Molecular Biology: Genes and Expression
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What is the primary function of a gene?

  • To produce energy
  • To code for a specific protein (correct)
  • To regulate cell division
  • To synthesize carbohydrates

    • All genes in the human genome are expressed in every cell at all times.

    False

    What are the two main functional units of a eukaryotic gene?

    Promoter region and coding region

    The process by which DNA is converted into RNA is called __________.

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

    Match the following types of genes with their characteristics:

    <p>Constitutive gene = Expressed at a constant rate Regulated gene = Expressed under specific conditions Housekeeping genes = Examples include enzymes of glycolysis Insulin gene = Expressed in pancreas</p> Signup and view all the answers

    Which of the following elements is NOT a conserved eukaryotic promoter element?

    <p>Poly-A tail</p> Signup and view all the answers

    Enhancers are always located close to the genes they enhance.

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

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

    <p>To carry information from DNA to produce proteins.</p> Signup and view all the answers

    The process of synthesizing RNA from a DNA template is called ______.

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

    Match the following DNA sequences to their related function:

    <p>CAAT box = Promoter element TATA box = Promoter element Silencers = Depress transcription Enhancers = Enhance transcription</p> Signup and view all the answers

    What is the primary role of transcription factors?

    <p>To enhance or depress transcription</p> Signup and view all the answers

    What enzyme catalyzes the process of reverse transcription?

    <p>Reverse transcriptase</p> Signup and view all the answers

    What is the role of the TATA box in transcription?

    <p>It is a consensus promoter necessary for transcription initiation.</p> Signup and view all the answers

    The RNA transcript is a copy of the antisense strand of DNA.

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

    What is the purpose of the 5' capping in RNA processing?

    <p>To protect the 5' end of the primary RNA transcript from degradation by ribonuclease.</p> Signup and view all the answers

    The primary transcript RNA is converted into mature RNA through a process called _____ modifications.

    <p>post-transcriptional</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>5' Capping = Addition of 7-methylguanosine to the RNA transcript 3' Polyadenylation = Addition of approximately 250 adenine residues RNA Splicing = Removal of introns from pre-mRNA Ribonuclease = Enzyme that degrades RNA into smaller components</p> Signup and view all the answers

    Which RNA polymerase is most sensitive to α-amanitin?

    <p>RNA Polymerase II</p> Signup and view all the answers

    HIV is an example of a retrovirus.

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

    What is the primary role of transcription factors in eukaryotic transcription?

    <p>They recognize and initiate transcription at specific promoter sequences.</p> Signup and view all the answers

    The final product formed during transcription is __________.

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

    Match the transcription factors with their primary roles:

    <p>TFIID = Recognizes TATA box TFIIB = Positions RNA polymerase at the start site TFIIF = Stabilizes RNA polymerase interaction TFIIH = Unwinds DNA and phosphorylates RNA polymerase CTD</p> Signup and view all the answers

    Which RNA polymerase is specifically responsible for synthesizing mRNA?

    <p>RNA Polymerase II</p> Signup and view all the answers

    RNA polymerases I and III transcribe mRNA.

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

    How many core peptides are there in RNA Polymerase II?

    <p>10</p> Signup and view all the answers

    Transcription occurs in the __________ of eukaryotic cells.

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

    What essential domain of RNA Polymerase II is required for transcription initiation?

    <p>C-terminal domain</p> Signup and view all the answers

    Which of the following is NOT a conserved eukaryotic promoter element?

    <p>Silencer region</p> Signup and view all the answers

    Enhancers are always located close to the genes they enhance.

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

    What is the primary function of transcription factors?

    <p>To regulate transcription by binding to enhancer or silencer regions.</p> Signup and view all the answers

    The region of DNA that initiates transcription of a particular gene is known as the __________.

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

    Match the following transcription elements to their functions:

    <p>Enhancers = Increase transcription likelihood Silencers = Decrease transcription rate Promoters = Initiate transcription Transcription factors = Regulate gene expression</p> Signup and view all the answers

    What type of RNA polymerase is responsible for synthesizing mRNA in eukaryotic cells?

    <p>RNA Polymerase II</p> Signup and view all the answers

    The __________ region is recognized by RNA polymerase II within the eukaryotic promoter.

    <p>CAAT box</p> Signup and view all the answers

    What is the primary role of transcription factors in eukaryotic transcription?

