Central Dogma of Molecular Biology

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Questions and Answers

In eukaryotes, what is the primary function of general transcription factors during transcription?

  • To help position RNA polymerase and initiate the transcription process. (correct)
  • To modify the chromatin structure for gene expression.
  • To signal the termination of transcription.
  • To degrade the RNA polymerase enzyme.

In prokaryotes, RNA transcription ends after encountering a polyadenylation signal.

False (B)

What is the initial modification that marks an RNA molecule as an mRNA-to-be?

addition of 7-methylguanosine cap

The process of removing introns from a pre-mRNA molecule is called RNA ______.

<p>splicing</p> Signup and view all the answers

Match each RNA type with its primary function:

<p>mRNA = Codes for proteins rRNA = Forms the structural and catalytic core of ribosomes tRNA = Central to protein synthesis as adaptors between mRNA and amino acids. snRNA = Functions in a variety of nuclear processes including splicing of pre-mRNA</p> Signup and view all the answers

According to the central dogma, what is the correct flow of information?

<p>DNA -&gt; RNA -&gt; Protein (B)</p> Signup and view all the answers

The information content is the same in DNA, mRNA and protein.

<p>False (B)</p> Signup and view all the answers

What enzyme is responsible for transcribing DNA into an RNA intermediary?

<p>RNA polymerase</p> Signup and view all the answers

MRNA molecules are exported from the nucleus to the ______, where they can be translated into proteins.

<p>cytosol</p> Signup and view all the answers

Match the following:

<p>transcription = DNA to RNA translation = RNA to protein replication = DNA to DNA replication</p> Signup and view all the answers

Which of the following best describes the function of a poly-A tail in mRNA processing?

<p>It is important for export from the nucleus and later protein synthesis. (A)</p> Signup and view all the answers

All RNA molecules code for proteins.

<p>False (B)</p> Signup and view all the answers

What is the name of the complex that carries out RNA splicing?

<p>spliceosome</p> Signup and view all the answers

Genetic information stored in chromosomes must be read and converted into proteins in the ______ in order to be useful

<p>cytosol</p> Signup and view all the answers

Match the RNA polymerase found in Eukaryotic cells with its genes transcribed:

<p>RNA polymerase I = 5.8S, 18S, and 28S rRNA genes RNA polymerase II = all protein-coding genes RNA polymerase III = tRNA genes, 5S rRNA genes</p> Signup and view all the answers

Which of the following is removed during mRNA processing?

<p>Introns (B)</p> Signup and view all the answers

Transcription generates a double-stranded RNA molecule that is complementary to the DNA template strand.

<p>False (B)</p> Signup and view all the answers

What is the function of the nuclear export receptor?

<p>guides mature mRNA through the nuclear pore complex into the cytosol</p> Signup and view all the answers

Extension or RNA chain requires ______, which uses ATP hydrolysis to help RNA polymerase move along chromatin.

<p>elongation factors</p> Signup and view all the answers

Match

<p>mRNA = cytosol RNA synthesis = nucleus</p> Signup and view all the answers

According to the central dogma, what is the correct flow of genetic information?

<p>DNA -&gt; RNA -&gt; Protein (A)</p> Signup and view all the answers

In eukaryotes, transcription requires only RNA polymerase binding directly to the promoter sequence to initiate transcription.

<p>False (B)</p> Signup and view all the answers

What is the key function of RNA polymerase during transcription?

<p>synthesizing RNA</p> Signup and view all the answers

The process by which mRNA molecules are exported from the nucleus to the cytosol where they can be made into proteins by ribosomes is called ______.

<p>translation</p> Signup and view all the answers

Match the RNA polymerase type in eukaryotes with the genes they transcribe:

<p>RNA polymerase I = 5.8S, 18S, and 28S rRNA genes RNA polymerase II = all protein-coding genes, plus snoRNA genes, miRNA genes, siRNA genes, and most snRNA genes RNA polymerase III = tRNA genes, 5S rRNA genes, some snRNA genes and genes for other small RNAs</p> Signup and view all the answers

What is the primary function of messenger RNA (mRNA)?

