Lab 3: Cell Cycle, Cancer, and Histology Notes

Lab 3, Part 1: The Cell Cycle

• Cell Cycle Overview

  • The cell cycle includes:
    • G1 phase (Growth)
    • S phase (Growth and DNA synthesis)
    • G2 phase (Growth and final preparations for M division)
    • M phase (Mitosis), which includes: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
  • Checkpoints:
    • G1 checkpoint (restriction point)
    • G2 checkpoint

• Chromosomes

  • Chromosomes are built by copying DNA.
  • The original chromatid is copied, and the copy is attached to the original at the centromere.
  • This structure is then called a chromosome.

• Chromatin vs. Chromosomes

  • Chromatin:
    • Duplicates itself and coils up into chromosomes.
  • Chromosomes.

• Chromosome Structure

  • DNA double helix (2-nm diameter)
  • Chromatin ("beads on a string") structure with nucleosomes.
    • Nucleosome (10-nm diameter): eight histone proteins wrapped by two winds of the DNA double helix.
    • Linker DNA.
  • Tight helical fiber (30-nm diameter).
  • Looped domain structure (300-nm diameter).
  • Chromatid (700-nm diameter).
  • Metaphase chromosome (at midpoint of cell division) consists of two sister chromatids.

• Chromosome Components

  • Telomere.
  • Homologous chromosomes.
  • Sister chromatids.
  • Short arm (P).
  • Centromere.
  • Long arm (Q).

• Sister Chromatids

  • During S Phase, two identical “sister” chromatids are formed and attached in the middle at the centromere.
  • When cells divide, “sister” chromatids separate, and one goes to each new cell.

• Definitions

  • Chromosome: A thread-like structure of nucleic acids and proteins found in the nucleus, carrying genetic information in the form of genes.
  • Chromatid: Each of the two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double-helix of DNA.
  • Chromatin: The material of which the chromosomes of organisms other than bacteria (e.g., eukaryotes) are composed, consisting of proteins, RNA, and DNA

• Cell Cycle Phases and Checkpoints

  • Interphase
    • S phase (DNA replication)
    • S phase entry commitment point.
  • M phase (segregation of cellular content)
    • Mitotic entry commitment point.
    • Mitotic exit commitment point.
  • Cell Cycle exit.
  • Cellular separation.
  • Decision window.
  • Centriole duplication.
  • Duplicated chromosomes.
  • Mitotic spindle.
  • Chromosome alignment.
  • Anaphase.
    • Chromatid separation.
  • Metaphase.
    • Separation window.
  • Prophase.

• Cancer and Cell Cycle Checkpoints

  • Cancer is a genetic disease.
  • G_2 checkpoint:
    • Pass if:
      • Chromosomes have replicated successfully.
      • DNA is undamaged.
      • Activated MPF is present.
  • Metaphase checkpoint:
    • Pass if:
      • All chromosomes are attached to the spindle apparatus.
  • G_1 checkpoint:
    • Pass if:
      • Cell size is adequate.
      • Nutrients are sufficient.
      • Social signals are present.
      • DNA is undamaged.
      • Mature cells do not pass this checkpoint (they enter G_0 state).
  • Mutations leading to cancer:
    • Mutation inactivates a DNA repair gene.
    • Mutation of a proto-oncogene creates an oncogene.
    • Mutation inactivates a tumor suppressor gene.
    • Mutation inactivates several more tumor suppressor genes.
    • Cells proliferate.

• Normal vs. Cancerous Cells

  • Normal Cells:
    • Many cells that continue to grow and divide.
  • Cancerous Cells:
    • Variations in size and shapes of cells.
    • Nucleus that is larger and darker than normal.
    • Abnormal number of chromosomes arranged in a disorganized fashion.
    • Cluster of cells without a boundary.

• Homeostasis and Tumor Formation

  • Normal:
    • Normal Cell Division.
    • Normal Apoptosis.
    • Increased Cell Division.
    • Normal Apoptosis.
  • Tumor:
    • Normal Cell Division.
    • DECREASED Apoptosis.
    • INCREASED Cell Division.
    • Normal Apoptosis.