    <p>Recognize and bind to specific promoter sequences</p> Signup and view all the answers

    RNA polymerase II is responsible for transcribing tRNA genes.

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

    Name the RNA polymerase that is most sensitive to α-amanitin.

    <p>RNA Polymerase II</p> Signup and view all the answers

    Transcription factors interact with __________ at the promoter region to initiate transcription.

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

    Match the following RNA polymerases with their primary functions:

    <p>RNA Polymerase I = Transcribes rRNA genes RNA Polymerase II = Transcribes mRNA RNA Polymerase III = Transcribes tRNA and other small RNAs</p> Signup and view all the answers

    Which transcription factor is responsible for recognizing the TATA box?

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

    Enhancer sequences are always located downstream of the genes they enhance.

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

    What role does TFIIH play in transcription initiation?

    <p>Unwinds DNA and phosphorylates the RNA polymerase CTD</p> Signup and view all the answers

    The __________ region is crucial for the accurate positioning of RNA polymerase at the start site of transcription.

    <p>BRE element</p> Signup and view all the answers

    Which of the following regions is found upstream of a eukaryotic gene and is critical for transcription initiation?

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

    Enhancer sequences must be located immediately adjacent to the gene they regulate.

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

    What is the role of transcription factors in gene expression?

    <p>To facilitate the binding of RNA polymerase to the promoter region and regulate the transcription of genes.</p> Signup and view all the answers

    The enzyme responsible for synthesizing messenger RNA (mRNA) in eukaryotic cells is called __________.

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

    Match the following RNA polymerases with their functions:

    <p>RNA polymerase I = Synthesis of rRNA RNA polymerase II = Synthesis of mRNA RNA polymerase III = Synthesis of tRNA RNA polymerase IV = Involved in RNA silencing</p> Signup and view all the answers

    What is the function of the TATA box in eukaryotic transcription?

    <p>To serve as a binding site for RNA polymerase</p> Signup and view all the answers

    Silencers are DNA sequences that enhance the transcription of adjacent genes.

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

    What sequences in the eukaryotic gene help regulate transcription aside from the promoter and enhancers?

    <p>Silencers and other regulatory elements.</p> Signup and view all the answers

    The __________ boxes, such as CAAT and GC boxes, are important promoter elements in eukaryotic genes.

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

    Study Notes

    Gene

    • Is the fundamental unit of inheritance and determines all phenotypes.
    • Every gene contains instructions for a specific protein.
    • The human genome contains an estimated 30,000 to 120,000 genes.
    • Only a fraction of genes are expressed in a particular cell at any given time.

    Gene Structure

    • Most eukaryotic genes consist of coding sequences (exons) interrupted by noncoding DNA (introns).
    • The average gene has 7-10 exons spread over 10-16kb of DNA.
    • Gene structure includes exons, start signals, stop signals, and regulatory control elements.
    • The two main functional units are the promoter region and the coding region.

    Gene Expression

    • The process by which a gene's information is converted into a biologically functional molecule of either protein or RNA.
    • Gene expression is assumed to be controlled at various points in the sequence leading to protein synthesis.
    • The central dogma of molecular biology describes the flow of genetic information: DNA → RNA → protein.
      • Transcription: DNA → RNA
      • Translation: RNA → protein

    Types of Genes

    • Constitutive genes (Housekeeping genes)
      • Are expressed at a constant rate in everyday processes.
      • Not subjected to regulation.
      • Examples include enzymes of glycolysis.
    • Regulated genes
      • Expressed only under certain conditions.
      • Expressed in all cells or a subset of cells.
      • Example: the expression of the insulin gene in the pancreas.

    Flow of Genetic Information in Prokaryotes vs. Eukaryotes

    • Prokaryotes
      • Transcription and translation occur simultaneously.
    • Eukaryotes
      • Transcription occurs in the nucleus followed by RNA processing.
      • Translation occurs in the cytoplasm.

    Eukaryotic Promoter

    • Is a region of DNA that initiates transcription of a particular gene.
    • Located near the transcription start sites of genes, upstream on the DNA (towards the 5’ region of the sense strand).
    • Promoters can be about 100–1000 base pairs long.
    • Conserved eukaryotic promoter elements
      • CAAT box
      • TATA box
      • GC box
      • CAP site
    • Consensus sequence
      • GGCCAATCT (CAAT box)
      • TATAA (TATA box)
      • GGGCGG (GC box)
      • TAC (CAP site)

    Enhancer Sequences

    • Are regulatory DNA sequences that enhance the transcription of an associated gene when bound by specific proteins called transcription factors.
    • Can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or thousands of nucleotides away.

