Download chapt09_lecture

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

NEDD9 wikipedia, lookup

Nucleic acid tertiary structure wikipedia, lookup

Nucleosome wikipedia, lookup

Chromosome wikipedia, lookup

Gel electrophoresis of nucleic acids wikipedia, lookup

Genealogical DNA test wikipedia, lookup

Mitochondrial DNA wikipedia, lookup

Mutagen wikipedia, lookup

Oncogenomics wikipedia, lookup

Polycomb Group Proteins and Cancer wikipedia, lookup

Nutriepigenomics wikipedia, lookup

Human genome wikipedia, lookup

DNA polymerase wikipedia, lookup

Minimal genome wikipedia, lookup

DNA damage theory of aging wikipedia, lookup

History of RNA biology wikipedia, lookup

DNA vaccination wikipedia, lookup

Epigenomics wikipedia, lookup

Frameshift mutation wikipedia, lookup

Cancer epigenetics wikipedia, lookup

Genetic engineering wikipedia, lookup

Non-coding RNA wikipedia, lookup

Molecular cloning wikipedia, lookup

Genome (book) wikipedia, lookup

Genomic library wikipedia, lookup

Cell-free fetal DNA wikipedia, lookup

Genome evolution wikipedia, lookup

Epitranscriptome wikipedia, lookup

Nucleic acid double helix wikipedia, lookup

Designer baby wikipedia, lookup

Epigenetics of human development wikipedia, lookup

Genomics wikipedia, lookup

RNA-Seq wikipedia, lookup

Mutation wikipedia, lookup

DNA supercoil wikipedia, lookup

Site-specific recombinase technology wikipedia, lookup

Genome editing wikipedia, lookup

Genetic code wikipedia, lookup

Replisome wikipedia, lookup

Extrachromosomal DNA wikipedia, lookup

No-SCAR (Scarless Cas9 Assisted Recombineering) Genome Editing wikipedia, lookup

Cre-Lox recombination wikipedia, lookup

Non-coding DNA wikipedia, lookup

Therapeutic gene modulation wikipedia, lookup

Vectors in gene therapy wikipedia, lookup

Gene wikipedia, lookup

Helitron (biology) wikipedia, lookup

Nucleic acid analogue wikipedia, lookup

Microevolution wikipedia, lookup

Deoxyribozyme wikipedia, lookup

Point mutation wikipedia, lookup

Primary transcript wikipedia, lookup

History of genetic engineering wikipedia, lookup

Artificial gene synthesis wikipedia, lookup

Transcript
Lecture PowerPoint to accompany
Foundations in
Microbiology
Seventh Edition
Talaro
Chapter 9
Microbial Genetics
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
9.1 Genetics and Genes
Genetics – the study of heredity
The science of genetics explores:
1. Transmission of biological traits from parent
to offspring
2. Expression and variation of those traits
3. Structure and function of genetic material
4. How this material changes
2
3
Levels of Structure and Function of
the Genome
• Genome – sum total of genetic material of a cell
(chromosomes + mitochondria/chloroplasts and/or
plasmids)
– Genome of cells – DNA
– Genome of viruses – DNA or RNA
• DNA complexed with protein constitutes the genetic
material as chromosomes
• Bacterial chromosomes are a single circular loop
• Eukaryotic chromosomes are multiple and linear
4
Figure 9.2
5
Chromosome is subdivided into genes, the
fundamental unit of heredity responsible for a
given trait
–
–
Site on the chromosome that provides information
for a certain cell function
Segment of DNA that contains the necessary code to
make a protein or RNA molecule
Three basic categories of genes:
1. Genes that code for proteins – structural genes
2. Genes that code for RNA
3. Genes that control gene expression – regulatory
genes
6
• All types of genes constitute the genetic
makeup – genotype
• The expression of the genotype creates
observable traits – phenotype
7
Genomes Vary in Size
• Smallest virus – 4-5 genes
• E. coli – single chromosome containing
4,288 genes; 1 mm; 1,000X longer than cell
