Central Dogma of Gene Expression

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Questions and Answers

In prokaryotes, where do both transcription and translation occur?

  • In the mitochondria
  • In the endoplasmic reticulum
  • In the nucleus
  • In the cytoplasm (correct)

Which of the following processes takes place in the nucleus of eukaryotic cells?

  • Translation
  • Both B and C (correct)
  • Transcription
  • RNA processing

What is true regarding rRNA and tRNA synthesis?

  • They are transcribed and translated from genes
  • They are transcribed but not translated (correct)
  • They are not produced in cells
  • They are proteins encoded by other proteins

What distinguishes eukaryotic cells from prokaryotic cells in terms of the central dogma?

<p>Eukaryotes have a nucleus where transcription occurs (B)</p> Signup and view all the answers

Which statement about transcription and translation is correct?

<p>Translation takes place in the cytoplasm, where proteins are synthesized (C)</p> Signup and view all the answers

Which type of RNA is primarily responsible for coding for proteins?

<p>Messenger RNA (mRNA) (A)</p> Signup and view all the answers

What is the primary role of ribosomal RNA (rRNA) in the cell?

<p>Serve as a structural component of ribosomes (D)</p> Signup and view all the answers

Which statement is true about transfer RNA (tRNA)?

<p>It transports amino acids during the translation process. (C)</p> Signup and view all the answers

Which of the following statements correctly describes the abundance of different types of RNA?

<p>mRNA is much more abundant than both tRNA and rRNA. (D)</p> Signup and view all the answers

What is the main difference between the roles of messenger RNA (mRNA) and transfer RNA (tRNA)?

<p>mRNA acts as a template for protein synthesis, while tRNA transports amino acids. (B)</p> Signup and view all the answers

What is the function of the template strand of DNA during transcription?

<p>It guides the synthesis of RNA transcript. (D)</p> Signup and view all the answers

Which statement correctly describes the non-template (coding) strand of DNA?

<p>It has a base sequence identical to that of the RNA transcript. (B)</p> Signup and view all the answers

What is true about the RNA transcript in relation to the template strand?

<p>It is complementary to the base sequence of the template strand. (B)</p> Signup and view all the answers

How does the base sequence of the template strand relate to the other DNA strand?

<p>It is complementary to the coding strand sequence. (C)</p> Signup and view all the answers

Which statement is incorrect regarding the strands of DNA during transcription?

<p>The non-template strand must be transcribed first. (A)</p> Signup and view all the answers

What corresponds with the 5' end of a coding DNA strand?

<p>N-terminus of a peptide/protein (C)</p> Signup and view all the answers

Which statement accurately describes the polarity of RNA strands?

<p>RNA strands contain both a 5' and a corresponding 3' end. (D)</p> Signup and view all the answers

What is the relationship between the 3' end of the coding DNA strand and the resulting mRNA?

<p>It corresponds with the C-terminus of the peptide/protein. (D)</p> Signup and view all the answers

What is the significance of the 3' sugar-OH end in nucleotide strands?

<p>It plays a critical role in defining the polarity of nucleic acid strands. (A)</p> Signup and view all the answers

Which of the following correctly matches the ends of coding DNA, mRNA, and proteins?

<p>3' end of coding DNA - 5' end of mRNA - C-terminus of protein (A)</p> Signup and view all the answers

What direction does RNA polymerase travel along the DNA strand during transcription?

<p>3' to 5' (A)</p> Signup and view all the answers

Which of the following processes is NOT facilitated by RNA polymerase during transcription?

<p>Synthesizing DNA strands (B)</p> Signup and view all the answers

What type of bond connects ribonucleotides during RNA synthesis?

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

What is one of the main advantages of RNA synthesis by RNA polymerase?

<p>It allows for multiple RNA copies to be synthesized in a short time. (D)</p> Signup and view all the answers

Which enzyme is primarily responsible for forming the transcription bubble during transcription?

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

What is the primary function of RNA polymerase I in eukaryotic cells?

<p>To transcribe ribosomal RNA (rRNA) (A)</p> Signup and view all the answers

Which component is crucial for the initiation of transcription in bacterial cells?