• Cancer Development

  • An epithelial cell becomes partially transformed.
  • This cell multiplies, forming a mass of dysplastic cells.
  • These dysplastic cells grow rapidly, forming a localized cancerous tumor.
  • The cancer cells secrete chemicals that allow them access to other tissues, the lymphatic system, and the blood stream.

• Cell Cycle Checkpoints (Detailed)

  • G_1 phase:
    • Cell growth, preparation for DNA replication.
    • Early.
    • Late.
    • Restriction Point.
    • Stop Checkpoint: G_1/S DNA damage.
  • S phase:
    • DNA replication.
    • Synthesis phase.
  • G_2 phase:
    • Cell growth, preparation for mitosis.
    • Stop Checkpoint: G_2/M DNA damage.
  • M (Mitotic) phase:
    • Mitosis and cytokinesis.
    • Division into two identical daughter cells.
    • Stop Checkpoint: Spindle assembly.
  • G_0 phase:
    • Quiescence.
    • Entry to G_1: Mitogenic signals.
  • Eukaryotic cell cycle.

• Normal vs. Mutated Genes in Cancer

  • Normal tumor-suppressor gene:
    • Negative regulator of cell cycle.
    • Loss of function: reduction or loss of production.
    • Cell cycle under control.
    • Normal cells.
  • Mutated tumor-suppressor gene.
    • Abnormal cell cycle.
  • Normal proto-oncogene:
    • Positive regulator of cell cycle.
  • Mutated proto-oncogene = oncogene.
    • Gain of function: increase in production or a modified protein.
    • Cancer cells.

• Cancer Progression

  • A tumor grows from a single cancer cell.
  • Cancer cells invade neighboring tissue.
  • Cancer cells spread through lymph and blood vessels to other parts of the body.
  • A small percentage of cancer cells may metastasize to another part of the body.

• Prostate Cancer

  • Incidence rates per 100,000.
  • Primary cancer rates per 100,000 people.
  • Progression of prostate cancer.
  • Stage IVB Prostate Cancer
    • Prostate cancer spreads to other parts of the body.
    • Distant lymph nodes.
    • Bone.
  • RATE OF NEW PROSTATE CANCERS BY AGE GROUP UNITED STATES, 2019.

• Breast and Prostate Cancer Statistics

  • Breast Cancer
    • 1 in 8 women will be diagnosed with breast cancer.
    • 42,690 estimated deaths.
    • Increased since 2019.
    • $150 Million Yearly Research Funding From the U.S. Department of Defense.
  • Prostate Cancer
    • 1 in 9 men will be diagnosed with prostate cancer.
    • 33,330 estimated deaths.
    • Increased since 2019.
    • $110 Million Yearly Research Funding From the U.S. Department of Defense.

• Cancer by Stage (Breast and Prostate)

  • Among women in Canada, 2015: 1 in 4 new cancer cases, 14% of cancer-related deaths.
    • Early detection, 2011-2015: More than 80% of female breast cancer was detected at stages 1 and 2. Over 50% of these cases were diagnosed in women aged 60 to 79.
  • Among men in Canada, 2015: 1 in 5 new cancer cases, Less than 10% of cancer-related deaths.
    • Early detection, 2011-2015: 74% of prostate cancer cases were diagnosed at stages 1 and 2. Almost 78% of these cases were diagnosed in men aged 60 to 79.
  • Stages of cancer:
    • STAGE 1: Tumour is small and contained within the organ in which it started.
    • STAGE 2: Tumour is larger and may have begun to spread.
    • STAGE 3: Tumour is large and has spread into nearby tissues and lymph nodes.
    • STAGE 4: Cancer has spread through the blood or lymphatic system to distant sites in the body.

Lab 3, Part 2: Mitosis

• Mitosis Overview

  • Mitosis = Cell Division
  • ALL CELLS ARISE FROM OTHER CELLS…

• Interphase

  • Interphase: when a cell is between cell divisions. It consists of distinct phases: G1, S, G2
  • G_1 phase: Growth phase: the time when cells grow, increase protein synthesis, and reproduce organelles. They perform routine functions. Centrioles begin to replicate.
  • S phase: DNA replicates to provide identical copies of genetic material for the two new cells.
  • G_2 phase: proteins required for cell division are formed; Centriole replication is finished.

