Genetics – science of heredity (how genes operate)
Chromosomes –
Structures containing DNA,
Carry hereditary information,
Contain genes
Bacteria usually have single circular chromosome
Animals have multiple linear chromosomes
Genes – segments of DNA that code for functional
products (proteins)
Haploid – have one set of chromosomes
Ex: bacteria
Diploid – have two sets of chromosomes
Ex: animals
DNA and RNA
Composed of nucleotides
A. Sugar
B. Phosphate
C. Base
Adenine (A)
Guanine (G)
Cytosine (C).
Thymine (T) (DNA only)
Uracil (U) (RNA only)
DNA – double stranded
RNA – single stranded
DNA exhibits complementary base pairing
A – T
C – G
Genotype
Genetic properties (genes)
Potential properties
Phenotype
Actual, expressed properties
Can see or measure
The flow of genetic information (DNA replication and
gene expression)
DNA transcriptionà mRNA translationà protein
|
| DNA replication
V
DNA
DNA replication (short version) (Fig. 8.3)
A. Enzymes
unwind and “unzip” DNA stands
B. DNA
polymerase adds a complementary nucleotide to each nucleotide in the original
strands
C. Two
identical DNA molecules are formed
DNA replication (detailed version)
A. DNA
structure
DNA is double stranded
Each strand has 3’ and 5’ ends
The two strands are antiparellel (Fig 8.4)
One strand runs 3’ to 5’
Other strand runs 5’ to 3’
DNA polymerase adds nucleotides to 3’ end only, so
DNA replication can only go in the 5’ à 3’ direction
B. Events of
DNA replication (Fig 8.6)
1. Enzymes
unwind and unzip DNA strands
2. Leading
strand synthesized continuously (5’ to 3’) by DNA polymerase
3. Lagging
strand synthesized discontinuously
a. RNA
polymerase synthesizes a short RNA primer (provides a 3’ end to build on)
b. DNA
polymerase extends DNA from RNA primer to the last RNA primer that was
installed
c. DNA
polymerase replaces previous RNA primer with DNA
d. DNA ligase
does final joining of the fragments
Gene Expression (mRNA and Protein Synthesis)
A. Transcription
(DNA à mRNA) (Fig. 8.8)
1. RNA
polymerase binds to promoter, DNA unwinds
2. RNA
synthesized by complementary base pairing
3. Site of
RNA synthesis moves along DNA, transcribed DNA rewinds
4.
Transcription reaches terminator
5. RNA and RNA
polymerase released, DNA helix reforms
B.
Translation (mRNA à
protein)
1. Codons
Language of mRNA
Groups of 3 nucleotides
Codons code for amino acids (Fig. 8.9)
Code is degenerate (redundant)
More than one codon can code for the same amino acid
Protects microbe from effects of radiation
Type of codons
a. Sense
codons – code for amino acids
b. Nonsense
codons (Stop codons)
UAA, UAG, UGA
Signal the end of protein synthesis
c. Start
codon
AUG
Initiates the synthesis of protein
In addition, codes for Methionine
2. tRNA
Carries correct amino acid to ribosome
Has anticodon on one end that binds to codon of mRNA
Has specific amino acid that is bound onto the other
end
3. The
process of translation (Fig. 8.10)
(1) tRNA,
ribosomal subunits and mRNA come together
(2) tRNA with
Met bind to start codon on mRNA in P site of ribosome
(3) tRNA with
second amino acid binds to second codon in the A site of ribosome. Peptide bond forms between amino acids.
(4) First
tRNA is released
(5) Ribosome
move along mRNA until second RNA is in P site.
Third tRNA binds to third codon in A site.
(6) Process
repeated, more amino acids added
(7) Ribosome
reaches stop codon, polypeptide released
(8) Last tRNA
released, ribosome comes apart, polypeptide folds into protein
Mutation – change in base sequence of DNA (i.e., a
change in genotype)
Variation – a change in the appearance of a microbe
due to a change in its genotype
A. Types of
mutations
1. Base
Substitution (Point mutations) – one base substituted by different
base (Fig. 8.16)
a. Silent
No change in amino acid coded for
No effect on finished protein
Ex: UCA à UCG
serine serine
b. Missense
mutation (Fig. 8.17b)
New codon codes for different amino acid
Ex: sickle-cell anemia due to one missense mutation
in hemoglobin gene (Aà
T)
c. Nonsense
mutation (Fig. 8.17c)
Change in base resulting in a stop codon in middle of
mRNA
Translation stops in middle of protein synthesis
2. Frameshift
mutations (Fig. 8.17d)
One or more bases deleted or inserted
in the DNA
à Translational reading frame shifted
à Coding drastically altered
à Inactive (defective) protein
B. Mutagens –
agents that cause mutations
1. Chemical
mutagens
a.