<p>To carry genetic information from DNA to ribosomes for protein synthesis (A)</p> Signup and view all the answers

The information content of mRNA is greater than that of the original DNA from which it was transcribed.

<p>False (B)</p> Signup and view all the answers

What distinguishes transcription in eukaryotes from transcription in prokaryotes regarding RNA polymerases?

<p>Eukaryotes have 3 different RNA polymerases, while prokaryotes have one.</p> Signup and view all the answers

In eukaryotes, transcription terminates after RNA polymerase reaches a ______.

<p>polyadenylation signal</p> Signup and view all the answers

Match each type of RNA with its function.

<p>mRNA = Code for proteins rRNA = Form the basic structure of the ribosome and catalyze protein synthesis tRNA = Transfer RNA, central to protein synthesis as adaptors between mRNA and amino acids snRNA = Small nuclear RNAs, function in a variety of nuclear processes, including the splicing of pre-mRNA</p> Signup and view all the answers

What is the function of elongation factors during RNA transcription?

<p>To help RNA polymerase move along chromatin (A)</p> Signup and view all the answers

Most eukaryotic RNA can be functional without post-transcriptional processing.

<p>False (B)</p> Signup and view all the answers

What is the first modification that occurs after the 5' end of RNA exits polymerase during mRNA processing?

<p>addition of 7-methylguanosine cap</p> Signup and view all the answers

Intervening sequences, known as ______, interrupt the actual coding sequences in most protein-coding genes.

<p>introns</p> Signup and view all the answers

Match the following components involved in pre-mRNA processing with their roles:

<p>Introns = Non-coding sequences excised from pre-mRNA Exons = Coding sequences that remain in the mature mRNA Spliceosome = Complex that removes introns and splices exons Poly-A tail = Added to the 3' end of mRNA</p> Signup and view all the answers

What purpose does the addition of a poly-A tail serve during pre-mRNA processing?

<p>It is important for export from the nucleus and later protein synthesis (C)</p> Signup and view all the answers

Mature mRNA can be exported from the nucleus even if it is not fully processed.

<p>False (B)</p> Signup and view all the answers

Where does protein synthesis occur in the cell, in relation to where RNA synthesis and processing occur?

<p>cytosol</p> Signup and view all the answers

Mature mRNA binds to a ______ receptor to guide it to the ______ for translation.

<p>nuclear export, cytosol</p> Signup and view all the answers

Match the type of non-coding RNA with its function.

<p>snRNAs = Pre-mRNA splicing snoRNAs = Ribosome assembly tRNAs = Protein synthesis siRNAs and miRNAs = Regulation of gene expression</p> Signup and view all the answers

Explain the central dogma of molecular biology in your own words, highlighting the flow of information.

<p>The central dogma states that information flows from DNA to RNA to protein. DNA contains the genetic code, which is transcribed into RNA, and then RNA is translated into protein, the functional molecules of the cell.</p> Signup and view all the answers

What is the significance of transcription in the central dogma, and which enzyme primarily facilitates this process?

<p>Transcription is the process where DNA is used as a template to create an RNA molecule. This is a crucial step in the central dogma as it converts the genetic code into a form that can be read by ribosomes to synthesize proteins. RNA polymerase is the primary enzyme involved in transcription.</p> Signup and view all the answers

Describe the role of mRNA in protein synthesis and how it differs from the roles of other types of RNA.

<p>mRNA carries the genetic information from DNA to the ribosome for protein synthesis. It contains the codons that specify the amino acid sequence. Other RNAs like tRNA and rRNA have structural and catalytic roles in translation, while mRNA carries the actual code for the protein.</p> Signup and view all the answers

What are the key differences between transcription in prokaryotes and eukaryotes?

<p>In prokaryotes, transcription and translation occur in the same compartment (cytosol) and transcription is simpler, using only one RNA polymerase. In eukaryotes, transcription occurs in the nucleus, and translation in the cytosol, with transcription requiring general transcription factors and three different RNA polymerases.</p> Signup and view all the answers

Explain the process of RNA splicing and its importance for generating protein diversity.

<p>RNA splicing removes introns (non-coding sequences) from pre-mRNA and joins exons (coding sequences) together. Alternative splicing allows for different combinations of exons to be included, producing multiple protein isoforms from a single gene, thus increasing protein diversity.</p> Signup and view all the answers

Describe the function of the 5' cap and the poly-A tail in mRNA processing.

