Cellular Level of Organization PDF

Chapter 4 Cells 1 Cell Theory  Cell theory-all organisms are composed of cells.  3 principles: 1. All organisms are composed of one or more cells within which the processes of life occur. What does that mean? What does it mean to be a...

Chapter 4 Cells 1 Cell Theory  Cell theory-all organisms are composed of cells.  3 principles: 1. All organisms are composed of one or more cells within which the processes of life occur. What does that mean? What does it mean to be alive? Metabolism Homeostasis Growth and Reproduction Heredity 2. Cells are the smallest living thing (Nothing smaller than a cell is considered alive) BUT what is smaller than a cell? Atoms, Molecules, Macromolecules, Organelles All of these things MAKE UP the cell…but a cell is the smallest LIVING thing 3. Cells arise only from the division of an existing cell. You arise from two cells (sperm and egg) uniting and dividing over and 2 Cells  Not all cells are the same size; most very small  Smaller cells function more efficiently than large cells.  Why do you think this is true?  All movement inside of a cell AND movement between a cell and the environment is regulated by a centralized control center.  Larger cell=slower communication simply because of the time it takes for molecules to move to and from the control center  Small cells also have large surface area.  What is surface area?  The amount of area available for interactions/exchange between the cell and the environment  So, how do small cells have large surface area?  Interior volume of large cells increase as they grow much more than the surface area resulting in less surface area per unit volume.  So, do large cells not function well?  No. They have special features that increase their surface area.  Osteoclasts, Neurons, Squamous Cells, Microvilli 3 Types of Cells  There are two major types of cells:  Prokaryotic:  Lacks a nucleus  Uniform interior not divided into compartments  What are compartments?  Membrane bound compartments=organelles or nucleus  All bacteria and archaea have this cell type  Eukaryotic  Has a nucleus and internal membrane-bound compartment.  All organisms other than archaea and bacteria have this cell type. 3 Prokaryotic Cells  Prokaryotes are the simplest cellular organisms.  Very diverse but all have a similar organization:  They are single-celled organisms  The cells are small  The cells are enclosed by a plasma membrane  They lack cellular compartments  Many bacteria have additional outer layers to their plasma membrane:  Cell wall composed of carbohydrates gives them a more rigid structure  Capsule may surround the cell wall 3 Spherical (cocci) Streptomyoces is a spherical (cocci) bacterium 3 which forms chains mainly found in soil…mainly saprophytic Can be pathogenic Skin infection Streptococcus pyogenes causes strep throat 3 Rod (bacilli) Bacillus is a rod shaped (bacilli) bacterium Bacillus anthracis occurs naturally in soil People get infected 3 with anthrax when spores get into the body When anthrax spores get inside the body, they can be “activated.” spread 3 Spiral (spirilla) 3 Treponema pallidum is a coil shaped or spiral (spirilla) bacterium that causes syphilis Primary infection-small painless sore called chancre appears where bacteria enters body…~3 weeks after exposure. Discharge. Heals pretty quick Secondary infection-non-itchy rash possible sores in mouth and genitals (wart like), flu like symptoms. May disappear or come back. Latent syphilis-no symptoms for years Tertiary infection-may damage brain, nerves, eyes, heart, blood vessels, liver, bones, joints. May appear many years after primary infection Neurosyphilis-brain and nervous system damage Congenital syphilis- contracted across placenta. May lead to deafness, teeth deformities and deformed nose (saddle nose-bridge of nose collapses). Vibrio cholerae is found in contaminated water and causes diarrheal illness 4 Eukaryotic Cells  Eukaryotic cells are larger and complex than prokaryotic cell:  Have a plasma membrane that surrounds the cytoplasm.  What is a plasma membrane?  Lipid bilayer with proteins throughout that control cell’s permeability to water and dissolved substances  What is cytoplasm?  Semifluid matrix between nucleus and cell membrane made of sugars, amino acids, proteins, organelles  4  Animal Cell 4,5 Plasma Membrane  All living cells are surrounded by a plasma membrane  Plasma membranes have the same general structure of proteins that are embedded in a sheet of lipids, referred to as the fluid mosaic model.  Assortment of molecules (proteins and lipids) that are constantly moving while still maintaining a barrier between the outside environment and inside of the cell  Modified fat molecules called phospholipids form the lipid layer of the plasma membrane. 4,5 Plasma Membrane  Phospholipids have polar heads and two nonpolar tails.  