Chapter 7: Microbial Genetics Flashcards by Elisabeth Spencer

Structure of Nucleic Acids

T:A
G:C
A:T

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Structure of Prokaryotic Genome

2 Structures: chromosomes

Plasmids

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Prokaryotic Chromosmes

Main part of DNA
Assoc proteins RNA
Packaged in 1-2 distinct chromosomes
Have single copy of each chrom: haploid

Circular molecule of DNA in nucleoid

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Plasmids

Small molecules DNA
Replicate independently 
Carry info for own replication 
Not essential for bac. metabolism/growth/repro
Confer survival b.advantages 
Fertility,Resistance,Bacteriocin: factor
Virulence,Cryptic: plasmids

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Eukaryotic Genome

Nuclear DNA
Extra nuclear DNA
More than one per cell
Linear and sequestered in membrane bound nucleus
2 copies of each chrome: diploid

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Extranuclear DNA of Eukaryotes

Codes for about 5% RNA
Nuclear DNA codes 95% RNA
Some Protozoa and fungi carry plasmids
Circular and resemble chromosomes of Prokaryotes

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DNA Replication

Anabolic polymerization
Requires monomers
And energy
Key is complimentary structure of 2 strands
Semiconservative: new strands composed of one original strand and one daughter strand

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Process in DNA Replication

Polymerase binds to stnd
Adds nucleotides to hydroxyl group at 3’ end of nucleic acid
Leading strand synthesized continuously
Lagging strand synthesized discontinuously

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Eukaryotic DNA

Similar to bacteria replication
Some differences:
4 DNA polymerases
Thousands of replication origins

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Genotype

Set of genes in the genome

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Phenotype

Physical features and functionality traits

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Transcription

Information in DNA is copied as RNA nucleotide sequences

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Translation

Polypeptides synthesized from RNA to nucleotide sequences

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RNA from DNA

RNA primers
mRNA
rRNA
tRNA
Occurs in nucleotide of prokaryotes

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Initiation of Transcription

Attachment of RNA polymerase
Unzip DNA
Movement of RNA polymerase

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Genome

The entire genetic complement of an organism

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Elongation

Growing RNA molecule

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RNA polymerase

No helicase
Slower than DNA polymerase
Uracil
Proofreading function is less efficient

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Termination

RNA polymerase released
RNA transcriptase released
Self: stem loop
Rho dependent: protein moves along RNA

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Transcription in Eukaryotes

In nucleus mitochondria chloroplasts
3 types
Transcription factors 
mRNA processed before translation 
Capping
Polyadenylation
Splicing

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Stages of Translation

Initiation elongation termination
Require additional protein factors
GTP: required for initiation and elongation

RNA Translation

Release factors recognize stop codons
Modify ribosome to activate enzymes
Ribosomes dissociate into subunits
Polypeptides released at termination may function alone or together

Gene Expression

75% expressed at all times

Regulation of protein synthesis

Half transcription

Stops translation directly

Other gene expression

Only transcribed or translated when cells need them | Allows for conservation of energy

Inducible Operon

Activated by inducers | •lactose Operon

Repressible Operon

Transcribed continuously until deactivated | •tyryptophan operon

Mutation

Change in the nucleotide base sequence of a genome Deleterious Sometimes gives the organism an improvement of ability

Point Mutations

Most common One base pair affected Insertions deletions substitutions of nucleotides

Frame shift mutations

Insertion or deletion of a nucleotide Reading frame to shift Protein too long or too short

Silent Mutation

Point mutation No effect on function Code for same amino acid

Missense Mutation

Point mutation | Different amino acid

Nonsense Mutation

Point mutation | Stop codon where there should not be one

Ionization Radiation

Breaks in chromosomes | Mutagens

Non ionizing radiation

Pyrimadine dimers | Mutagens

Nucleotide Analogs

Disrupt DNA/ RNA replication •cause point mutations Chemical mutagen

Nucleotide-altering chemicals

Base pair substitution mutations •missense mutations Chemical mutagen

Frame shift mutagen

Nonsense mutations Chemical mutagen

DNA light repair

Use light activated enzyme to replicate the base pair of the thymine dimer

DNA dark repair

Repair enzyme gaps a chunk of mutated nucleotide sequence DNA polymerase 1 and ligase pair to repair gap

Base excision repair

Enzymes remove incorrect nucleotide DNA polymerase 1 and ligase repair with correct nucleotide

Mismatch DNA

Enzyme removes incorrect segment | DNA polymerase III repair with new segment

Recombinants

Cells with DNA molecules that contain new nucleotide sequences

Vertical gene transfer

Organisms replicate their genomes | Provide copies to descendants

Exchange of nucleotide sequences

Mediated by DNA segments composed of homologous sequences

Horizontal gene transfer

Donor contributes part of genome to recipient Transformation Transduction Bacterial Conjugation

DNA is genetic material

Due to it being the transforming Agent

Competent cells

Cells that take up DNA Alterations in cell wall and cytoplasmic membrane • allow DNA to enter cell

Generalized transduction

Transfixing phage carries random DNA segment from donor to recipient

Specialized transduction

Only certain donor DNA sequences are transferred

Bacterial conjugation

Pilus draws cells together Cell contact Plasmid DNA transfer Synthesis

Transposons

Segments of DNA that move locations in same or different host Frame shift insertion Palindromic sequences at each end Simplest: insertion sequences with no more than two inverted repeats/ gene for transposase Complex: one or more genes not connected with transposition