Download Microbial Genetics and Taxonomy

Microbial Genetics
Nestor T. Hilvano, M.D., M.P.H.
Learning Objectives
You should be able to:
1.
Compare and contrast the genomes of prokaryotes and eukaryotes.
2.
Describe the structure of DNA.
3.
Describe the structure and function of plasmids.
4.
State the central dogma of genetics and explain the roles of DNA and
RNA in polypeptide synthesis.
5.
Compare and contrast the steps in RNA transcription and the
translation of polypeptides.
6.
Describe three types of point mutations and their effects.
7.
Describe types of mutagens and their effects.
8.
Discuss DNA repair.
9.
Define genetic recombination.
10. Contrast vertical gene transfer with horizontal gene transfer.
11. Define biotechnology and recombinant DNA technology, mention its
applications.
12. Discuss the safety and ethics of recombinant DNA technology.
Structure and Replication of Genomes
• Genes – specific sequences of nucleotides
that code for polypeptides
• Genomes - sum of all genetic material in a
cell or virus
• Prokaryotic and eukaryotic cells – use DNA
as genetic materials
• Viruses – use either DNA or RNA
Structure of Nucleic Acids
• DNA and RNA Bases
1. Purine = Adenine (A); Guanine (G)
2. Pyrimidine = Cytosine (C); Thymine
(T); Uracil (U)
• Complimentary bases: A-T and GC for DNA; A-U and G-C for RNA
• Chromosomes – double stranded;
anti-parallel (5’-3’ and 3’-5’)
• histones not present in bacteria
Prokaryotic Genomes
• Single copies of 1 or 2 chromosomes
- circular molecules of DNA
- localized in region of cytoplasm called ____.
a. nucleus b. nucleoid c. both d. neither
• Contain plasmids w/c function to - regulate bacterial
conjugation; resistance to antimicrobial drugs, heavy
metals, or toxins; destruction of competing bacteria; and
pathogenicity
Eukaryotic Genomes
• Nuclear chromosomes in linear pair/s
- contain proteins called histones
- arranged as nucleosomes
- form chromatin fibers
• Also contain extrachromosomal DNA in
mitochondria, chloroplasts, and plasmids
Central Dogma of Genetics
• DNA Replication- Semiconservative; DNA
polymerase and DNA ligase enzymes
• Transcription- Synthesis of mRNA (codons)
from DNA template; RNA polymerase; mRNA- Introns
(nonsense codons) & exons (sense codons); Splicing of
exons (mRNA-carrier of genetic information to manufacture
polypeptide)
• Translation- interpretation of mRNA into the
amino acid language of proteins
Translation
• mRNA to tRNA (polypeptides with specific amino
acid sequences)
• rRNA (has A site; P site) on ribosomes, where
A.A. are assembled into protein
• tRNA (anticodon)- chain of A.A.(polypeptide
forming protein)
Mutations of Genes
• Change in the nucleotide sequence
• Point mutations:
1. Substitutions
2. Frameshift Insertion or Frameshift Deletion
• Effects of Substitution:
a.) silent – no change
b.) missense – different A.A. sequence
c.) nonsense – polypeptide synthesis stops
• Effects of frameshift insertion and frameshift
deletion – major difference in A.A. sequence
Mutagens
Cancer causing agents other than viruses:
• Radiation – ionizing radiation (X-rays);
nonionizing radiation (UV light)
• Nucleotide analogs - 2 amino adenine; 5 bromouracil; azidothymine (AZT)
• Aflatoxins (Aspergilus flavus) - causing
missense mutation and liver CA
• Acridine orange in dye - frameshift (base
insertion)
• Nitrous acid – base substitution
Genetic Recombination
• Exchange of nucleotide sequences
• Vertical gene transfer – transmission of genes
from parents to offspring
• Horizontal gene transfer – DNA from donor cell
is transmitted to a recipient cell
1. transformation = competent recipient
cell takes up DNA from the environment (in
lab)
2. transduction = virus (bacteriophage)
3. conjugation = bacterial sex; gram – (pili);
gram + (direct contact)
Recombinant DNA Technology and
Biotechnology
• Recombinant DNA technology – process of modifying
genomes of organisms
ex. insulin production of E. coli
• 3 main goals of Recombinant DNA technology
1. To eliminate undesirable phenotypic traits
2. To combine beneficial traits of organisms to create valuable
new organisms
3. To create organisms that synthesize products that human
need
Medical Applications
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Protein synthesis – inserted genes for insulin synthesis
Vaccines – hepatitis B vaccine
Genetic screening - for inherited forms of breast CA
DNA fingerprinting – use gel electrophoresis and southern
blotting to identify unique DNA sequences of individuals or
organisms
Gene therapy – missing or defective genes are replaced
with normal genes (in SCID- Severe Combined Immunodeficiency)
Medical diagnosis – use PCR, fluorescent genetic probes,
and DNA microassays in diagnostic applications
Cloning – nuclear transfer
Stem cell research – adult; embryonic
Agricultural Applications
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Herbicide resistance
Salt tolerance
Freeze resistance
Pest resistance
Improvements in nutritional value and yield
Ethics and Safety of Recombinant DNA
Technology
• Concerns over accidental release of altered
organisms into the environment
• Ethics of altering animals for human use
• Potential for creating genetically modified
biological weapons
• Unknown long-term effects and unforeseen
problems
• Other ethical issues – rights to screen people for
genetic disease; rights to privacy and
confidentiality of genetic data
Homework
1. Define terms – frameshift mutation,
transcription, translation, genes, genome,
plasmid, semiconservative, codon, anticodon,
mutagens, recombinant DNA technology
2. Describe the central dogma of genetics.
3. List 3 medical applications and 2 agricultural
applications of recombinant DNA technology.
4. List the uses of DNA fingerprinting.
5. Differentiate vertical gene transfer from
horizontal gen transfer.
6. List the 3 main goals of recombinant DNA
technology.