DNA-modifying agents
Alters bases and makes them bond with incorrect base
Causes point mutations
Ex: Nitrous
acid (Fig. 8.18)
b. Nucleoside
analogs
Substitutes in place of base
Analog binds with incorrect base during replication
Causes point mutation
Ex:
2-aminopurine (Fig. 8.19)
c. Frameshift
mutagen
Insert between base pairs à cause frameshift mutation
Often potent carcinogens
Ex:
benzpyrene, in smoke and soot
aflatoxin, produced by mold that grows on peanuts
2. Radiation
a. Ionizing
radiation
X-rays and gamma rays
Ionizes cellular constituents
Ions bind with DNA à errors in DNA replication à mutations
b.
Non-ionizing radiation
UV
Causes thymine dimers à stops DNA transcription or replication (Fig. 8.20)
Body repairs, but sometimes replaces with incorrect
bases à mutation
C. The
frequency of mutation
1.
Spontaneous mutations: 1 in 106
replicated genes
2.
Mutagens: increases 10-1000
times à up to 1 in 103
replicated genes
D.
Identifying Chemical Carcinogens à Ames test (Fig. 8.22)
1. Background
for Ames test
Prototroph – normal microbe
Auxotroph – prototroph that mutated
à Now can’t synthesize some essential nutrients
Revertant – auxotroph that had a reverse mutation
back to prototroph
Prototroph mutationà
Auxotroph Reverse
mutation à Revertant
(His + Salm.) ( His- Salm.)
due to mutagen
(His+ Salm.)
2. Procedure
of Ames test
a. Put auxotroph on Media lacking histidine and containing suspected mutagen
b. Incubate
c. Count
colonies (any colonies will be revertants)
If count few colonies à due to spontaneous mutations
If count many colonies
à compound is mutagenic
à compound is probably carcinogenic (most carcinogens
are also mutagens)
Genetic Recombination (in bacteria) – the exchange of
genes between two DNA molecules
A.
Transformation
Genes are transferred from one bacterium to another
as “naked” DNA in
solution
Griffith’s genetic transformation experiment (Fig.
8.24)
The mechanism of genetic transformation (Fig. 8.25)
1. Recipient
cell takes up DNA fragments from donor cells
2. Recombination
occurs between donor DNA and recipient DNA
B.
Conjugation
Genes are transferred from one bacterium to another
by direct contact (often via a sex pilus) (Fig. 8.26)
1. Types of
cells involved in conjugation
a. F+ cell
Has F factor on a plasmid
Donor
b. F- cell
Does not have an F factor
Recipient
c. Hfr cell
(High frequency of recombination
Has F factor integrated into chromosome (Fig. 8.27b)
Donor
2. Mechanisms
of conjugation (determined by donors)
a. F+ donors
(Fig. 8.27a)
(1) Sex pilus
forms
(2) A copy of
plasmid (with F factor) is transferred through sex pilus from F+ to F- cell
(3) F- cell
is converted into an F+ cell
b. Hfr donors
(Fig. 8.27c)
(1) Sex pilus
forms
(2) A copy of
chromosome is transferred through sex pilus from Hfr to F- cell (F factor is
transferred last)
(3) Fragile
sex pilus usually breaks stopping process before completion
à Part of chromosome transferred, but not F factor
à recipient stays F-
(4)
Recombination occurs between Hfr chromosome fragment and F- chromosome
C.
Transduction
Genes are transferred from one bacterium to another
via a bacteriophage or phage (virus that infects bacteria)
1.
Generalized transduction – random genes are transferred (Fig. 8.28)
a. Phage
infects donor bacterial cell
b. Phage DNA
and proteins made, bacterial chromosome broken
c.
Occasionally bacterial DNA packaged in viral capsid
d. Phage
infects new host cell (recipient cell)
e.
Recombination occurs between donor and recipient bacterial DNA
2.
Specialized transduction – similar process, but only certain bacterial
genes are transferred
Chapter
9 Biotechnology and Recombinant DNA
Biotechnology – the use of microorganisms or cells to
make products
Genetic engineering
= Recombinant DNA technology
= Artificial techniques for exchanging genes between
DNA molecules
Genetic engineering and applications (Fig. 9.1)
A. Gene of
interest is cut out of chromosome using restriction enzymes (restriction
endonucleases)
A. Gene is
inserted into a plasmid
B. Plasmid is
taken up by a cell (usually bacterium)
C. Cells
cloned (copied) during log phase of bacterial growth
D. Products
harvested
1. Genes
harvested
Copies of genes are inserted into other organisms to
give desirable properties
Ex: gene for
pest resistance is inserted into plants
2. Protein
harvested
Altered cells make a protein product
Ex: Various
enzymes, pharmaceuticals
Pharmaceutical Products of Genetic Engineering (Table
9.1)
Know at least three products
Chapter
12 The Eukaryotes: Fungi, Algae, Protozoa, and Helminths
Mycology -
study of fungi
Fungi
Eukaryotic
Cell wall of chitin
Chemoheterotrophs
Most are saprophytes (saprotrophs) à feed on dead organic matter
A. Three
morphological groups of fungi
1. Molds
Consist of hyphae à long filaments of cells joined together
Mass of hyphae à mycelium
Almost all are aerobic
a. Types of
hyphae based on septa (cross walls) (Fig 12.1)
(1) Septate
hyphae – contain septa
(2)
Coenocytic hyphae – no septa, long continuous cells with many nuclei
b. Types of
hyphae based on function (Fig 12.2)
(1)
Vegetative hyphae – obtain nutrients
(2)
Reproductive or aerial hyphae – reproduction, bears spores
2. Yeasts
Nonfilamentous,
unicellular
Most are facultative anaerobes
Reproduce asexually by
a. budding -
dividing unevenly (Fig. 12.3)
Ex: Saccharomyces
(Brewer’s yeast)
b. fission -
dividing evenly
3. Dimorphic
fungi
Can grow either as a mold or a yeast (Fig. 12.4)
B. Life cycle
of Fungi
1. Asexual
Reproduction
Produces asexual spores formed by the hyphae of one
organism (Fig. 12.5)
a.
Conidiospore
Not enclosed in a sac
Produced in chains at end of aerial hyphae
b.
Arthrospore
Not enclosed in a sac
Formed by fragmentation of hyphae
c.
Blastoconidia
Not enclosed in a sac
Formed by buds coming off the parent cell
d.
Chlamydospore
Thick-walled spore formed within hyphae
e.
Sporangiospore
Enclosed in a sac at end of aerial hyphae
2. Sexual
reproduction
Produces sexual spores
a. Process
(1)
Plasmogamy
Haploid nucleus of a donor cell (+) penetrates the
cytoplasm of a recipient cell (-)
(2) Karyogamy
The (+) and (-) nuclei fuse to form a diploid zygote
nucleus
(3) Meiosis
Diploid nucleus à haploid nuclei (sexual spores)
b. Types of
sexual spores
(1) Zygospores
(2)
Ascospores
(3)
Basidiospores
C. Medically
important Phyla of Fungi
Phyla determined by sexual spores produced
1. Zygomycota
(Fig. 12.6)
Produce zygospores
Saprophytic molds (obtains nutrients from dead
organic matter)
Coenocytic hyphae
Ex: Rhizopus
nigricans (common black bread mold)
2. Ascomycota
(Fig. 12.7)
Produce ascospores enclosed in a saclike ascus
Molds with septate hyphae and some yeasts
Ex: Histoplasma
capsulatum (causes Histoplasmosis)
3.
Basidiomycota (Fig. 12.8)
Produce basidiospores on base pedestal called a
basidium
Ex:
“mushrooms”
4.
Deuteromycota
“holding category” for fungi whose sexual cycle has
not been observed yet
D. Fungal
diseases à mycoses
1. Systemic
mycoses
Infections deep within body à Affect tissues and organs
Transmission by inhalation of spores
Ex:
Histoplasmosis
2.
Subcutaneous mycoses
Infections beneath skin
Transmission by spores entering puncture wound
Ex:
Sporotrichosis
3. Cutaneous
mycoses
Infection of the skin
Transmission by direct contact
Ex: Tinea
capitis (ringworm) (Fig 21.16a)
4.
Superficial mycoses
Infection of hair and dead layers of epidermis
Transmission by direct contact
Ex: Tinea
versicolor
Algae
Unicellular or multicellular
Eukaryotic
Photoautotrophs
Examples:
A. Brown algae
(kelp) (Fig. 12.11b)
B. Green
algae (green pond scum)
C.
Dinoflagellates (Fig. 12.14)
à some produce neurotoxin
à mussels and clams concentrate
à paralytic shellfish poisoning (PSP)
Protozoa
Unicellular
Eukaryotic
Chemoheterotrophic
A. Many can have
two forms
1.
