Warm up
1. Why do many scientists classify viruses
as non-living?
2. Draw the basic structure of a virus.
Warm up
1. Draw the lytic/lysogenic cycle
2. What stage of the lytic-lysogenic
cycle is a virus virulent? Temperate?
Warmup
1. Define conjugation, transduction and
transformation
2. Draw and label the lac operon. Explain
CH 18-19
Microbial Models
Microbes make great models for genetics due to their simplicity, fast growth and accessibility.
Hepatitis Virus
BACTERIA
VIRUS
Both have DNA or RNA and proteins
Prokaryotic cell
Few are parasitic;
most free living
Relatively large
Many cured by
antibiotics; some are resistant
Nucleic acid
surrounded by capsid
Intracellular parasite
1/1000 size of
bacteria
Infection=Prevention
by vaccine
NO CURES some
Process of Science: Discovery of viruses
Researchers discovered viruses by studying a plant disease - Tobacco Mosaic Virus
The small size of the TMV
A virus = nucleic acid of DNA or RNA enclosed in a
protective protein capsid & sometimes a membraneous
How to be a Virus
Invader
Viruses can reproduce only within a host cell
The viral genome is inserted into the cell along with enzymes.
The cells DNA is broken up. The cell begins to copy the viral genome and reads it to make viral proteins
Animal viruses are
diverse in their modes of infection and
replication
Researchers ask:
1. Does it have DNA or RNA
2. Is it double stranded
(DS)or single stranded (SS) 3. Does it have an
Enveloped viruses have different
methods of lytic reproduction in animal cells.
The membraneous envelope comes from the host cell, forming around
them as they exit. This envelope
makes it hard for a host’s immune
Proviruses replicate in the host’s nucleus. These viruses have an envelope that comes from a host’s nuclear membranes.
The viral genome can join with the hosts DNA, in a lysogenic fashion. This lets the virus lie
dormant for long periods of time, emerging from time to time
Herpes is a provirus.
Provirus=
eukaryote host
Prophage=
Retro viruses use an RNA genome
Retro viruses use an enzyme called
reverse transcriptase
that turns their RNA into DNA.
Retro viruses insert into the host’s DNA and can lie dormant for years before
beginning a
Retro viruses use an RNA genome
HIV is a retrovirus.
HIV+ means the virus is in your DNA.
AIDS means the
Other Human Viruses
New Emerging Human Viruses
Ebola Viruses Hanta Viruses
New viruses can mutate from an old one. RNA viruses, like flu, mutate often. They can also
Viroids
Circular RNA molecules,several hundred nucleotides in length
Infects plants
Cause errors in regulatory
systems that control plant growth
Eg. coconut palms in
Prions
Midfolded, infectious proteins that cause
misfolding of normal proteins
Causes degenerative brain diseases in animals
(spongiform encephalopathy)
Eg. scrapie (sheep), mad cow disease (BSE),
Diseases caused by prions
Prions act slowly – incubation period of at least
10 years before symptoms develop
Prions are virtually indestructible (cannot be
denatured by heating)
How prions propagate
The Genetics of Bacteria
Bacteria evolve quickly due to their short
reproductive cycle,
mutations and genetic recombination
Binary Fission-begins at origin and copies in both directions
Bacterial Reproduction
Bacteria exchange DNA in several ways:
Transduction
Transformation
• bacteria takes up naked, foreign DNA from
surrounding environment
Transduction
Transduction usesviruses to move DNA from cell to cell
When the new virus invades a new cell,
the bacterial fragment recombines with the host’s DNA.
Specialized
transduction involves lysogenic viruses.
When the virus starts a lytic cycle it
Conjugation
Conjugation= joining two
bacteria with a tube called a sex pili.
Only smaller round DNA
genomes called
Conjugation
The ability to form a sex pili (male) is carried on an F plasmid. F stands for fertile.
Here an F plasmid is transferred to another bacteria. It will now be able to make sex pili as well.
Plasmids act as supplemental DNA sources. They replicate along with the main
Conjugation
A plasmid can also be incorporated into the main chromosome. This makes an Hfr cell,
which stands for high frequency of recombination
Conjugation
Here an F plasmid is transferred to another bacteria by an Hfr cell. Only portions of the entire chromosome transfer before the sex pili disconnects.
