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MBB 222 > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

What are mobile genetic elements?

A

nucleic acid segments (DNA or RNA) that can move in and out of cells or between different regions of the cell genome

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2
Q

How do mobile genetic elements affect host cells?

A
  • some of these elements become integrated into the “host” genome and are replicated and expressed along with host cell genes
  • some replicate independently of the host genome
  • some can do both
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3
Q

Which mobile genetic elements require host cell of replication?

A

all, they exploit the host cells’ machinery and metabolism to propagate

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4
Q

How can mobile genetic elements be used as tools to study cell machinery?

A

Used as vectors

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5
Q

Are Mobile genetic elements evolutionarily related or not

A

Yes they are

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6
Q

3 types of mobile genetic elements?

A

Plasmids, viruses, transposable elements (transposons)

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7
Q

Describe plasmids

A

self-replicating (using host proteins), extra-chromosomal double-stranded DNA circles found in bacteria, yeast and fungi
plasmids lack a protein coat and generally cannot move independently from cell to cell (but can move from one cell to another by cell “conjugation”)

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8
Q

Describe viruses?

A

self-replicating (using host proteins), infectious DNA- or RNA-containing elements that possess a protein coat and can move from cell to cell

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9
Q

Describe transposable elements (transposons)

A

mobile DNA elements that lack a coat and can insert into and move around the host genome via recombination

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10
Q

Are plasmids circular or linear DNA?

A

circular dna

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11
Q

How big are plasmids

A

Small <10kilobase pairs

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12
Q

Where are plasmids commonly found

A

Bacteria

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13
Q

How many copies of plasmids are there per cell?

A

2-50 (low vs.high #)

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14
Q

Are plasmids chromosomal or not?

A

normally do not integrate into the host genome (are extra- chromosomal) – replicate independently but use host proteins for replication

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15
Q

What do plasmids encode?

A

encode functions that are dispensable to the host, but may impart a selective advantage, e.g., antibiotic resistance
can carry genes for toxins, antibiotic resistance, catabolism
of unusual substrates

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16
Q

What is plasmid-mediated conjugation?

A

conjugative transfer of a plasmid from one cell to another - requires F-pilus to bring cell membranes together

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17
Q

How is replication of plasmid similar to that of host chromosome replication

A

plasmids have one origin of replication - sequence that allows initiation of replication

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18
Q

Which of these can plasmids do: sometimes plasmids can recombine with each other or with host cell chromosome, can integrate into host cell chromosome

A

Both

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19
Q

What four cell properties can be conferred by plasmid genes?

A

Drug (antibiotic resistance), virulence factors, metabolic activities, chromosome transfer

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20
Q

Describe drug (antibiotic resistance)

A

gene for an enzyme that can inactivate a drug (e.g., B-lactamase inactivates
B-lactam antibiotics like ampicillin and penicillins that inhibit bacterial growth)
gene for a variant protein which is unaffected by a drug (i.e., can substitute for the protein that is inactivated by a given antibiotic but is not itself inactivated)

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21
Q

Describe virulence factors

A

may contribute to or be essential for the virulence of a pathogenic bacterium
e.g., Bacillus anthracis and Clostridium tetanus toxins are encoded on plasmid genes

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22
Q

Describe metabolic activities

A

e.g., nitrogen fixation (N2->NH3) by
Klebsiella
e.g., degradation of octane by
Pseudomonas

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23
Q

Describe chromosome transfer?

A

conjugative plasmid integrates into the host chromosome and mobilizes the chromosome or parts of the chromosome for transfer to another cell

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24
Q

How do bacteriophage (phage) genomes comparable in size to plasmids

A

Bacteriophage (phage) genomes can be comparable in size to plasmids or can be much larger.

25
Q

Phage genomes and plasmids possess many of the same properties, suggesting?

A

A close evolutionary relationship, plasmids are related to bacterial virus (bacteriophage)

26
Q

Major difference between bacteriophage and plasmids?

A

phage/viral nucleic acid encodes viral coat proteins that allow it to be “packaged” and released from the host cell to infect another host cell. Plasmids are only found intracellularly – the do not get packaged as infections agents

27
Q

What are viruses?

A

Small intracellular parasites

28
Q

What do viruses require to propagate?

