Cell

• Cell is a fundamental component of life containing different organelles
• Nucleus


  Prominent organelle of the cell, nerve center or control center of cell
• Nucleus


  • Surrounded by a layer of nuclear envelope
  • Contains nuclear pores that allow movement of biochemicals
  • Contains nuclear lamina that provides mechanical support and holds nuclear pores in place
  • Contains nucleolus that produces ribosomes
  • Contains chromosomes, RNA and nucleoplasm

  
• Secretion: Making Milk


  1. Genes that encode milk proteins and certain enzymes are transcribed into mRNA

  2. mRNA exits through nuclear pores

  3. mRNA moves to surface of rough ER, where proteins are synthesized on ribosomes using amino acids in the cytoplasm

  4. Lipids are synthesized in the smooth ER

  5. Sugars are synthesized and proteins folded in the Golgi apparatus, then both are released in vesicles that bud off of the Golgi apparatus

  6. Protein- and sugar-laden vesicles move to the plasma membrane for release. Fat droplets pick up a layer of lipid from the plasma membrane as they exit the cell
• Endoplasmic Reticulum (ER)


  • Interconnected membranous tubules & sacs that wind from the nuclear envelope to the plasma membrane
  • Rough ER contains ribosomes and is involved in protein synthesis
  • Smooth ER does not contain ribosomes and is important in lipid synthesis
  • Proteins exit the ER in membrane-bounded, saclike organelles called vesicles
• Golgi Apparatus


  • Stack of interconnected flat, membrane-enclosed sacs that process and add sugars forming glycoproteins and glycolipids
  • Products are released into vesicles that bud off to the plasma membrane
• Peroxisomes


  • Sacs with outer membranes studded with several types of enzymes that break down lipids, rare biochemicals, synthesize bile acids, and detoxify compounds from exposure to oxygen free radicals
  • Abundant in liver and kidney cells
• Lysosomes


  • Membrane-bound sacs containing 43 types of digestive enzymes that dismantle bacterial remnants, worn-out organelles, and excess cholesterol
  • Engages in autophagy
• Mitochondria


  • Surrounded by two membranes that provide energy by breaking chemical bonds that hold together nutrient molecules in food
  • Freed energy is stored in adenosine triphosphate (ATP)
• Biological Membrane


  • Proteins aboard lipids contribute to cell's identity, transport molecules, and keep out toxins and pathogens
  • Some membrane proteins form channels for ions
• Plasma Membrane—Cell-to-Cell Communication


  • Molecules that extend from the plasma membrane are receptors
  • Signal transduction: Molecules form pathways that detect signals from outside the cell and transmit them inward
  • Cellular adhesion: Plasma membrane helps cells attach to certain other cells
• Structures and Functions of Organelles

  • Nucleus
  • Endoplasmic Reticulum (ER)
  • Golgi Apparatus
  • Peroxisomes
  • Lysosomes
  • Mitochondria
  • Biological Membrane
  • Plasma Membrane—Cell-to-Cell Communication

  
• Receptors


  Molecules that extend from the plasma membrane
• Signal transduction


  Molecules form pathways that detect signals from outside the cell and transmit them inward
• Cellular adhesion


  Plasma membrane helps cells attach to certain other cells
• Cytoskeleton


  • Meshwork of protein rods and tubules
  • Includes three major types of proteins: microtubules, microfilaments, and intermediate filaments
• Cilia


  Built of microtubules
• Cell division


  • Results in genetically identical daughter cells
  • Cells duplicate their genetic material
• Apoptosis


  Precise and genetically programmed cell death
• Cell cycle


  • Mitosis
  • Meiosis
• Interphase


  • Microscopically quiet
  • Active protein synthesis
  • Chromosomes not visible
  • Consists of G1, G2 and S phases
• G1 phase


  Protein synthesis, lipids and carbohydrates
• S phase


  Replication of chromosomes
• G2 phase


  DNA replication and mitosis
• Mitosis


  Walther Flemming described the motion of "threads" moving in an actively dividing cell
• Cell cycle checkpoints


  • Ensure critical events in DNA replication and chromosome segregation
  • Respond to damage by arresting cell cycle
• Telomeres


  • Lose 50-200 endmost bases after each cell division
  • After 50 divisions, shortened telomeres signal the cell to stop dividing
  • Sperm, eggs, bone marrow, and cancer cells produce telomerase that prevent shortening of telomeres
• Failure of cell cycle checkpoints


  Can lead to mutations and genomic instability, resulting in cancer and birth defects
• Birth defects


  • Most develop during the embryonic period and are more severe than those that arise during the fetal period
  • Some can be attributed to an abnormal gene
• Teratogens


  • Chemical or other agents that cause birth defects
  • Cause of birth defects depend on a woman's genes
  • Examples: thalidomide, cigarettes, alcohol, nutrients, occupational hazards, viral infections
• Chromosome


  • Primarily consists of DNA and protein
  • Distinguished by size and shape

  
• Essential parts of a chromosome

  • Telomeres
  • Origins of replication sites
  • Centromere

  
• Chromosome


  • Telomeres
  • Centromere
  • Sister chromatids
  • Heterochromatin
  • Euchromatin
  • Short arm (p)
  • Long arm (q)

  
• Karyotype


  • Chromosome chart
  • Confirm a clinical diagnosis
  • Reveal effects of environmental toxins
  • Clarify evolutionary relationships

  
• Nomenclature


  • International System for Human Cytogenetic Nomenclature
  • Autosomes numbered 1-22 in descending order of length
  • Identification based on size, centromere position, and other morphological features
• Chromosome morphology


  • Metacentric
  • Submetacentric
  • Acrocentric
  • Telocentric

  
• Visualizing chromosomes


  1. Obtain tissue from person

  2. Fetal tissue (amniocentesis, chorionic villi sampling, fetal cell sorting)

  3. Adult tissue (white blood cells, cheek swab)

  4. Chromosome microarray analysis

  
• Tissue sources for visualizing chromosomes

  • Fetal tissue
  • Adult tissue

  
• Amniocentesis


  • Fetal cells suspended in fluid around fetus are sampled
  • Detects about 1000 of over 5000 known chromosomal and biochemical problems
• Chorionic villus sampling


  • Cells of the chorion are sampled
  • Performed during 10-12th week of pregnancy
  • Provides earlier results than amniocentesis
  • Does not detect metabolic problems
  • Has greater risk of spontaneous abortion