Download MICR 130 Chapter 8

ninth edition
TORTORA  FUNKE  CASE
MICROBIOLOGY
an introduction
Chapter 8
Microbial Genetics
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Structure and Function of the Genetic Material
Genetics – science of heredity
Study of what genes are, how they determine the
characteristics of an organism, how they carry
information, how the information is copied, how
information is passed on to subsequent generations
and between organisms
Genome – all the genetic information in a cell
Includes chromosomes and plasmids
Genomics – sequencing, characterization of genomes
Structure and Function of the Genetic Material
Chromosomes – a structure that contains the DNA
Physically carries the hereditary information, genes
Bacteria typically have one circular chromosome
Attached to membrane at several points
DNA is twisted and supercoiled
to fit into cell
Chromosome is 1000x longer
than width of cell
Chromosome erupting from
one E. coli cell
Structure and Function of the Genetic Material
Genes – segments of DNA that carry information to
produce functional products, proteins
Genetic code – the set of rules that determines how a
nucleotide sequence of a gene is converted into the
amino acid sequence of a protein
Linear sequence of nucleotides, bases provides the
information for making proteins
Much of anabolism is making proteins from DNA
When a product is made, the gene is expressed
Structure and Function of the Genetic Material
Genotype – an organism’s genetic makeup
The information found in its DNA
Represents potential characteristics
Phenotype – an organism’s expressed properties
Eg, an ability to resist an antibiotic
Phenotype is the display of an organism’s genotype
Genotype is collection of DNA in cell
Phenotype is collection of proteins in cell
The Flow of Genetic Information
Genetic information can flow in a number of ways
“Horizontal gene
transfer”
“Vertical gene
transfer”
“DNA replication”
DNA Replication
One parental DNA molecule converted into 2 identical
daughter molecule
Parental DNA strand acts as template for new strand
Structure of DNA
Complementary base pairing
DNA has direction
3’ (3 prime) and 5’ (5 prime)
DNA strands are counter-parallel to each other
DNA has direction
Nucleotides added to 3’ OH
3’ OH required for nucleotide addition
DNA Replication
Structure of DNA
5’ end attached
to PO4
DNA strands run
anti-parallel
5’ 3’
3’ 5’
3’ end attached
to OH
DNA Replication
Overview
1 – double stranded
DNA unwound by
helicase enzyme
2 – exposed bases matched up
with bases in cytoplasm
A to T
C to G
3 - DNA polymerase joins
new nucleotides to forming
DNA molecule
4 – each new DNA
molecule contains one
parental strand, one
daughter strand semi-conservative
replication
DNA Replication
The Flow of Genetic Information
Genetic information can flow in a number of ways
“Horizontal gene
transfer”
“Vertical gene
transfer”
“DNA replication”
RNA and Protein Synthesis
Genetic information from DNA follows the “Central
Dogma of Biology”
DNA is used to make RNA, which is used to make
protein
DNA RNA Protein
DNA RNA = Transcription, RNA synthesis
RNA Protein = Translation, Protein synthesis
RNA and Protein Synthesis
Transcription – synthesis of RNA from DNA
Recall, RNA is single stranded, uses U instead of T
Three kinds of RNA
Ribosomal RNA, rRNA –integral part of ribosomes
Transfer RNA, tRNA – involved in protein synthesis
Messenger RNA, mRNA – carries information for
making protein
mRNA is synthesized from a gene by enzyme called
RNA polymerase
RNA and Protein Synthesis
Transcription begins when RNA polymerase binds to
the promoter sequence
RNA polymerase joins nucleotides into new mRNA
strand using DNA as template
RNA complementary to DNA template
AU
TA
CG
GC
RNA and Protein Synthesis
Transcription
2 – mRNA synthesized
by RNA polymerase
3 – RNA
polymerase binds to
DNA at the
promoter
1 – double stranded
DNA unwound by RNA
polymerase enzyme
RNA and Protein Synthesis
RNA polymerase synthesizes mRNA
using DNA as template
DNA template is read 3’ 5’
mRNA is made 5’ 3’
3’
5’
5’
3’
RNA and Protein Synthesis
RNA is complementary to DNA
If DNA template is CGATAAG
What is the RNA strand formed?