Trophozoite – feeding and growing stage
2. Cyst –
have protective capsule that forms during adverse conditions
B. Medically
Important Phyla of Protozoa
Classified according to type of motility
1. Archaezoa
(old name à Mastigophora)
Lack mitochondria
Move by flagella
Ex: Trichomonas
vaginalis (Fig. 12.17b) causes STD
Ex: Giardia
lamblia (Fig. 12.17c)
2.
Rhizopoda (old name à Sarcodina)
Move by pseudopodia
Ex: Amoeba
proteus (Fig 12.18a)
3.
Apicomplexa (old name à Sporozoa)
Not motile
Obligate intracellular parasites
Ex: Plasmodium
vivax – causes malaria
Life Cycle (Fig. 12.19)
a. Infected
mosquito bites human and transmits P. vivax
b. Asexual
reproduction in liver and red blood cells
c. Uninfected
mosquito bites infected human à mosquito infected
d. Sexual
reproduction in mosquito
Some Protozoa require 2 types of hosts
a. Definitive
host – harbors sexual reproducing stage(in this case, the mosquito)
b. Intermediate host – harbors asexually reproducing
stage(in this case, the human)
4. Ciliophora
Move by cilia
Examples:
Paramecium
(Fig. 12.20a)
Only ciliate that is a human parasite
Causes Ciliary dysentery
5. Euglenozoa
(old name à Mastigophora)
Move by flagella
Grouped together because of common genetic sequences
Examples:
Euglena
(Fig. 12.21)
Trypanosoma cruzi à Chaga’s disease
Helminths
Parasitic worms
Multicellular
Eukaryotic
Arrangements of reproductive organs
à Dioecious – separate males and females
à Monoecious – one individual has both male and female
reproductive organs
A.
Platyhelminths – flatworms
Most are monecious
1. Trematodes
– flukes
Flat, leaf-shaped bodies
Have ventral and oral suckers
Ex: Lung
fluke (Fig. 12.26)
Occurs throughout world
Life cycle
a. Adult
fluke lives in bronchioles of human à Reproduces sexually (definitive host)
b. Eggs à swallowed sputum à feces à water
c. Egg
hatches à snail à reproduces asexually (int. host)
d. Leave
snail à encyst in crayfish
(intermediate host)
e.
Undercooked crayfish eaten by human
f. Bores out intestine and into lung
2. Cestodes –
tapeworms (Fig. 12.27)
Intestinal parasites
Lack a digestive system à absorb food through cuticle
Has scolex (head) with suckers and hooks
Body consists of segments called proglottids
Ex: Taenia
saginata “beef tapeworm”
Life Cycle
a. Adults
live in human intestines (6 m long) (Defin. host)
b. Mature
proglottids and eggs shed in feces
c. Cattle eat
eggs (intermediate host)
d. Eggs
hatch, larvae bore through intestines to muscle
e. Human eats
beef
f. Scolex
anchors in small intestine
B. Nematodes
– roundworms
Cylindrical and tapered at each end
Complete digestive system (mouth, intestines, anus)
Most dioecious
1. Pinworm
(Fig. 12.29)
1 cm long
No damage to host
Life cycle:
a. Adults
live in human large intestine
b. Lay eggs
around anus
c. Eggs
ingested by contaminated hands or clothing
2. Ascaris
lumbricoides
30 cm long
Life cycle:
a. Adults
live in human small intestines
b. Eggs in
feces (can be viable in soil for 10 years)
c. Eggs ingested
d. Eggs hatch
in small intestine
e. Larvae
burrow out of intestines, enter blood
f. Carried to
lungs and grow
g. Coughed
up, swallowed, and return to small intestine
h. Mature
into adults
3. Hookworms
(Fig. 12.30)
Life cycle:
a. Adults
live in human small intestine
b. Eggs in
feces
c. Larvae
hatch in soil
d. Larvae
penetrates hosts skin (barefoot)
e. Larvae
enters blood, carried to lungs
f. Coughed
up, swallowed, and carried to small intestine
g. Mature
into adults
4. Trichinella
spiralis
Causes trichinosis
Life cycle:
a. Larvae
encysted in muscle of pigs or wild game
b. Other
animal (or human) eats undercooked infected meat
c. Mature and
reproduce in human small intestine
d. Larvae
migrate and encyst in tissue
Arthropods as Vectors
Vector = Arthropods that carry pathogenic
microorganisms
Arthropods
A. Arachnida
8 legs
Spiders, mites, ticks
Ex: Ixodes
(tick) carries microorganism that causes Lyme disease (Fig. 12.32)
B. Insecta
6 legs
Bees, flies, mosquitoes, lice
Ex: Anopheles
(mosquito) carries microorganism that causes malaria (Fig. 12.31)