Lecture4 Microbial Genetics(6)

7/18/2019 Lecture4 Microbial Genetics(6)

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MICROBIAL GENETICS

Lecture 4

NORBEL A. TABO, RM, SM



Learning Objectives

1. Describe the flow of genetic information.

2. Discuss the requirements of replication, transcription andtranslation.

3. Identify the mechanisms of mutation.

4. ompare and contrast the different types of recombination.

!. Identify the importance of genetic engineering.



"low of #enetic Information

Figure 8.2



DNA REPLICATION



• $olymer of nucleotides%

adenine, thymine,cytosine, guanine

•

&'ac(bone& isdeo)yribose*phosphate

• +trands held together by

hydrogen bonds

between - and #

D

Figure 8.4



/0$LI-I "

'-0/IL D

• I/L/ L0L0

• DNA POLYMERASE en5yme that replicatesD



• D replication is semi*conser6ati6e 7each D

molecule has one old strand and one new strand8

D /eplication

Figure 8.7/eplication "or( nimations

http://www.maxanim.com/genetics/Replication%20Fork/Replication%20Fork.htm

http://www.maxanim.com/genetics/Replication%20Fork/Replication%20Fork.htm



PROTEINSYNTHESIS



$/-0I +9-:0+I+

• "L; "

I"/-I

• $roteins are

composed of a!no

a"!ds



•R!bosoes carry out

protein synthesis

/ibosomes

Figure 8.2

#arge

sa##



• m/ is translated

in "odons 73 m/

nucleotides8

• odons <encode=

for each amino acid

in a protein

-ranslation

Figure 8.2



•R!bosoes carry out

protein synthesis

/ibosomes

Figure 8.2

#arge

sa##



/ibosomes

Figure 8.2

R!bosoe o$es

%#e&' 'o r!gh' !n

d!agra(

Pe)'!de bond&ora'!on

$rotein +ynthesis nimations

http://www.maxanim.com/genetics/Protein%20Synthesis/Protein%20Synthesis.htm

http://www.maxanim.com/genetics/Protein%20Synthesis/Protein%20Synthesis.htm



M*TATION



• hange in the D

• utations may cause changes in protein

structure>function

• S)on'aneo+s +'a'!ons% ccur in the absence

of a mutagen• M+'agen% gent that causes mutations

– /adiation 7? radiation8

– hemicals 7carcinogens8

– ?iruses 7retro6iruses8

utation

ddition and Dele

tion utations n

imations

http://www.maxanim.com/genetics/Addition_and_deletion_mutations/Addition%20and%20Deletion%20Mutations.htm








utation



RECOMBINATION



D/ /0I$I0-

/0'I-I• Gene'!" Re"ob!na'!on

– 0)change of genes between two Dmolecules to form new gene combinations

– er'!"a# gene 'rans&er

• ccurs during reproduction, between generations

of cells

– Hor!-on'a# gene 'rans&er

• -ransfer of genes between cells of the same

generation



• P#as!ds% self*replicating, gene*containing circular

pieces of non*chromosomal D – ften contribute to genetic recombination

– D!ss!!#a'!on )#as!ds% 0ncode en5ymes for

catabolism of unusual compounds 7Pse+doonas(

– R %res!s'an"e( &a"'ors% 0ncode antibiotic

resistance in #ram*negati6e bacteria

– thers plasmids contribute to the pathogenicity of

microbes 70). Streptococcus mutans% cause ofca6ities8.

$lasmids



$lasmids

Figure 8.29



#enetic -ransfer and

/ecombination

• 0)amples of recombination%

1. -/+"/-I

2. @#-I

3. -/+D-I



-/+"/-I

• D /0L0+0D ;:0 D/ 0LL

DI0+

• D is ta(en up by adAacent cells

• -he ability to ta(e up foreign D is

termed "o)e'en"e

– E. An'!b!o'!" res!s'an"e



-/+"/-I

• -he #ram*positi6e species that are able to

ta(e up e)ogenous D includeStreptococcus pneumoniae,

Staphylococcus aureus and Bacillus

subtilis.

• #ram*negati6e bacteria that can be

transformed by e)ogenous D includeNeisseria meningitis, Neisseria gonorrhea,

Haemophilus influenzae, and Escherichia

coli .



@#-I

•

onAugation% transfer of a plasmid 7"* factor8D from one bacterium to another – In6ol6es direct cell*to cell contact



@#-I• $lasmid transfer in #ram*negati6e bacteria occurs

only between strains of the same species or

closely*related species.

•onAugation begins with the

e)trusion of a se) pilusB the tip of

the se) pilus adheres to the outer

membrane of #ram*negati6e cell

walls.



@#-I• $lasmid*mediated conAugation occurs in Bacillus

subtilis, some Streptococcus species, and

Enterococcus faecalis but is not found as

commonly in the #ram*positi6e bacteria.



onAugation

Figure 8.27a



onAugation

Figure 8.27b



-/+D-I• ?I/+ //I0+ D "/ 0 '-0/I

- -:0/



• -his can often lead to changes in microbial

pathogenicity

– 'otulism to)in of Clostridium botulinum

– apsule of Streptococcus pneumoniae

–

E. coli 1!C%:C to)in 7bloody diarrhea8

-/+D-I



• In spontaneous D mutation, bacterial D

7genetic material8 may mutate 7change8

spontaneously. Drug*resistant tuberculosis

arises this way.

• In 'rans&ora'!on or "on/+ga'!on, one

bacterium may ta(e up D from anotherbacterium. $encillin*resistant gonorrhea results

from this process.

• /esistance can be acquired from a smallcircle of D 7plasmid8. In 1EF, 12,!GG people

in #uatemala died in an epidemic of +higella

diarrhea. -he microbe harbored a plasmid

carrying resistances to four antibiotics.

Lecture4 Microbial Genetics(6)

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