Mim Lecture 17

Front 1

17.1

transformation

Back 1

- pick up of bacterial DNA found in the extracellular environment by a bacterium
- extracellular DNA can be the remnants of lysed, dead bacterial cells
- absorbed DNA is then combined with the host genome -> DNA scavenging

Front 2

17.2

transduction

Back 2

- injection of genetic info tino a bacterium by a bacterial virus (bacteriophage)

Front 3

17.3

conjugation

Back 3

- transfer of genetic info from one bacterium to another
- requires the presence of an extra-chromosomal DNA molecule called a plasmid
- also requires cell-to-cell contact

Front 4

17.4

streptococcal pneumonae

Back 4

- avirulent strain (rough strain)
- lacks a carbohydrate capsule

Front 5

17.5

general recombination

Back 5

- occurs when any fragment that comes in contact with the cell is absorbed in an attempt to transform the cell
- requires a large region of homology between the fragment of DNA and the host genome
- requires a number of gene products. (RecA = very important)
- is a non-additive process. The new DNA replaces the corresponding host DNA

Front 6

17.6

recA

Back 6

- it makes sure that the two strands for recombination lines up correctly and overall mediates the recombination process

Front 7

17.7

single stranded DNA binding protein

Back 7

- shield single-stranded DNA from digestion
- protects the single-stranded DNA until it is intertwined with the resident chromosome before recombination

Front 8

17.8

phases of cell growth

Back 8

- initially: lag phase = growth is slow
- 2nd: log phase = burst of exponential growth
- 3rd: late log phase = growth slows

Front 9

17.9

when does the cell become competent

Back 9

- during the late log phase and early stationary phase of the bacteria growth curve

Front 10

17.10

competence factor

Back 10

- needed for cell to become competent
- small protein
- made and secreted out into the environment
- act on cell receptors on the same cell or on a different nearby cell to induce signal cascade -> expression of new genes
- these genes produce proteins that are also secreted and then acts to modify the cell surface, allowing DNA to be taken up (exposing DNA receptors on the cell surface)
- when competence factors are secreted in an environment, all the surrounding cells become competent, not just one

Front 11

17.11

constitutively competent

Back 11

- can take up DNA all the time, because they have an internal mechanism that allows them to be competent without a competent factor

Front 12

17.12

Com proteins

Back 12

- help with the entrance into the cell
- form a pore in the hydrophobic membrane of the cell
- DNA enters into the cell via the pore, and is digested by a nuclease, which fragments the double stranded DNA -> single strand
- remaining strand is protected by a single-stranded DNA binding protein

Front 13

17.13

endonucleases

Back 13

- if DNA fragments are too long and can't enter the cell, surface endonucleases will shorten these longer fragments.

Front 14

17.14

quorum sensing

Back 14

- occurs when the population of the cells is high enough to produce a critical concentration of the signaling molecules
- microorganisms communicate and coordinate their behavior by the accumulation of signaling molecules
- a form of cell-to-cell communication

Front 15

17.15

biofilms

Back 15

- bacteria flock to each other, forming communities

Front 16

17.16

receptor protein

Back 16

- DNA entrance into the cell
- associated with the inner cell wall pore, taking the DNA out from the periplasmic space

Front 17

17.17

second receptor protein (DR)

Back 17

- found in gram-negative bacteria
- screens DNA as it comes into the cell
- acts as a gate-keeper that only allows DNA with specific sequences that are common to the particular bacterial species

Front 18

17.18

internally competent

Back 18

- a form of competence that does not involve a secreted external environmental factor
- ex: haemophilus influenzae

Front 19

17.19

transformasomes

Back 19

- found on the surface of competent cells, serve as receptors for DNA
- fragments can recognize and bind to these receptors, but the receptors only recognize specific base pair sequences scattered about the DNA
- only 'self' strains of DNA are taken into the cell
- DNA enters the cell through transformasome

Front 20

17.20

chemical induction

Back 20

- solution containing a high concentration of salt in introduced to the bacterial strain
- followed by alternating periods of heat and cold shock, which destabilizes membrane molecules, allowing extracellular DNA to enter the bacterium
- artificially induce competence

Front 21

17.21

electroporation

Back 21

- bacterial cells are electrocuted
- electrocuted produces transient pores or channels with electric voltages
- extracellular DNA can be transfered into the cell via electric shock
- artificially induce competence

Front 22

17.22

filamentous

Back 22

- a type of virus
- simplest form of bacteria, loop of nucleic acid with a helix of protein around it, contains approx. 3-10 genes

Front 23

17.23

icosohedral

Back 23

- still simple bacteria, but more complex than filamentous bacteriophage
- has spike to anchor the bactiophage at the ends and has an icosahedra shape to the head.
- will contain 10-20 genes

Front 24

17.24

complex

Back 24

- contain multiple parts: head, tail, appendages
- contain 30-300 genes

Front 25

17.25

nucleic acid of bacteriophages

Back 25

- double stranded DNA
0 single stranded DNA, single stranded RNA and double stranded RNA are possible, but less frequently

Front 26

17.26

capsid

Back 26

- protein coat of bacteriophages

Front 27

17.27

nucleocapsid

Back 27

- a capsid surround nucleic acid

Front 28

17.28

lytic infection

Back 28

- results in the killing of the infected bacterial cell
- involves infection by virulent phage
- early genes -> instructions for the process of DNA replication
- late genes -> mass production of the structures of the bacteriophage (head and tail)
- lysis of the bacterium -> release more phages into the environment to propagate infection

Front 29

17.29

lysin

Back 29

- protein that dissolves the cell wall, releaseing the phage into the environment

Front 30

17.30

temperate phase

Back 30

- the phage DNA is incorporated and integrated into the host genome and establishes a relationship with the host
- viral DNA will then be replicated along with the host genome producing colonies of infected bacteria
- phage that enters this route is termed a Progphage
- sometimes, a prophage will exit the bacterial chromosome and initiate the lytic cycle

Front 31

17.31

characteristics of the temperate phase:

Back 31

- additive recombination of the bacterial and phage chromosomes
- site specific recombination, observed at certain positions
- requires only a small region of homology
- a viral protein, integrase, is involved in recorgnizing the integration site, called ATT site

Front 32

17.32

repressor gene

Back 32

- there is a struggle between which path the phage will choose (lytic growth or lysogenic growth), dpending on the expression of this gene
- when this gene is expressed, the gene product will block the promoter for the genes that produce the structures of the page -> lysogenic phase
- most of the time, ene is not expressed -> phage enters lytic phase