<p>The 5' cap (7-methylguanosine) protects the mRNA from degradation and enhances translation initiation. The poly-A tail (a string of adenine bases) also enhances translation, increases mRNA stability, and facilitates export from the nucleus.</p> Signup and view all the answers

Outline the steps involved in pre-mRNA processing in eukaryotes before it can be exported from the nucleus.

<p>Pre-mRNA processing involves the addition of a 5' cap, RNA splicing to remove introns, and the addition of a poly-A tail at the 3' end. These modifications ensure mRNA stability, efficient translation, and proper export from the nucleus.</p> Signup and view all the answers

How do snRNAs contribute to RNA splicing, and what complex do they form?

<p>snRNAs are components of small nuclear ribonucleoproteins (snRNPs) that recognize splice sites on pre-mRNA. snRNPs assemble to form the spliceosome, which catalyzes the splicing reaction, removing introns and joining exons.</p> Signup and view all the answers

Besides mRNA, what are the major types of RNA found in cells, and what are their primary functions?

<p>Besides mRNA, major types of RNA include ribosomal RNA (rRNA), which forms the structural and catalytic core of ribosomes, and transfer RNA (tRNA), which carries amino acids to the ribosome for protein synthesis. Also, small nuclear RNAs (snRNAs) which function in a variety of nuclear processes, including the splicing of pre-mRNA.</p> Signup and view all the answers

Explain how the regulation of transcription and translation ensures high fidelity in gene expression.

<p>Both transcription and translation are highly regulated processes with energy-dependent steps, contributing to high fidelity. Proofreading mechanisms during transcription and translation, along with quality control checkpoints, ensure that errors are minimized, producing accurate RNA and protein molecules.</p> Signup and view all the answers

What is the role of elongation factors during RNA transcription?

<p>Elongation factors are required for the extension of the RNA chain during transcription. They use ATP hydrolysis to help RNA polymerase move along the chromatin, ensuring efficient and accurate transcription.</p> Signup and view all the answers

Contrast the termination signals for RNA transcription in prokaryotes and eukaryotes.

<p>In prokaryotes, RNA transcription stops when RNA polymerase encounters a terminator sequence. In eukaryotes, transcription ends after reaching a polyadenylation signal, which triggers cleavage and poly-A tail addition.</p> Signup and view all the answers

How does the cell ensure that only fully processed mRNA is exported from the nucleus?

<p>Only fully processed, mature mRNA is exported. Export depends on the removal of some proteins (e.g. snRNPs) and the addition or retention of others (exon junction complex at splice sites, cap-binding proteins, poly-A binding proteins, etc.)</p> Signup and view all the answers

Describe the role that RNA polymerase I, II, and III play in eukaryotes.

<p>RNA polymerase I transcribes the genes for 5.8S, 18S, and 28S rRNA. RNA polymerase II transcribes all protein-coding genes, plus snoRNA genes, miRNA genes, siRNA genes, and most snRNA genes. Finally, RNA polymerase III transcribes tRNA genes, 5S rRNA genes, some snRNA genes, and genes for other small RNAs.</p> Signup and view all the answers

Explain how miRNAs and siRNAs regulate gene expression.

<p>MicroRNAs (miRNAs) regulate gene expression typically by blocking translation of selective mRNAs. Small interfering RNAs (siRNAs) turn off gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures.</p> Signup and view all the answers

Why is fidelity important in transcription and translation, and what mechanisms ensure it?

<p>Fidelity in transcription and translation is crucial to ensure that the correct proteins are synthesized, maintaining proper cellular function. Mechanisms include proofreading by RNA polymerase during transcription and by aminoacyl-tRNA synthetases during translation, as well as ribosome surveillance mechanisms to detect and degrade faulty mRNAs.</p> Signup and view all the answers

Explain the purpose of a poly-A tail. Be sure to outline the 3 steps.

