Cell Biology PDF

Module 1 Introduction to the cell Introduction A cell is the basic, living, structural, and functional unit of the body. Parts of a Cell A generalized view of the cell is a composite of many different cells in the body No single cell includes all of the features seen in the...

Module 1 Introduction to the cell Introduction A cell is the basic, living, structural, and functional unit of the body. Parts of a Cell A generalized view of the cell is a composite of many different cells in the body No single cell includes all of the features seen in the generalized cell. Parts of a Cell The cell can be divided into three principal parts for ease of study. Plasma (cell) membrane Cytoplasm ○ Cytosol ○ Organelles (except for the nucleus) Nucleus The Lipid Bilayer Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids Hydrophobic Tail Hydrophilic Head  Fluid Mosaic Model Membrane is a mosaic of ○ Phospholipids ○ Glycolipids ○ Sterols (Cholesterol) ○ Proteins Most phospholipids and some proteins can drift through membrane The Plasma Membrane Membrane Permeability Plasma membranes are selectively permeable. ○ Some things can pass through and others cannot. The lipid bilayer portion of the membrane is permeable to small, nonpolar, uncharged molecules but impermeable to ions and charged or polar molecules. The membrane is also permeable to water. Membrane Permeability Plasma membranes are selectively permeable. ○ Some things can pass through and others cannot. Substance Permeable? Small non-polar, uncharged molecules (ie, steroids) Polar molecules (ie, glucose) Ions (ie, Na+) Water Membrane Permeability Transmembrane proteins that act as channels or transporters increase the permeability of the membrane to molecules that cannot cross the lipid bilayer. Macromolecules are unable to pass through the plasma membrane except by vesicular transport. Gradients Across the Plasma Membrane A concentration gradient is the difference in the concentration of a chemical between one side of the plasma membrane and the other. Oxygen and sodium ions are more concentrated outside the cell membrane with carbon dioxide and potassium ions more concentrated inside the cell membrane. Gradients Across Membrane Concentration gradient Electrical gradient Transport Across the Plasma Membrane Cells require mechanisms to transport molecules into and out of the cell Some molecules can cross the lipid bilayer, others need to go through channels These processes are either active or passive Passive and Active Transport Three types of passive processes are ○ diffusion through the lipid bilayer ○ diffusion through ion channels ○ facilitated diffusion Active transport requires cellular energy. Materials can also enter or leave the cell through vesicle transport. Transport Proteins Principles of Diffusion Diffusion is the random mixing of particles that occurs in a solution as a result of the kinetic energy of the particles. This process is always passive. Diffusion rate across plasma membranes is influenced by several factors: ○ Steepness of the concentration gradient ○ Temperature ○ Size or mass of the diffusing substance ○ Surface area ○ Diffusion distance Principles of Diffusion Steepness of the concentration gradient ○ The greater the difference between the inside and the outside of the cell, the faster the rate of diffusion Principles of Diffusion Temperature ○ Diffusion occurs more rapidly in warmer environments Size or mass of the diffusing substance ○ Larger, more massive molecule diffuse more slowly Principles of Diffusion Surface area ○ The membrane surface area available for diffusion will influence its rate. More surface area results in faster diffusion. Diffusion distance ○ The farther a molecule has to diffuse, the longer it takes. Diffusion in lungs occurs because the lungs place the blood very close to the air you breath.  Diffusion Crystal of dye placed in a cylinder of water Net diffusion from the higher dye concentration to the region of lower dye Equilibrium has been reached in the far right cylinder  Diffusion Through the Lipid Bilayer Nonpolar, hydrophobic molecules such as respiratory gases, some lipids, small alcohols, and ammonia can diffuse across the lipid bilayer. It is important for gas exchange in the lungs and at tissues Diffusion Through Membrane Channels Most membrane channels are ion channels, allowing passage of small, inorganic ions which are hydrophilic. Ion channels are selective and specific and may be gated or open all the time. Gated channels may randomly open and closed or regulated by electrical of chemical