Molecular Genetics Lecture 21

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Questions and Answers

What is the primary role of the 5-methyl modification of C in DNA?

It prevents proteins from binding to DNA.

It enhances the base pairing with G.

It recruits proteins that promote gene expression.

It is recognized by proteins that recruit HDAcs for gene repression. (correct)

How does the 5-methyl modification of cytosine influence gene expression?

It enhances transcriptional activity.

It ensures continued repression of gene expression. (correct)

It inhibits the formation of RNA polymerase complexes.

It leads to increased demethylation of DNA.

Which base does the modified cytosine pair with?

Thymine

Uracil

Adenine

Guanine (correct)

What type of enzymes are recruited by proteins that bind to methylated DNA?

Histone deacetylases (HDAcs) Signup and view all the answers

What is the potential consequence of the 5-methyl modification of C when DNA is replicated?

It does not alter the normal DNA replication process. Signup and view all the answers

What is the main purpose of recombinant DNA technology?

To locate, isolate, alter, and amplify DNA segments Signup and view all the answers

How does genetic engineering differ from recombinant DNA technology?

Genetic engineering is a practical application of recombinant DNA technology Signup and view all the answers

Which of the following describes synthetic biology?

The engineering of biological systems to create new functions Signup and view all the answers

What is one of the key functions of Taq DNA polymerase?

It is essential for DNA replication at high temperatures Signup and view all the answers

Which process is involved in generating recombinant DNA molecules?

Restriction enzyme digestion Signup and view all the answers

What is the primary purpose of cloning vectors in recombinant DNA technology?

To introduce foreign DNA into host cells Signup and view all the answers

How is DNA gel electrophoresis primarily used in molecular biology?

To visualize and separate DNA fragments based on size Signup and view all the answers

Which of the following is a potential application of genetic engineering?

Creating crops resistant to pests Signup and view all the answers

What is a primary function of modern plasmid vectors?

To provide resistance to antibiotic ampicillin Signup and view all the answers

What is the role of a polylinker or multiple cloning site in plasmid vectors?

To provide unique restriction sites for enzymes Signup and view all the answers

How do restriction enzymes function in DNA cloning?

They cut DNA at specific sites Signup and view all the answers

What is the purpose of an inducible bacterial promoter in plasmid vectors?

To control gene expression in response to an inducer Signup and view all the answers

Why are restriction enzymes important to bacteria?

They protect bacteria from viruses and foreign DNA Signup and view all the answers

Which feature is commonly NOT found in modern plasmid vectors?

Introns from mammalian DNA Signup and view all the answers

What enzymatic group do restriction endonucleases belong to?

DNAses Signup and view all the answers

In the context of DNA cloning, what do recombination enzymes do?

Facilitate the combination of DNA fragments Signup and view all the answers

What is the role of the LacI repressor in the absence of lactose?

It binds to the lacO operator to prevent transcription. Signup and view all the answers

In which condition is the lac operon efficiently transcribed?

In the presence of lactose and absence of glucose. Signup and view all the answers

What happens in the presence of both glucose and lactose?

LacI does not bind to lacO, but transcription is still low. Signup and view all the answers

Which of the following is true about the lac operon in the absence of lactose?

Very little lac mRNA is produced due to the LacI repressor. Signup and view all the answers

What occurs to the lac operon when glucose is present and lactose is absent?

The operon is completely inactive. Signup and view all the answers

Which of the following factors increases the recruitment of RNA polymerase to the lacP promoter?

The CAP-cAMP complex. Signup and view all the answers

What phenotype is exhibited by lacZ-, lacY-, lacP-, and lacIs mutations?

Uninducible expression of the lac operon. Signup and view all the answers

Which protein is associated with the activation of transcription for the lac operon in the presence of lactose?

CAP. Signup and view all the answers

What is the primary effect of the acetylation of histone tails on gene expression?

It enhances the accessibility of DNA to transcription factors. Signup and view all the answers

Which process allows for heritable changes in gene expression without altering the DNA sequence?

Epigenetic inheritance. Signup and view all the answers

What happens to the X chromosome inactivation during early embryonic development in females?

The inactivated X chromosome forms heterochromatin. Signup and view all the answers

What role does DNA methylation play in gene expression?

It decreases gene expression by preventing transcription factor binding. Signup and view all the answers

What best describes an organism with female X chromosome inactivation?

It creates functional mosaics of gene expression across different cells. Signup and view all the answers

Which is a characteristic of epigenetic modifications?

They can be influenced by environmental factors. Signup and view all the answers

What is a common method of stable modification of DNA that leads to gene regulation?

DNA methylation. Signup and view all the answers

Which of the following statements about epigenetic inheritance is true?

It can be passed on through both mitosis and meiosis. Signup and view all the answers

How is the migration of DNA molecules in an electric field related to their size?

Inversely proportional to the log of the size of the molecule Signup and view all the answers

What role do fluorescent dyes, like ethidium bromide, play in DNA analysis?

They bind to dsDNA for visualization Signup and view all the answers

In agarose gel electrophoresis, how do small DNA molecules behave compared to larger ones?

They migrate faster and are found closer to the bottom Signup and view all the answers

What factors primarily influence the migration speed of DNA in an electric field?

Size and shape of the DNA molecule Signup and view all the answers

Why is agarose gel electrophoresis a widely used technique for DNA analysis?

