Download Genetics and Microbiology

Genetics and Microbiology
•  Genetics studies genes!
•  Genes are units of information made of DNA; they carry
information about particular traits. They are also the
basis of heredity; they are copied and passed on to
future generations
•  Genetic processes are fundamentally similar in all
organisms, from bacteria to people.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
DNA Structure
•  DNA is a polymer of nucleotides, which come in four
varieties; A, G, C and T
•  In nature, DNA is found as a double-helix, in which two
anti-parallel strands are joined by hydrogen bonds
between the bases (A-T and G-C combinations)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
The Central Dogma of Molecular Biology
•  Information flows from DNA to RNA to Proteins.
•  DNA copies itself before cell division in a process
called replication.
•  DNA makes an RNA copy (mRNA) of itself during
the process of transcription.
•  Messenger RNA directs the synthesis of a protein
during translation.
•  A gene holds the information necessary to build a
particular protein!
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Genetic recombination processes unique to bacteria
•  NO MATTER WHAT ANYONE EVER TELLS YOU,
BACTERIA NEVER, EVER HAVE SEXUAL
RELATIONS OR SEXUAL LIFE CYCLES!!!!!
•  Usually, recombination is caused by sexual processes.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Recombination 1: Transformation
•  Transformation was discovered by Griffith in an
experiment that eventually led to the idea that DNA is
the genetic material.
•  His experiment involved Streptococcus pneumoniae
bacteria and mice.
•  Smooth strains of S. pneumoniae produced illness in
the mice; rough strains did not
(we now know this was because of the capsule)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
His experiment
•  Inject live smooth strain bacteria into mouse = DEATH
•  Inject live rough strain bacteria into mouse = NO
PROBLEM
•  Inject dead smooth strain bacteria into mouse = NO
PROBLEM
•  Mix living rough strain bacteria with dead smooth strain
bacteria, inject into mouse = DEATH! WHY?
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
WHY?
•  He reasoned that something from the dead smooth
cells was able to TRANSFORM the rough cells into
smooth cells. He was right. The transforming agent was
DNA.
•  Transformation is defined as the uptake of naked DNA
by a cell.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Recombination 2: Conjugation
(which is not sex!!!!!!!!!!)
•  Conjugation is defined as the transfer of genetic
material from one bacterial cell (the donor) to another
(the recipient) by direct contact.
•  Conjugation was initially discovered while studying a
plasmid called the F factor.
•  During conjugation, the plasmid copies itself, and directs
the formation of a pilus, through which the copy (or a
part of it) moves to a recipient cell.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Conjugation
•  This superficially resembles sex, but is not!
•  Cells containing the F factor are referred to as F+, and
can change cells without it (F-) to F+.
•  If the F factor becomes integrated into the bacterial
chromosome, we call that an Hfr strain because when it
conjugates it causes a high frequency of recombination
of bacterial genes.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Recombination 3: Transduction
•  Transduction is defined as the transfer of bacterial
genes from one cell to another mediated by a
bacteriophage (a virus that infects bacteria).
•  When the virus infects a bacterial cell, it replicates its
own DNA and degrades the bacterial DNA.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Transduction
•  Sometimes, by mistake, bacterial genes become
incorporated into the new infective phage particles.
•  If this phage now infects another bacterium, these new
genes can be transferred to the new cell, often allowing
it to express a new trait.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings