Unit 2 Cells

Cell Structure Plasma membrane Cytoplasm: cytosol + organelles Nucleus

Cell Membrane Phospholipid bilayer Cholesterol Proteins (integral and peripheral) Attached carbohydrates (glycolipids and glycoproteins)

Membrane Function Barrier between inside and outside of cell Controls entry of materials: transport Receives chemical and mechanical signals Transmits signals between intra- and extra- cellular spaces

Intercellular Junctions – Connect adjacent cell membranes Tight junctions Close space between cells Located among cells that form linings Prevent movement of substances between cells Desmosomes Form “spot welds” between cells Located among outer skin cells Structural reinforcement Gap junctions Tubular channels between cells Located in cardiac muscle cells Allow ions to pass from cell to cell for communication 3-6

Cell Adhesion Molecules Guide cellular movement Selectin – allows white blood cells to “anchor” Integrin – guides white blood cells through capillary walls Important for growth of embryonic tissue Important for growth of nerve cells 3-7

Terminology: Body Fluid Pools Intracellular (ICF) Within cells: 2/3 of total Extracellular (ECF): Between cells = Interstitial In blood vessels = Plasma In lymphatic vessels = Lymph

Terminology: Solutions Solvent: Liquid doing the dissolving Usually water Solute: Dissolved material (particles or gas) Concentration: Amount of solute in a given amount of solvent Concentration gradient: Difference in concentration between 2 areas of solution

Principle of Diffusion Copyright 2010, John Wiley & Sons, Inc.

Passive Transport: Simple Diffusion Requirements: Concentration gradient Pathways: Across lipid bilayer Lipid-soluble (O2, CO2, N2, fatty acids, steroids, fat-soluble vitamins), or if Polar molecules (H2O, urea) Pass through Ion Channels (which may be gated: gates open and close) if Ions such as K+, Ca2+, Cl–

Copyright 2010, John Wiley & Sons, Inc. Simple Diffusion Copyright 2010, John Wiley & Sons, Inc.

Facilitated Diffusion Requires a carrier in membrane but not ATP Solute goes DOWN concentration gradient Maximum transport speed depends on number of carriers Ex: Insulin increases number of carriers for glucose in plasma membrane Copyright 2010, John Wiley & Sons, Inc.

Facilitated Diffusion Copyright 2010, John Wiley & Sons, Inc.

Facilitated Diffusion Copyright 2010, John Wiley & Sons, Inc.

Osmosis Diffusion of water across selectively permeable membrane: Permeable to solvent Impermeable to solute Types of solutions surrounding human RBCs Isotonic: solution outside RBC has same concentration of solute as RBC: 0.9% NaCl Hypotonic: solution outside of RBC has lower concentration: 0% NaCl  Hemolysis Hypertonic: solution outside of RBC has higher concentration: 4% NaCl  Crenation

Copyright 2010, John Wiley & Sons, Inc. Osmosis Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Active Transport Requires a carrier (called a pump) Requires energy (ATP) Can transport UP a concentration gradient Critical for moving important ions Major active transport in most cells is sodium-potassium (Na+/K+) pump Copyright 2010, John Wiley & Sons, Inc.

Active Transport Example: Sodium-potassium pump 1 2 3 4 3 Na+ expelled ADP P 2 K+ imported K+ gradient Na+ Na+/K+ ATPase Extracellular fluid Cytosol 2K+ ATP 2 3 4 Active Transport Example: Sodium-potassium pump Copyright 2010, John Wiley & Sons, Inc. Copyright 2009 John Wiley & Sons, Inc. 18 18

Transport in Vesicles Requires energy (ATP) Involves small membrane sac Endocytosis: Importing of materials into cell Phagocytosis: Ingestion of Particles such as bacteria into white blood cells (WBCs) Pinocytosis: Ingestion of Fluids Exocytosis: Exporting materials

Copyright 2010, John Wiley & Sons, Inc. Transcytosis Endocytosis followed by Exocytosis Transports a substance rapidly through a cell EX: HIV crossing a cell layer Copyright 2010, John Wiley & Sons, Inc. 3-24

Cell Organelles: Cytoskeleton Flagella, cilia & centrioles Endoplasmic reticulum Golgi apparatus Mitochondrion Nucleus, nucleolus, nuclear envelope Vesicles, e.g. lysosome

Cytoskeleton Maintains shape of cell Positions organelles Changes cell shape Includes: microfilments, intermediate filaments, microtubules

Centrosome Structure: Two centrioles arranged perpendicular to each other Function: moves chromosomes to ends of cell during cell division

Cilia and Flagella Specialized for motion Flagellum: single tail like structure on sperm Propels sperm forward in reproductive tract Cilia: in groups Found in respiratory system: move mucus

Ribosomes Made within the nucleus (in nucleolus) Sites of protein synthesis (on E.R. or freely within cytoplasm) Consist of ribosomal RNA (rRNA) + proteins

Endoplasmic Reticulum (E.R.) Structure: network of folded membranes Functions: synthesis, intracellular transport Types of E.R. Rough E.R.: studded with ribosomes (sites of protein synthesis) Smooth E.R. lacks ribosomes. Functions: lipid synthesis release of glucose in liver cells into bloodstream drug detoxification (especially in liver cells) storage and release of Ca2+ in muscle cells (where smooth E.R. is known as sarcoplasmic reticulum or SR)

Golgi Complex Structure: Functions: Flattened membranes (cisterns) with bulging edges (like stacks of pita bread) Functions: Modify proteins  glycoproteins and lipoproteins that: Become parts of plasma membranes Are stored in lysosomes, or Are exported by exocytosis

Small Bodies Lysosomes: contain digestive enzymes Help in final processes of digestion within cells Carry out autophagy (destruction of worn out parts of cell) and death of old cells (autolysis) Tay-Sachs: hereditary disorder; one missing lysosomal enzyme leads to nerve destruction Peroxisomes: detoxify; abundant in liver Proteasomes: digest unneeded or faulty proteins Faulty proteins accumulate in brain cells in persons with Parkinson or Alzheimer disease.

Mitochondria Structure: Function: Sausage-shaped with many folded membranes (cristae) and liquid matrix containing enzymes Have some DNA, ribosomes (can make proteins) Function: Nutrient energy is released and trapped in ATP; so known as “power houses of cell” Chemical reactions require oxygen Abundant in muscle, liver, and kidney cells These cells require much ATP

Nucleus Round or oval structure surrounded by nuclear envelope with nuclear pores Contains nucleolus: makes ribosomes that pass into cytoplasm through nuclear pores Store genetic material (DNA) in genes arranged in 46 chromosomes (the human genome containing 30,000 genes!) DNA contains information for directing protein synthesis:

Protein Synthesis 2 steps: Nuclear = transcription Cytoplasmic = translation

Transcription In nucleus RNA polymerase (enzyme) transcribes DNA into RNA; complementary base pairs C-G, G-C, T-A, A-U Types of RNA formed: 1. Messenger RNA (mRNA) 2. Ribosomal RNA 3. Transfer RNA (tRNA)

Anatomy of a Chromosome X Telomere Telomere Centromere Telomere Telomere Chromatid Chromatid Chromosome

Somatic Cell Division In all body cells except gametes Interphase Period of growth and development of cell Preparation for reproduction: DNA synthesis Mitotic Phase = division of nucleus karyokinesis 4 phases Cytokinesis = division of cytoplasm Apoptosis – orderly programmed cell “death”

Prophase Chromatin condenses into chromatids connected at centromeres Centrosomes form the mitotic spindle (composed of microtubules) Some chemotherapy drugs fight cancer cells by inhibiting formation of the mitotic spindle Nuclear envelope and nucleolus break down

Metaphase Centromeres are aligned at the center (“equator”) of the metaphase plate

Anaphase Centromeres split, separating “sister chromatids” (chromosomes) Chromosomes are pulled to opposite ends Cytokinesis (division of cytoplasm) begins by the formation of a cleavage furrow

Telophase Chromosomes revert to threadlike chromatin Nuclear envelope and nucleolus reappear Mitotic spindle breaks up Cytokinesis is completed

Cellular Diversity Because structure determines function, cells differ in structure related to their functions. Nerve cells may reach several feet in length to carry nerve impulses from spinal cord to toe Microvilli increase surface area of intestinal cells to maximize absorptive ability Most cells are microscopic; the diameter of the largest human cell (an oocyte) can barely be seen with the unaided eye.

Aging A number of factors contribute to aging: Decreased rate of mitosis; nerve cells and skeletal muscle cells cannot be replaced Telomeres (DNA at tips of chromosomes) Telomeres shorten with aging Progeria (rapid aging): profound telomere shortening Free radicals damage. (See Focus on Wellness: action of antioxidants to reduce effects of free radicals.)

Abnormal Cell Division (cancer) Neoplasm -tumor Oncology – study of tumors – Oncologist Carcinogen – cancer causing agent

Tumors benign – usually remains localized Two types of tumors benign – usually remains localized malignant – invasive and can metastasize through the bloodstream or lymph system; cancerous Genes that cause cancer oncogenes – activate other genes that increase cell division tumor suppressor gene – normally regulate mitosis; if inactivated they will not regulate mitosis 3-31

Stem and Progenitor Cells Stem cell can divide by mitosis to form two new stem cells can divide to form a stem cell and a progenitor cell totipotent – can give rise to any cell type Differentiation – process of specializing cell types due to gene activation Progenitor cell committed cell (i.e. epithelial, connective, muscle, nervous) pluripotent – can give rise to a restricted number of cell types 3-32

What are Stem Cells? http://ed.ted.com/lessons/what-are-stem-cells-craig-a-kohn