RNA synthesized is GCUAUUC
RNA and Protein Synthesis
Transcription continues until RNA polymerase reaches
site on DNA called the terminator
mRNA, RNA polymerase
“fall off” DNA
5’
mRNA strand
Transcription
RNA and Protein Synthesis
Translation – protein synthesis from mRNA
“Translates” the “language” of nucleic acids into
“language” of proteins
Codons – groups of three bases used to translate
nucleic acids into amino acids
Each codon “codes” for an amino acid
Sequence of codons on mRNA determines
sequence of amino acids
Codons to amino acids is the genetic code
Translation: The Genetic Code
The Genetic Code
Written as mRNA, 5’ to 3’
Two types of codons
Sense codons – code for amino acids
61 codons for 20 amino acids
Degeneracy of genetic code – amino
acids coded for by multiple codons
Nonsense codons – code for stops in
translation
Aka stop codons
RNA and Protein Synthesis
Translation starts with AUG start codon
Codes for amino acid methionine
In Bacteria, proteins start with formylmethionine
tRNA carries amino acids to ribosomes
tRNA carries amino acid
on one end …
… and has anticodon at
other end
Anticodon recognizes codon in mRNA
What’s the codon this tRNA recognizes?
RNA and Protein Synthesis
RNA and Protein Synthesis
3 – tRNA binds to
next codon
1 - ribosome binds
at start codon
3’
5’
2 - ribosome moves
along mRNA in 5’ to
3’ direction
RNA and Protein Synthesis
4 – ribosome forms
peptide bond
between amino acids
3’
5’
RNA and Protein Synthesis
5 – translation continues
until ribosome reaches
stop codon
RNA and Protein Synthesis
6 – ribosome breaks up,
mRNA, protein released
Translation
Mutation: Change in the Genetic Material
Mutation – change in the nucleotide, or base, sequence
of DNA
Change in nucleotide sequence can cause change
in protein sequence
Change in protein sequence can cause change in
protein function
Can become less active, more active, bind
different substrate(s), etc…
The effect of a mutation depends on type of mutation
Mutation: Change in the Genetic Material
Type of mutations
Base substitution (point mutation) – one base is
replaced by a different base
May cause change in one amino acid, stop codon
Frameshift mutation – one or a few bases are deleted
of inserted (not in multiples of three)
Shifts “translational reading frame” of mRNA
Causes change in all amino acids after frameshift
Almost always results in nonfunctional protein
Mutation: Change in the Genetic Material
Results of mutations
Silent mutations - mutations that have no effect
Change in base, no change in amino acid
Due to degeneracy of genetic code
Missense mutations - mutations that result in an amino
acid substitution in protein
Nonsense mutations - mutation that introduces
premature stop codon
Mutation: Change in the Genetic Material
Missense mutation
Mutated DNA molecule, makes
Mutated mRNA with codons AUG,
AAG, UUU, AGC, UAA, makes
“Normal” DNA molecule, makes
“Normal” mRNA with codons AUG,
AAG, UUU, GGC, UAA, makes
“Normal” protein Met-Lys-Phe-Gly
Mutated protein Met-Lys-Phe-Ser
Mutation: Change in the Genetic Material
Nonsense mutation
Mutated DNA molecule, makes
Mutated mRNA with codons AUG,
UAG, UUU, GGC, UAA, makes
“Normal” DNA molecule, makes
“Normal” mRNA with codons AUG,
AAG, UUU, GGC, UAA, makes
“Normal” protein Met-Lys-Phe-Gly
Mutated short protein Met
Mutation: Change in the Genetic Material
Frameshift mutations
Result in dramatic changes to protein
Mutated DNA molecule, makes
Mutated mRNA with codons AUG,
AAG, UUG, GCU, AA…, makes
“Normal” DNA molecule, makes
“Normal” mRNA with codons AUG,
AAG, UUU, GGC, UAA, makes
“Normal” protein Met-Lys-Phe-Gly
Mutated protein Met-Lys-Leu-Ser-…
Mutations
Mutagens
Spontaneous mutations – occur due to occasional
errors in DNA replication
Mutagens – environmental agents that cause mutations
May be physical or chemical
Any agent that interacts with DNA is potential mutagen
Mutagens
Chemical mutagens – interact with DNA to cause
improper base pairing, deletions, insertions
HNO2 alters A
“A” binds with C instead of T
Analogs of DNA look like bases
But don’t base pair properly
Mutagens
Radiation
Ionizing radiation – X-rays, gamma rays
Ionize molecules
Cause structural damage to DNA, leads to errors in
DNA replication
Mutations
Transcription and Translation
Consider the following "Template" strand of DNA
AGA GGA TTA TAC TAT TCG TGG CGC AGT ATG TAA ACT TCT
1. Transcribe this DNA molecule
2. Translate the mRNA to find the "hidden message" in the protein.
a. Hint #1 - Start at the first codon, not the first AUG
b. Hint #2 - Use the first letter of each amino acid to spell out the
message
3. What would happen if the 10th base (a "T") in the template strand was
deleted? What type of mutation(s) would result?
4. What would happen if the 26th base (a "G") were substituted with a
"C"? What type of mutation(s) would result?