Chp. 11 - Exam 3 Bio 190
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Questions and Answers

What is the primary function of TERC in relation to telomerase?

  • It serves as a guide for telomerase binding. (correct)
  • It acts as a primer for DNA replication.
  • It helps in the degradation of mRNA.
  • It silences target genes.

    • HOTAIR is an ncRNA that enhances gene expression by modifying histones.

    False

    What does telomerase add to the end of the chromosome, and what is its purpose?

    Excess DNA, to create room for future primer.

    The ncRNA known as ______ regulates transcription by forming a scaffold for protein complexes.

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

    Match the following terms with their definitions:

    <p>Double-stranded RNA = More potent at inhibiting mRNA Antisense RNA = Less effective than double-stranded RNA miRNAs = Regulate gene expression post-transcriptionally siRNAs = Target specific mRNA for degradation</p> Signup and view all the answers

    What percentage of transcription in a typical human cell is associated with making ncRNAs?

    <p>80%</p> Signup and view all the answers

    Non-coding RNAs can only bind to DNA.

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

    What is a ribozyme?

    <p>A ribozyme is an RNA molecule capable of acting as an enzyme to catalyze biochemical reactions.</p> Signup and view all the answers

    NcRNAs can affect processes of __________, transcription, and translation.

    <p>DNA replication</p> Signup and view all the answers

    Match the following functionalities of ncRNAs with their respective roles:

    <p>Bind to DNA = Affects DNA replication Scaffold proteins = Supports protein assembly Bind small molecules = Forms binding sites Affects transcription = Regulates gene expression</p> Signup and view all the answers

    Which of the following is NOT a function of non-coding RNAs?

    <p>Providing genetic information</p> Signup and view all the answers

    Only a small portion of ncRNAs have roles in human diseases.

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

    What is the primary difference between coding and non-coding RNAs?

    <p>Coding RNAs carry the genetic information for protein synthesis, while non-coding RNAs do not code for proteins but serve other functions.</p> Signup and view all the answers

    What is the repeat sequence found in human telomeres?

    <p>5ʹ–GGGTTA–3ʹ</p> Signup and view all the answers

    As cells divide, telomeres become longer.

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

    What enzyme is responsible for adding repeating sequences to telomeres?

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

    The ends of the chromosomes cannot be fully replicated by __________.

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

    What happens to a cell when its telomeres become too short?

    <p>The cell undergoes programmed cell death.</p> Signup and view all the answers

    What is the function of telomeres?

    <p>To protect the ends of chromosomes from becoming tangled or broken.</p> Signup and view all the answers

    Telomere lengthening occurs in _______ steps.

    <p>3</p> Signup and view all the answers

    What is one primary function of the Signal Recognition Particle (SRP)?

    <p>To guide the ribosome to the endoplasmic reticulum (ER)</p> Signup and view all the answers

    SRP is composed solely of protein.

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

    What must bind GTP for SRP to bind to its receptor in the ER membrane?

    <p>Proteins within SRP and the SRP receptor</p> Signup and view all the answers

    The SRP changes a protein's function to open a __________ for the polypeptide.

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

    What is the result of GTP hydrolysis in the SRP and SRP receptor complex?

    <p>It releases SRP, allowing translation to resume</p> Signup and view all the answers

    During translation, SRP pauses the process upon binding to an ER signal __________.

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

    What is the relationship between SRP and non-coding RNA (ncRNA)?

    <p>SRP is composed of ncRNA and protein.</p> Signup and view all the answers

    Match the following components with their roles in the SRP pathway:

    <p>SRP = Guides ribosome to ER GTP-binding proteins = Cause SRP release ER receptor = Binds SRP ncRNA = Part of SRP structure</p> Signup and view all the answers

    What is the role of the Cas9 protein in the interference phase?

    <p>It cleaves bacteriophage DNA</p> Signup and view all the answers

    NcRNAs have no impact on human diseases.

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

    Name one type of cancer where abnormal expression levels of certain miRNAs have been found.

    <p>Breast cancer</p> Signup and view all the answers

    HOTAIR behaves as an ______ when overexpressed.

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

    Match the following roles of ncRNAs with their applications:

    <p>Tumor suppressor = Reduces cancer progression Oncogene = Promotes cancer development miRNA = Regulates gene expression HOTAIR = Associated with cancer</p> Signup and view all the answers

    What is the primary function of the CRISPR-Cas system in bacteria?

    <p>Defense against bacteriophages</p> Signup and view all the answers

    The type II CRISPR-Cas system contains multiple types of CRISPR-associated genes.

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

    What proteins form a complex to recognize and cleave foreign bacteriophage DNA during the adaptation phase?

    <p>Cas1 and Cas2</p> Signup and view all the answers

    In the interference phase, the tracrRNA-crRNA-Cas9 complex binds to the __________ protein.

    <p>Cas9</p> Signup and view all the answers

    Match the following stages of the CRISPR-Cas system with their descriptions:

    <p>Adaptation = Insertion of bacteriophage DNA into the Crispr gene Expression = Transcription of Crispr, tracr, and Cas9 genes Interference = Cleavage of bacteriophage DNA by the Cas9 protein</p> Signup and view all the answers

    Which non-coding RNA is involved in the CRISPR-Cas system's defense mechanism?