changes inside or outside of the cell Osmosis (diffusion of water) Diffusion of water molecules across a selectively permeable membrane Direction of net flow is determined by water concentration gradient Side with the most solute molecules has the lowest water concentration Osmosis  Osmotic Pressure Osmotic pressure of a solution is proportional to the concentration of the solute particles that cannot cross the membrane. Tonicity Tonicity is a measure of a solution’s ability to change the volume of cells by altering their water concentration. In an isotonic solution, red blood cells maintain their normal shape. In a hypotonic solution, red blood cells undergo hemolysis. In a hypertonic solution, red blood cells undergo cremation. Tonicity Filtration Filtration is the passage a solvent and dissolved substances through a membrane or a filter Carrier transport Substances that cannot diffuse freely across the plasma membrane may be carried across by a transport protein Solutes that move across membranes via a transporter include glucose, urea, fructose, galactose, and ions (Na+, K+ etc) Facilitated Diffusion of Glucose Transport in Vesicles A vesicle is a small membranous sac formed by budding off from an existing membrane. ○ endocytosis ○ exocytosis Endocytosis In endocytosis, materials move into a cell in a vesicle formed from the plasma membrane. Exocytosis In exocytosis, membrane-enclosed structures called secretory vesicles that form inside the cell fuse with the plasma membrane and release their contents into the extracellular fluid.  Exocytosis vs Endocytosis Exocytosis Endocytosis  Cytoplasm Cytosol, the intracellular fluid, is the semifluid portion of cytoplasm that contains inclusions and dissolved solutes. Cytosol Cytosol is the fluid inside the cell It is composed mostly of water, plus proteins, carbohydrates, lipids, and inorganic substances. Functionally, cytosol is the medium in which many metabolic reactions occur. Organelles Organelles are specialized structures that have characteristic shapes and perform specific functions in cellular growth, maintenance, and reproduction. You will be required to know the structure and function of various organelles in a cell  Cytoskeleton Network of protein filaments throughout the cytosol Functions ○ cell support and shape ○ organization of chemical reactions ○ cell & organelle movement Continually reorganized  The Cytoskeleton The cytoskeleton is a network of several kinds of protein filaments that extend throughout the cytoplasm and provides a structural framework for the cell. It consists of microfilaments, intermediate filaments, and microtubules.  Microfilaments Most microfilaments are composed of actin and function in movement and mechanical support. Intermediate Filaments Intermediate filaments are composed of several different proteins and function in support and to help anchor organelles such as the nucleus. Microtubules Microtubules are composed of a protein called tubulin and help determine cell shape and function in the intracellular transport of organelles and the migration of chromosome during cell division.  Centrosomes Centrosomes are dense areas of cytoplasm containing the centrioles, which are paired cylinders arranged at right angles to one another, and serve as centers for organizing microtubules in interphase, and the mitotic spindle during cell division.  Actin and Tubulin Fluorescence Stain of Various Cells Tubulin stained yellow Tubulin stained green Actin stained red DNA stained yellow Actin stained green DNA stained blue Ribosomes Ribosomes are tiny spheres consisting of ribosomal RNA and several ribosomal proteins; they occur free (singly or in clusters) or together with endoplasmic reticulum. Functionally, ribosomes are the sites of protein synthesis. We will look closely at their function in the lecture on protein synthesis. Endoplasmic Reticulum The endoplasmic reticulum (ER) is a network of membranes that form flattened sacs or tubules called cisternae.  Endoplasmic Reticulum Rough ER is continuous with the nuclear membrane and has its outer surface studded with ribosomes. Smooth ER extends from the rough ER to form a network of membrane tubules but does not contain ribosomes on its membrane surface. The ER transports substances, stores newly synthesized molecules, synthesizes and packages molecules, detoxifies chemicals, and releases calcium ions involved in muscle contraction.  Golgi Apparatus The Golgi apparatus consists of three to twenty stacked, flattened membranous sacs (cisterns) referred to as cis, medial, and trans.  