<p>The poly-A tail has three primary purposes related to pre-mRNA processing. First, the 3' end of the original RNA is cleaved off. Second, a series of ~200 A's are added by a poly-A polymerase. Third, Poly-A binding proteins come in and bind to the poly-A tail, which is critical for export from the nucleus and later protein synthesis.</p> Signup and view all the answers

How does knowing the S values help a scientist better understand sedimentation and the RNAs?

<p>The rRNAs are named according to their 'S' values, which describes their rate of sedimentation during ultracentrifugation experiments. This value helps identify the size of an RNA.</p> Signup and view all the answers

In what ways are snoRNAs helpful the the overall pathway described by the central dogma?

<p>Small nucleolar RNAs (snoRNAs) are used to process and chemically modify rRNAs.</p> Signup and view all the answers

In general, what do noncoding RNAs do?

<p>Noncoding RNAs function in diverse cell processes, including telomere synthesis, X-chromosome inactivation, and the transport of proteins into the ER.</p> Signup and view all the answers

Flashcards

Transcription

The process where DNA information is copied into an RNA intermediary by RNA polymerase.

mRNA (messenger RNA)

The type of RNA that carries genetic information from DNA to ribosomes for protein synthesis.

Translation

The process where mRNA is decoded to produce a specific protein.

Central Dogma of Molecular Biology

The flow of genetic information from DNA to RNA to protein

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Promoters

Special DNA sequences where transcription is initiated.

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Transcription Factors

Proteins that help position RNA polymerase on DNA and initiate transcription in eukaryotes.

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Polyadenylation Signal

Sequences in RNA that signal the end of transcription in eukaryotes.

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5' Capping

The addition of a 7-methylguanosine to the 5' end of RNA

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Introns

Non-coding sequences within a gene that are removed from the pre-mRNA during splicing.

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Exons

Coding sequences within a gene that are spliced together to form the mature mRNA.

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RNA Splicing

The process of removing introns and joining exons to form a mature mRNA.

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Spliceosome

A complex made of snRNAs and proteins that catalyzes RNA splicing.

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Poly-A Tail

The addition of multiple adenine bases to the 3' end of the RNA transcript.

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Poly-A Binding Proteins

Proteins that bind to the poly-A tail and are important for mRNA export from the nucleus.

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Nuclear Export Receptor

A receptor that guides mature mRNA through the nuclear pore complex into the cytosol.

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rRNA (ribosomal RNA)

RNA that forms the structural and catalytic core of ribosomes.

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tRNA (transfer RNA)

RNA that functions as adaptors between mRNA and amino acids during protein synthesis.

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snRNA (small nuclear RNAs)

RNA that functions in a variety of nuclear processes, mainly the splicing of pre-mRNA

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RNA Polymerases

Enzymes that synthesize RNA by using a DNA template.

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Central Dogma

The principle that genetic information flows from DNA to RNA to protein in all prokaryotes and eukaryotes.

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Elongation Factors

Proteins that facilitate the movement of RNA polymerase along chromatin during transcription.

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Terminator

A special DNA sequence that signals the end of transcription in prokaryotes.

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5' cap

Addition of 7-methylguanosine to the 5’ end of RNA, marking it as an mRNA precursor.

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Ribosomal RNAs (rRNAs)

RNAs that make up the structural and catalytic core of ribosomes, essential for protein synthesis.

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Transfer RNAs (tRNAs)

Transfer RNAs are central to protein synthesis as adaptors between mRNA and amino acids

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RNA Polymerase I, II, III

The three RNA polymerases in eukaryotic cells

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siRNAs

Small interfering RNAs, turn off gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures

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mRNA Processing

First modification occurs immediately after 5' end of RNA exits polymerase: marks RNA as an mRNA-to-be

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High Fidelity

Ensuring accuracy of transcription and translation through energy-dependent steps.

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RNA Polymerase Synthesis Direction

RNA synthesized 5' to 3', DNA read 3' to 5' by a complex enzyme.

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Chromatin Modification

Modification to chromatin structure which is vital for transcription activation in eukaryotes.

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Study Notes

  • The central dogma describes information flow from DNA to RNA to protein.

