Microbial Genetics - Harford Community College

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Dec 14, 2012 (4 years and 4 months ago)

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Gene Transfer,Genetic Engineering,and
Genomics





1.


Genetic recombination.


2.


Genetic engineering.


3. Microbial genomics.








A. Genetic Terminology

Genotype



The genetic compliment of an organism


Types of genotypic changes


Mutation


Conjugation


Transduction


Transformation

Phenotype



The genetic expression of an organism


Types of phenotypic expressions


Morphology


Cultural


Physiological

B. The Bacterial Chromosome

Introduction



DNA is arranged as a single molecule
with no histones present, and with no
dominance or recessiveness in the
genes.


Bacterial chromosome is located in the
nucleoid.


In E. coli there are 4000 genes spread
over 1.5mm of DNA in less than 1
micrometer of space



Loop domain structure allows for
compaction of DNA


Replication of the chromosome



DNA polymerase


The semiconservative method


Replication of a closed loop
chromosome


Okazaki fragments


Rolling circle method

Plasmids



Fragments of DNA in the cytoplasm


R Factors
-

confer drug resistance


Bacteriocins
-
proteins toxic to other
bacteria and human cell


Many plasmids are found in Gram
-
Negative bacteria

C. Bacterial Mutation

Permanent alteration in the DNA




Example: nonpathogenic
Yersinia pestis


have genes that cause them to remain in


mid gut, pathogenic Y. pestis do not have


these genes


Types of mutations



Spontaneous


Induced

Spontaneous mutations



Occurs every 10
6

to 10
10

replications


1 mutation in every billion bacteria


Example:
Neisseria gonorrhoeae

penicillin
resistance original mutation was
spontaneous


Example: Salmonella strains antibiotic
resistance

Induced mutations



Chemical or Physical agents enhance
mutation rate


Mutagens


Ultraviolet light

mechanism of action


Chemicals


Chromosomal changes

Mutation Type




Point (substitution)






(leu) (ser) (arg)



Normal AAT AGT GCC




(leu)
(cyst)

(arg)



Mutant AAT
T
GT GCC



Mutation Type




Frameshift (deletion)






(leu) (ser) (arg)



Normal AAT AGT GCC




(leu)
(val)

(pro)



Mutant AAT
A
GT

G
CC

A




Mutation Type




Frameshift (insertion)






(leu) (ser) (arg)



Normal AAT AGT GCC




(leu)
(glut)

(cyst)



Mutant AAT
CAG
T

GC
C



Repair Mechanisms



DNA repair enzymes


Many enzymes


Constantly checking for errors


Repair mechanisms


Mismatch repair “proofreads”


Damage repair


Excision repair


Dimer repair (UV light)

Mismatch Repair

Excision Repair

Transposable genetic elements



Insertion sequences


Small DNA segments


Provide no genetic information


Located at several places on the
chromosome


Transposons


Larger than Insertion sequences


Provide information for protein
synthesis



Sections A & B repeating but reversed “palindrome”

Ames Test


C. Bacterial Recombination

Transformation



Description


Griffith's experiments


Modern interpretation: Avery,McLeod &
McCarty


Mechanism


Competence

Conjugation




Male and female cells


Role of F factors (plasmids)


High frequency of recombination strains


Mechanism of Hfr conjugation


Sexduction

Simple Conjugation

Hfr Conjugation

Transduction



Description


Role of the bacteriophage


The lytic cycle


Lysogeny


Generalized transduction


Lysogeny

F. Control of protein synthesis


1. Mechanism proposed by Jacob



and Monod




2. The operon theory



3
.
Repressor
-
inductor model

D. Genetic Engineering

Genetic Engineering Was Born from Genetic
Recombination



Genetic engineering involves changing the genetic
material in an organism to alter its traits or products



A recombinant DNA molecule contains DNA
fragments spliced together from 2 or more organisms

Genetic Engineering

History of Genetic Engineering



Discovery of endonucleases


Plasmids and sticky ends

Modern applications



Pharmaceutical production


Insulin, interferon, hormones,
vaccines etc.


Genetically engineered plants


Animal gene alterations


Gene probes


DNA fingerprinting


The human genome initiative

E. Genomics

Microbial Genomes Have Been Sequenced


Hundreds of microbial genomes have been
sequenced since the first in 1995


Many of which are pathogens


Segments of the Human Genome May Have
“Microbial Ancestors”


As many as 200 of the 35,000 human genes are
essentially identical to those of
Bacteria


They were passed down from early ancestors of
humans

Microbial Genomics Will Advance Our Understanding
of the Microbial World


Knowing genomes of bacteria that cause food
-
borne diseases can help us:


develop detection methods


make food safer



It can help us identify microbes that cannot be
cultured in the lab



Environmental genomics helps us understand
how microbial communities function

Microbial Genomics Will Advance Our Understanding of
the Microbial World


Environmental genomics can help develop
bioremediation techniques



Genomics can help develop detection methods for
potential bioweapons organisms and other agents of
warfare

Comparative Genomics Brings a New Perspective to


Defining Infectious Diseases


Studying Evolution

Types of Genomics



Functional genomics

attempts to discover:

the function of proteins coded for in a genome

how the genes interact, allowing the microbe to
grow and reproduce

Comparative genomics

compares the DNA
sequence of one microbe to another similar or
dissimilar organism