There are many plasmids in the bacterial
world. Some can carry genes for resistance to antibiotics. Plasmids that carry these
resistances are R plasmids.
Some R plasmids can carry resistance for up to ten
different antibiotics.
Transposons: transposable genetic
elements or “jumping genes”; genes that have no permanent location and move
from place to place
Transposons
Transposase: enzyme that catalyzes movement
within genome
Transposons include extra genes such as
antibiotic resistance
Control of Gene Expression
Negative
feedback by the end products of biochemical
pathways can
Operons
This is the trp operon. It contains the genes to manufacture the amino acid trytophan- if it is not available.
Operons
Between the promoter and the genes is a special site called the operator-the on/off switch that can block RNA polymerase
The operon contains a promoter site for RNA
Repressible Operons
The gene will be transcribed and translated and tryptophan will be made.
Trp is a repressible operon - it is always on
Repressible Operons
The active repressor now binds to the operator and shuts down the trp operon. This is negative feedback by the end product trytophan.
Inducible operons
This is the lac operon, which makes enzymes to metabolize the sugar lactose.
If glucose supplies fall, and lactose is present then this operon gets switched on.
Cells prefer to metabolize glucose. So this
Inducible operons
Without cAMP, the initiation factor can not bind, and neither can RNA polymerase. This operon shuts down when both sugars are present.
Warm up
1. How is DNA packaged into Chromosomes?
2. What are pseudogenes?
3. Contrast DNA methylation to histone
Warm up
1. Why are transposons important in genetics?
2. How and why do cells differentiate?
Control of Eukaryotic Genome-ch19
Eukaryotic
chromosomes are much more complex
than the single
circular chromosome found in prokaryotes.
These chromosomes are made of DNA and a complex of proteins. This material is called
Chromatin structure
is based on levels of DNA packing.
1. Protein histones wind DNA into
nucleosome beads 2. Nucleosome
beads coil and fold up with the help of other
proteins that act as scaffolds
Genome Organization at the DNA Level Tandem DNA=
repeating short patterns of DNA nucleotides;
has a different density than
regular DNA and forms a “satellite” bands when
centrifuged.
Fragile X is a
mutation where an
Gene families have evolved by duplication of ancestral genes
Hemoglobin is a protein with quaternary
structure.
Made of four globular proteins These duplicated genes are called multigene families
There are many repeats of this
protein in human DNA, similar but not identical. They turn on and off at different times. They can all be traced back to an individual
Gene amplification can add extra sources of
mRNA when needed, as in a developing embryo. Re-arrangement can alter a cell's genome
A transposon can knock out a gene by copying into its middle, or turn one on or off
The Control of Gene Expression
Each eukaryotic cell
expresses only a small fraction of its genes.
Differentiation determines which genes turn on and off as an embryo develops.
The control of gene
expression can occur at any step in the pathway from
Chromatin modifications= affect the availability of genes for transcription. Epigenetic changes do not affect the sequence of the code, only the reading of the code
DNA methylation = deactivates sections of a chromosome (Barr bodies in females);
A Eukaryotic Gene
Transcription initiation is controlled by
transcription factors. These factors bind to the
Control of Transcription Initiation
Close to the promoter are control elements, and another set of control elements called enhancers
Activators attach to the enhancers. Together with initiation factors that binds to the TATA end of a promoter, a site for RNA polymerase binding forms.
The DNA bends and helps hold together the transcription factors. This creates a
transcription
initiation complex
.
Processing of mRNA introns and exons in different ways can control protein production, especially by adding regulatory sites.
The Molecular Biology of Cancer
Cancer results from genetic changes that affect the cell cycle. Proto-oncogenes promote normal cell growth.
Oncogene proteins with faulty tumor-suppressor
proteins can interfere with normal signaling pathways.
The ras protein plays a vital role in controlling cell growth. If it is
transformed into a
hyperactive state, cell growth is
overstimulated .
An initiation factor called
Multiple mutations underlie the development of cancer
Combinations of the loss of tumor supressors with the addition of hyperactive oncogenes
