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DNA
Genetic information used by all living organisms
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Microbial gene
- 4,000
- Human genome - 22.000
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How many genes are in the genome of E. coli?
about 4000 genes
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DNA function as:
- Long term information storage-DNA polymerase
- Blueprint for gene expression-Gene expression basics
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DNA polymerase
Replicates chromosome form origin of replication sites prior to cell division
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Gene Expression Basics
- 1. DNA (gene) transcribed by RNA polymerase into mRNA (e.g. mRNA)
- 2. mRNAs tanslated on ribosome into PRO
- -mRNA read as 3 nt codons
- -codon sequence specifies protein's amino acid sequence
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Important roles of DNA and RNA
- Cell Division-Replicatioin
- Gene Expression-Transcription & Translation
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Mutation
- Occur during DNA replication
- Contribute to species and strain differences
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All RNA is _____ from a _____ template.
All RNA is transcribed from a DNA template
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tRNAs
Carry amino acids and can read codons in mRNA
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Where does translation occur
Ribosomes
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Codon
3 nucleotides that code for specific amino acids sequence
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Translation
- Occurs on ribosomes
- 1.Ribosomes attaches to mRNA
- 2. tRNA anticodon attaches to the matching mRNA codon
- 3. A second tRNA attaches at next codon on mRNA
- 4. Peptide bind forms enzymatically between first two amino acids
- 5. Ribosome moves along mRNA as next tRNA attaches to next codon
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Protein lengthened until ribosome reads
stop codon
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Genetic Code
lists all codons and which amino acid they specify
- Transcription
- DNA---RNA from DNA template
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tRNA
Can read codons in mRNA
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Translation
- Occurs on ribosome in the cytoplasm
- Anticodon on the tRNA pairs with the codon of the mRNA
- froms peptide bonds that connect amino acids
- 1.Initiation 2. Elongation 3.Stop Codon -- release of PRO
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Genetic Code
Lists codons and amino acids they specify
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Transcription and translation (prokaryotes)
Occur simultaneously in prokaryotes because there are no organelles to separate process
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Vertical gene transfer
Mother to daughter
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Microbial Diversity is generated
- 1. Mutations in DNA
- 2. Horizontal gene transfer -- Donor cell to recipient cell which produces and a recombinant cell
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Primary source of genetic diversity in microbes
Horizontal gene transfer
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Types of Horizontal gene transfer
- 1. Transformation
- 2. Transduction
- 3. Conjugation
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Transformation
- Griffith
- Free DNA taken up by recipient cell and integrated into that cells genome
- Only competent cells can take up DNA
- Use in genetic engineering
- Provided evidence that DNA (not protein) was the ling sought after genetic material
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Competence factor
Expression by recipient or chemical treatment
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Bacterial Transformation
- 1. Naked DNA fragments from disintegrated cells (DNA released by dead cells) in the area of potential recipient cells
- 2. Entry of naked DNA into competent, correct genus, physiologic condition cell
- 3. Recombination, Some DNA fragments replace original host cell DNA. Now genetically transformed and will pass to offspring
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transduction
- Bacteriphage transfer of DNA from donor bacteria to recipient
- Phage injects DNA into bacterial cell
- Bacterial DNA is fragmented as phage replicates
- Fragmented of bacterial DNA is incorporated into phage head. Bacterial cell is lysed, and new phage is released
- Phage contained DNA infects new cell
- Genes from first bacterial host are incorporated into chromosome of new host
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Transduction:Virus transfers DNA
- Bacterophage virus injects nucleic acid, may kill quickly (lytic) or integrate into host chromosome (lysogenic)
- Virus life cycle always involved packaging of viral genome into new virons
- DNA from host cell is integrated into viral DNA during packaging
- Phage transfers this new DNA to another host cell/bacteria
- Could be gene or toxin/antibiotic resistance
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When does transduction occur?
As bacterial DNA from donor (infected) cell is mis-packaged into new virus
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Conjugation
- Plasmid transfer via conjugation (sex) pillus -- transfers largest amount of DNA
- F+ (male) transfer plasmid to F- (female)
- Plasmid duplicated in new cell
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Bacterial conjunction
- Transfers plasmid DNA
- both cells then contain plasmid
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Plasmid
- Small, circular, self-replicating extra-chromosomal DNA
- Specialized non-essential genes (dont need to survive)
- Often contain antibiotic resistance genes
- Important molecular biology tool
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Transposons
"Jumping" DNA sequence, move randomly between plasmids, chromosomes
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Transposons Composed
- Transposase gene allows transposition
- Recognition (insertion) sequences at ends
- often include resistance gene(s)
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