a thicker supercoil • Looping and folding further packs the DNA, making it difficult for RNA polymerase and other transcription proteins to make contact with the DNA • Histones participate in short-term switching on and off genes by loosening their grip on DNA • Nonhistoneal chromosomal proteins control the histones

8. Factors involved in eukaryotic transcription • Each gene usually has its own promoter and other control sequences, and activator proteins are more important. • Transitional factors- regulator proteins that work in addition to RNA polymerase • Activators bind to enhancer DNA sequences • Enhancers are usually far away from the gene they regulate and may be on either side of it • Enhancers, when bound with other transcription factor proteins force the DNA molecule to bend, then bind at the promoter site. This facilitates the binding of RNA polymerase and the beginning of transcription of that section

9. Repressor proteins called silencers may bind to DNA to inhibit transcription • Eukaryotes process or modify the RNA transcripts of DNA before it leaves the nucleus • Additional nucleotides may be added to the ends of RNA transcripts • Cap of “G” at one end and a tail of string of “A” ‘s at the other protect RNA from attack by cellular enzymes and help ribosome to recognize it as mRNA • Nonsense codons interspersed through DNA and are removed from mRNA • Exons-regions that code for genes that are expressed • Interons- nonsense sequences between exons • RNA splicing used to remove introns to make the final coding sequence of mRNA

10. Introns regulate gene expression • Controls how and when mRNA leaves nucleus • Cells can splice mRNA different ways- alternative splicing • Translation and later gene expression regulation • Lifetime of mRNA determines the amount of protein made from it • Long-lived: more produced, fewer chances to change in response to the environment (bacteria are just opposite) • A large number of translation, polypeptides may be cut into smaller, active products • Other proteins control by triggering the breakdown of selected proteins, limiting their function Review fig. 11.9 • Different mRNA molecules can be made from the same RNA transcript

11. Embryonic development • Patterning of gene expression and cell-to-cell signaling direct embryonic dev. • Communication begins in female ovary between unfertilized egg cell and surrounding follicular cell • One of the first genes activated codes for a protein that leaves the egg cell and signals adjacent follicle cells • Follicle cells are stimulated to create proteins that make preparations and signal back to the egg

12. The egg begins to localize mRNA that defines the body planes and body part positions • After the egg is fertilized, it undergoes mitotic divisions, changing from a zygote to an embryo • Genes begin a cascade of expression and cells begin cell to cell communication for further gene expression sequences, which triggers others to express • Cell to Cell signaling • Proteins and other molecules carry messages from signaling to target cells • Key mechanism for cell development and coordination of cell activities

13. Signal-transduction pathway- a series of molecular changes that converts a signal on a target cell surface into a specific response in the cell • Main response is the signaling of a cell to transcribe a gene • Signal cell secretes signal molecule • Signal molecule binds to a receptor protein in target cell membrane • Relay proteins in target cell cytoplasm activate in turn carrying messages • Last relay protein in series activates a transcription factor • Transcription of a specific gene begins • Translation of mRNA produces a protein

14. Homeotic gene- a master control gene that determines the body structure of a developing organism • They are thought to control the developmental fate of groups of cells • Homeoboxes- a 180 nucleotide sequence within a homeotic gene that encodes for part of the protein that binds to DNA of the genes regulated by the protein, allowing those genes to turn on or off • Very similar genes in all different organisms suggesting that these genes are evolutionarily very ancient and have not changed much

15. DNA Technology • Transferring of DNA by bacteria in nature • Can happen in 3 different ways in nature • Transformation- bacteria takes up DNA from another cell by taking in extracellular fluid • Transduction- a phage (virus) transfers fragments from a former host bacterial cell into a new host bacteria cell • Conjunction- the union of cell where a mating bridge is formed between cells and a piece of DNA is transferred from one to another

16. “male” bacteria will have sex pili, one of which attaches to the female • Sex pili and conjunction genes are carried on f-factor DNA, which also has an origin of replication site • F-factor can also exist as a plasmid- a small circular DNA molecule separate from the much larger bacterial chromosome • Plasmids can carry more than just f-factor genes • Genes can be added to the plasmid artificially, making the plasmid a vector • R plasmids carry genes that are resistant to antibiotics

17. Tools of recombinant genetic technology>biotechnology • “good” genes attached to plasmids using enzymes and then are cloned to produce multiple copies of the gene • Inserting radioactive molecules called probes in sequences of DNA to tag genes • Automation of DNA sequencing to “map” chromosomes • Human genome project- mapping of the 23 sets of chromosome • Most of human DNA is repetitive DNA- present in many places of the genome

18. Ethical Questions • Who decides what research is done and how that information is used and by whom? • Governments? • Insurance Companies? • Employers? • Who decides who lives and who dies? • In the face of overpopulation?