MIC 115 Lecture 18: Telomere Maintenance in Human Cells
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Questions and Answers

What is the primary sequence of the telomeric DNA found in human cells?

  • ATCGTA
  • GGTACC
  • CCTAGG
  • TTAGGG (correct)

Which component of telomerase provides the template for DNA synthesis?

  • Reverse transcriptase
  • Accessory protein subunits
  • RNA subunit (correct)
  • Telomerase complex

Which cell types predominantly express telomerase in humans?

  • Cardiac muscle cells
  • Germ line cells and stem cells (correct)
  • All fully differentiated somatic cells
  • Only skin cells

What is one major function of telomeres in eukaryotic cells?

<p>To protect chromosome ends from DNA repair processes (A)</p> Signup and view all the answers

Where is the assembly of the telomerase holoenzyme believed to be completed?

<p>In the Cajal Bodies (D)</p> Signup and view all the answers

What is a key feature of telomerase-directed DNA synthesis?

<p>Synthesis occurs in a 5' to 3' direction only (B)</p> Signup and view all the answers

Which of the following best describes how telomerase is disrupted?

<p>By inhibiting the RNA subunit function (A)</p> Signup and view all the answers

What is the structural composition of telomerase?

<p>A ribonucleoprotein complex with multiple accessory proteins (C)</p> Signup and view all the answers

What is the purpose of the first filter in a fluorescent microscope?

<p>To allow only excitation wavelengths to pass (B)</p> Signup and view all the answers

Which step follows the incubation of a sample with a primary antibody in immunofluorescence staining?

<p>A fluorescent dye-labeled secondary antibody is applied (A)</p> Signup and view all the answers

What is a key feature of immunofluorescence staining methods?

<p>Multiple molecules of secondary antibody can bind to each primary antibody (B)</p> Signup and view all the answers

Why are cells treated with a detergent during immunofluorescence staining?

<p>To allow antibody access to cell components by permeabilizing membranes (D)</p> Signup and view all the answers

In fluorescence in situ hybridization (FISH), what is the role of the oligonucleotide probe?

<p>To visualize specific nucleic acid sequences directly in cells (B)</p> Signup and view all the answers

What is the importance of using a powerful light source in fluorescence microscopy?

<p>To ensure adequate illumination for the specimen (D)</p> Signup and view all the answers

Which statement is true regarding the filters used in fluorescent microscopy?

<p>The second filter blocks excitation light and transmits emitted fluorescence (B)</p> Signup and view all the answers

What result does merging different dye-conjugated antibodies in a sample allow?

<p>Visualization of different proteins in the same specimen (C)</p> Signup and view all the answers

What role does telomerase play in the S phase of the cell cycle?

<p>It interacts with shelterin to maintain telomere length. (A)</p> Signup and view all the answers

What happens to telomeres in normal human somatic cells during each cell division?

<p>They shorten due to the end-replication problem. (C)</p> Signup and view all the answers

Which statement best describes the outcome when telomerase is inhibited in stem or cancer cells?

<p>Cells undergo apoptosis or achieve growth arrest. (B)</p> Signup and view all the answers

What is a main characteristic of replicative senescence?

<p>Cells exhibit increased metabolic activity and size. (A)</p> Signup and view all the answers

How does telomerase activity in mouse somatic cells differ from that in human cells?

<p>Telomerase is active in mouse somatic cells. (D)</p> Signup and view all the answers

What is the primary use of fluorescence microscopy?

<p>To stain and visualize specific cellular components. (C)</p> Signup and view all the answers

What is a consequence of the end-replication problem in somatic cells?

<p>Telomeres progressively shorten with each division. (C)</p> Signup and view all the answers

During which phases of the cell cycle does telomerase remain sequestered in CBs in human somatic cells?

<p>G1 and G2 phases. (C)</p> Signup and view all the answers

Flashcards

Telomere Structure

Telomeres are repetitive DNA sequences at the ends of linear chromosomes in eukaryotic cells.

Human Telomere Sequence

Human telomeres contain repeating TTAGGG sequences, followed by a G-rich 3' overhang.

Telomerase Function

Telomerase extends telomeres by adding telomeric repeats.

