Microbiology Chapter 9

Microbiology Chapter 9
Genetics - Science of the study of heredity, variations in
organisms that are transferable from generations to
DNA is the key to understanding genetics, DNA is the
genetic material of life and the macromolecule is
responsible for storing all the information necessary to the
function of an organism
Genes – units of heredity, segments of DNA; they code for
functional products (proteins) – these products, cause
something – synthesis of pigments, enzymes etc. Result in
some observable trait
Genome is the total genetic information in a cell (all of the
potential information, coded in the total DNA)
Microbiology Chapter 9
DNA double helix, two strands held together
by Hydrogen bonds
Microbiology Chapter 9
Chromosome – structures that carry the
DNA (genes), often in Eukaryotic organisms
there is protein associated with the genes.
Chromosomes - can have many linear ones
as in the eukaryotic cells. Single and
circular chromosomes in bacteria
Plasmids – bacteria can have an extra
piece of genetic information separate from
the chromosome (extrachromosomal DNA)
Microbiology Chapter 9
Microbiology Chapter 9
Genotype – the genetic make up of an
organism, sum total of all the information
(expressed and unexpressed)
Phenotype – the actual expressed
information (what you can see or detect)
color of a colony, abilities to ferment sugars,
Microbiology Chapter 9
Serratia marcesens; temp. dependent
colony pigment, genotype for pigment,
cooler temp. than 37 to see it; Phenotype
Microbiology Chapter 9
Structure of DNA - its chemical make up (transparency of
pg 251)
3 parts: 5 carbon sugar (deoxyribose), a nitrogenous base,
and a phosphate
1. Together they form what we call a nucleotide
2. There are four bases so there are four possible
3. These are adenine, guanine, cytosine, thymine
4. These nucleotides are combined to form long chains
5. In DNA the chains are paired into a ladder like double
6. The bases on one chain pair with bases on the
corresponding chain by weak hydrogen bonds (A-T and GC)
Microbiology Chapter 9
DNA double helix, two strands held together
by Hydrogen bonds
Microbiology Chapter 9
******* BE SURE TO LOOK OVER FIG. 9.5 PG 252. 9.6, pg 254 Go to web and view the animation on
Mcgraw-Hill web site******* Slide 13
DNA replication – the process of making an exact copy of DNA molecule
DNA replication has to occur before cell division in order for each cell to have a
copy of
the genetic information
1. One strand of DNA acts as template for the formation of the corresponding strand
2. 2. Replication is carried out in an orderly sequence
a. It is biosynthesis, making macromolecules from smaller nucleotide subunits
b. ATP is used to drive this biosynthesis process
3. Replication starts by unwinding of the double helix and the two strands separate exposing the now
unpaired nitrogenous bases
a. The two strands act as templates for the formation of the other strand
Microbiology Chapter 9
DNA replication
Microbiology Chapter 9
b. Specific enzymes are required and of course the precursor molecules must
be available
c. The most important enzyme is DNA polymerase
d. The enzyme cause bonds to form and new chains are formed – everywhere
on the parent strand an adenine appears, a thymine will be linked to form the
compliment on the forming daughter strand (see page 252, 254)
e. Note that the forming strands are linked by joining phosphate of one
nucleotide monomer with the OH of the other (note the nucleoside has a triphosphate and two phosphates are removed when one nucleoside is joined to
the other)
f. Each chain has a 3’ end and 5’ end (pg 254) – lots of detail and we can’t
begin to cover it all
Microbiology Chapter 9
DNA polymerase - one on leading strand, continuous
DNA polymerase - one on lagging strand, discontinuous
Requires Ligase to stitch the pieces together
We will see it in animation on the DNA video
Fig. 9.5
Chapter 9
Transcription: PG. 259 The assembly of a complimentary mRNA strand from a DNA
(remember there are 3 kinds of RNA: mRNA, rRNA, tRNA)
1. Messenger RNA carries a message to site of protein synthesis – make a chain of
amino acids with this specific sequence
2. Transfer rRNA is involved in protein synthesis, it carries the amino acids to the
ribosome where they are assembled (SEE PG. 258, 260, 262)
3. Ribosomal RNA forms the ribosome unit where proteins are assembled
DNA codes for a specific messenger RNA with a specific sequence of nucleotide
(RNA has ribose, and the bases are adenine, guanine, cytosine, and uracil) A pairs
with U and of course G pairs with C, (A-U, G-C)
Microbiology Chapter 9
Fig. 9.8
Microbiology Chapter 9
RNA polymerase is the enzyme that causes mRNA to form
Translation: the process of actually translating the genetic information,
coded on DNA, transferred to mRNA and then expressed by the
specific synthesis of a particular protein see pages 260 - 263
1. Codon – triplet code on the mRNA
2. Anticodon – corresponding code on tRNA
3. tRNA carries specific amino acid, codon-anticodon match insures
proper sequence of amino acids (see pg. 261 – codons code for only
specific amino acids) transparency
Microbiology Chapter 9
Transcription – to Translation
As Polypeptide forms it coils and folds into a specific
Figure 9.9
Figure 9.10
Figure 9.12
Figure 9.13
Figure 9.14
Figure 9.16
Very “too” Cool
Figure 9.18
Differences in eukaryote and prokaryote DNA: Exon and introns
Exons: Coding regions; genetic information, transcribed and then translated
Introns: Interspersed between exons, and don’t code for protein
Microbiology Chapter 9
Mutations: an inheritable change in an organisms genetic
information, in its DNA
1. Can be simple as one base pair, or complex involving
many bases
2. Can be natural (spontaneous - random mistakes),
biological (jumping genes – transposable elements –
transposons – can jump around and when inserted
they can alter the genetic make up of a cell)
3. Induced – created in the laboratory as result of use of
chemicals (mutagens) or radiation
Transformation: Naked DNA
fig. 9:24
Conjugation: Sex pilus and plasmid
Figure 9.23
Transduction; Phage assisted DNA transfer

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