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3 Cell Structure and Function Studying Cells Cells- building blocks of the human body Cell Theory: Four Basic Concepts • Basic building blocks of all animals and plants • Smallest functional units of life • Products of cell division • Basic homeostatic units Studying Cells The Diversity of Cells in the Human Body Studying Cells CytologyStudy of structure and function of cells Cytology depends on seeing cells • Light microscopy (LM) • Electron Microscopy (EM) • Scanning EM (SEM) • Transmission EM (TEM) Studying Cells Overview of Cell Anatomy: • Extracellular Fluid • Watery medium surrounding a cell • Interstitial Fluid • Fluid found between cells in a tissue • Cell Membrane • Phospho-Lipid barrier between the inside(cytoplasm) and outside (extracellular) environment • Cytoplasm (intracellular fluid) • • • • All contents within the cell membrane Cytosol + Organelles Cytosol- liquid portion of cytoplasm Organelles- intracellular structures Anatomy of a Cell Cell Parts & Functions Cell Parts & Functions The Cell Membrane Functions of the plasma membrane: • Physical Isolation- provides a physical barrier between the intracellular and extracellular environment • Regulation of Exchange with the Environment- the cell membrane controls movement of ions, nutrients, & waste into and out of the cell • Sensitivity- the cell membrane contains receptors to changes in the external environment • Structural Support- gives tissues a stable structure due to connection between cell membranes The Cell Membrane The Cell Membrane Membrane Structure: • Phospholipid Bilayer- 2 layer membrane made of phospholipids • Phospholipid- a Phosphate “head” with 2 Fatty Acid “tails” Movement Through The Cell Membrane • Non-polar substances can easily pass through the lipid bilayer • Ex: O2 & CO2 • Polar substances do not pass through the lipid bilayer • Ex: ions(Na+, K+) and water soluble compounds Functions of Membrane Proteins • • • • • • Receptors Channels Carriers Enzymes Anchors Identifiers - Some membrane proteins are in fixed positions and others are free to move around within the membrane Membrane Proteins Membrane Carbohydrates Membrane carbohydrates form complex molecules with proteins and lipids on the outer surface of the membrane\ Ex: glycolipids and glycoproteins Functions: cell lubricants, adhesives, receptors, cell identifiers(antigens) Membrane Transport Selectively permeable membrane: -the cell membrane only allows certain molecules to pass through • Permeability factors: • Molecular size • Electrical charge • Molecular shape • Lipid solubility Membrane Transport Definitions Diffusion- net movement of molecules from high to low concentration - Random movement down a concentration gradient (from higher to lower concentration) Membrane Transport Processes • Passive Transport- movement of ions or molecules with out expending cellular energy(ATP) • Diffusion • Filtration • Osmosis • Carrier-Mediated Transport- these processes use carrier proteins and channels to move substances across the cell membrane • Facilitated Transport • Active Transport(* requires energy (ATP)) Diffusion Across Cell Membranes Membrane Transport Definitions • Osmosis- diffusion of water across the cell membrane - water tends to flow to areas of higher solute concentration (low H2O concentration) Solute- substance dissolved in water - The cell membrane is freely permeable to water but not to solutes Osmosis The Cell Membrane Key Note: Things tend to even out, unless something—like a cell membrane— prevents this from happening. Across a freely permeable or water permeable membrane, diffusion and osmosis will quickly eliminate concentration gradients. Osmotic Effects of Solutions on Cells Osmotic Pressure- force of water movement into and out of a cell • Isotonic Solution- does not cause movement of water into or out of a cell • Cells maintain normal size and shape • Hypertonic Solution- cells loose water because the solution has a high concentration of solute • Cells lose water osmotically and shrink and shrivel • Hypotonic Solution- water flows into cells because the solution has a low concentration of solutes • Cells gain water osmotically and swell and may burst Osmotic Flow Across Cell Membrane Other Passive Membrane Transport Filtration • Hydrostatic pressure pushes on water • Water crosses membrane • Solute follows water • Ex: kidneys- urine, liver- blood Carrier-Mediated Transport - Carrier Mediated Transport: uses membrane proteins as carriers • Facilitated diffusion (no ATP required) Active Transport Active transport (ATP consumed) • Independent of concentration gradients • Ion pumps (e.g., Na+ / K+ exchange) Vesicular Transport • Membrane vesicles transport LARGE molecules into and out of the cell membrane • Transport in both directions: • Endocytosis • Movement into cell • Receptor-mediated • Pinocytosis • Phagocytosis • Exocytosis • Movement out of cell Ligands EXTRACELLULAR Ligands binding FLUID to receptors Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Endocytosis Exocytosis Ligand receptors Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. CYTOPLASM Coated vesicle Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. Lysosome Ligands removed Fused vesicle and lysosome The membrane containing the receptor molecules separates from the lysosome. The vesicle returns to the surface. Phagocytosis Cell membrane of phagocytic cell Lysosomes A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Vesicle Lysosomes fuse with the vesicle. Foreign object Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID This fusion activates digestive enzymes. CYTOPLASM Undissolved residue The enzymes break down the structure of the phagocytized material. Residue is then ejected from the cell by exocytosis. The Cytoplasm Cytoplasm All the “stuff” inside a cell, not including the cell membrane and nucleus. The “stuff”: • The cytosol • The organelles The Cytoplasm The Cytosol Contains: • Intracellular fluid • Dissolved nutrients and metabolites • Ions(Na+, K+, Ca2+, etc…) • Soluble proteins • Structural proteins The Cytoplasm Intracellular-Extracellular Differences Substance Inside Outside K+ High Low Na+ Low High Enzymes High Low The Cytoskeleton • The cytoskeleton is an internal protein framework of threadlike filaments & hollow tubes • Provides cytoplasmic strength and form • Main components • Microfilaments (actin) • Intermediate filaments (varied materials) • Microtubules (tubulin) The Cytoskeleton Non-membranous Organelles • Centrioles—Direct chromosomes in mitosis • Microvilli—Surface projections increase external surface area for absorption • Ex: found in intestinal cells to absorb nutrients • Cilia—Move fluids across cell surface • Ex: found in esophageal cells to move mucus • Flagella—Moves cell through fluid • Ex: tail on sperm makes it mobile • Ribosomes—Make new proteins • Free Ribosomes- found throughout the cytosol • Attached Ribosomes- attached to rough E.R. • Proteasomes—Digest and recycle damaged proteins • Contain enzymes called proteases Membranous Organelles • Endoplasmic Reticulum(ER)—Network of tubular intracellular membranes located just outside the nuclear membrane • Rough ER (RER) • Contains ribosomes • Supports protein synthesis • Smooth ER (SER) • Lacks ribosomes • Synthesizes proteins, carbohydrates The Endoplasmic Reticulum Golgi Apparatus -The Golgi receives new proteins from the Rough ER Major Functions: 1) modify & package hormones and enzymes 2) repair of the cell membrane 3) packaging of enzymes for use in the cytosol Endoplasmic reticulum EXTRACELLULAR CYTOSOL FLUID Lysosomes Cell membrane Secretory vesicles Transport vesicle Golgi apparatus (a) Membrane renewal vesicles (b) Exocytosis Vesicle Incorporation in cell membrane Lysosomes • Packets of digestive enzymes • Defense against bacteria • Cleaner of cell debris • Hazard for autolysis • “Suicide packets” Peroxisomes- similar to lysosomes but smaller - carry different enzymes - absorb and break down fatty-acids and other organic substances The Cytoplasm Key Note: Cells respond directly to their environment and help maintain homeostasis at the cellular level. They can also change their internal structure and physiological functions over time. Mitochondria - The mitochondria provides energy for the cell • 95% of cellular ATP supply comes from the mitochondria • Double membrane structure • Cells requiring more energy(i.e. muscle cells) contain larger #’s of mitochondria Mitochondria Mitochondria Key Note: Mitochondria provide most of the energy needed to keep your cells (and you) alive. They consume oxygen and organic substrates, and they generate carbon dioxide and ATP. The Nucleus Properties of the Nucleus: • Largest structure in an animal cell • Controls cellular operations • Determines cellular structure • Directs cellular function • Nuclear envelope- surrounds nucleus and separates the nucleus from the cytoplasm • Nuclear pores- enables nucleuscytoplasm exchange • Ex: ions & RNA can pass out of nucleus The Nucleus Chromosome Structure The Nucleus Key Note: The nucleus contains DNA, the genetic instructions within chromosomes. The instructions tell how to synthesize the proteins that determine cell structure and function. Chromosomes also contain various proteins that control expression of the genetic information. The Cell Life Cycle Cell division—The reproduction of cells Apoptosis—Genetically programmed death of cells Mitosis—The nuclear division of somatic cells Meiosis—The nuclear division of sex cells The Cell Life Cycle • Highly Variable •Interphase duration •Mitotic frequency Stages of The Cell Cycle G1(gap 1)- normal cell functions & cell growth, duplication of organelles, protein synthesis S(synthesis)- DNA replication G2(gap 2)- protein synthesis M(mitosis)- cell division Apoptosis- cell death Cell Division Mitosis- A process that separates and encloses the duplicated chromosomes of the original cell into two identical nuclei • Four phases in mitosis • • • • Prophase Metaphase Anaphase Telophase Cytokinesis Division of the cytoplasm to form two identical daughter cells The Cell Life Cycle Mitotic Phases: • Prophase • Chromosomes condense • Chromatids connect at centromeres • Metaphase • Chromatid pairs align at metaphase plate • Anaphase • Daughter chromosomes separate • Telophase • Nuclear envelopes reform Interphase Nucleus Early prophase Mitosis begins Spindle fibers Centrioles (two pairs) Metaphase Late prophase Centromeres Anaphase Chromosome with two sister chromatids Telophase Separation Daughter chromosomes Cytokinesis Metaphase plate Cleavage furrow Daughter cells The Cell Life Cycle Key Note: Mitosis is the separation of duplicated chromosomes into two identical sets and nuclei in the process of somatic cell division. The Cell Life Cycle Cell Division and Cancer • Abnormal cell growth • Tumors (also called, neoplasm) • Benign • Encapsulated • Malignant • Invasion • Metastasis • Cancer—Disease that results from a malignant tumor Cell Diversity and Differentiation Somatic Cells • All have same genes • Some genes inactivate during development • Cells thus become functionally specialized • Specialized cells form distinct tissues • Tissue cells become differentiated Cancer Key Note: Cancer results from mutations that disrupt the control mechanism that regulates cell growth and division. Cancers most often begin where cells are dividing rapidly, because the more chromosomes are copied, the greater the chances of error. Guess What? END OF CHAPTER 3 NOTES!!!
