BIOL 2051 Exam 3 Questions with 100% Verified
Answers Latest Update
Question: Do pili present in Gram negative or Gram positive bacteria?
Answer:
both Gram negative and Gram positive
Question: What are pili (fimbriae)?
Answer:
Hair-like, filamentous structures found on the surface of bacterial cells; present in both
Gram + and - bacteria
Question: What are pili (fimbriae) made of?
Answer:
Protein subunits called pilins or fimbrins
Question: What is the primary function of pili?
Answer:
Help bacteria attach to surfaces, host cells, and each other
Question: What is the function of conjugative pili?
Answer:
To form a bridge between bacterial cells for gene transfer (conjugation)
Question: How many conjugative pili are usually expressed per cell?
Answer:
About 1-2 pili per cell
Question: What is the approximate length and diameter of a conjugative pilus?
Answer:
Length ≈ 1.89 ± 1.2 µm Diameter ≈ 14.85 ± 1.89 nm
Question: Why are pili medically significant in bacteria such as E. coli and Salmonella (both
Gram-negative)?
Answer:
Because they enable attachment to host tissues and facilitate gene transfer, which can
spread virulence or antibiotic resistance genes.
,Question: What is the main function of pili during bacterial conjugation?
Answer:
To form a physical bridge between donor and recipient cells, allowing DNA transfer.
Question: What is bacterial conjugation?
Answer:
A mechanism where DNA is transferred from a donor cell to a recipient cell through a
complex apparatus that is encoded by a transfer system.
Question: In E. coli, which plasmid is primarily responsible for conjugation?
Answer:
F (fertitlity) plasmid
Question: How many genes are found in the transfer (tra) region of the F plasmid?
Answer:
About 40 genes
Question: Name the five classes of genes required for bacterial conjugation.
Answer:
1. Pilus synthesis
2. Surface exclusion
3. Mating pair stabilization (MPS)
4. Regulation
5. Origin of transfer (oriT), nicking, and DNA mobilization
Question: What happens if mutations occur in the tra genes?
Answer:
Conjugation cannot occur; DNA transfer is completely blocked.
Question: What type of DNA strand is transferred during conjugation?
Answer:
single-stranded
Question: Where are Type IV pili typically located on bacterial cells?
Answer:
Can be localized to one pole of the cell
Question: How are pili often expressed/arranged?
, Answer:
Peritrichously; all around the bacteria surface
Question: Why is mating pair stabilization (MPS) important?
Answer:
Helps maintain physical contact (compacted) between donor and recipient cells during DNA
transfer
Question: What enzyme initiates plasmid DNA transfer during conjugation?
Answer:
relaxase
Question: At what site does relaxase cleave the DNA?
Answer:
At the nic site within the origin of transfer (oriT)
Question: What complex recruits the relaxosome for transfer?
Answer:
T4SS (Type IV Secretion System) via the T4CP (Type IV coupling protein)
Question: What happens to the donor’s DNA after nicking?
Answer:
The donor cell replicates the uncleaved strand to maintain a complete plasmid copy.
Question: How is the single-stranded DNA guided into the recipient cell?
Answer:
The relaxase acts as a pilot protein, moving the ssDNA through the T4SS channel with help
from T4CP.
Question: What reaction occurs in the recipient cell to complete the plasmid circle?
Answer:
A reverse nicking reaction that re-ligates the single strand into a circular plasmid.
Question: How is a double-stranded plasmid restored in the recipient cell?
Answer:
The recipient synthesizes a complementary DNA strand to the transferred ssDNA.
, Question: What provides the energy for the DNA transfer process?
Answer:
ATPase activity of the T4CP protein
Question: What is the nic site?
Answer:
specific DNA sequence where nicking occurs to initiate transfer
Question: What is the oriT (origin of transfer)?
Answer:
starting point of DNA transfer
Question: What is relaxase?
Answer:
enzyme that nicks and pilots the DNA strand
Question: What is T4SS?
Answer:
protein complex forming the channel between donor and recipient
Question: What is T4CP?
Answer:
coupling protein that links the relaxosome to the secretion system and provides energy for
transfer
Question: What are the three main functions of pili?
Answer:
1. Adhesion to surfaces or host tissues
2. Acting as receptors for bacteriophages
3. Facilitating DNA uptake and transfer (conjugation or transformation)
Question: What type of pili are responsible for DNA uptake during transformation?
Answer:
Type IV competence pili
Question: How do type IV competence pili interact with DNA?