Telomerase components

A ribonucleoprotein complex consisting of a reverse transcriptase, an RNA template, and accessory proteins.

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Telomere Protection

Telomeres protect chromosome ends from being mistaken for DNA damage.

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Telomere Replication

Telomeres allow for complete replication of linear chromosomes.

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Telomerase Expression in Cells

Telomerase is mainly active in germline cells, stem cells, and many cancer cells.

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Shelterin Complex

Protein complex that binds to telomeric DNA, protecting telomeres.

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Telomeres shortening

Telomeres become shorter with each cell division, due to the end-replication problem and nucleolytic attack.

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Replicative senescence

A state where cells stop dividing permanently, and become large, flat, but metabolically active.

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Cellular Senescence Protection

Cellular senescence prevents uncontrolled cell division and cancer development.

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Telomerase and Cancer

Telomerase inhibition can induce cell death or growth arrest in cancer cells.

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CBs (Co-Centric Bodies)

Membrane-less organelles that consist of proteins and RNA, and contain telomerase during interphase.

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End-Replication Problem

The inability of DNA polymerase to fully replicate the ends of linear chromosomes.

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Telomere Length Homeostasis

A state where shortening and lengthening of telomeres are balanced by telomerase, maintaining stable telomere length.

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Fluorescence

The emission of light by a substance that has absorbed light of a shorter wavelength.

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Fluorescent Microscopy

A type of microscopy that uses fluorescent dyes to visualize specific structures or molecules within cells or tissues.

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Immunofluorescence Staining

A technique that uses fluorescently labeled antibodies to detect specific proteins in cells or tissues.

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Primary Antibody

An antibody that binds specifically to the protein of interest.

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Secondary Antibody

A fluorescently labeled antibody that binds to the primary antibody.

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Fluorescence In Situ Hybridization (FISH)

A technique that uses fluorescently labeled probes to visualize specific DNA sequences in cells or tissues.

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Fixation

The process of preserving cells or tissues in their natural state using chemical crosslinkers.

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Permeabilization

The process of making cell membranes permeable to antibodies using a detergent.

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Study Notes

Telomere Maintenance in Human Cells

  • Telomeres are located at the ends of linear chromosomes in eukaryotic cells
  • They consist of repetitive sequences (TTAGGG) and a G-rich 3' overhang
  • Telomeres protect chromosome ends from being misprocessed as double-stranded DNA breaks
  • Telomeres shorten with each cell division, partly because of the end replication problem
  • Telomerase is a ribonucleoprotein complex that extends telomeres
  • Telomerase contains a reverse transcriptase that adds TTAGGG repeats to the 3' end of telomeres
  • Telomerase uses its RNA subunit as a template for synthesis
  • Telomerase is typically active in germline cells, stem cells, and cancer cells
  • Human somatic cells lack detectable telomerase activity
  • Loss of telomerase activity leads to cellular senescence, where cells stop dividing
  • Loss of telomeres can activate DNA damage pathways and trigger cellular senescence

Telomere Maintenance in Human Cells: Differences Between Humans and Mice

  • Telomerase is active in mouse somatic cells.
  • Telomerase activation isn't critical for mouse tumorigenesis.
  • Mouse models aren't always ideal for studying telomerase activity regulation in cancer.

Microscopy Techniques

  • Light microscopy: uses lenses to magnify images of specimens. Magnification up to 1000x.
  • Fluorescence microscopy: uses fluorescent molecules that emit light at a different wavelength than the excitation light.
  • Immunofluorescence staining: allows for the localization of specific proteins in cells/tissue. This method uses a primary antibody that binds to the target protein and secondary antibody conjugated with a fluorescent dye to detect the protein of interest.
  • Fluorescence in situ hybridization (FISH): visualizes nucleic acids (genes/mRNA) in cells or tissue. It involves using fluorescently tagged DNA or RNA probes that hybridize to their complementary DNA sequences

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Description

Explore the intricate mechanisms of telomere maintenance in human cells. This quiz covers key concepts such as the role of telomeres, telomerase activity, and the implications of telomere shortening on cellular aging and cancer. Understand the differences in telomere biology between humans and mice.

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