1 / 38

What you need to know about genetics All organisms have DNA and RNA as genetic material

What you need to know about genetics All organisms have DNA and RNA as genetic material All organisms use the same nucleotides All organisms replicate, transcribe and translate DNA. The central dogma of molecular biology. What is different in prokaryotes from eukaryotes?

trory
Download Presentation

What you need to know about genetics All organisms have DNA and RNA as genetic material

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What you need to know about genetics All organisms have DNA and RNA as genetic material All organisms use the same nucleotides All organisms replicate, transcribe and translate DNA

  2. The central dogma of molecular biology

  3. What is different in prokaryotes from eukaryotes? The prokaryotic genome is circular, so it is repli- cated differently than linear eukaryotic DNA What is gene expression? transcription: synthesis of RNA from a DNA template translation: formation of a protein (amino acid sequence) from mRNA sequence How does this process differ in prokaryotes?

  4. DNA replication in prokaryotes • Always starts at same site • Exact copy is made • “semiconservative”: each DNA molecule contains one original strand and one new strand

  5. Transcription in prokaryotes • Product is mRNA • Initiation, elongation, termination • mRNA contains “coding sequences” for proteins

  6. In prokaryotes, an mRNA molecule can carry information for several genes e.g., all of the genes in a biosynthetic pathway (this doesn’t happen in eukaryotes) The RNA polymerase in constructed differently in prokaryotes Process consists of initiation, elongation, termination Same steps are seen in translation

  7. Differences between prokaryotes and eukaryotes

  8. The entire genomes (DNA sequences) of many bacteria are known >1000 times smaller than human genome

  9. Gene expression is carefully controlled. Bacteria must be able to adapt to environment and divide quickly Some genes are constitutive (always expressed) Some are inducible (only expressed when needed) example: enzymes that metabolize lactose Some are repressible ( expressed most of the time, but can be turned off) example: enzymes involved in biosynthesis These genes are organized into operons

  10. Operons: a group of genes expressed together

  11. Repressor: binds to operator (a region of DNA adjacent to genes) If something is bound to operator, transcription cannot occur Inducer: binds to repressor so it can’t bind to operator Therefore transcription can take place Example: lactose operon. genes are expressed only if lactose (inducer) is present

  12. Biosynthetic genes are also arranged in operons In this case, the repressor is the end product of the pathway Catabolite repression: “preferred” carbon source is used first

  13. Gene regulation in eukaryotes is more complex • Transcription is more complex • RNAi: specific RNA sequences are degraded (so that translation will not take place) • Microbes can alter expression of certain genes in response to changes in environment. Prokaryotic mechanisms: • Quorum sensing • Antigenic variation • Regulatory systems that turn off one system and turn on another

  14. Some fundamentals of bacterial genetics Bacterial DNA (like any DNA) can be altered by mutations Mutations can result in changes in proteins diversity acquisition of resistance new traits can be transmitted to other microbes

  15. What happens when DNA is mutated? Bases (nucleotides) are changed (base substitution) Bases are inserted or deleted Sequences of DNA move around the genome (transposons)

  16. Point mutation: a single amino acid is changed

  17. Frameshift mutation How many amino acids are changed?

  18. Mutations can occur spontaneously, or can be induced By chemicals By radiation

  19. DNA damage occurs fairly frequently Cells have several repair pathways available to them Repair of errors in base incorporation Repair of thymine dimers (due to UV irradiation) Repair of damaged DNA Bypass of damaged DNA (SOS repair)

  20. In bacteria, mutants can be identified by plating on special minimal medium Auxotrophs have lost the ability to synthesize certain substances (Prototrophs: retain the ability to do so) A variety of selective strategies have been developed

  21. The Ames test uses bacteria to test chemicals for capacity to cause mutations, as well as carcinogens (cancer-causing chemicals) Much more rapid and inexpensive than testing animals Results have been reliable and reproducible Several tester strains are used, since chemicals can cause point or frameshift mutations (but not both)

  22. The Ames test

  23. How does gene transfer occur in bacteria? Only part of the bacterial DNA is transferred The new DNA replaces existing DNA (homologous recombination) Transformation- uptake of “naked” DNA Transduction- by bacteriophages Conjugation- bacterial cells come in direct contact with each other. Plasmid is often transferred

  24. Transformant identified by selection

  25. Recipient bacteria must be “competent” to take up and incorporate DNA Few strains of bacteria are naturally competent (generally Gram positive) Bacteria can be made artificially competent calcium solutions electric current

  26. Transduction: transfer of DNA by viruses • “packaging” error in forming new viruses • Host DNA is incorporated into virus • DNA incorporated into genome of host • Chance of this happening is very low!

  27. Conjugation Direct contact between donor and recipient must occur Sex pilus is encoded by fertility (F) plasmid

  28. Note role of plasmids in conjugation What is a plasmid? Small, circular double-stranded DNA Common in prokaryotes May vary widely in size Can encode a variety of genes; usually not essential bacterial genes but may give bacterium new properties

  29. R plasmids- resistance to antibiotics, metals Virulence factors (that make bacteria pathogenic, or disease causing) Transposons can insert themselves into genome (and out of it) Thus bacteria have many ways of obtaining new genes to enhance survival

  30. Natural methods of gene transfer have been modified in biotechnology Deliberate introduction of genes into recipient bacteria or other cells Genes could not otherwise be exchanged “recombinant DNA”

  31. Plasmid may be able to replicate frequently, so many copies of the DNA are made The gene may be expressed, so the protein product in made in large quantities e.g., recombinant human insulin, as opposed to extracts from pig pancreases Genetic analysis determining DNA sequences analyzing gene products expressing DNA in a variety of cells What do the proteins do?

  32. Summary DNA replication, transcription and translation occur in all cells Prokaryotes have a single, circular DNA genome They have different enzymes and ribosomes but use the same nucleotides They acquire new traits through incorporating mutations. These can be analyzed through selection techniques

  33. Bacteria do not reproduce sexually but can acquire new DNA through transformation, transduction or conjugation These natural processes have been modified so that DNA can be deliberately incorpor- ated into host microbes- even genes that would normally never be transferred this way

More Related