Answer:
Answers Latest Update
Question: Do pili present in Gram negative or Gram positive bacteria?
Answer:
both Gram negative and Gram positive
Question: What are pili (fimbriae)?
Answer:
Hair-like, filamentous structures found on the surface of bacterial cells; present in both
Gram + and - bacteria
Question: What are pili (fimbriae) made of?
Answer:
Protein subunits called pilins or fimbrins
Question: What is the primary function of pili?
Answer:
Help bacteria attach to surfaces, host cells, and each other
Question: What is the function of conjugative pili?
Answer:
To form a bridge between bacterial cells for gene transfer (conjugation)
Question: How many conjugative pili are usually expressed per cell?
Answer:
About 1-2 pili per cell
Question: What is the approximate length and diameter of a conjugative pilus?
Answer:
Length ≈ 1.89 ± 1.2 µm Diameter ≈ 14.85 ± 1.89 nm
Question: Why are pili medically significant in bacteria such as E. coli and Salmonella (both
Gram-negative)?
Answer:
Because they enable attachment to host tissues and facilitate gene transfer, which can
spread virulence or antibiotic resistance genes.
,Question: What is the main function of pili during bacterial conjugation?
Answer:
To form a physical bridge between donor and recipient cells, allowing DNA transfer.
Question: What is bacterial conjugation?
Answer:
A mechanism where DNA is transferred from a donor cell to a recipient cell through a
complex apparatus that is encoded by a transfer system.
Question: In E. coli, which plasmid is primarily responsible for conjugation?
Answer:
F (fertitlity) plasmid
Question: How many genes are found in the transfer (tra) region of the F plasmid?
Answer:
About 40 genes
Question: Name the five classes of genes required for bacterial conjugation.
Answer:
1. Pilus synthesis
2. Surface exclusion
3. Mating pair stabilization (MPS)
4. Regulation
5. Origin of transfer (oriT), nicking, and DNA mobilization
Question: What happens if mutations occur in the tra genes?
Answer:
Conjugation cannot occur; DNA transfer is completely blocked.
Question: What type of DNA strand is transferred during conjugation?
Answer:
single-stranded
Question: Where are Type IV pili typically located on bacterial cells?
Answer:
Can be localized to one pole of the cell
Question: How are pili often expressed/arranged?
, Answer:
Peritrichously; all around the bacteria surface
Question: Why is mating pair stabilization (MPS) important?
Answer:
Helps maintain physical contact (compacted) between donor and recipient cells during DNA
transfer
Question: What enzyme initiates plasmid DNA transfer during conjugation?
Answer:
relaxase
Question: At what site does relaxase cleave the DNA?
Answer:
At the nic site within the origin of transfer (oriT)
Question: What complex recruits the relaxosome for transfer?
Answer:
T4SS (Type IV Secretion System) via the T4CP (Type IV coupling protein)
Question: What happens to the donor’s DNA after nicking?
Answer:
The donor cell replicates the uncleaved strand to maintain a complete plasmid copy.
Question: How is the single-stranded DNA guided into the recipient cell?
Answer:
The relaxase acts as a pilot protein, moving the ssDNA through the T4SS channel with help
from T4CP.
Question: What reaction occurs in the recipient cell to complete the plasmid circle?
Answer:
A reverse nicking reaction that re-ligates the single strand into a circular plasmid.
Question: How is a double-stranded plasmid restored in the recipient cell?
Answer:
The recipient synthesizes a complementary DNA strand to the transferred ssDNA.
, Question: What provides the energy for the DNA transfer process?
Answer:
ATPase activity of the T4CP protein
Question: What is the nic site?
Answer:
specific DNA sequence where nicking occurs to initiate transfer
Question: What is the oriT (origin of transfer)?
Answer:
starting point of DNA transfer
Question: What is relaxase?
Answer:
enzyme that nicks and pilots the DNA strand
Question: What is T4SS?
Answer:
protein complex forming the channel between donor and recipient
Question: What is T4CP?
Answer:
coupling protein that links the relaxosome to the secretion system and provides energy for
transfer
Question: What are the three main functions of pili?
Answer:
1. Adhesion to surfaces or host tissues
2. Acting as receptors for bacteriophages
3. Facilitating DNA uptake and transfer (conjugation or transformation)
Question: What type of pili are responsible for DNA uptake during transformation?
Answer:
Type IV competence pili
Question: How do type IV competence pili interact with DNA?
Answer:
