Genetics: Chapter 7
What is genetics? The science of heredity; includes the study of genes, how they carry information, how they are replicated, how they are expressed
What do you know about DNA? Chromosomes made of DNA contain an organism’s entire genome DNA codes for genes….genes code for proteins Chemical composition is nucleotides It exists in most cells as a double stranded structure
DNA is used for many things
DNA Structure
DNA Replication
Enzymes necessary for DNA replication Primase DNA Polymerase DNA gyrase DNA ligase Helicase
Nucleotides are added to the 3’ position (OH group)
DNA replication…a closer lookreplication…a closer look
DNA replication…closer look
Gene Expression…why is it important? Transcription Translation
What do you know about gene expression? Work with a partner to make a list about what you already know about gene expression
Transcription: RNA is transcribed from DNA
Transcription: Promoter orients direction of transcription
Transcription: DNA to RNA Requires an enzyme….. RNA nucleotides Base pairing rules for building RNA from a DNA template Process proceeds in the direction 5’--->3’ Process begins at the promoter region and ends at the terminator sequence
Transcription: RNA synthesis
What are the possible products from transcription? Messenger RNA (mRNA) Transfer RNA (tRNA) Ribosomal RNA (rRNA)
Quick check….. Do we have a protein yet? What have we made? What is next?
Translation: RNA to protein What is needed for the process? –mRNA –Ribosomes –Amino acids –tRNA
Translation: RNA to protein What is needed for the process? –mRNA –Ribosomes –Amino acids –tRNA
Translation: reading frame determines the protein
The Genetic code
Translation
Both processes occur at the same time in bacteria…why??
Eukaryotic cells differ in transcription and translation Ribosomes are different size 5’ end of mRNA has cap (methylated guanine) 3’ end of mRNA has poly A tail Introns are excised, exons spliced together Translation is monocystronic
Is it important to regulate protein synthesis? Yes! Three types of protein regulation –Enyme inhibition (feedback inhibition) –Repression (tryptophan operon) –Induction (lactose operon)
Are all genes under regulation? No! Genes to produce enzymes for glucose metabolism are constitutive (always made) Other genes are induced…only made when needed Other genes are repressed…turned off when not needed
Models for transcriptional regulation with repressors
Transcriptional regulation by activators
Lactose Operon as a model Used to understand control of gene expression in bacteria Operon consists of three genes needed to degrade lactose Repressor gene(codes for repressor protein) outside of operon coding region inhibits transcription unless something else bind to the repressor protein
Lactose Operon
Diauxic growth curve of E. coli
What conditions are needed for the lactose operon to be turned “on”? No glucose Lactose present Increasing levels of cAMP cAMP binds to CAP, then complex binds next to lactose operon promoter at the activator region RNA polymerase binds to promoter
How do organisms adapt to other changes in their environment? Some organisms turn genes on/off as needed Some organisms alter gene expression
Gene regulation systems in bacteria Signal transduction –Two component regulatory system
Gene regulation systems in bacteria Signal transduction - Quorum sensing
Gene expression is influenced by natural selection Random changes enhance survival of some cells in population Antigenic variation of pathogens Phase variation –Switching on/off of certain genes