A

Host metabolic and biosynthetic machinery

29
Q

What can viruses infect?

A

Bacteria (these viruses called bacteriophage), plants, animals

30
Q

What allows viruses to move from cell to cell?

A

an RNA or DNA genome surrounded by a protective, virus-encoded protein coat

31
Q

What can happen when viruses overtake cellular machinery for their own reproduction?

A
  • often cause disease –

e. g., polio virus, influenza virus, human immunodeficiency virus (HIV)

32
Q

How big are viruses?

A

can be extremely small (e.g., <100 nm in diameter)

33
Q

What happens to the cell when viruses multiply

A

often lethal to the cell – overtakes, lyses cell

34
Q

How do viruses vary?

A
  • type of nucleic acid in genome, structure of viral chromosome
  • structure of coat
  • presence of membrane “envelope”
  • mode of entry into or exit from the host cell
  • site and mechanism of replication
35
Q

What kind of genome types can viruses have?

A

DNA, RNA, single-stranded, double-stranded, linear, circular, segmented.

36
Q

How do viruses structures vary in terms of nucleic acid?

A

Either RNA or DNA genome

37
Q

What is the coat protein on viruses fxn?

A

Surrounds and protects the nucleic acid

38
Q

What is the fxn of nucleoprotein in viruses? How do they vary

A

Packages the viral genome

- Not on all viruses

39
Q

How do viruses structures vary in terms of envelope

A
  • some viral coats are surrounded by a lipid bilayer (envelope)
  • envelope is derived from the host cell membrane
  • envelope may contain viral-encoded glycoproteins on its surface
40
Q

Viral proteins are encoded by ___ but synthesized by ____

A
  • the viral genome

- the cellular machinery

41
Q

The virus is packaged in the cell (genome + proteins) – enveloped viruses bud off the cell and get coated in the cell membrane -> envelope.

A

.

42
Q

What is lytic phage genome?

A

does not integrate into the host chromosome. It is replicated extra-chromosomally. Assembled phage
often lyse their host cell when they are released, killing the cell.
13: Mobile genetic elements

43
Q

What is lysogenic phage genome?

A

becomes integrated (lysogenizes) into the host cell chromosome (via site specific recombination), is replicated along with the bacterial (or other host) chromosome, and is passed on to daughter cells. (Integration/excision occurs via site-specific recombination, utilizes integrases/recombinases.)

44
Q

Lytic phage that infect E. coli?

A

T4 phage

45
Q

Nickname for transposable elements

A

“jumping genees”

46
Q

What are transposable elements?

A

mobile DNA segments that can “jump” or transpose from one site on the chromosome to another

47
Q

Size of transposable elements?

A

transposons range in size from 100’s to ~104 bps

48
Q

How many transposable element per cell?

A

Multiple copies

49
Q

What do transposable elements encode?

A

multiple proteins including transposases - enzymes that catalyze transposition

50
Q

What is transposition

A

transposition moves transposable elements from one site to another random site in the genome

51
Q

How often does transposition occur?

A

transposition events are tightly regulated, occur infrequently (random transposition can be lethal to cell)

52
Q

How does transposition differ from homologous or site-specific recombination?

A

transposition is a form of genetic recombination that is distinct from homologous or site-specific recombination - DNA homology is not usually required

53
Q

What cells are transposons found in?

A

All cell types

54
Q

How do transposons spread

A

transposons can spread from one cell to another, carried on plasmids, to confer new properties on the acceptor cell (e.g., antibiotic resistance in bacteria)

55
Q

What are the 2 types of transposons in bacteria?

A

Direct (simple) and replicative

56
Q

What is Direct (simple) transposition

A

Direct (simple) transposition - the transposon segment is moved from the donor site to the target site

57
Q

Role of transpose enzymes in direct (simple transposition)

A

Transposase enzymes recognize inverted repeat segments in DNA (terminal repeats), brings them together, excising the transposon that lies between the repeats.

58
Q

What is replicative transposition

A

Replicative transposition – the transposon is copied and inserted at a separate site in the DNA

  • the entire transposon is replicated to produce a “cointegrate” intermediate, in which the donor and target DNA are covalently linked
  • the cointegrate is resolved with the aid of a separate site-specific recombination system

MBB 222 (12 decks)

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