• Human cell – 46 chromosomes containing
31,000 genes; 6 feet; 180,000X longer than
cell
8
Figure 9.3 E. coli cell has spewed out its DNA
9
DNA
• Two strands twisted into a double helix
• Basic unit of DNA structure is a nucleotide
• Each nucleotide consists of 3 parts:
– A 5 carbon sugar – deoxyribose
– A phosphate group
– A nitrogenous base – adenine, guanine, thymine,
cytosine
• Nucleotides covalently bond to form a sugarphosphate linkage – the backbone
– Each sugar attaches to two phosphates –
• 5′ carbon and 3′ carbon
10
DNA
• Nitrogenous bases covalently bond to the 1′
carbon of each sugar and span the center of the
molecule to pair with an appropriate
complementary base on the other strand
– Adenine binds to thymine with 2 hydrogen bonds
– Guanine binds to cytosine with 3 hydrogen bonds
• Antiparallel strands 3′ to 5′ and 5′ to 3′
• Each strand provides a template for the exact
copying of a new strand
• Order of bases constitutes the DNA code
11
Figure 9.4
12
Significance of DNA Structure
1. Maintenance of code during reproduction
- Constancy of base pairing guarantees
that the code will be retained
2. Providing variety - order of bases
responsible for unique qualities of each
organism
13
DNA Replication
• Making an exact duplicate of the DNA involves
30 different enzymes
• Begins at an origin of replication
• Helicase unwinds and unzips the DNA double
helix
• An RNA primer is synthesized at the origin of
replication
• DNA polymerase III adds nucleotides in a 5′ to 3′
direction
– Leading strand – synthesized continuously in 5′ to 3′
direction
– Lagging strand – synthesized 5′ to 3′ in short
segments; overall direction is 3′ to 5′
14
• DNA polymerase I removes the RNA
primers and replaces them with DNA
• When replication forks meet, ligases link
the DNA fragments along the lagging strand
to complete the synthesis
• Separation of the daughter molecules is
complete
15
Figure 9.5
16
DNA replication is semiconservative because
each chromosome ends up with one new
strand of DNA and one old strand.
18
Figure 9.7 Completion of chromosome replication
19
9.2 Applications of the DNA code
• Information stored on the DNA molecule is
conveyed to RNA molecules through the
process of transcription
• The information contained in the RNA
molecule is then used to produce proteins in
the process of translation
20
21
Gene-Protein Connection
1. Each triplet of nucleotides on the RNA
specifies a particular amino acid
2. A protein’s primary structure determines its
shape and function
3. Proteins determine phenotype. Living things
are what their proteins make them.
4. DNA is mainly a blueprint that tells the cell
which kinds of proteins to make and how to
make them
22
Figure 9.9 DNA-protein relationship
23
RNAs
• Single-stranded molecule made of nucleotides
– 5 carbon sugar is ribose
– 4 nitrogen bases – adenine, uracil, guanine, cytosine
– Phosphate
24
RNA
• 3 types of RNA:
– Messenger RNA (mRNA) – carries DNA message
through complementary copy; message is in triplets
called codons
– Transfer RNA (tRNA) – made from DNA;
secondary structure creates loops; bottom loop
exposes a triplet of nucleotides called anticodon
which designates specificity and complements
mRNA; carries specific amino acids to ribosomes
– Ribosomal RNA (rRNA) – component of ribosomes
where protein synthesis occurs
25
26
Figure 9.10
27
Transcription:
The First Stage of Gene Expression
1. RNA polymerase binds to promoter region upstream
of the gene
2. RNA polymerase adds nucleotides complementary
to the template strand of a segment of DNA in the 5′
to 3′ direction
3. Uracil is placed as adenine’s complement
4. At termination, RNA polymerase recognizes signals
and releases the transcript