• Mitosis

  • Mitosis is the distribution of the two sets of chromosomes into two separate nuclei.
  • Results in two new cells with the same number and kind of chromosomes.
  • Mitosis is a continuous process, with one stage merging imperceptibly into the next stage.
  • Stages: prophase, metaphase, anaphase, telophase.

• Importance of Mitosis

  • It is an orderly process that ensures each new cell will receive the same number and kind of chromosomes as the original cell.

• Prophase

  • Chromosomes become visible. Chromatin condenses forming rod-like structures.
  • Chromosomes are composed of two sister chromatids.
  • Each sister chromatid is an identical DNA molecule (result of DNA replication).
  • The two chromatids are joined at the centromere.
  • The DNA coils tightly so that it can be more easily moved around inside the dividing cell.
  • The chromatids are connected at a spot called the centromere.
  • The nuclear membrane breaks down and is absorbed into the cytosol.
  • The nucleolus disappears.
  • Two chromatids are attached by a centromere. The centromere is important for moving the chromosome to the opposite pole of the cell.
  • Each centrosome with its centrioles moves to opposite “poles” of the cell and forms the mitotic spindle (composed of spindle fibers).
  • Microtubules called “asters” extend from the centrosomes.
  • Spindle fibers attach to the centromere.

• Metaphase

  • The centromeres line up at the “equator” of the cell (metaphase plate).
  • Spindle fibers are completely formed.

• Anaphase

  • Centromeres split. Each sister chromatid becomes a “daughter chromosome.”
  • Two sister chromatids move to opposite poles of the cell.
  • Shortest phase.

• Telophase

  • Chromosomes stop moving.
  • Chromosomes uncoil and resume the thread-like chromatin form.
  • The nucleolus re-appears.
  • The nuclear membrane re-appears.
  • Spindle fibers disappear.
  • Plasma membrane forming to divide the two cells.
  • Cytokinesis occurs. This is the division of the cytoplasm and organelles into two cells (It may begin at the end of anaphase).

• Cytokinesis

  • Is the division of cytoplasm and organelles into two “daughter” cells (It is a process, not a stage of mitosis).
  • It may begin in late anaphase or telophase.
  • A slight indentation of the plasma membrane becomes the “cleavage furrow” and gradually deepens until opposite surfaces make contact and the cell is split in two.
  • When cytokinesis is complete, Interphase begins.

• Cells Undergoing Mitosis

  • Cells that divide for growth or to replace dead or damaged cells. For example: skin cells, cells that line the digestive tract, cells that form blood cells.

• Cells That Do Not Undergo Mitosis

  • Neurons, adipose cells, skeletal muscle cells, mature red blood cells in the circulation.

• Meiosis

  • Process occurs in the formation of eggs and sperm.
  • Nuclear division that reduces the number of chromosomes by half.
  • Results in four cells, each with one set of chromosomes (23).

• Cells Undergoing Meiosis

  • Cells that form sperm and eggs (ova).

• When Does Meiosis Occur?

  • During the development of sperm.
  • During the development of ova- completed after ovulation.

Lab 3, Part 3: Histology

• Epithelial and Nervous Tissues

  • Stratified Squamous Epithelium.
  • Basement Membrane (Basal Layer).
  • Embryonic Layers.
  • Mature Layers.

• Cellular Differentiation

  • Cellular differentiation is a complex process that involves the coordinated regulation of genes by a multitude of cellular pathways including DNA binding proteins.
  • Differentiation results in the varied types of cells and tissues in multicellular organisms.

• Differentiation

  • Histone Protein.
  • Nucleus.
  • Genomic DNA.
  • Chromatin.
  • Regulation.
  • Blood Cell.
  • Muscle Cell.
  • Neuron.

• Tissues

  • Tissues are groups of cells that are similar in structure and perform a common or related function.
  • The study of tissues is called histology.
  • Histology is very important for the study of pathology since many diseases are first diagnosed at the tissue level.
  • Inner lining of the esophagus.

