AP Biology Chapter 18
What is a prophage?
Viral DNA integrated by genetic recombination
What does the operator control?
Access of RNA polymerase
What generally must be present for the sex pili to donate DNA during conjugation?
An F factor
What did Ivanowsky conclude that built on Mayer's work?
Bacteria can be small enough to pass through a filter, or they could make a toxin that could.
Where are the most complex capsids found?
Bacteriophages
What is the name for a protein shell enclosing the viral genome?
Capsid
What are the subunits of capsids?
Capsomeres
What are viroids?
Circular RNA molecules that infect plants
How is the DNA arranged in the nucleoid region of the bacterial genome?
Coiled very tightly
What is the process of direct transfer of genetic material between two bacterial cells that are the temporarily joined?
Conjugation
What joins two bacterial cells for a transfer of genetic material?
Cytoplasmic mating bridge
Describe the process of binary fission
DNA synthesis at single origin of rep - all the way around until two circles and then cells separate
What kind of nucleic acids are the viral genomes made of?
Double stranded DNA/RNA, single stranded DNA/RNA
Define transposable elements.
Elements of the cells genome that never exist independently but can be moved in chromosomal/plasmid DNA
What is a common name for transposable elements?
Jumping genes
What is the phage reproductive cycle that replicates the phage genome without destroying the host?
Lysogenic cycle
What is the phage reproductive cycle that culminates in the death of the host cell?
Lytic cycle
What is the key advantage of grouping genes of related function in to one transcription unit?
A promoter can code for the production of multiple related enzymes at once.
Does the use of a viral envelope to enter the host kill the host cell?
Not necessarily
What is a plasmid?
Small circles of DNA
How do bacteria defend themselves against phages?
- Natural selection - Phage DNA cut up by restriction enzymes in bacteria
List the full steps of the simplified viral reproductive cycle.
1. A virus enters the cell and is uncoated, releasing viral DNA and capsid proteins 2. Host enzymes replicate the viral genome 3. Host enzymes transcribe the viral genome into viral mRNA, which other host enzymes use to make more viral proteins 4. Viral genomes and capsid proteins self-assemble into new virus particles, which exit the cell
What are the two ways that metabolic control can occur within bacteria?
1. Cells adjust activity of present enzymes 2. Cells adjust how much of a certain enzyme is made
Describe the reproductive cycle of an enveloped RNA virus
1. Glycoproteins on envelope bind to receptor molecules on host 2. Capsid and viral genome enter 3. Viral genome becomes template for synthesis of RNA strands by a viral enzyme 4. New copies of RNA are made 5. RNA function as mRNA that translate into capsid + glycoproteins for viral envelope 6. Vesicles transport envelope glycoproteins to the plasma membrane 7. Capsid assembles around each viral genome molecule 8. New virus buds with glycoproteins on membrane
List and explain the two major routes that plant viruses spread
1. Horizontal transmission - infected from external source 2. Vertical transmission - inherits viral infection from parent
List the generalized steps of transduction
1. Phage infects the cell 2. It breaks down cellular DNA 3. Phages pick your DNA 4. Phage inserts cell DNA into new cell 5. New cell incorporates DNA into genome
Describe the reproductive cycle of HIV, a retrovirus
1. Virus fuses with cells plasma membrane, capsid releases viral proteins and RNA 2. Reverse transcriptase catalyzes the synthesis of a DNA strand 3. Reverse transcriptase catalyzes the 2nd DNA strand 4. Double stranded DNA is incorporated as provirus into cells DNA 5. Proviral genes transcribed into RNA molecules 6. Viral proteins include reverse transcriptase and envelope glycoproteins 7. Vesicles transport the glycoproteins from the ER to cells plasma membrane 8. Capsids are assembled around viral genomes and reverse transcriptase molecules 9. New viruses bud off from the host cell
What are the steps of the lytic cycle of a T4 phage?
1. attachment 2. entry of phage DNA and degradation of host DNA 3. synthesis of viral genomes and proteins 4. assembly 5. release
What are the three processes that contribute to the emergence of viral diseases?
1. mutation of existing viruses 2. spread of existing viruses from one host to another 3. dissemination of viral disease from small isolated population
How small are viruses?
20 nm in diameter
What is an episome?
Genetic element that can replicate either as part of the bacterial chromosome or independently
What are vaccines?
Harmless variants of pathogenic microbes that stimulate the immune system to mount defenses against actual pathogen
How and what did Dr. Mayer discover specifically in 1883?
He could transmit diseases from plant to plant by rubbing sap from diseased plants onto healthy ones.
Define prions
Infectious proteins - degenerative brain diseases in animals
What is the name for the simplest transposable elements?
Insertion sequences.
What is special about the F plasmid?
It can undergo reversible integration into cells chromosome. It is a little circle that can enter the cell directly.
What is the main component of most bacterial genomes?
One circular DNA molecule with a small amount of protein
Define transduction
Phages carry bacteriazed genes from one host cell to another
What are retroviruses and how do they use reverse transcriptase?
RNA animal viruses with the most complicated reproductive cycles.
What are phages called that are capable of using both modes of reproduction?
Temperate phages
What is an example of the interaction between a prophage and a bacterium?
The bacteria that causes the human diseases diphtheria, botulism, and scarlet fever aren't harmless because prophage genes cause host bacteria to make toxins
What logic did Beijerinck use to lead to the idea of a virus?
The infectious agent could reproduce and can't be cultivated on nutrient media. So, he imagined a reproducing particle smaller than bacteria
Define host range
The range of host cells the virus can affect
What is the use of a viral envelope in animal viruses?
Used to enter the host cell through glycoproteins
What are R plasmids and why are these a problem to humans?
They are plasmids resistant to certain antibiotics.
Why do mutations make such a large contribution to bacterial genetic variation as compared to humans?
They are rare, but can significantly increase genetic diversity when reproductive rates are high
What is an example of the benefit to bacteria of these transposable elements?
They help bacteria adapt to new environments or carry antibiotic resistance.
What are viral envelopes and what is their function?
They surround the capsid. The contain a combination of viral and host cell molecules.
What is the process of alteration of a bacterial cell's genotype by the uptake of naked, foreign DNA from the surrounding environment?
Transformation
What is the name for transposable elements that are no longer and more complex than insertion sequences?
Transposons
Explain the experiment and the results that demonstrated evidence of genetic recombination in bacteria
Two mutant strains - grown in medium - only samples from mixed gave rise to colonies
What kind of phage only reproduces by a lytic cycle?
Virulent phage
Is it believed that viruses evolved before or after the first cells appeared and what evidence is used to support the idea?
Viruses most closely related to host and may have arisen from broken off host DNA, evidence: plasmids are separate from chromosome
How was the existence of a virus finally confirmed and by whom?
Wendell Stanley crystallized the infection particle.
Where is an operator positioned?
Within the promoter or between the promoter and enzyme coding gene