It allows for visualization and separation of DNA fragments efficiently Signup and view all the answers

Which statement about the mobility of DNA fragments during electrophoresis is correct?

Smaller fragments move faster than larger fragments Signup and view all the answers

Which factors can affect the separation of DNA molecules in agarose gel electrophoresis?

DNA concentration and gel composition Signup and view all the answers

What is the primary advantage of using fluorescent DNA intercalators in DNA analysis?

They enhance the clarity of the DNA bands Signup and view all the answers

Study Notes

DNA Cloning

DNA cloning is a set of molecular tools used to locate, isolate, alter, amplify, or study DNA segments.
Genetic engineering is the application of recombinant DNA technology to solve problems in biology, medicine, veterinary medicine, agriculture, and other areas.
Synthetic biology designs complex, biologically based systems that exhibit functions not found in nature.
Hot springs in Yellowstone National Park are the source of Taq DNA polymerase.

Overview of Molecular Genetics (Lecture 21)

Molecular genetics lectures cover mutations, DNA repair, the dynamic genome, transcription, DNA replication, regulation (in bacteria and eukaryotes), DNA cloning techniques, the genetic code, protein synthesis, genomics, and the human genome.
Mutations can be studied in relation to DNA repair.
Transcription, regulation, and translation relate to the central dogma of gene expression.
DNA cloning is a specific area of molecular genetics.

The Lac Operon of E. coli

The lac operon contains genes for enzymes that metabolize lactose.
When lactose is absent, the lac repressor binds to the operator, preventing transcription.
With lactose present and glucose absent, the rate of synthesis of the three enzymes increases about 1,000-fold within 2-3 minutes. This is called induction.
ß-galactosidase hydrolyzes lactose.
Lactose permease transports lactose into the cell.
Transacetylase modifies lactose.

Constitutive and Uninducible Lac Operon Mutations

Constitutive mutants express the lac operon even without lactose.
Uninducible mutants fail to express the lac operon even with lactose present.
Mutations in various genes (lacZ, lacy, lacl, laco, lacP) can result in constitutive or uninducible phenotypes.

Transcriptional Regulation of the Lac Operon

The lac operon is regulated by the presence or absence of lactose and glucose.
In the absence of lactose, the lac repressor binds the operator to prevent transcription.
In the presence of lactose, allolactose acts as an inducer for the lac operon.
In the presence of glucose and lactose, cAMP + CAP bind.

Cis-acting Regulatory Sequences in Eukaryotic Genes

There are three major classes of cis-regulatory sequences in eukaryotic protein-coding genes: promoters, promoter-proximal elements, enhancers, and silencers.
Enhancers and silencers are located upstream or downstream of the promoter.
Enhancers increase transcription, silencers reduce transcription.

The Problem with Chromatin

Eukaryotic DNA is packaged tightly into chromatin.
Euchromatin is open chromatin, genes in euchromatin are transcribed.
Heterochromatin is condensed chromatin, genes in heterochromatin are silenced.
Chromatin remodeling can expose genes for transcription.

Chromatin Remodeling Protein

Even in open chromatin, a promoter might be inaccessible to RNA polymerase II if the TATA box happens to be tightly bound to a nucleosome.
Chromatin remodeling complexes displace nucleosomes.

Histone Tail Acetylation and Methylation

Acetylation occurs on lysine residues. Acetylated histones lead to open chromatin.
Deacetylation leads to inactive chromatin..
Methylation occurs on cytosine.
Methylated DNA is often associated with repressed gene expression.

Epigenetic Inheritance

Heritable modification in gene function or expression that does not alter the base sequence of DNA.
Epigenetic states can be inherited through mitosis and meiosis.
X chromosome inactivation is an example of epigenetic inheritance.

Parental Imprinting

Some autosomal genes are systematically silenced during gametogenesis, so only the paternal copy is expressed in the progeny.

Recombinant DNA Technology

Recombinant DNA technology is a suite of molecular tools used for locating, isolating, altering, amplifying, or studying DNA segments.

Cloning Vectors

Cloning vectors are stable, self-replicating DNA molecules.
They typically contain an origin of replication, selectable markers, and unique cloning sites.
Plasmids and bacteriophage vectors are common cloning vectors.
Plasmids are small, circular extrachromosomal DNA molecules.
Cosmids are used to insert large DNA fragments.
BACs are similar to plasmids in several ways.
YACs can encompass even larger inserts.

Restriction Enzymes

Restriction enzymes recognize specific DNA sequences and cut the DNA at those sites in a process called restriction digestion.
Restriction enzymes can generate blunt ends or sticky ends.
Compatible sticky ends allow fragments to be joined together.

PCR

PCR is a method for rapidly amplifying small DNA fragments.
It uses a heat-stable DNA polymerase (e.g., Taq polymerase).
It involves repeated cycles of heating and cooling to denature and anneal DNA strands and extend the primers.

Gel Electrophoresis

Gel electrophoresis separates DNA molecules based on their size and charge.
DNA fragments are separated in an agarose or polyacrylamide gel.
Fluorescent dyes are used to visualize DNA fragments.

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Description

Explore the fascinating world of molecular genetics in this quiz based on Lecture 21. Cover topics such as DNA cloning, mutations, transcription, and the Lac operon. Enhance your understanding of how these concepts apply to biology and genetics.