<p>Sigma factors (A)</p> Signup and view all the answers

What type of RNA is transcribed by RNA polymerase III?

<p>Transfer RNA (tRNA) (C)</p> Signup and view all the answers

What effect does Actinomycin D have on transcription?

<p>Binds to double-stranded DNA and prevents RNAP from transcribing (C)</p> Signup and view all the answers

Which RNA polymerase class in eukaryotes is responsible for mRNA transcription?

<p>RNA polymerase II (A)</p> Signup and view all the answers

Which of the following describes the RNAP core enzyme in bacteria?

<p>It cannot initiate transcription alone. (D)</p> Signup and view all the answers

What component is essential for the initiation of transcription?

<p>Promoter region (D)</p> Signup and view all the answers

In which direction does RNA elongation occur during transcription?

<p>5’ to 3’ direction (C)</p> Signup and view all the answers

What is the typical rate of RNA synthesis in bacteria?

<p>42-54 nucleotides/second (C)</p> Signup and view all the answers

What event signals the termination of transcription?

<p>Reaching the termination site (C)</p> Signup and view all the answers

What is the primary role of RNA polymerase during the elongation phase of transcription?

<p>To synthesize RNA from DNA (B)</p> Signup and view all the answers

What is the role of the σ subunit in bacterial RNA polymerase?

<p>It binds the promoter region to initiate transcription. (D)</p> Signup and view all the answers

Which of the following correctly identifies the location of the Pribnow box in relation to the transcription start site?

<p>It is located at -10, upstream of the transcription start site. (C)</p> Signup and view all the answers

How are sites designated upstream or downstream relative to the transcription start site?

<p>Upstream sites are labeled with a minus sign. (A)</p> Signup and view all the answers

What describes the term 'consensus sequences' in the context of E. coli promoters?

<p>They are short, conserved nucleotide sequences that may not be identical. (A)</p> Signup and view all the answers

What is the significance of the -35 consensus sequence in the context of transcription initiation?

<p>It provides a recognition site for the RNA polymerase to bind. (B)</p> Signup and view all the answers

Which element is specifically recognized by transcription factors to regulate gene transcription?

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

What is the role of the TATA box in eukaryotic promoters?

<p>It provides a landing site for RNA polymerase. (A)</p> Signup and view all the answers

In what context would the Downstream Promoter Element (DPE) be considered important?

<p>It may be located approximately 30 nucleotides downstream from the transcription start point. (D)</p> Signup and view all the answers

Which of the following statements is true regarding eukaryotic promoters when compared to prokaryotic promoters?

<p>Eukaryotic promoters may lack some consensus sequences altogether. (B)</p> Signup and view all the answers

Which sequence is known to surround the transcription start point in eukaryotic promoters?

<p>Inr (A)</p> Signup and view all the answers

Which transcription factor initiates transcription by binding to the TATA box?

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

What is the function of the BRE sequence recognized by TFIIB?

<p>Facilitating transcription initiation (C)</p> Signup and view all the answers

Which regions can regulate eukaryotic gene transcription?

<p>Both upstream and downstream regulatory regions (C)</p> Signup and view all the answers

Which transcription factor category is specific to RNA polymerase II?

<p>TFII (D)</p> Signup and view all the answers

Where is the TATA-binding protein (TBP) found within the transcription process?

<p>Part of the TFIID complex (C)</p> Signup and view all the answers

What feature of intrinsic termination in transcription allows for the dissociation of the RNA transcript?

<p>Presence of inverted repeats (B)</p> Signup and view all the answers

Which factor is essential for rho (ρ) dependent termination in transcription?

<p>Termination factor rho (C)</p> Signup and view all the answers

What role does the hairpin structure play during the termination of transcription?

<p>It facilitates the easy dissociation of the RNA transcript. (B)</p> Signup and view all the answers

What occurs immediately after the formation of the hairpin structure at the termination site?

<p>Rho (ρ) factor begins binding to RNA. (B)</p> Signup and view all the answers

Which of the following best describes how weak A-U base pairing affects transcription termination?

<p>It leads to the release of the RNA transcript. (A)</p> Signup and view all the answers

Flashcards

Central Dogma

The flow of genetic information from DNA to RNA to protein.