    Silencers

    • Are regions of DNA that depress the rate of transcription when bound by specific transcription factors called repressors.

    Transcription

    • Is the process by which certain areas of DNA are copied (transcribed) to mRNA, which carries the information needed for protein synthesis.
    • Processes include DNA replication, DNA repair, genetic recombination, and RNA synthesis (transcription).

    Messenger RNA (mRNA)

    • mRNA is a type of RNA that is necessary for protein production.
    • It uses the information in genes to create a blueprint for making proteins.

    Reverse Transcription

    • Is the synthesis of DNA from an RNA template catalyzed by reverse transcriptase enzyme.
    • Retroviruses contain RNA as their genetic material.
    • The retroviral RNA serves as a template for synthesis of DNA by reverse transcriptase.
    • Examples of retroviruses: HIV (AIDS), Hepatitis C.

    Transcription in Eukaryotes

    • Pre-messenger RNA is formed, with the involvement of RNA polymerase enzymes.
      • RNA Polymerase Reads DNA and makes an RNA copy of one strand/one gene.

    RNA Polymerase

    • RNA polymerases I and III transcribe rRNA and tRNA genes, respectively.
    • Pol III transcribes a few other RNAs.
    • All three are big, multimeric proteins (500-700 kD).
    • All have two large subunits with sequences similar to those in E.coli RNA polymerase (Prokaryotes).
    • Pol II is the most sensitive to α-amanitin, an octapeptide from Amanita phalloides ("destroying angel mushroom").

    Transcription Factors

    • The three polymerases (I, II and III) interact with their promoters via so-called transcription factors.
    • Transcription factors recognize and initiate transcription at specific promoter sequences.

    Transcription in Eukaryotes: Post-Transcriptional Modifications or Gene Processing

    • The process by which primary transcript RNA is converted into mature RNA.
    • The pre-mRNA molecule undergoes three main modifications:
      • 5' Capping
      • 3' polyadenylation
      • RNA splicing

    Capping

    • Involves the addition of 7-methylguanosine (m7G) to the 5' end of the pre-mRNA.
    • Protects the 5' end of the primary RNA transcript from attack by ribonuclease.

    Cleavage and Polyadenylation

    • Involves cleavage of the 3' end of the pre-mRNA molecule and the addition of about 250 adenine residues to form a poly(A) tail.
    • Protects the 3' end from ribonuclease digestion.

    RNA Splicing 

    • The pre-messenger RNA contains introns that are not required for protein synthesis.
    • The sequence AAUAAA in hnRNA serves as a signal for cleavage and addition of the poly(A) tail.
    • The pre-messenger RNA is chopped up to remove the introns and create messenger RNA (mRNA).

    The Structure of a Eukaryotic Gene and its Products

    • 5' flanking region
      • Promoter
    • Transcribed region
      • Intron
      • Exon
    • Enhancer
    • CAAT box
    • GC boxes
    • TATA box
    • Protein
      • Cap site
      • Start signal
    • Left splice site
    • Right splice site
    • Protein stop signal
    • Poly (A) addition signal
    • Polyadenylation site

    Synthesis of Messenger RNA (mRNA) in Eukaryotes: hnRNA, heterogeneous nuclear RNA.

    • Nucleus
      • 5' cap
      • Intron
      • 3' poly (A)
    • DNA
    • Nuclear envelope
    • Nuclear pore

    Clinical Correlates

    • The most common causes of β-thalassemia are defects in mRNA splicing of the ẞ-globin gene.
    • Mutations that affect splicing create aberrant transcripts that are degraded before they are translated.
    • Thalassemia minor is a mild anemia caused by inheriting a single mutated gene.
    • Thalassemia major is a severe transfusion-dependent anemia caused by inheriting two mutated genes.

    Synthesis of Ribosomal RNA (rRNA) and Assembly of Ribosomes

    • Nuclear organizer

      • 5'
      • 3'

    • Nuclear envelope

    • Nucleolus

    • Nuclear pore

    • Cytoplasm

    • 45S rRNA precursor

    Synthesis of Transfer RNA (tRNA)

    • Nucleus

      • Intron
      • tRNA precursor
      • tRNA
      • tRNA

    • DNA

    • Nuclear pore

    • Cytoplasm

    • tRNA modification

      • D, T, W, and (representing other modified nucleotides) are unusual nucleotides produced by post-transcriptional modifications.

