Lecture 20: Viruses and Bacteria Flashcards
Do viruses and bacteria use the same genetic material and genetic code as humans?
YES
What do viruses do to cells?
Tell cells to stop doing cell stuff and start making viruses instead
True or False : Viruses can be very small
True, influenza is less than 10 genes
Are viruses smaller than bacteria?
Yes
What did Dmitri Ivanovsky do?
Discovered viruses
What is a virion?
A viral particle that typically consists of a protein coat or capsid(protein shell of a virus) and nucleic acid
How are viruses classified?
- Host specificity and pathology (tomato bushy stunt virus (infects tomatoes and causes stunted and bushy plants)
-Defined by their genetic material (RNA/DNA)
-Defined by their size/shape
What is a bacteriophage?
-Virus that infects bacteria
Virulent phage vs Temperate phage?
Virulent Phage undergo the lytic reproductive cycle
Temperate Phage undergo the lysogenic reproductive cycle
Lytic Reproductive Cycle
- Phage binds to bacteria
- Injects its DNA
- Bacteria produces more phages and more phage DNA instead of its own
- Cell destruction occurs and phage are released
Lysogenic Reproductive Cycle
- Phage inserts its DNA into the bacterial chromosome(prophage)
- Bacteria now divides and replicates the prophage along with its own DNA
- When the time is right the prophage leaves the chromosome and resumes the lytic cycle
Do all viruses follow the lytic/lysogenic cycle?
Only phage(bacteriophage)
When do phage choose to undergo the lysogenic cycle?
-If they think the bacteria is not a good host( not enough food, ressources)
Are viruses haploid or diploid?
Haploid(n), only one allele
RNA and DNA eukaryotic viruses are similar to?
Lytic phages, infect cells and make copies of themselves
Retroviruses?
-Similar to lysogenic phages
- Cell converts the retroviral RNA into DNA
- This is then inserted into the DNA of the host cell
-The cell then produces more retroviruses
What does reverse transcriptase do?
Transforms RNA into DNA
How do phage and eukaryotic viruses create new phenotypes?
Recombination (DNA strands are broken and then repaired producing new alleles)
Phage vs human viruses?
Human viruses typically have a membrane surrounding them
- Can have proteins sticking out of the membrane that are encoded for a viral genome
Where does the viral protein get the membrane?
-From the cell it infects, then it add on viral proteins
What is the role of viral proteins outside of the virus?
These proteins are sticky for the cells they want to infect, not for the ones they don’t want to infect
How do bacteria reproduce?
-Bacteria undergo something similar to mitosis, however since they only have on chromosome they only produce clones
What is bacterial sex?
-A way for bacteria to exchange genetic material
Specialized Transduction
When a prophage exits a chromosome sometimes it takes bacterial genes from the chromosome. The bacterial gene then becomes part of the viral genome and will be inserted into another bacteria when infected by the phage
Generalized Transduction
Bacterial host DNA is packaged in a viral capsid (virion). When the virions infect other bacteria the bacterial DNA will be injected into the other bacterias chromosome
Transformation
Bacteria can take up DNA floating in their environment.
Genomic DNA: Can be integrated into the genome via recombination
Non-genomic DNA (plasmids) : Are not integrated but are duplicated and can carry/express a few genes
Conjugation
- Two bacteria are connected via a conjugation tube(sex pilus)
- This tube allows one strand of the plasmid to transfer into the other bacteria
- Each bacteria then replicates a reverse complimentary copy of the strand
What are plasmids?
Circular DNA that replicate independently of chromosomes
High frequency recombination
Same as conjugation except the plasmid is first integrated into the chromosome.
2. Then when the plasmid goes through the sex piles it takes some of the bacterial chromosome with it
3. This then recombines with the other chromosome
Why is conjugation good?
- Adding a plasmid into another bacteria means conjugation can occur even more often
Genes through the sex piles and through transferred?
The order in which the genes go through the sex pilus is the same order in which genes are transferred to the other bacteria
What is antibiotic resistance and how is it achieved?
-Genes that allow bacteria to resist certain antibiotics
-Achieved by sharing plasmids between bacteria
Why is gene regulation important?
- Expressing different genes is important to live in different environments
- Changing environments must be able to change genes being expressed
- Don’t want to make any unnecessary genes
Inducible operon vs Constitutive Operon
Inducible: always off until induced on
Constitutive: always on until induced off
Lac operon
-An inducible gene
-Only on when lactose is in the system
-To digest lactose bacteria must express the following:β-galactosidase, β-galactoside permease, β-galactoside
transacetylase.
What happens to the lac-operon in the presence of lactose?
The lactose binds to the repressor protein causing it to undergo a conformational change. Now it can no longer bind to the operator and prevent transcription.
The genes are then transcribed/expressed
What happens to the lac-operon when no lactose is present?
The regulatory gene creates a repressor protein that binds to the operator and prevents transcription
What is the promoter?
Promotes the transcription of genes
What is the operator?
A stretch of DNA that is found in front of the DNA that encodes for the proteins
Between the genes and the promoter
Blocking trascription
Lac repressor binds to operator preventing the promoter from reaching the genes and RNA from binding to promoter
To allow transcription
No regulatory gene binds to the operator the RNA polymerase is able to transcribe the DNA by passing over the operator and promoter
Tryp Operon: Tryp present in the body
-Tryptophan will bind to the repressor causing a conformation; change that allows the repressor to bind to the operon and prevent expression of tryptophan genes
Tryp Operon: No Tryp present
- The repressor is not able to bind to the operator and the gene to create tryptophan is transcribed
Positive vs Negative Feedback
Positive: Presence of the regulatory element increases transcription(a lot of lactose increase transcription)
Negative: Presence of the regulatory element decreases transcription
