Lecture 20: Viruses and Bacteria

Question 1

Do viruses and bacteria use the same genetic material and genetic code as humans?

Answer 1

YES

Question 2

What do viruses do to cells?

Answer 2

Tell cells to stop doing cell stuff and start making viruses instead

Question 3

True or False : Viruses can be very small

Answer 3

True, influenza is less than 10 genes

Question 4

Are viruses smaller than bacteria?

Answer 4

Yes

Question 5

What did Dmitri Ivanovsky do?

Answer 5

Discovered viruses

Question 6

What is a virion?

Answer 6

A viral particle that typically consists of a protein coat or capsid(protein shell of a virus) and nucleic acid

Question 7

How are viruses classified?

Answer 7

• 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

Question 8

What is a bacteriophage?

Answer 8

-Virus that infects bacteria

Question 9

Virulent phage vs Temperate phage?

Answer 9

Virulent Phage undergo the lytic reproductive cycle
Temperate Phage undergo the lysogenic reproductive cycle

Question 10

Lytic Reproductive Cycle

Answer 10

1. Phage binds to bacteria
2. Injects its DNA
3. Bacteria produces more phages and more phage DNA instead of its own
4. Cell destruction occurs and phage are released

Question 11

Lysogenic Reproductive Cycle

Answer 11

1. Phage inserts its DNA into the bacterial chromosome(prophage)
2. Bacteria now divides and replicates the prophage along with its own DNA
3. When the time is right the prophage leaves the chromosome and resumes the lytic cycle

Question 12

Do all viruses follow the lytic/lysogenic cycle?

Answer 12

Only phage(bacteriophage)

Question 13

When do phage choose to undergo the lysogenic cycle?

Answer 13

-If they think the bacteria is not a good host( not enough food, ressources)

Question 14

Are viruses haploid or diploid?

Answer 14

Haploid(n), only one allele

Question 15

RNA and DNA eukaryotic viruses are similar to?

Answer 15

Lytic phages, infect cells and make copies of themselves

Question 16

Retroviruses?

Answer 16

-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

Question 17

What does reverse transcriptase do?

Answer 17

Transforms RNA into DNA

Question 18

How do phage and eukaryotic viruses create new phenotypes?

Answer 18

Recombination (DNA strands are broken and then repaired producing new alleles)

Question 19

Phage vs human viruses?

Answer 19

Human viruses typically have a membrane surrounding them
- Can have proteins sticking out of the membrane that are encoded for a viral genome

Question 20

Where does the viral protein get the membrane?

Answer 20

-From the cell it infects, then it add on viral proteins

Question 21

What is the role of viral proteins outside of the virus?

Answer 21

These proteins are sticky for the cells they want to infect, not for the ones they don’t want to infect

Question 22

How do bacteria reproduce?

Answer 22

-Bacteria undergo something similar to mitosis, however since they only have on chromosome they only produce clones

Question 23

What is bacterial sex?

Answer 23

-A way for bacteria to exchange genetic material

Question 24

Specialized Transduction

Answer 24

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

Question 25

Generalized Transduction

Answer 25

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

Question 26

Transformation

Answer 26

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

Question 27

Conjugation

Answer 27

1. Two bacteria are connected via a conjugation tube(sex pilus)
2. This tube allows one strand of the plasmid to transfer into the other bacteria
3. Each bacteria then replicates a reverse complimentary copy of the strand

Question 28

What are plasmids?

Answer 28

Circular DNA that replicate independently of chromosomes

Question 29

High frequency recombination

Answer 29

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

Question 30

Why is conjugation good?

Answer 30

1. Adding a plasmid into another bacteria means conjugation can occur even more often

Question 31

Genes through the sex piles and through transferred?

Answer 31

The order in which the genes go through the sex pilus is the same order in which genes are transferred to the other bacteria

Question 32

What is antibiotic resistance and how is it achieved?

Answer 32

-Genes that allow bacteria to resist certain antibiotics
-Achieved by sharing plasmids between bacteria

Question 33

Why is gene regulation important?

Answer 33

1. Expressing different genes is important to live in different environments
2. Changing environments must be able to change genes being expressed
3. Don’t want to make any unnecessary genes

Question 34

Inducible operon vs Constitutive Operon

Answer 34

Inducible: always off until induced on
Constitutive: always on until induced off

Question 35

Lac operon

Answer 35

-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.

Question 36

What happens to the lac-operon in the presence of lactose?

Answer 36

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

Question 37

What happens to the lac-operon when no lactose is present?

Answer 37

The regulatory gene creates a repressor protein that binds to the operator and prevents transcription

Question 38

What is the promoter?

Answer 38

Promotes the transcription of genes

Question 39

What is the operator?

Answer 39

A stretch of DNA that is found in front of the DNA that encodes for the proteins
Between the genes and the promoter

Question 40

Blocking trascription

Answer 40

Lac repressor binds to operator preventing the promoter from reaching the genes and RNA from binding to promoter

Question 41

To allow transcription

Answer 41

No regulatory gene binds to the operator the RNA polymerase is able to transcribe the DNA by passing over the operator and promoter

Question 42

Tryp Operon: Tryp present in the body

Answer 42

-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

Question 43

Tryp Operon: No Tryp present

Answer 43

• The repressor is not able to bind to the operator and the gene to create tryptophan is transcribed

Question 44

Positive vs Negative Feedback

Answer 44

Positive: Presence of the regulatory element increases transcription(a lot of lactose increase transcription)

Negative: Presence of the regulatory element decreases transcription