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Questions and Answers
Which type of plasmid is responsible for the digestion of unusual substances?
Which type of plasmid is responsible for the digestion of unusual substances?
- Degradative plasmids (correct)
- Virulence plasmids
- Resistance plasmids
- Col plasmids
Virulence plasmids can transform a bacterium into a pathogen.
Virulence plasmids can transform a bacterium into a pathogen.
True (A)
Which type of plasmid can be transferred from cell to cell through conjugation?
Which type of plasmid can be transferred from cell to cell through conjugation?
- Episomes
- Transmissible plasmids (correct)
- Nontransmissible plasmids
- Resistance plasmids
Why are plasmids considered extrachromosomal?
Why are plasmids considered extrachromosomal?
Nontransmissible plasmids can be transferred between cells without assistance.
Nontransmissible plasmids can be transferred between cells without assistance.
Col plasmids contain genes that code for __________.
Col plasmids contain genes that code for __________.
What are plasmids?
What are plasmids?
Match the following plasmid types with their primary functions:
Match the following plasmid types with their primary functions:
What term describes the proteins coded by col plasmids that can kill other bacteria?
What term describes the proteins coded by col plasmids that can kill other bacteria?
Which method involves the transfer of genes between cells in physical contact?
Which method involves the transfer of genes between cells in physical contact?
Which of the following describes a mutation that changes a single nucleotide in DNA?
Which of the following describes a mutation that changes a single nucleotide in DNA?
A frameshift mutation can result from the deletion or insertion of nucleotides.
A frameshift mutation can result from the deletion or insertion of nucleotides.
Match the types of plasmids with their characteristics:
Match the types of plasmids with their characteristics:
Episomes are a type of plasmid that can integrate with bacterial chromosomes.
Episomes are a type of plasmid that can integrate with bacterial chromosomes.
What is the frequency range of mutations per bacterium per division?
What is the frequency range of mutations per bacterium per division?
Resistance plasmids provide resistance against __________.
Resistance plasmids provide resistance against __________.
Which of the following is NOT a class of plasmids based on function?
Which of the following is NOT a class of plasmids based on function?
Transduction is the process by which DNA is transferred through physical contact between two bacterial cells.
Transduction is the process by which DNA is transferred through physical contact between two bacterial cells.
What is the term for the bacteria that can take up free DNA during transformation?
What is the term for the bacteria that can take up free DNA during transformation?
In transformation, DNA is released into the environment when a bacterial cell undergoes __________.
In transformation, DNA is released into the environment when a bacterial cell undergoes __________.
Match the following processes with their definitions:
Match the following processes with their definitions:
Which type of transduction can transfer virtually any genetic marker?
Which type of transduction can transfer virtually any genetic marker?
Plasmids are rarely transferred between bacterial cells during conjugation.
Plasmids are rarely transferred between bacterial cells during conjugation.
What is the primary role of a sex pilus in the conjugation process?
What is the primary role of a sex pilus in the conjugation process?
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Study Notes
RNA Structure and Function
- RNA contains uracil instead of thymine
- Three types of RNA:
- Messenger RNA (mRNA): carries genetic information from DNA to ribosomes
- Ribosomal RNA (rRNA): forms the core of the ribosome
- Transfer RNA (tRNA): brings amino acids to the ribosome for protein synthesis
Genetic Code
- Codon: a sequence of three nucleotides that codes for a specific amino acid
- 64 different codons:
- 61 specify amino acids
- 3 are stop codons (UAG, UAA, UGA)
- AUG is the start codon
- Stop codons signal the end of protein synthesis
Plasmids
- Extrachromosomal DNA molecules
- Circular and double-stranded
- Encode traits not essential for bacterial survival
- Can replicate independently of the bacterial chromosome
- Can integrate with the bacterial chromosome (episomes)
- Found in both Gram-positive and Gram-negative bacteria
Plasmid Types
-
Transmissibility:
- Transmissible plasmids:
- Can be transferred between cells via conjugation
- Contain genes for sex pilus synthesis and transfer enzymes
- Nontransmissible plasmids:
- Cannot be transferred between cells
- Lack transfer genes
- Depend on the host cell for replication
- Transmissible plasmids:
-
Function:
- Fertility (F) plasmids: contain genes for conjugation and sex pilus expression
- Resistance (R) plasmids: contain genes for antibiotic or poison resistance
- Col plasmids: contain genes for bacteriocins (proteins that kill other bacteria)
- Degradative plasmids: enable the digestion of unusual substances
- Virulence plasmids: turn bacteria into pathogens
Mutations
- Random, heritable variations in DNA
- Caused by changes in the base sequence of DNA (addition, deletion, or substitution)
- Affect gene function
- Can result in altered phenotypes
Types of Mutations
-
Small DNA Alterations:
- Point mutation: change in a single nucleotide
- Silent mutation: no change in amino acid sequence
- Missense mutation: change in amino acid sequence
- Nonsense mutation: introduction of a stop codon
- Frameshift mutation: insertion or deletion of one or more nucleotides, altering the reading frame
- Point mutation: change in a single nucleotide
-
Large DNA Alterations:
- Involve larger segments of DNA
Mutagens
- Agents that increase the frequency of mutations
- Examples: nitrous acid, alkylating agents, base analogs
Effects of Mutations
- Altered drug susceptibility
- Changes in antigenic structure
- Altered virulence
- Changes in bacteriophage susceptibility
- Altered colony morphology and pigment production
- Affects capsule or flagella production
Gene Transfer in Bacteria
- Horizontal gene transfer: transfer of DNA between cells
- Three main mechanisms: conjugation, transduction, and transformation
Conjugation
- Transfer of genes through direct contact between cells
- Requires donor and recipient cells
- Mediated by sex pilus
- Primarily involves transfer of plasmids
Transduction
- Transfer of genes via bacteriophages (viruses that infect bacteria)
- Generalized transduction: any bacterial gene can be transferred
- Specialized transduction: only genes adjacent to the viral DNA in the prophage are transferred
Transformation
- Transfer of free DNA from one cell to another
- DNA is released from a dead cell and taken up by a recipient cell
- Only some bacteria are competent (able to take up free DNA)
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