Prokaryotic Transcription/Translation

Both steps happen in the cytoplasm.

Eukaryotic Transcription

Takes place inside the nucleus.

Eukaryotic Translation

Happens in the cytoplasm.

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Prokaryotic Cell

Do not possess a nucleus.

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mRNA

Messenger RNA; carries genetic information from DNA to ribosomes for protein synthesis.

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tRNA

Transfer RNA; brings specific amino acids to the ribosome during translation.

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rRNA

Ribosomal RNA; forms a major part of ribosomes, the machinery for protein synthesis.

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Transcription

The process of making RNA from a DNA template.

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Template Strand

The DNA strand used as a template for RNA synthesis during transcription. Its sequence is complementary to the RNA transcript.

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Antisense Strand

Another name for the Template Strand, emphasizing that its sequence is complementary to the RNA transcript.

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Non-Template Strand

The DNA strand that is NOT transcribed. Its sequence is identical to the RNA transcript (except for thymine replaced with uracil).

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Sense Strand

Another name for the Non-Template Strand, emphasizing that its sequence matches the RNA transcript (with uracil) and 'makes sense' in the genetic code.

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Coding Strand

Yet another name for the Non-Template Strand, emphasizing that it contains the genetic code that will be translated into protein.

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DNA Polarity

A DNA strand has a 3' end with a sugar –OH group and a 5' end with a phosphate group.

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RNA Polarity

An RNA strand also has a 3' end with a sugar –OH group and a 5' end with a phosphate group.

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Protein Polarity

Proteins have an N-terminus (amino, +ve) and a C-terminus (carboxyl, -ve).

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DNA & RNA Correspondence

The 5' end of the coding strand (DNA) corresponds to the 5' end of the mRNA transcript, which in turn corresponds to the N-terminus of a peptide/protein. The 3' end of the coding strand (DNA) corresponds to the 3' end of the mRNA transcript, which in turn corresponds to the C-terminus of a peptide/protein.

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Central Dogma of Molecular Biology

The flow of genetic information from DNA to RNA to protein.

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RNA Polymerase

An enzyme responsible for synthesizing RNA from a DNA template during transcription. It unwinds DNA, adds ribonucleotides, and creates a messenger RNA (mRNA) molecule.

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Transcription Bubble

A temporary unwound region of DNA created during transcription. RNA polymerase separates the two DNA strands within this bubble to access the template strand.

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DNA-RNA Base Pairing

The process where ribonucleotides (A, U, G, C) in RNA bind to complementary nucleotides on the DNA template strand.

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RNA Polymerase Direction

RNA polymerase travels along the DNA template strand in the 3' to 5' direction, synthesizing RNA in the 5' to 3' direction.

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Proofreading in Transcription

RNA polymerase has some ability to proofread the newly synthesized RNA transcript, ensuring accuracy in copying DNA information.

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Eukaryotic RNA Polymerases

Three types of RNA polymerases (I, II, and III) in eukaryotes, each responsible for transcribing specific sets of genes.

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RNA Pol I

The RNA polymerase responsible for transcribing ribosomal RNA (rRNA), crucial for protein synthesis.

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RNA Pol II

The RNA polymerase responsible for transcribing messenger RNA (mRNA), which carries genetic information from DNA to ribosomes.

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RNA Pol III

The RNA polymerase responsible for transcribing transfer RNA (tRNA), which brings amino acids to ribosomes during translation, and some small RNAs.

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Bacterial RNA Polymerase (RNAP)

A single RNA polymerase in bacteria responsible for transcribing all types of RNA: mRNA, rRNA, and tRNA.

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Sigma Factor (σ)

A protein subunit of bacterial RNA polymerase that helps recognize specific DNA sequences called promoters, initiating transcription.

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Transcription Initiation

The process where RNA polymerase binds to the promoter region of the template DNA strand, marking the start of transcription.

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Transcription Elongation

The stage where RNA polymerase reads the template DNA strand and adds complementary ribonucleotides to build an RNA molecule.

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Transcription Termination

The process where RNA polymerase recognizes a termination site in the DNA and detaches from the template strand, ending transcription.