    Synthesis of Transfer RNA (tRNA)

    • RNA polymerase III produces tRNA.
    • The promoter is located within the coding region of the gene.
    • Primary transcripts for tRNA are cleaved at the 5' and 3' ends.
    • Some precursors contain introns that are removed.
    • During processing of tRNA precursors, nucleotides are modified.
    • Post-transcriptional modification includes the conversion of uridine to pseudouridine (Ψ), ribothymidine (T), and dihydrouridine (D).
    • Other unusual nucleotides are also produced.
    • Addition of the sequence CCA to the 3' end is catalyzed by nucleotidyl transferase.

    tRNA

    • Found in all tRNAs
    • Not found in all tRNAs.Other variable sites are shown in blue as well
    • The modified bases are:
      • I = inosine
      • ml = methylinosine
      • T = ribothymidine
      • UH₂ = dihydrouridine
      • m₂G = dimethylguanosine
      • ψ = pseudouridine

    Eukaryotic Transcription

    • Transcription is the process of copying DNA into RNA.
    • DNA is transcribed by RNA polymerase into messenger RNA (mRNA), which carries the genetic information needed for protein synthesis.
    • Eukaryotes have three RNA polymerases (I, II, and III) that are involved in transcribing different types of RNA.
    • RNA polymerase II is responsible for synthesizing mRNA.

    Eukaryotic Promoter

    • A promoter is a DNA sequence that initiates transcription of a gene.
    • Promoters are located upstream of the transcription start site of genes.
    • Common eukaryotic promoter elements include:
      • CAAT box
      • TATA box
      • GC box
      • CAP site

    Enhancers and Silencers

    • Enhancers are regulatory DNA sequences that increase the likelihood of transcription.
    • They can be located thousands of nucleotides away from the gene they enhance.
    • Silencers are regulatory DNA sequences that decrease the likelihood of transcription.

    Transcription Factors

    • Transcription factors are proteins that bind to promoters and other regulatory sequences.
    • They regulate the transcription of genes by interacting with RNA polymerase and other proteins.
    • General transcription factors are required for the initiation of transcription by RNA polymerase II.
    • These include: TFIID, TFIIB, TFIIF, TFIIE, and TFIIH.

    Post-Transcriptional Modifications

    • Pre-messenger RNA (hnRNA) is processed into mature mRNA through three main modifications:
      • 5' capping
      • 3' polyadenylation
      • RNA splicing

    5' Capping

    • 7-methylguanosine (m7G) is added to the 5' end of the pre-mRNA molecule.
    • Capping protects the mRNA from degradation and helps initiate translation.

    3' Polyadenylation

    • A poly(A) tail is added to the 3' end of the pre-mRNA molecule.
    • The tail protects the mRNA from degradation and helps with translation.

    RNA Splicing

    • Introns (non-coding sequences) are removed from the pre-mRNA.
    • Exons (coding sequences) are joined together to form mature mRNA.
    • Splicing is essential for producing functional mRNA.

    Ribosomal RNA (rRNA) Synthesis

    • rRNA is synthesized in the nucleolus, a specialized region within the nucleus.
    • The 45S rRNA precursor is processed into different rRNA molecules that are assembled into ribosomes.

    Transfer RNA (tRNA) Synthesis

    • tRNA is synthesized in the nucleus and is responsible for transporting amino acids to the ribosome for protein synthesis.
    • The primary tRNA transcript is processed into mature tRNA through cleavage, intron removal, and post-transcriptional modifications.
    • Post-transcriptional modification includes the conversion of uridine to pseudouridine, ribothymidine, and dihydrouridine.
    • Other modified nucleotides, like inosine and methylguanosine, are also produced.

    Clinical Correlations

    • Beta-thalassemia is a genetic disorder that results from defects in the splicing of the beta-globin gene.

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    Lecture 5: Gene Expression & Transcription in Eukaryotes PDF

    Description

    Explore the fundamental aspects of genes, including their structure and the process of gene expression. This quiz covers key topics such as the human genome, gene coding sequences, and the central dogma of molecular biology. Test your knowledge on how genetic information is processed and utilized in living organisms.

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