Which part of a phospholipid is water soluble?  Head…hydrophilic  Fatty acid chains that make up tails are nonpolar and are not water soluble… hydrophobic 4,5 Plasma Membrane  When phospholipids placed in water they assemble with the nonpolar tails facing each other and the polar heads facing the environment=lipid bilayer  Because the interior of the bilayer is completely non-polar it repels any water soluble molecules trying to pass through  Plasma membrane also contains proteins and 4,5 Plasma Membrane  Membrane proteins float within the bilayer and function as transporters, receptors, and cell surface markers.  Transmembrane Proteins  These proteins span the entire membrane  How?  Protein within the interior made of non- polar AAs  So it stays anchored in and water avoids contact  Provide passage for ions and polar molecules 4,6 Nucleus  The nucleus contains most of the cell’s genetic information.  Acts as a control center for the cell  Directs protein synthesis and cellular reproduction  The nucleus is surrounded by a nuclear envelope a double layered membrane.  Barrier between nucleus and cytoplasm  Substances move through Nuclear pores and allow for exchange between the nucleus and the remainder of the cell. 4,6 Nucleus  The nucleoplasm is similar to the cytoplasm, it is inside the nuclear envelope.  Chromosomes=DNA plus protein. How heredity info physically transmitted from one generation to the next  Proteins allow DNA to wind and condense during cell division  After cell division, chromosomes uncoil and extend into chromatin.  From chromatin, protein synthesis can begin  RNA copies genes in nucleus  RNA with code from DNA leaves nucleus through pores and enter cytoplasm where protein will be synthesized  At the center of the nucleus is the nucleolus. This is where ribosomes are created.  4,7 The Endomembrane System  The cell contains an extensive internal membrane system.  One component this is the endoplasmic reticulum (ER).  Channel transport of molecules through cell interior  Place where cells make proteins intended for export such as enzymes  Two types of ER exist: 1. Rough ER  Contains ribosomes on the surface  Site of protein synthesis 2. Smooth ER  No ribosomes on the surface..many enzymes  Involved in the synthesis of carbohydrates and lipids. 4,8 Golgi Complex  New molecules made in ER passed to Golgi Bodies which package, collect, and distribute all substances manufactured in cell  All golgi bodies together known as Golgi Complex  Products synthesized in the ER will be transported to the Golgi via transport vesicles.  Those products are modified and then leave the Golgi via secretory vesicles.  The ER and Golgi work together as what is called the Endomembrane transport system. 4,8 The Endomembrane System  Endomembrane system  Collection of organelles that interact in order to produce, modify, and export organic molecules (proteins/lipids)  How it works 1. Transport vesicles fuse with membrane of golgi bodies, dumping contents into golgi Rough=proteins Smooth=lipids/carbs/toxic chemicals 2. Vesicle enters Golgi and are processed Modified for export or adapted to perform function within cell Example proteins become digestive enzymes. 4,8 Lysosomes  Vesicles that are derived from the Golgi complex  Contain hydrolytic digestive enzymes that break down macromolecules  Recycling centers of the cells  Digests old, worn-out organelles and cellular debris  Play a role in cell death 4 Energy Harvesting Organelles  Eukaryotic cells contain organelles that can harvest energy  Contain their own circular DNA separate from other cells that contain genes that code for proteins used to harvest energy  Mitochondria  ~size of bacteria cell  Energy from food using cellular respiration  Energy from glucose released  Contains smooth outer membrane and folded inner membrane (cristae)  Cristae form two compartments:  Inner matrix-fluid contains enzymes and molecules used in cellular respiration  Outer intermembrane space-between inner and outer membrane 4 The Cytoskeleton-Dense network of protein fibers  Creates framework of cell  Anchors organelles  Dynamic  Three fibers comprise the cytoskeleton: 1.Actin filaments (Microfilaments) 2.Microtubules 3.Intermediate filaments 4 1. Actin filaments (Microfilaments)  Each filament contains two protein fibers that twist together like a string of beads.  Each bead on the filament is a protein called actin.  These filaments are responsible for cellular movements that include pinching during cell division, contraction and formation of cell extensions. 2. Microtubules  Hollow tubes composed of tubulin proteins that are arranged side by side  Help stabilize cell structure  Help organize intracellular transport and metabolism  Allow chromosomes to move during cell division 3. Intermediate filaments  Made of overlapping twists of protein that are bundled into cables.  