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Transcription Rate

The speed at which RNA polymerase adds nucleotides to an RNA molecule.

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Promoter

A DNA sequence located upstream of the transcription start site (+1) that signals RNA polymerase where to begin transcription.

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σ Subunit

A protein subunit of bacterial RNA polymerase that helps recognize and bind to the promoter region, initiating transcription.

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-35 Sequence

A consensus sequence located approximately 35 base pairs upstream of the transcription start site in bacterial promoters.

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-10 Sequence (Pribnow Box)

A consensus sequence located approximately 10 base pairs upstream of the transcription start site in bacterial promoters.

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Upstream/Downstream

Upstream refers to sequences located before the transcription start site (+1), while downstream refers to sequences located after the start site.

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Eukaryotic Promoters

Regions of DNA that initiate transcription in eukaryotic cells. They are larger and more complex than prokaryotic promoters, containing multiple consensus sequences.

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Initiator (Inr)

A short DNA sequence that surrounds the transcription start point (+1) in eukaryotic promoters. It is essential for RNA polymerase II to initiate transcription.

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TATA Box

A DNA sequence found in many eukaryotic promoters, located about 25 base pairs upstream of the transcription start point (-25). It helps position RNA polymerase II for transcription.

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BRE (TFIIB Recognition Element)

A DNA sequence found in some eukaryotic promoters, recognized by transcription factor IIB (TFIIB). It helps stabilize the transcription initiation complex.

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Downstream Promoter Element (DPE)

A DNA sequence sometimes found about 30 nucleotides downstream of the transcription start point (+30) in eukaryotic promoters. It plays a role in initiating transcription.

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Transcription Factor II

A type of protein involved in regulating the transcription of genes in eukaryotic cells. Specifically, these factors help control the activity of RNA Polymerase II, the enzyme responsible for transcribing protein-coding genes.

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TFIID

A transcription factor that binds to the TATA box in eukaryotic promoters. It contains a TATA-binding protein (TBP) that specifically recognizes the TATA box sequence, which is essential for positioning RNA Polymerase II accurately at the start of transcription.

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TFIIB

A transcription factor that recognizes the BRE sequence located near the TATA box in eukaryotic promoters. It helps stabilize the transcription initiation complex, which is formed by RNA Polymerase II and other transcription factors.

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Regulatory Regions

DNA sequences located near genes that can either enhance or repress transcription. They are often upstream or downstream of the gene's coding region and influence how much RNA is produced from the gene.

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What are upstream and downstream regions in Transcription?

In the context of transcription, upstream refers to the DNA sequence located before the transcription start site (+1), while downstream refers to the sequence located after the start site. These regions contain regulatory elements that can influence the transcription process.

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Intrinsic Termination

A mechanism of transcription termination in which a hairpin structure forms in the RNA transcript, followed by a run of uracil bases, causing the RNA polymerase to detach.

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Hairpin Structure

A secondary structure formed within an RNA transcript when a sequence of inverted repeats in the DNA template folds back on itself, forming a stem-loop structure with a loop at the top.

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Rho-dependent Termination

A mechanism of transcription termination that requires the Rho protein, which binds to the RNA transcript and moves towards RNA polymerase, causing the polymerase to detach.

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Weak A-U Base Pairing

The weaker bonding between adenine (A) and uracil (U) nucleotides in the RNA transcript after the hairpin structure facilitates the dissociation of the transcript from RNA polymerase.

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What makes Rho-dependent termination different from intrinsic termination?

Rho-dependent termination relies on the Rho protein to help detach RNA polymerase from the DNA, while intrinsic termination solely depends on the hairpin structure and the weak A-U base pairing in the RNA.

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Study Notes

Central Dogma of Gene Expression

  • All cells, from bacteria to humans, follow the Central Dogma, which describes the flow of genetic information.

Prokaryotic Gene Expression

  • Prokaryotes lack a nucleus.
  • Both transcription and translation occur in the cytoplasm.
  • rRNA and tRNA are transcribed but not translated from genes.

Eukaryotic Gene Expression

  • Eukaryotes possess a nucleus.
  • Transcription occurs within the nucleus.
  • RNA processing happens within the nucleus.
  • Translation occurs in the cytoplasm.

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