100-1,200 bases long
28
Figure 9.11
29
Translation:
The Second Stage of Gene Expression
• All the elements needed to synthesize
protein are brought together on the
ribosomes
• The process occurs in five stages: initiation,
elongation, termination, and protein folding
and processing
30
Figure 9.12
31
The Master Genetic Code
• Represented by the mRNA codons and the
amino acids they specify
• Code is universal
• Code is redundant
32
Figure 9.13
33
Figure 9.14
34
Translation
• Ribosomes assemble on the 5′ end of an
mRNA transcript
• Ribosome scans the mRNA until it reaches
the start codon, usually AUG
• A tRNA molecule with the complementary
anticodon and methionine amino acid enters
the P site of the ribosome and binds to the
mRNA
35
36
Translation
• A second tRNA with the complementary
anticodon fills the A site
• A peptide bond is formed
• The first tRNA is released and the ribosome
slides down to the next codon
• Another tRNA fills the A site and a peptide
bond is formed
• This process continues until a stop codon is
encountered
37
Translation Termination
• Termination codons – UAA, UAG, and
UGA – are codons for which there is no
corresponding tRNA
• When this codon is reached, the ribosome
falls off and the last tRNA is removed from
the polypeptide
38
Figure 9.15
39
Polyribosomal complex allows for the synthesis of
many protein molecules simultaneously from the
same mRNA molecule.
40
Eukaryotic Transcription and
Translation
1. Do not occur simultaneously – transcription
occurs in the nucleus and translation occurs in
the cytoplasm
2. Eukaryotic start codon is AUG, but it does not
use formyl-methionine
3. Eukaryotic mRNA encodes a single protein,
unlike bacterial mRNA which encodes many
4. Eukaryotic DNA contains introns – intervening
sequences of noncoding DNA – which have to be
spliced out of the final mRNA transcript
41
Figure 9.17
42
Genetics of Animal Viruses
• Viral genome - one or more pieces of DNA
or RNA; contains only genes needed for
production of new viruses
• Requires access to host cell’s genetics and
metabolic machinery to instruct the host cell
to synthesize new viral particles
43
44
45
9.3 Regulation of Protein Synthesis
and Metabolism
• Genes are regulated to be active only when
their products are required
• In prokaryotes this regulation is coordinated
by operons, a set of genes, all of which are
regulated as a single unit
46
Operons
• 2 types of operons:
– Inducible – operon is turned ON by substrate:
catabolic operons - enzymes needed to metabolize
a nutrient are produced when needed
– Repressible – genes in a series are turned OFF by
the product synthesized; anabolic operon –
enzymes used to synthesize an amino acid stop
being produced when they are not needed
47
Lactose Operon: Inducible Operon
Made of 3 segments:
1. Regulator – gene that codes for repressor
2. Control locus – composed of promoter and
operator
3. Structural locus – made of 3 genes each coding
for an enzyme needed to catabolize lactose –
b-galactosidase – hydrolyzes lactose
permease – brings lactose across cell membrane
b-galactosidase transacetylase – uncertain function
48
Lac Operon
• Normally off
– In the absence of lactose, the repressor binds
with the operator locus and blocks transcription
of downstream structural genes
• Lactose turns the operon on
– Binding of lactose to the repressor protein
changes its shape and causes it to fall off the
operator. RNA polymerase can bind to the
promoter. Structural genes are transcribed.
49
Figure 9.18
50
Arginine Operon: Repressible
• Normally on and will be turned off when
the product of the pathway is no longer
required
• When excess arginine is present, it binds to
the repressor and changes it. Then the
repressor binds to the operator and blocks
arginine synthesis.
51
Figure 9.19
52
9.4 Mutations:
Changes in the Genetic Code
• A change in phenotype due to a change in
genotype (nitrogen base sequence of DNA) is
called a mutation
• A natural, nonmutated characteristic is known
as a wild type (wild strain)
• An organism that has a mutation is a mutant
strain, showing variance in morphology,
nutritional characteristics, genetic control
