DNA Replication Mechanism Quiz

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Questions and Answers

What is the primary function of RNA primase during DNA replication?

To remove RNA primers

To synthesize the leading strand continuously

To initiate replication by providing a free 3’–OH end

To synthesize RNA molecules without needing a free 3’–OH end (correct)

What distinguishes the elongation process between prokaryotic and eukaryotic DNA replication?

Eukaryotes synthesize their leading strand with pol epsilon (correct)

Prokaryotes synthesize the leading strand discontinuously

Eukaryotes have a faster rate of replication

Prokaryotes utilize multiple DNA polymerases

What is the role of DNA ligase in the replication process?

To initiate synthesis of Okazaki fragments

To remove RNA primers from the DNA

To add nucleotides to the growing strand

To seal gaps between DNA fragments (correct)

What is one major difference between prokaryotic and eukaryotic genomes in terms of replication?

Eukaryotic genomes consist of multiple linear chromosomes Signup and view all the answers

Which enzyme is responsible for RNA primer removal in prokaryotes?

DNA polymerase I Signup and view all the answers

What occurs during the transcription process leading to an RNA transcript?

Uracil replaces thymine in the RNA transcript Signup and view all the answers

What role does topoisomerase IV play in prokaryotic termination of DNA replication?

It reseals the chromosomes after replication Signup and view all the answers

How do the rates of nucleotide addition during replication compare between prokaryotes and eukaryotes?

Prokaryotes add nucleotides at a rate of 1000 nucleotides/sec Signup and view all the answers

What initiates the process of transcription in bacteria?

Binding of RNA polymerase to the promoter sequence Signup and view all the answers

During elongation in bacterial transcription, which statement accurately describes the process?

DNA is unwound ahead of the core enzyme. Signup and view all the answers

What is a key difference between prokaryotic and eukaryotic mRNA?

Eukaryotic mRNAs are monocistronic. Signup and view all the answers

Which component is essential for the termination of transcription in bacteria?

Rho protein Signup and view all the answers

Which statement about DNA replication is correct?

It is a semiconservative process. Signup and view all the answers

What modification is made to eukaryotic pre-mRNA before it is transported to the cytoplasm?

Addition of the 5’ cap Signup and view all the answers

What is the role of topoisomerase II during DNA replication?

It relaxes supercoiled DNA strands. Signup and view all the answers

What occurs during the transcription process?

RNA is synthesized from a DNA template. Signup and view all the answers

How does RNA polymerase synthesize RNA during the transcription process?

By adding RNA nucleotides to the 3’-OH group Signup and view all the answers

What role do snRNPs play in eukaryotic transcription?

They facilitate RNA splicing Signup and view all the answers

Which characteristic describes the Y-shaped replication fork?

It forms when helicase unzips DNA strands. Signup and view all the answers

What is the purpose of the 3’ poly A tail added to eukaryotic mRNA?

It prevents the degradation of mRNA. Signup and view all the answers

How does DNA polymerase III function during DNA replication?

It requires a preexisting 3' OH group to add nucleotides. Signup and view all the answers

Which statement correctly matches the DNA structure to its interaction during replication?

The unzipping of DNA strands is facilitated by helicase breaking hydrogen bonds. Signup and view all the answers

Which feature is specific to eukaryotic DNA replication compared to prokaryotic replication?

Multiple origins of replication are often utilized. Signup and view all the answers

What is the role of plasmids in bacterial genetics?

They replicate independently of the chromosomal DNA. Signup and view all the answers

Study Notes

DNA Replication

Initiation: Begins at the origin of replication, a specific nucleotide sequence.
- In prokaryotes, this origin is called oriC.
- Topoisomerase II (DNA gyrase) relaxes supercoiled DNA.
- Helicase unwinds the DNA by breaking hydrogen bonds.
- Single-stranded binding proteins prevent single-stranded DNA from rejoining.
- A Y-shaped replication fork is created, allowing for bidirectional replication.
Elongation: The process of adding nucleotides to a growing strand of DNA.
- DNA polymerase III adds nucleotides to the new strand in the 5’ to 3’ direction.
- Leading strand is synthesized continuously, requiring only one primer.
- Lagging strand is synthesized discontinuously, creating Okazaki fragments that require a new primer for each fragment.
- DNA polymerase I removes RNA primers.
- DNA ligase seals the gaps between fragments.
Termination: The end of the DNA replication process.
- In prokaryotes, circular genomes are concatenated (interlocked) and Topoisomerase IV reseals the chromosomes.
- The exact mechanism in eukaryotes is not fully understood.

Eukaryotic DNA Replication Differences

Multiple linear chromosomes.
Multiple origins of replication.
Slower rate of replication (100 nucleotides per second) compared to prokaryotes (1000 nucleotides per second).
Elongation is facilitated by different DNA polymerase enzymes.
- Leading strand: pol epsilon (ε).
- Lagging strand: pol delta (δ).
RNA primer removal is done by Ribonuclease H (RNase H).

RNA Transcription

The process of copying information encoded in DNA into an RNA molecule.
One DNA strand serves as a template.
The resulting RNA transcript is complementary to the template strand, with uracil (U) replacing thymine (T), making it almost identical to the non-template strand.
Transcription occurs in the 5’ to 3’ direction.
In eukaryotes, DNA is longer than the cell, requiring DNA supercoiling by topoisomerase called DNA gyrase and histone-like proteins.

Extrachromosomal DNA

DNA found outside of the main chromosome, but still part of the genome.
Circular chromosomes in mitochondria and chloroplasts in eukaryotes.
DNA of latent viruses within host cells.
Plasmids:
- Not essential for cellular growth.
- Involved in horizontal gene transfer.
- Utilized in genetic transfer research and biotechnology.

Functions of DNA

Responsible for heredity, passed from parent to offspring through DNA replication with minimal errors (Vertical Transfer).
Direct and regulate protein synthesis, essential for cell growth and reproduction.
- One gene one enzyme hypothesis.

Central Dogma: DNA → RNA → Protein

Transcription: Information from DNA is transferred to RNA (mRNA).
Translation: Information from mRNA is used to build polypeptide proteins.

DNA Replication in Bacteria

Initiation: Occurs at the origin of replication.
- Topoisomerase II (DNA gyrase) relaxes supercoiled DNA strands.
- Helicase unzips DNA strands by breaking hydrogen bonds.
- Single-stranded binding proteins prevent single-stranded DNA from rejoining.
Replication begins: DNA polymerase III adds nucleotides to the growing DNA strand in the 5’ to 3’ direction.

Transcription in Bacteria

Only one RNA polymerase involved.
Five subunits compose the polymerase core enzyme that adds RNA nucleotides.
The sigma factor directs RNA polymerase to the promoter region.
RNA polymerase does not require an RNA primer.

Transcription Steps

Initiation: RNA polymerase binds to the promoter sequence on DNA.
- The initiation site (start) is designated +1.
- Nucleotides before the initiation site are upstream.
- Nucleotides after the initiation site are downstream.
Elongation: Begins when the sigma factor dissociates, allowing the core enzyme to synthesize RNA.
- The core enzyme synthesizes RNA complementary to the DNA template in the 5’ to 3’ direction.
- The RNA polymerase unwinds DNA ahead of it and rewinds it behind it.
Termination: RNA polymerase dissociates from the DNA template.
- The newly formed RNA is released.
- Termination is signaled by repeated nucleotide sequences.
- Can be Rho-dependent (influenced by the Rho protein) or Rho-independent (influenced by RNA hairpin formation).

Transcription in Eukaryotes

Uses three different RNA polymerases.
Eukaryotic mRNAs are monocistronic (encode a single polypeptide) while prokaryotic mRNAs are polycistronic (encode multiple polypeptides).
Pre-mRNA is processed before transport to the cytoplasm:
- Addition of a 5’ cap: prevents degradation and is recognized by translational factors.
- Addition of a 3’ poly A tail: a string of 200 adenine nucleotides for further protection against degradation.
RNA splicing: removal of introns and re-joining of exons.
- Facilitated by the spliceosome, made of snRNPs (snurps).
- Introns are non-coding regions of DNA.
- Exons are coding regions of DNA.

Translation

mRNA is translated into the language of amino acids by ribosomes.
The genetic code is the relationship between an mRNA codon and its corresponding amino acid.

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Description

Test your understanding of the DNA replication process, including initiation, elongation, and termination. This quiz covers key enzymes and their roles, as well as the differences between leading and lagging strands. Challenge yourself to ensure you grasp the essentials of molecular biology.