• Four Types of Tissue

  • Connective tissue.
  • Epithelial tissue.
  • Muscle tissue.
  • Nervous tissue.

• Epithelial Tissue Examples

  • Nasal passage: Pseudostratified ciliated columnar.
  • Kidney tubules: Simple cuboidal.
  • Esophagus lining: Stratified squamous.
  • Lungs: Simple squamous.
  • Urinary system: Transitional.
  • Intestines: Simple columnar.

• Epithelial Patterns

  • apical.
  • Can form a sheet in cross section.
  • basolateral.
  • Possibly with distinct apical and basal morphology.

• Characteristics of Epithelial Tissue

  • Closely Packed Cells
    • Cells fit close together, must be attached to another cell or basement membrane.
    • Cancer cells can survive without being attached to anything, thus can travel around the body.

• Polarity

  • One surface (apical side) is exposed to the exterior or a cavity of an internal organ (only true of coverings and linings, NOT glands).

• Supported by a Basement Membrane

  • Supported by connective tissue; the unexposed surface (basal side) rests on a basement membrane.

• Other Characteristics of Epithelial Tissue

  • Avascular (without blood vessels) only true of coverings and linings. Glands are supplied with blood vessels.
  • Innervated = supplied with nerves.
  • Regeneration = damaged cells can be replaced with new cells.

• Functions of Epithelial Tissue

  • Protection.
  • Coverings, linings.
  • Absorption into the blood.
  • Secretion.
  • Excretion of wastes.
  • Filtration.
  • Reproduction (egg, sperm production).

• Epithelial Patterns

  • Simple.
    • Simple Squamous.
    • Simple Cuboidal.
    • Simple Columnar.
  • Stratified.
    • Stratified squamous.
    • Stratified cuboidal.

• Single-Layers of Epithelia

  • lumen

• Simple Squamous Epithelium

  • Where passage of materials into and out of compartments is important.
  • Internal body coverings, linings.
  • Examples: capillary, air sacs in lungs.

• Stratified Squamous Epithelium

  • Protects tissue from abrasion
  • Examples: skin, esophagus, lining of mouth.

• Simple Cuboidal Epithelium

  • In places of secretion and absorption.
  • Tubules and ducts.
  • Example: kidney tubules, ducts of glands.

• Simple Columnar Epithelium

  • Absorption, secretion (especially secretion of mucus).
  • Example: cells lining the stomach and intestine; fallopian tube.

• Pseudostratified Columnar Epithelium

  • Some cells do not reach the free surface, all are attached to the basement membrane.
  • Function: secretion - usually mucus
  • Have cilia to move mucus.
  • Example: trachea.

• Examples of Epithelia

  • Simple squamous e.: Lung alveolar epithelium
  • Simple cuboidal e.: Kidney tubule epithelium
  • Simple columnar e.: Intestinal epithelium
  • Pseudostratified ciliated columnar e.: Tracheal epithelium
  • Stratified squamous e.: Esophageal epithelium, Epidermis epithelium
  • Transitional e.: Urinary bladder epithelium

• Nervous Tissue

  • Neuronas.
  • Célula microglial.
  • Astrocitos.
  • Oligodendrocito.
  • Vaina de mielina.

• Neurons

  • The structural unit (cell) of the nervous system specialized to generate and transmit electrical signals (impulses).

• Characteristics of Neurons

  • Highly specialized.
  • Respond to stimuli.
  • Conduct impulses.
  • Have a long life span (up to 100+ years).
  • Most do not divide.
  • High metabolic rate (require lots of oxygen and glucose).
  • Vary in shape but all have a cell body and one or more thin processes.

• Neuron Microscopic Anatomy

  • axon.
  • axon hillock.
  • glia.
  • nucleus.
  • nucleolus.
  • dendrite.

• Brain Histology

  • Axons and dendrites.
  • Glia.
  • Neurons.
  • Capillary.

• Nervous Tissue

  • neuron.
  • glia.
  • Neurons are dark because they were stained.
  • Glia are still invisible (except for their nucleus) because they did not take up the neuron-specific stain.