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Genetics

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The study of what genes are, how they carry information, how information is expressed, and how genes are replicated

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Gene

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A segment of DNA that encodes a functional product, usually a protein (but it can be an RNA)

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Chromosome

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Structure containing DNA that physically carries hereditary information

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Genome

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All the genetic information in a cell

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Genomics

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The molecular study of genomes

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Genotype

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The genes of an organism

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Phenotype

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Expression of genes

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DNA

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-Polymer of nucleotides
-Double helix associated with proteins
-Backbone is deoxyribose-phosphate
-strands held together by h-bonds
-strands are antiparallel

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E. coli chromosome

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4.6 million base pairs

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DNA replication

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Double helix of DNA separates, new h-bonds are formed while each strand of parental DNA forms new pairs. Enzymes make backbone between new stand to thus form 2 separate daughter strands.

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DNA backbone bond

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Covalent

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DNA complementary strand bond

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Hydrogen bond

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DNA synthesis

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DNA is copied by DNA polymerase
5' -> 3' direction
Initiated by RNA primer

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Leading strand

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Synthesized continuously

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Lagging strand

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Synthesized discontinuously

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DNA pol III

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Make DNA

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DNA pol I

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Joins backbones

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Transcription

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DNA is transcribed to make RNA (mRNA, tRNA, rRNA, and other RNAs). Begins when RNA pol binds to the promoter sequence in DNA

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Transcription proceeds in the
5' -> 3' direction and stops when it reaches the

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Terminator sequence

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Memorize 5 steps of

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Transcription

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mRNA

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Messenger RNA
2-4%

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tRNA

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Transfer RNA
10%

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rRNA

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Ribosomal RNA
85%

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Primary RNA transcript

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Extra step inside the nucleus between transcription and mRNA

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Introns in primary RNA transcript

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Segments of RNA transcript that are derived from DNA introns that are cut out. Basically parts that shouldn't become mRNA

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Exon joining in primary RNA transcript

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Processing involves snRNP in the nucleus to remove the intron-derived RNA and slice together the exon-derived RNA into mRNA

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Primary RNA transcript: last step

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After further modification, the mature mRNA travels to cytoplasm, where it directs protein synthesis.

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Translation

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mRNA is translated into codons, starts at start codon

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Start codon

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AUG= met

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Nonsense codon aka STOP codon

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UAA, UGA, UAG= stop

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64 Sense codons

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On mRNA
Encodes 20 amino acids
genetic code is degenerate
tRNA carries the complementary anticodon

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Constitutive genes

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Expressed at a fixed rate(constantly). All others are only expressed as needed

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Operon

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[Control region (promoter and operator)] [structural genes]

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An inducible operon

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For the most part, the Repressor is active, and therefore the operon is mainly off.

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The repressor protein

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Binds to operator and prevents transcription from the operon

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Inducible operon: operon on

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When the inducer (allolactose) binds to the repressor protein, the inactivated repressor no longer blocks transcription. Transcription happens and leads to genes=> enzymes needed for lactose catabolism (in example)

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Repressive operon: structure

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Promoter and operator sites, and structural genes. Operon regulated by product of regulatory gene.

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Lag time of glucose-lactose consumption

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Intracellular cAMP increases, lac operon is transcribed, more lactose is transported into cell, and ?-galactosidase is synthesized to break down lactose

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Methylating nucleotides

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(off) genes are passed to offspring cells, are not permanent, and have biofilm behavior

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Mutation

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A change in genetic material. Can be neutral, beneficial, or harmful

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Mutagen

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Agent that causes mutations

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Spontaneous mutations

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Occur in the absence of a mutagen

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Base substitution

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Change in one base

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Missense mutation

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Base substitution that results in changes in amino acid

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Nonsense mutation

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Base substitution that results in a nonsense codon aka stop

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Frame shift mutation

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Insertion or deletion of one or more nucleotide pairs (not multiples of 3) and causes a shift in the reading frame

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Frequency of mutation

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Spontaneous mutation:
1 in 10000000000 base pairs
1 in 1000000000 relocated genes

Mutagens
Increase it to:
1 in 10,000 base pairs
1 in 100 replicated genes

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Oxidation of nucleotides

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Makes a mutagen
(ex. A bonds with C instead of T)

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UV radiation

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Causes thymine dimers

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Photolyases

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Separate thymine dimers. Repair

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Nucleotide excision repair

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Repairs

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Genetic transfer:
Vertical gene transfer

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Occur during reproduction between generations of cells

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Genetic transfer:
Horizontal gene transfer

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The transfer of genes between cells of the same generation

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Genetic recombination:
Exchange of genes b/t 2 DNA molecules

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Crossing over occurs when 2 chromosomes break and rejoin

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Horizontal transfer example

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Genetic movement between different cells

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Vertical transfer example

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Kid from parents... DNA to RNA

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Genetic recombination due to crossing over

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1) DNA (nicked) from one cell aligns with recipient cell's DNA.

2) Donor DNA aligns with complementary base pairs in recipient DNA.

3) RecA protein catalyzes the joining of 2 strands.

4) DNA pol and DNA ligase. Donor DNA then destroyed.

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DNA transfer

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Transformation, conjugation, transduction

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DNA Transfer:
Transformation

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Cellular DNA that is naked, or released from other cell

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DNA Transfer:
Conjugation

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Cell-to-cell transfer

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DNA Transfer:
Transduction

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Viral based transfer

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Genetic transformation:
Griffith's experiment

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Bacteria injected into mouse. Different types:
living encapsulated: died

Living non encapsulated: lived

Heat-killed encapsulated: lived

Live non encapsulated and heat killed encapsulated: died

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Griffith's conclusion

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Used Streptococcus pneumoniae

The heat killed encapsulated Bacteria's DNA was transferred over to nonencapsulated bacteria. And DNA recombination made fatal living capsulated bacterial cell. Mouse died

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Capsulated

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Smooth strain of streptococcus pneumoniae

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W/o capsule

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Rough strain of Streptococcus pneumoniae

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Competent cell

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Has physiological ability to take in foreign DNA

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Bacterial conjugation

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Sex pilus between F and F- cell
Mating bridge

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When a F factor (a plasmid) is transferred from a donor (F ) to a recipient (F-)

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The F- cell is converted to an F

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Bacterial conjugation:
When F factor is integrated into the chromosome of an F cell

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It makes the cell a high frequency of recombination (Hfr) cell

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Bacterial conjugation:
When an Hfr donor passes portion of chromosome into F- recipient

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A recombinant F- cell results

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Study 11 steps of

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Transduction

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Conjugative plasmid

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Carries genes for sex pili and transfer of the plasmid

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Dissimilation plasmids

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Encode enzymes for catabolism of unusual compounds

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R factors

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Encode antibiotic resistance

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Transposons

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Segments of DNA that can move from one region of DNA to another

Contain insertion sequences for cutting and resealing DNA (transposase)

Complex transposons carry other genes

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Insertion sequence

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Simplest transposons
Contains a gene for transposase, the enzyme that catalyzes transposition. The transposase gene is bound at each end of the inverted repeat sequences that function as recognition sites for the transposon.

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Insertion sequence example

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IS1

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Complex transposons

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Carry other genetic material in addition to transposase genes. Tn5 is an example. Carries the gene for kanamycin resistance and has complete copies of IS1 at each end.

MICR33 – Microbiology – Flashcards

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