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

    The expression phase occurs after the bacterial cell has been exposed to a bacteriophage for the first time.

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

    What happens to the pre-crRNA during the expression phase?

    <p>It is cleaved into many small crRNA molecules.</p> Signup and view all the answers

    Study Notes

    CRISPR-Cas System

    • Chinese scientist He Jiankui claimed to use CRISPR to genetically edit babies.
    • He offered no evidence or data to support his claims.
    • This act could open the door to "designer babies."

    RNA Interference (RNAi)

    • Double-stranded RNA is more potent at inhibiting mRNA than antisense RNA.
    • The phenomenon was termed RNA interference.
    • microRNAs (miRNAs): transcribed from endogenous eukaryotic genes and regulate gene expression. miRNAs are partially complementary to their mRNA targets.
    • Small interfering RNAs (siRNAs): come from exogenous sources, and are usually perfectly complementary to their target mRNA. They play a role in preventing viral infections.

    Non-coding RNAs (ncRNAs) and Gene Regulation

    • ncRNAs bind to other molecules and macromolecules.
    • ncRNAs have several common functions:
      • Scaffold: bind to multiple components, act as scaffold for formation of a complex.
      • Guide: guide one molecule to a specific location in the cell.
      • Alteration of protein function or stability: bind to ncRNA to affect protein function/stability.
      • Ribozyme: RNA molecule with catalytic function, for example peptidyltransferase activity of ribosome.
      • Blocker: prevents or blocks a cellular process (binding to ribosomes inhibiting translation).
      • Decoy: recognizes other ncRNAs and sequesters them, preventing them from working.

    ncRNAs and Human Disease

    • Abnormal expression levels of miRNAs have been found in nearly all forms of human cancer.
    • Some miRNAs are tumor suppressors, some are oncogenes.
    • HOTAIR is expressed in several cancers, behaving as an oncogene when overexpressed.
    • Various ncRNAs are associated with neurological disorders (Alzheimer's disease) and cardiovascular diseases (arrhythmias).

    ncRNAs in Plant Health

    • Abnormalities in ncRNAs play essential roles in plant health.
    • Their study is important for agriculture.
    • Examples of ncRNAs involved in plant health include miRNA-156, COOLAIR, and IPS1.

    Telomeres and DNA Replication

    • The ends of linear eukaryotic chromosomes have telomeres composed of repeat sequences (e.g. 5' - GGGTTA-3' in humans)
    • Telomeres protect the ends of chromosomes from entanglement and breakage.
    • Telomeres shorten with each cell division; when they are too short, the cell can no longer successfully divide, leading to programmed cell death.
    • Some cells express telomerase, an enzyme that adds repeating sequence and extends the telomeres.
    • Telomeres cannot be fully replicated by DNA polymerase due to the 5' overhang of DNA.
    • RNA primers are required for DNA polymerase to begin replication; primers are removed.
    • Telomerase is the solution for synthesizing the full length of the top strand, which counteracts the problem of limited DNA replication at the end of DNA strands.
    • Telomere length is regulated through TERC, an ncRNA that facilitates the binding of telomerase.

    HOTAIR

    • HOTAIR is an ncRNA in humans and other mammals
    • It regulates transcription by forming a scaffold that binds two protein complexes and guides them to particular genes.
    • The protein complexes covalently modify histones, leading to the silencing of target genes.

    Signal Recognition Particle (SRP)

    • SRP is composed of protein and ncRNA.
    • It chaperones the ribosome to the ER.
    • As a polypeptide is being made, SRP binds to the ER signal sequence, causing translation to pause.
    • SRP binds to an SRP receptor in the ER membrane.
    • GTP molecules bound to SRP and the SRP receptor are hydrolyzed, thereby releasing SRP.
    • Translation resumes, and the polypeptide is threaded through a channel into the ER lumen.

    CRISPR-Cas System (in detail)

    • Some bacteria and archaea have a system called the CRISPR-Cas system that defends against bacteriophages (and transposons).
    • The type II CRISPR-Cas system was described.
    • The system involves three main components:
      • Crispr genes (with repeats and spacers)
      • TracrRNA (a noncoding RNA)
      • Cas genes (encoding associated proteins, e.g., Cas9).
    • Defense occurs in three phases:
      • Adaptation: after bacterial exposure to a bacteriophage. Cas1 and Cas2 proteins cleave the bacteriophage DNA, and a piece of that DNA is added to the Crispr gene.
      • Expression: tracrRNA bonds to complementary sequences of pre-crRNA; pre-crRNA is then cleaved into small crRNA molecules; each tracrRNA-crRNA complex binds to the Cas9 proteins.
      • Interference: the tracrRNA-crRNA- Cas9 complex binds to bacteriophage DNA due to complementary base pairing. The Cas9 protein cleaves the bacteriophage DNA, thereby inactivating it.

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    Chapter 11 Notes - Exam 3 PDF

    Description

    This quiz explores the functions and characteristics of non-coding RNAs (ncRNAs) and telomerase, including their roles in gene expression and chromosome maintenance. Test your knowledge on the differences between coding and non-coding RNAs, the significance of telomerase, and how ncRNAs regulate various cellular processes.

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