Lecture 5 — Microbial Genetics
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1
What is genetics?
The study of inheritable traits as expressed in an organism’s genome.
2
What is the central dogma of biology?
DNA → RNA → protein.
3
What is transcription?
The process of copying information from DNA into RNA.
4
What enzyme carries out transcription?
RNA polymerase.
5
What is translation?
The process of using mRNA instructions to build a protein.
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What cellular structure carries out translation?
The ribosome.
7
Why is RNA made from DNA before a protein is built?
RNA provides a working copy of genetic instructions while DNA remains the stored copy.
8
What is a genotype?
An organism’s genetic makeup.
9
What is a phenotype?
The observable characteristics produced by an organism’s genes and environment.
10
What is the genetic code?
The set of rules that relates mRNA codons to amino acids.
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What is a codon?
A sequence of three nucleotides in mRNA.
12
What is the usual start codon?
$AUG$.
13
In which direction is mRNA read during translation?
$5′ \rightarrow 3′$.
14
How does the mRNA sequence compare with the DNA coding strand?
It has the same sequence except RNA uses U instead of T.
15
What is an operon?
A group of genes regulated together under shared control.
16
What is an inducible operon?
An operon that is usually off and can be switched on.
17
What is a repressible operon?
An operon that is usually on and can be switched off.
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What is negative gene regulation?
Regulation in which a repressor protein reduces gene expression.
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What is positive gene regulation?
Regulation in which an activator protein increases gene expression.
20
What is the lac operon used for?
Regulating genes involved in lactose use.
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What happens to the lac operon when lactose is absent?
The repressor binds the operator and blocks transcription.
22
What happens to the lac operon when lactose is present?
Lactose-derived allolactose binds the repressor, allowing transcription.
23
What is the trp operon used for?
Regulating genes involved in tryptophan synthesis.
24
What happens to the trp operon when tryptophan is abundant?
Tryptophan helps activate the repressor, reducing transcription.
25
What is a mutation?
A change in the nucleotide sequence of DNA.
26
What is a spontaneous mutation?
A mutation that occurs naturally, often because of an error during DNA replication.
27
How frequent are spontaneous replication mutations according to the lecture?
Approximately once per \(10^9\) nucleotides copied.
28
What are induced mutations?
Mutations caused by external factors such as radiation or chemicals.
29
What are transposons?
DNA segments that can move and insert themselves into different locations in a genome.
30
How can ionizing radiation damage DNA?
High-energy radiation such as X-rays and gamma rays can damage or break the DNA backbone.
31
How does ultraviolet radiation damage DNA?
It can cause adjacent thymine bases to form thymine dimers.
32
Why are thymine dimers harmful?
They distort DNA and can interfere with replication and transcription.
33
Why can mutations contribute to evolution?
Rare beneficial mutations can provide advantages that natural selection acts on.
34
Are most mutations beneficial?
No. Most are harmful or have little effect; a small number can be advantageous.
35
What is horizontal gene transfer?
The movement of genetic material between organisms rather than inheritance from parent to offspring.
36
What is vertical gene transfer?
The transfer of genetic information from parent to offspring.
37
What is transformation?
The uptake of free DNA from the environment by a cell.
38
What is conjugation?
DNA transfer between bacterial cells through direct cell-to-cell contact.
39
What is transduction?
The transfer of bacterial DNA from one cell to another by a bacteriophage.
40
What is generalized transduction?
A phage accidentally packages bacterial DNA, potentially transferring different regions of the bacterial genome.
41
What is specialized transduction?
A phage transfers specific bacterial genes near the site where its DNA was integrated.
42
What is a plasmid?
A small, independently replicating DNA molecule, commonly found in bacteria.
43
How can horizontal gene transfer affect bacteria?
It can introduce new traits, including traits that may improve survival or cause disease.
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