Exam 3- Genome Flashcards by Emily Hershberger

What do most bacteria divide by?

binary fission

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Where does replication in bacteria begin?

at a single origin (oriC)

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What forms after initiation?

a replication bubble

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Explain replication bubble.

contains two replication forks that move in opposite directions around the chromosome

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Where does replication end?

the termination site (ter)

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What does semiconservative mean in regards to DNA replication?

each new double-stranded DNA molecule contains one old (parental) strand & one new (daughter) strand

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Bacterial chromosomes have a single…

point of origin

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Eukaryotes usually have more than one…

origin of replication per chromosome

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What has to happen in order to replicate DNA?

the double helix must unwind, exposing bases that can pair with another base on the growing strand

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What does helicase do in DNA replication- initiation?

breaks the hydrogen bonds between nitrogenous bases, opening the DNA helix

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What do single-stranded binding proteins do in DNA replication- initiation?

bind to the newly exposed single-stranded DNA & block formation of hydrogen bonds between nitrogenous bases

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What does Topoisomerase II (DNA gyrase) do in DNA replication- initiation?

relieves the supercoiling of the chromosome by breaking & resealing the DNA

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What does partial unwinding of the helix at the origin do?

generates a replication bubble with a replication fork at each end

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What happens during DNA replication- elongation?

new DNA is synthesized by DNA polymerase III, using old DNA as a template

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What is every new strand of SNA initiated with?

an RNA primer

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What does primase do?

builds the short RNA primer

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What does a protein sliding clamp do?

helps hold DNA pol III onto the chromosome during replication

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What happens to the leading strand?

it is synthesized continuously

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What happens to the lagging strand?

it is synthesized discontinuously in Okazaki fragments

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What needs to happen to connect the small Okazaki fragments of the lagging strand into one continuous strand of DNA?

DNA pol I removes RNA primers & dills the resulting gap with DNA & DNA ligase seals the gaps between adjacent fragments of DNA

What is at the end of replication?

2 concatenated double-stranded circular chromosomes

What does Topoisomerase IV do?

cuts the circular chromosomes, then reseals the DNA after the two circular chromosomes separate

What happens to newly synthesized DNA?

it is methylated

What happens during replication prior to methylation?

old DNA is recognized by methylation; allowing mismatches to be repaired in the new strand of DNA

What happens to uncorrected mistakes?

results in mutations

When do spontaneous mutations occur?

during replication

How is a species maintained?

by producing offspring that have DNA inherited from their parents

What is the error rate of DNA replication in enteric bacteria?

estimated to be 1 in 10 million base pairs

What is a mutation?

a base pair different from that of the pre-existing parent cell

What is vertical gene transfer?

the transmission of an entire genome from parent to offspring

What is horizontal gene transfer (lateral gene transfer)?

the acquisition of a piece of DNA from another cell, not through traditional reproduction

What are the 3 main mechanisms of horizontal transfer?

transformation, transduction, conjugation

Explain transformation.

the uptake & expression of exogenous free DNA from the environment

What are competent cells?

cells that are able to take up free DNA & be transformed

Explain transduction.

the transfer of DNA from one cell to another by a bacteriophage

Explain generalized transduction.

involves the lytic life cycle of the phage & can more any gene

Explain specialized transduction.

lysogenic cycle, moves only genes connected to site of prophage insertion

What is conjugation?

transfer of DNA between bacteria through direct contact

What does conjugation require?

cell-to-cell contact, special transfer plasmid

What can F-factor integrate into?

the chromosome

What happens when F factor integrates into the chromosome of an F+ cell?

the cell becomes a high frequency of recombination (Hfr) cell

What species does conjugation mostly occur in?

Gram-negative species

Describe Agrobacterium tumefaciens.

- Rhizobium radiobacter - bacterial species that causes crown gall disease (tumors) - contains a tumor-inducing plasmid (Ti) that can be transferred via conjugation to plant cells - used in lab for inserting foreign genes into plants

Once a new piece of DNA has entered a cell, what happens to it?

if the new DNA is a self-replicating plasmid, the plasmid will coexist in the cell separate from the host chromosome

What is recombination?

an enzyme-mediated process in which two DNA molecules exchange portions by breaking & reforming their sugar phosphate backbones

Explain DNA repair.

- useful to fix mutations - does not involve foreign DNA - cells with damaged chromosomes can use DNA from other cells of the same species to repair the damaged region

What are the consequences of horizontal transfer?

bacteria can gain new metabolic capabilities, antibiotic resistance, increased virulence

Describe Corynebacterium diphtheriae.

Gram positive; pleomorphic rod, no specific arrangement, produces diphtheria toxin, toxin is encoded by a bacteriophage that has integrated into the bacterial chromosome

Describe Diphtheria.

- old disease not commonly seen anymore - symptoms: sore throat, fever, swollen glands in neck, pseudomembrane - transmission by direct contact, or through air - treatment: antitoxin & antibiotics - there is a vaccine