39 Questions
Enhancers can enhance any gene nearby by:
Allowing maximum level of transcription
What is the role of silencers in gene regulation?
Blocking enhancers
Which process is inhibited by compact chromatin structure?
Transcription
What is the function of RISC in gene regulation?
Inducing gene silencing
In bacterial gene regulation, most of the regulation occurs during:
Transcription
What is the main role of siRNA in gene regulation during a viral infection?
Cleaving double-stranded RNA
'Gene regulation in Bacteria' suggests that bacterial genes require:
Continuous or regulated transcription
Which type of mutation results in a stop codon?
Nonsense mutation
Which DNA repair mechanism involves genetic material swapping between homologous DNA molecules?
Homologous recombination repair
Which mutation causes a triplet code to code for the same amino acid as before?
Silent mutation
Which type of mutation replaces a pyrimidine with another pyrimidine or a purine with another purine?
Transition mutation
Which DNA repair mechanism occurs before replication of the DNA and repairs double-strand breaks?
Nonhomologous end joining
Which type of mutation results in a triplet code that codes for a different amino acid?
Missense mutation
Which type of mutation involves swapping a pyrimidine for a purine?
Transversion mutation
Which hypothesis states that mutations arise from adaptations to the environment?
Lamarckism
What type of control does a repressor protein exert on transcription?
Negative control
Which type of control initiates transcription through an activator protein?
Positive control
What is the role of chaperone proteins in the heat shock response?
They inhibit sigma 32 at normal temperatures
What is a riboswitch?
A noncoding mRNA segment
What happens to the usual sigma factor during the heat shock response?
It is unstable at hot temperatures
What is the role of the allosteric domain in activator proteins?
It binds an allosteric compound
What is an operon?
A region of linked genes that are all under control of one promoter
What is the role of the DNA binding domain in repressor proteins?
It binds to regulatory DNA sequences
Which of the following is a cause of spontaneous DNA mutations?
Deamination of nucleotides
What is the result of replication slippage during DNA replication?
A daughter strand with less DNA
What is a tautomeric shift in DNA?
A spontaneous switch between different isomers of purines and pyrimidines
What is the result of depurination in DNA?
A nucleotide loses a purine
Which of the following is an example of an induced DNA mutation?
Base analogs
What is the effect of deaminating agents on DNA?
They remove amino groups from nucleotides
What is the effect of alkylating agents on DNA?
They add bulky carbon chains to bases
Which of the following is a common cause of induced DNA mutations?
UV radiation
What is the role of the Lac operon?
To encode for the enzyme that degrades lactose into glucose and galactose
What happens when glucose is present in high levels?
The Lac operon turns off
What is the role of the CRP-cAMP complex?
It binds to the lac promoter and turns on the Lac operon
What is the function of the LacI protein?
It turns off the Lac operon
What is the effect of allo-lactose on the Lac operon?
It turns on the Lac operon
What genes are included in the Lac operon?
lacZ, lacY, and lacA
What happens in the absence of the CRP-cAMP complex?
Transcription of lacZYA is very low
What is the effect of a mutant promoter sequence (P-) on the Lac operon?
It decreases transcription
Study Notes
Types of Mutations
- Spontaneous mutations occur naturally during DNA replication
- Replication slippage: template strand forms loops, leading to missed DNA segments and resulting in diseases like Fragile-X syndrome and Huntington's disease
- Tautomeric shifts: spontaneous switches between purine and pyrimidine isomers, causing non-complementary base pairing
- Depurination: random loss of purine, filled with adenine by DNA polymerase
- Deamination: random loss of amino group, resulting in base changes (e.g., cytosine to uracil)
Induced Mutations
- Occur due to chemical mutagens, radiation, or transposable DNA elements
- Base analogs: replace purines or pyrimidines, increase tautomeric shifts and UV radiation sensitivity
- Deaminating agents: remove amino groups
- Alkylating agents: add bulky carbon chains to bases
- Trans-acting elements: coding regions of DNA that code for regulators
- Enhancers: allow for maximum transcription level, can enhance any nearby gene
- Silencers: block enhancers, restricting enhancement to target genes
RNA Interference
- RNA-induced gene silencing: regulates translation
- siRNA: forms during viral infection, produces double-stranded RNA, cleaved by dicer
- microRNA: non-coding RNA, inhibits gene expression
- RISC: RNA-induced silencing complex
- RITS: RNA-induced transcriptional silencing complex
Gene Regulation in Bacteria
- Most regulation occurs during transcription
- Two types of transcriptional regulation: promoter and operator
- Lac operon: encodes for β-galactosidase, degrades lactose into glucose and galactose
- Lac operon is usually off, but turns on in the presence of lactose and absence of glucose
- Glucose inhibits production of adenylate cyclase, which produces cAMP
- cAMP binds to CRP, and the complex binds to the lac promoter, turning on the lac operon
- Lac operon is repressed by lacI, and induced by allo-lactose
DNA Repair
- Two types: homologous recombination repair and nonhomologous end joining
- Homologous recombination: genetic material swapped between homologous DNA molecules
- Nonhomologous end joining: occurs in G1, repairs double-strand breaks
Mutation Hypotheses
- Luria and Delbrück proved the random mutation hypothesis
- Adaptation hypothesis: mutations arise from adaptations to the environment
- Random mutation hypothesis: mutations occur randomly and not in response to the environment
Types of Mutations
- Missense: changes a base, resulting in a different amino acid
- Nonsense: changes a base, resulting in a stop codon
- Silent: changes a base, resulting in the same amino acid
- Transition: a pyrimidine replaces another pyrimidine or a purine replaces another purine
- Transversion: a pyrimidine is swapped for a purine
Gene Regulation
- Negative control: repressor protein binds to DNA, inhibiting transcription
- Positive control: activator protein binds to DNA, initiating transcription
- Heat shock response: abnormally hot temperatures activate expression of heat stress genes
- Riboswitches: noncoding mRNA segments that control downstream gene expression by binding a metabolite
Test your knowledge on the DNA repair mechanisms including homologous recombination and nonhomologous end joining. Learn about the process of genetic material swap and repair of double strand breaks in different organisms.
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