mechanisms, resistance to chemicals, etc.
53
Figure 9.20
54
Causes of Mutations
• Spontaneous mutations – random change
in the DNA due to errors in replication that
occur without known cause
• Induced mutations – result from exposure
to known mutagens, physical (primarily
radiation) or chemical agents that interact
with DNA in a disruptive manner
55
56
Categories of Mutations
• Point mutation – addition, deletion, or
substitution of a few bases
• Missense mutation – causes change in a
single amino acid
• Nonsense mutation – changes a normal
codon into a stop codon
• Silent mutation – alters a base but does not
change the amino acid
57
Categories of Mutations
• Back-mutation – when a mutated gene
reverses to its original base composition
• Frameshift mutation – when the reading
frame of the mRNA is altered
58
59
Repair of Mutations
• Since mutations can be potentially fatal, the cell
has several enzymatic repair mechanisms in
place to find and repair damaged DNA
– DNA polymerase – proofreads nucleotides during
DNA replication
– Mismatch repair – locates and repairs mismatched
nitrogen bases that were not repaired by DNA
polymerase
– Light repair – for UV light damage
– Excision repair – locates and repairs incorrect
sequence by removing a segment of the DNA and
then adding the correct nucleotides
60
Figure 9.21
61
The Ames Test
• Any chemical capable of mutating bacterial
DNA can similarly mutate mammalian DNA
• Agricultural, industrial, and medicinal
compounds are screened using the Ames test
• Indicator organism is a mutant strain of
Salmonella typhimurium that has lost the ability
to synthesize histidine
• This mutation is highly susceptible to backmutation
62
Figure 9.22
63
Positive and Negative Effects of
Mutations
• Mutations leading to nonfunctional proteins are
harmful, possibly fatal
• Organisms with mutations that are beneficial in
their environment can readily adapt, survive, and
reproduce – these mutations are the basis of
change in populations
• Any change that confers an advantage during
selection pressure will be retained by the
population
64
9.5 DNA Recombination Events
Genetic recombination – occurs when an
organism acquires and expresses genes
that originated in another organism
3 means for genetic recombination in bacteria:
1. Conjugation
2. Transformation
3. Transduction
65
66
Conjugation
• Conjugation – transfer of a plasmid or
chromosomal fragment from a donor cell to
a recipient cell via a direct connection
– Gram-negative cell donor has a fertility
plasmid (F plasmid, F′ factor) that allows the
synthesis of a conjugative pilus
– Recipient cell is a related species or genus
without a fertility plasmid
– Donor transfers fertility plasmid to recipient
through pilus
67
Figure 9.23 (1)
68
Figure 9.23 (2)
69
Conjugation
• High-frequency recombination – donor’s
fertility plasmid has been integrated into the
bacterial chromosome
• When conjugation occurs, a portion of the
chromosome and a portion of the fertility
plasmid are transferred to the recipient
70
Figure 9.23 (3)
71
Transformation
• Transformation – chromosome fragments
from a lysed cell are accepted by a recipient
cell; the genetic code of the DNA fragment is
acquired by the recipient
• Donor and recipient cells can be unrelated
• Useful tool in recombinant DNA technology
72
Figure 9.24
Insert figure 9.23
transformation
73
Transduction
• Transduction – bacteriophage serves as a
carrier of DNA from a donor cell to a recipient
cell
• Two types:
– Generalized transduction – random fragments of
disintegrating host DNA are picked up by the phage
during assembly; any gene can be transmitted this
way
– Specialized transduction – a highly specific part of
the host genome is regularly incorporated into the
virus
74
Figure 9.25
Generalized
transduction
75
Figure 9.26
Specialized
transduction
76
Transposons
• Special DNA segments that have the
capability of moving from one location in
the genome to another – “jumping genes”
• Cause rearrangement of the genetic material
• Can move from one chromosome site to
another, from a chromosome to a plasmid,
or from a plasmid to a chromosome
• May be beneficial or harmful
77
Figure 9.27
Transposons
78