The Big Picture

  • Genetic information residing in chromosomes must be interpreted to produce proteins within the cytosol to be functional.
  • DNA-encoded data is first transcribed into an RNA intermediary by RNA polymerase.
  • Following transcription, the RNA molecule undergoes processing steps to become a mature messenger RNA (mRNA).
  • mRNA molecules are then exported from the nucleus to the cytosol, to be translated into proteins via ribosomes.
  • Some RNA molecules do not code for proteins, and are processed differently from mRNA.
  • Both transcription and translation are rigorously controlled, and use many energy-dependent steps to guarantee precision.
  • Information flows from DNA to RNA to protein in prokaryotes and eukaryotes.
  • Although the mechanisms are very similar between prokaryotes and eukaryotes, there are several differences that address specific difficulties in eukaryotes.
  • Information content decreases from DNA to mRNA to protein.

RNA Transcription

  • Transcription produces a single-stranded RNA molecule complementary to the DNA template strand.
  • RNA is synthesized in the 5' to 3' direction and DNA is read in the 3' to 5' direction by RNA polymerase, which is a complex multi-subunit enzyme.
  • Eukaryotes have three different RNA polymerases that synthesize different RNAs, while prokaryotes have only one RNA polymerase.
  • Transcription begins at specific DNA sequences called promoters.
  • In prokaryotes, the RNA polymerase enzyme binds strongly to the promoter sequence.
  • In eukaryotes, transcription requires the binding of general transcription factors, which help position RNA polymerase to start the process.
  • Additional proteins are required to modify chromatin structure in eukaryotes so transcription can be fully activated.
  • Extension of the RNA chain requires elongation factors, which utilize ATP hydrolysis to aid RNA polymerase movement along chromatin.
  • RNA transcription stops after RNA polymerase encounters a special DNA sequence.
  • This sequence is called a terminator in prokaryotes.
  • In Eukaryotes transcription stops after reaching a polyadenylation signal
  • Most eukaryotic RNAs require post-transcriptional processing to become functional.

mRNA processing

  • Processing is critical before RNAs can function to encode proteins and can be considered mature mRNA.
  • The first modification occurs right after the 5' end of RNA exits polymerase.
  • Specifically, 7-methylguanosine "cap" is added to the 5' end of RNA, marking it for export.

Pre-mRNA Processing

  • Protein-coding genes often contain intervening sequences (introns) that interrupt the actual coding sequences (exons).
  • Introns must be removed via RNA splicing.
  • Splicing is carried out by the spliceosome.
  • The spliceosome consists of small nuclear ribonucleoproteins (snRNPs), or small nuclear RNAs (snRNAs) and multiple proteins.
  • RNA sequences at intron-exon boundaries direct the process.
  • The spliceosome assembles on pre-mRNA while it is still being transcribed, but splicing may be delayed.
  • Splicing is adaptable, and one transcript can have many possible splicing patterns.
  • Once transcription is complete, the RNA 3' end receives a poly-A tail.
  • Firstly, the 3' end original RNA molecule is cleaved off.
  • A series of around 200 A's are then added by a poly-A polymerase.
  • Poly-A binding proteins then recognize the tail.
  • This is important for export from the nucleus and eventual protein synthesis.

mRNA Export

  • RNA synthesis coupled with processing occurs inside the nucleus, but protein synthesis occurs in the cytosol.
  • Only fully processed, mature mRNA gets exported from the nucleus.
  • Export is dependent on the removal of some proteins (e.g., snRNPs) and addition or retention of others (exon junction complex at splice sites, cap-binding proteins, and poly-A binding proteins).
  • Mature mRNA binds to nuclear export receptor to be guided through the nuclear pore complex to the cytosol.

The "Other" RNAs

  • mRNA represents about 5% of cellular RNA.
  • As much as 80% of cellular RNA is ribosomal RNA (rRNA), forming the structural and catalytic core of ribosomes.
  • rRNA is synthesized by RNA pol I, specifically the 18S, 5.8S, and 26S subunits; in addition, RNA pol III synthesizes the 5S subunit .
  • rRNA is significantly processed and assembled with ribosomal proteins in the nucleolus.
  • Additional non-coding RNAs perform functions in pre-mRNA splicing (snRNAs), ribosome assembly (snoRNAs), protein synthesis (tRNAs), regulation of gene expression (siRNAs and miRNAs), and telomere synthesis.

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