Provide structural support to the cell 4,9 Flagella and Cilia  Flagella  Arise from microtubular structure (basal body) with groups of microtubules arranged in rows of 3.  Some of these microtubules extend into the flagella.  Circle of 9 microtubule pairs surrounding 2 central microtubules=9+2 arrangement  Used to move cell  Sperm  Cilia  Flagella organized in dense rows  Same structure as flagella; usually shorter  Upper respiratory tract o f humans 10 Membrane Transport  We must be able to transport things into and out of the cell, across the membrane.  Waste materials are eliminated  Nutrients, water and other substances enter the cell.  This membrane transport occurs in 3 ways: 1. Food particles are engulfed by the membrane. 2. Water and other solutes diffuse across the membrane. 3. Proteins in the membrane act as “gates” that only admit certain molecules. 11 Diffusion  Movement of molecules is random BUT will tend to produce uniform mixtures  This is because things move from areas of higher concentration to areas of lower concentration  DOWN a concentration gradient (concentration differences from one place to the next)  REMEMBER movement is random…so molecules do not know where they are going…they are just going to move…and if there are more of them in one location they will eventually move to where there are less of them  This net (total) random movement of molecules down a concentration gradient from high to low known as diffusion.  This continues until equilibrium achieved (no more movement from one place to the next. Still movement…just not movement in one direction over another) 11 Diffusion 12 Osmosis  Water in cells interacting with polar molecules (sugars, proteins, etc)  Hydration shells around polar molecules  Water ‘tied up’ so once in cell not really free to move once inside cell  Osmosis is diffusion for water  Water moves across the cell membrane from area of low solute concentration to higher solute concentration.  Another way to think of it  Water moves from where it is higher concentration than the solutes to an area where water is in lower concentration than solutes  OR the more water that is unbound because solute 12 Osmotic Concentration  The concentration of all the solutes in a solution is the osmotic concentration.  Several terms are used to describe the osmotic concentration:  Isotonic – osmotic concentrations of two solutions are equal.  Hypertonic – Solution with higher concentration of solutes is said to be hypertonic.  Hypotonic – Solution with lower concentration of solutes is said to be hypotonic.  Movement of water by osmosis creates osmotic pressure.  This pressure can cause a cell to change size and shape as water enters or exits.  Water will always move towards area of high solute concentration. 12 Osmotic Pressure and Animal Cells  When placed in a hypertonic solution, water will leave the cell (moving towards the surrounding solutes) and the cell will shrivel up – known as crenation.  When placed in an isotonic solution, water will enter and exit the cell at an equal rate – so no change in cell size or shape. (this is ideal for animal cells)  When placed in a hypotonic solution, water will move into the cell towards the higher solute concentration and the cells will swell and eventually burst – this bursting is know as lysis. 13 Bulk Transport  Bulk transport processes allow large amounts of a substance into or out of the cell.  Endocytosis  Brings substances into the cell  Exocytosis  Carries things out of the cell 13 Endocytosis  Allows cells to take in food and liquids  Cells extend their plasma membranes to surround the substance. Phagocytosis  Allows the cell to take in solid food particles.  Sometimes called “cell eating” Pinocytosis  Allows the cell to take in liquids and small solutes  Sometimes called “cell drinking” 13 Exocytosis  Allows cells to discharge contents using vesicles at membrane surface 14 Selective Permeability  Selective permeability allows a cell to choose what substances cross the membrane.  It accomplishes this by using membrane proteins as channels across the membrane.  Each channel allows the passage of only certain molecules.  Selective Diffusion  Channels act as door ways that are always open.  As long as the molecule fits through the channel they can diffuse in either direction (in or out of the ell)  Facilitated Diffusion  Uses carrier protein which only bind to specific types of molecules  Moves from high concentration to low concentration.  Limited number of carrier proteins 14 Active Transport  Active transport moves solutes across the membrane against the concentration gradient (from low concentration to high concentration.  This requires energy (in the form of adenosine triphosphate or ATP)  Sodium– Potassium Pump  Moves 3 sodium out of the cell and 2 potassium into the cell, uses 1 ATP energy