Golgi apparatus The principal function of the Golgi complex is to process, sort, and deliver proteins and lipids to the plasma membrane, lysosomes, and secretory vesicles.  Lysosomes Membrane-enclosed vesicles that contain powerful digestive enzymes. Functions ○ digest foreign substances ○ autophagy recycles own organelles ○ autolysis lysosomal damage after death Peroxisomes Peroxisomes are similar in structure to lysosomes, but are smaller. They contain enzymes (e.g., catalase) that use molecular oxygen to oxidize various organic substances. ○ part of normal metabolic breakdown of amino acids and fatty acids ○ oxidizes toxic substances such as alcohol and formaldehyde ○ contains catalase which decomposes H2O2  Mitochondria The mitochondrion is bound by a double membrane. The outer membrane is smooth with the inner membrane arranged in folds called cristae. ○ surface area for chemical reactions of cellular respiration ○ central cavity known as matrix Mitochondria Mitochondria are the site of ATP production in the cell by the catabolism of nutrient molecules. ATP is used to power many chemical reactions that require energy Mitochondria generate ATP and thus generate usable energy for the cell  The Nucleus Most body cells have a single nucleus; some (red blood cells) have none, whereas others (skeletal muscle fibers) have several. The parts of the nucleus include the nuclear membrane which is perforated by channels called nuclear pores, nucleoli, and genetic material (DNA), Within the nucleus are the cell’s hereditary units, called genes, which are arranged in single file along chromosomes. Function of the Nucleus Segregates and protects DNA from the rest of the cell Cell Cycle Cycle starts when a new cell forms During cycle, cell increases in mass and duplicates its chromosomes Cycle ends when the new cell divides  Interphase Usually longest part of the cell cycle Cell increases in mass Number of cytoplasmic components doubles DNA is duplicated Stages of Interphase G1 ○ Interval or gap after cell division S ○ Time of DNA synthesis (replication) G2 ○ Interval or gap after DNA replication Mitosis Period of nuclear division Ends at the same time as cytoplasmic division Four stages: Prophase Metaphase Anaphase Telophase Cytokinesis begins in late anaphase and ends when the cell have divided The Cell Cycle in Somatic Cells Interphase A cell in interphase shows a distinct nucleus and the absence of chromosomes. Mitosis Mitosis is the distribution of two sets of chromosomes, one set into each of two separate nuclei. Stages of mitosis are ○ Prophase ○ Metaphase ○ Anaphase ○ Telophase  Early Prophase - Mitosis Begins Duplicated chromosomes begin to condense Late Prophase New microtubules are assembled One centriole pair is moved toward opposite pole of spindle Nuclear envelope starts to break up  Transition to Metaphase Spindle forms Spindle microtubules become attached to the two sister chromatids of each chromosome Metaphase All chromosomes are lined up at the spindle equator Chromosomes are maximally condensed Anaphase Sister chromatids of each chromosome are pulled apart Once separated from its sister, each chromatid is a chromosome Telophase Chromosomes decondense (uncoil) Two nuclear membranes form, one around each set of unduplicated chromosomes Results of Mitosis Two daughter nuclei Each with same chromosome number as parent cell Chromosomes in unduplicated form  Figure 3.32: The stages of mitosis, p. 102. Centrioles Condensed Early mitotic Pair of Fragments of Polar (two pairs) chromatin spindle centrioles nuclear microtubules envelope Aster Kinetochore Nucleolus Centromere Nuclear Plasma Chromosome, consisting Kinetochore Spindle envelope membrane of two sister chromatids microtubule pole Interphase Early prophase Late prophase Human Anatomy and Physiology, 7e Copyright © 2007 Pearson Education, Inc., by Elaine Marieb & Katja Hoehn publishing as Benjamin Cummings.  Figure 3.32: The stages of mitosis (continued), p. 103. Metaphase plate Nucleolus Contractile forming ring at cleavage furrow Nuclear envelope Daughter Spindle forming chromosomes Metaphase Anaphase Telophase and cytokinesis Human Anatomy and Physiology, 7e Copyright © 2007 Pearson Education, Inc., by Elaine Marieb & Katja Hoehn publishing as Benjamin Cummings.  DNA Replication Replicated semi- conservatively Each parent strand remains intact Every DNA molecule is half “old” and half “new” new old old new Steps from DNA to Proteins Same two steps produce ALL proteins: 1) DNA is transcribed to form RNA ○ Occurs in the nucleus ○ RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins