Important words and
concepts from Chapter 7, Black, 1999 (3/28/2003):
by Stephen T. Abedon (abedon.1@osu.edu)
for Micro 509
at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
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(1) Chapter title: Microbial Genetics
(a)
Quite
a bit of microbial research involves a study of microbial genetics (including,
for whatever it is worth, my own research).
In keeping with our emphasis of studying predominantly medical microbiology, we
will consider particularly those aspects of microbial genetics that impact
significantly upon
(i)
our
understanding of what a microorganism is,
(ii)
how
the characteristics of microorganisms contribute to their ability to cause
infectious disease,
(iii)
and
our ability to prevent and cure infectious disease
(a)
Microbial
genetics is covered in our text over two chapters (7 and 8). We will cover
portions of both chapters in a single lecture, particularly considering
(i)
The
structure and function of DNA
(ii)
The
basics of transcription (so that later it will be easier
to understand the difference between plus-strand and minus-strand viruses)
(iii)
Three
mechanisms of DNA transfer
between bacteria (transduction, transformation, and conjugation)
(iv)
Plasmids and resistance factors
(which are transferred as DNA between bacteria and which increase bacterial
resistance to such things as antibiotics)
(v)
Genetic engineering and molecular techniques
(which represent significant aspects of the future of medicine as well as just
about everything else)
(a)
The
movement of information from parent to offspring
(b)
Heredity
is carried by nucleic acids
(c)
For
all cellular forms of life, that nucleic acid is DNA
(d)
For
some (but certainly not all) viruses, that nucleic acid is RNA
(e)
[heredity (MicroDude)] [index]
(a)
A
polymer of nucleic acid (i.e., long chain of
linked-together nucleotides)
(b)
In
cellular forms of life that polymer is DNA and a single chromosome consists of
that DNA hydrogen bonded with a complementary
strand of DNA, i.e., as a double helix
(c)
Some
viruses employ single-stranded (half of a double helix) chromosomes
(d)
Associated
with chromosomes are proteins that help in the arrangement of the chromosome
including the immense job of compacting the chromosome so that it can fit into
a single cell (i.e., a bacterial chromosome is about 1000 times longer than a
bacterial cell)
(e)
[chromosomes (MicroDude)] [index]
(a)
The
bacterial chromosome is closed circular
(b)
That
means that the two ends of the double helix attach, forming a circle
(c)
That
is, in the bacterial chromosome the DNA has no ends (just as the curved line
defining a circle is continuous)
(d)
[bacterial chromosome
(Google Search)]
[index]
(a)
Functional
units on chromosomes are called genes
(b)
Genes
are specific nucleotide sequences that serve to template the transcription
of RNAs
(c)
Usually,
but not always, the transcribed RNAs are used to template the translation of proteins (though many RNAs instead serve functional roles in
cells without being translated into proteins)
(d)
[gene
(MicroDude)]
[what is a gene? (MicroDude)]
[index]
(a)
A
heritable change in the nucleotide sequence of a gene is called a mutation
(b)
Mutations
are typically detrimental to the carrying organism (since they represent random
changes in highly evolved information) but mutations can also lead to
beneficial changes (beneficial to the carrying organism, for example)
(c)
[mutation (MicroDude)]
[index]
(a)
A
mutant (i.e., a microorganism that differs mutationally from a
"wild-type" version of that microorganism) is called an auxotroph if
the mutation leads to a new nutrient requirement
(b)
What
is going on is that the mutation led to an inability to synthesize some organic
compound (e.g., an amino acid) that now must be supplied from the environment
in order for the organism to live
(c)
Thus,
an auxotroph's nutrient needs are greater than those of its wild type ancestor
(d)
[auxotroph (Google Search)]
[index]
(a)
Another
name for wild type, to distinguish the wild type strain or phenotype from that
of the auxotroph
(b)
[prototroph (Google Search)]
[index]
(a)
Alleles
are different versions of the same gene, found at the same locations in the chromosomes
of different individuals
(b)
Alleles
(i.e., heritable variation) are initially generated via mutation but are
heritable so are therefore passed from parent to offspring
(c)
Differences
is alleles can result in different phenotypes displayed by carrying organisms,
for example, associated with greater pathogen virulence and others with less
pathogen virulence
(d)
For
example, different alleles of the same gene code for capsules or lack of
capsules in Streptococci, with only Streptococci with capsules appreciably
virulent
(e)
[allele (MicroDude)]
[index]
(a)
To
pass information from genotype (DNA-coded information in cells) to phenotype
(typically protein-coded information), an intermediary is RNA; the actual biochemical mechanism that
produces this RNA from a DNA template (i.e., from the DNA code) is called
transcription
(b)
RNA
is polymerized by enzymes (RNA polymerases) that employ a DNA template (again,
in cells; some viruses have RNA chromosomes, thus confusing matters)
(c)
The
DNA template represents a specific sequence of nucleotides
(d)
Additionally,
of the two DNA strands making up a double helix, a given gene will only be
found on one of those strands
(e)
Thus,
for a given gene there exists a template strand that is complementary to the
RNA that is transcribed from that gene
(f)
See Figure 7.5, The
transcription of RNA from template DNA
(g)
See Figure 7.4, DNA replication
in a prokaryote (to remind yourself that DNA is found as a double helix in cellular
organisms and therefore that transcription occurs in these organisms is
templated off of one strand that otherwise represents one-half of a DNA double
helix)
(h)
[transcription (MicroDude)]
[index]
(12) Vocabulary [index]
(a)
Allele
(b)
Auxotroph
(d)
Chromosome
(e)
Gene
(f)
Heredity
(g)
Mutation
(h)
Prototroph
(i)
Transcription