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Microbiology (PA 2205) > Microbial Genetics > Flashcards

Microbial Genetics Flashcards

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1
Q

Where are microbial genomes located?

A

Eukaryotes - nucleus
Prokaryotes - nucleoid region & extrachromosomal plasmids
Viruses - inside the (nucleo)capsid

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2
Q

Plasmids

A

Small circles of dsDNA
Encode inessential genes that give the bacterium a selective advantage
Antibiotic resistance
Pili (conjugation) F- –> F+

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3
Q

The Central Dogma of Molecular Biology

A

DNA -> RNA -> Protein

Flow of genetic information in cells from DNA to protein
True for eukaryotes and prokaryotes

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4
Q

DNA Replication

A

DNA replication is the process by which a genome produces an extra copy of itself

  • DNA used as a template to make more DNA
  • Essential part of cell division
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5
Q

Eukaryotic DNA Replication

A

Humans, fungi, parasites, plants
Occur in the NUCLEUS of the cell
During S phase (interphase) of the cell cycle
Super-coiled double stranded DNA is unwound & separated by DNA helicase

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6
Q

Helicase

A

Binds at origin and unwinds and separates DNA strands

DNA replication always occurs in the 5’ to 3’ direction

Leading Strand - continuously replicated
Lagging Strand - Okazaki fragments

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7
Q

Primer

A

For both fragments, a short piece of RNA called a primer is required as a starting point for the replication process

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8
Q

DNA Polymerase

A

Walks along the template strand, adding complementary nucleotides to the new strand in the 5’ to 3’ direction

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9
Q

DNA Ligase

A

Fills in any gaps in the newly replicated strand

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10
Q

Result of Eukaryotic DNA Replication

A

Two DNA molecules consisting of one new and one old chain of nucleotides (semi-conservative)
-Winds back up into double helix

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11
Q

Telomeres

A

To prevent the loss of genes as chromosome ends wear down, the tips of eukaryotic DNA have specialized caps called telomeres

  • Hundreds of repeats of the same short DNA sequence
  • Telomeres also grow shorter in length with each progressive cycle
  • Some cells can reverse telomere shortening by expressing telomerase
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12
Q

Bacterial DNA Replication

A

Conceptually like eukaryotic DNA replication (helicase, primers, DNA polymerase) – HOWEVER, takes place in the CYTOSOL, not nucleus

Both use semi-conservative replication using leading & lagging strand

DIFFERENCES: eukaryotic cell has 25 x MORE DNA than a prokaryotic cell!!

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13
Q

Prokaryotic DNA Replication

A
  • Prokaryotes (bacteria) have only one origin of DNA replication
  • DNA polymerase III is the primary enzyme involved in replicating DNA
  • Faster rate in prokaryotic cells
  • No telomeres (circular genomes)
  • Short replication in prokaryotes occurs almost continuously, but eukaryotic cells only undergo DNA replication during the S-phase of the cell cycle
  • Bacteria require the enzyme DNA gyrase to resolve supercoils as its circular genome unwinds
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14
Q

Bacterial Replication - Theta Replication

A

directional from a single origin site
-Following bacterial replication, the resulting circular genomes are concatenated (interlocked) - topoisomerase IV, cuts and reseals the circular chromosomes

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15
Q

Plasmids - Rolling Circle Replication

A

Plasmids replicate primarily through the rolling circle method
Special enzymes encoded by plasmids (RepA) nick the outer strand of plasmid circular dsDNA
This nick allows DNA polymerase to bind the intact stand which is used as a template
As elongation of this new strand begins, the nicked strand is displaced
The displaced strand is then coped into dsDNA
Method also used by human viruses that have circular dnDNA and bacteriophage

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16
Q

DNA Virus Replication

A

Viruses may have linear or circular genomes within their capsids
Viral DNA genomes may
-Be used directly as a template with or without association with host nuclear factors
-Linear DNA that circulates in the nucleus is called an “episome” - primarily rolling circle replication
-Integrate into the host genome, propagated with each cell cycle, transformed phenotype

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17
Q

Transcription

A

Process of using DNA as a template to make RNA

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18
Q

Three types of RNA

A 
rRNA = structural components of ribosomes (nucleolus)
mRNA = provides the blueprint for making proteins (transcript)
tRNA = uses the blueprint to incorporate the correct amino acids into the growing polypeptide (protein) chain
19
Q

Transcription requires a __________

A

DNA-dependent RNA polymerase

Process regulated by transcription factors – proteins that bind to promoter regions upstream of genes initiate or repress transcription

20
Q

Where does transcription occur?

A

Eukaryotes = nucleus
Prokaryotes = cytoplasm
Viruses use host ribosomes & often carry proteins that regulate transcription

21
Q

Introns

A

Intron = region of mRNA that do not code for proteins

  • Are NOT found in prokaryotes
  • Simple single celled eukaryotes have few introns compared to more complex eukaryotes
  • Some viral mRNAs contain introns that need to be spliced out before translation occurs
22
Q

Alternative Splicing

A

In eukaryotes, some genes also contain EXONS which can be differentially spliced out
-The resulting transcripts can code for multiple proteins - increased diversity of genetic output

AS can be found in some viruses (retroviruses like HIV-1 reproduce as one long RNA molecule that is alternatively spliced to generate transcripts (and proteins) of varying types)

23
Q

Translation

A 
RNA -> Protein
Occurs at the ribosome in the cytoplasm
Two subunits 
Eukaryotes: 60S + 40S = 80S
Prokaryotes: 50S + 30S = 70S

Ribosome reads the mRNA transcript three nucleotides at a time – CODON
Stop codon is detected, peptide chain released

24
Q

Translation of Viral Proteins

A

Viruses utilize the ribosomes of the cells they infect to make their proteins
Viral mRNA may also be translated into large polyproteins that are trimmed down into other functional proteins via the action of viral proteases

25
Q

Some viruses violate the central dogma!!! What does this mean?

A

RNA replication!

26
Q

Viral RNA Replication

A

Eukaryotes & prokaryotes cannot replicate their RNA as they lack an RNA-dependent RNA polymerase (RdRP)
RNA viruses carry or encode RdRP
(+) RNA = viral mRNA
RdRP can amplify RNA and convert to opposite sense

This is a “low fidelity” enzyme – it is error prone, leading to instability and high rates of mutation

27
Q

Reverse Transcription

A

RNA –> DNA (technically, complimentary or cDNA)
Group VI and VII viruses
These viruses must carry or encode reverse transcriptase
cDNA may integrate into the host chromosome and become a permanent part of the host – PROVIRUS

28
Q

Microbial Reproduction

A

Process by which microorganisms make offspring

Eukaryotes and prokaryotes may reproduce on their own, but viruses need living hosts to replicate

29
Q

Sexual vs. Asexual Reproduction

A

Sexual: combining/exchanging genetic material from two parents
Asexual: produces offspring genetically identical to the one parent (clones)

30
Q

Asexual Reproduction

A
  • Involves single parent
  • Parental genomes are duplicated and divided between two identical daughter cells (clones)
  • No increase in genetic diversity
  • All prokaryotes and some eukaryotes (mostly single-celled organisms) reproduce this way
31
Q

Methods of Asexual Reproduction

A
  • Binary fission
  • Budding
  • Asexual spores
  • Fragmentation
  • Schizogony (nuclear fission)
32
Q

Binary Fission

A

Parent replicates its genome
Cell elongates and divides into two identical daughter cells
Mitotic mechanism in single-cell eukaryotes (yeast & protozoa); NOT in bacteria as mitotic spindles are not made; and DNA replication and separation may occur simultaneously (no interphase)

PRIMARY mechanism of reproduction for bacteria; mitochondria!

33
Q

Budding

A

New organism develops from an outgrowth or bud d/t cell division at one site

Certain yeasts, molds, protozoa, and helminths

34
Q

Asexual Spores

A

Produced by many fungi, particularly those that are multicellular (molds)
Asexual fungal spores include conidia (threads) which can disperse easily
Asexual spores germinate to form a new vegetative body where they land

35
Q

Fragmentation

A

A piece of an organism breaks off and these fragments develop into matured organism, genetically and morphologically identical to the parent
Some pathogenic molds can have their hyphae or mycelium break off and a new vegetative body forms

36
Q

Schizogony

A

Form of asexual reproduction where multiple fission of the nucleus occurs
Found in some protozoa, especially parasitic sporozoans (malaria)

37
Q

Sexual Reproduction

A

-Requires two parents
-Each parent contributes a reproductive/sex cell (gamete) that contains half the chromosome number (haploid, n)
-When compatible gametes meet, they may fuse resulting in fertilization –> result is a zygote
Zygotes can then proliferate, grow or differentiate via mitosis
A zygote is diploid cell, which means it has the normal number of chromosomes

38
Q

A defining feature of sexual reproduction is an ______ in genetic diversity – offspring are _____ clones

A

increase in genetic diversity

NOT clones

39
Q

Methods of Bacterial “Sexual” Reproduction

A

Prokaryotes reproduce primarily via asexual routes
However, mechanism for lateral gene transfer exist that can be LIKENED to sexual reproduction in the sense that genetic recombination and increased genetic diversity are taking place

  1. Conjugation
  2. Transduction
  3. Transformation
40
Q

Conjugation

A

“To join together”
Transfer of genetic material b/w bacterial cells via a bridge-like connection called a pilus (pili)
Plasmids are commonly exchanged this way, rarely chromosomal DNA is transferred this way

F+ bacteria produce pili
If F- bacterium receives a copy of plasmid from F+ bacterium, both cells will be F+ and capable of performing conjugation

41
Q

Transduction

A

Process by which DNA is transferred frmo one organism to another by a virus
–Bacteriophage

42
Q

Transformation

A

Process in which the genetic makeup of a bacterial cell is changed by introduction of free DNA from the surrounding environment
Donor fragments can recombine with chromosomal DNA or plasmid DNA

43
Q

Do viruses “reproduce”?

A

NO!
Not technically, since they are not “living”
Viruses do not replicate spontaneously, or autonomously like other microorganisms can
They require a living host – obligate intracellular “parasite”
-Replication may occur alongside host replication and transcription, using host or viral factors (e.g. enzymes)
Viral proteins are always made using host ribosomes
Enveloped viruses take their envelopes from a host cell
Viral replication and assembly of progeny virions can occur silently, or may result in profound cell defects or interruption of physiological pathways

Microbiology (PA 2205) (12 decks)

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