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The Cell Structure and Function
Chapter 3
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CELLS ARE THE BASIC UNIT OF LIFE
Cell theory
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Development of the Cell Theory
Almost all cells are too small to see without the aid of a microscope Invention & development of the microscope enabled scientists to discover the cell.
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Robert Hooke Hooke was looking only at cell walls and empty space
In 1665 he looked at a thin slice of cork from the bark of an oak tree using a compound microscope He saw that cork was made of tiny hollow boxes similar to honeycomb. He called them cells because they reminded him of the small rooms in a monastery Hooke was looking only at cell walls and empty space
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Anton van Leeuwenhoek 1674 – became the one of the first people to describe living cells when he observed numerous single-celled organisms swimming in a drop of pond water He was studying new methods for making lenses to examine cloth He also looked at tooth tarter
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The microscope van Leeuwenhoek used is considered a simple light microscope because it contained one lens and used natural light to view objects. Leeuwenhoek make over 500 microscopes, and only few survive today. This is an example of one of his simple microscopes
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1830 two German Scientists 1838: Schleiden: observed plant cells
Viewed different organisms with a microscope and came up with important conclusions 1838: Schleiden: observed plant cells Concluded that all plants are composed of cells 1839: Schwann observed animal cells Concluded that all animal cells are composed of cells
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Rudolf Virchow 1855: Another German scientists reported that all cells come from pre-existing cells These ideas lead to basic ideas of modern biology; the cell theory
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The Cell Theory All organisms are composed of 1 or more cells
The Cell Theory is made of 3 main ideas: All organisms are composed of 1 or more cells The cell is the basic unit of organization All cells come from preexisting cells
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2 Basic Types of Cells As Scientists studied cells, they discovered 2 basic types Prokaryotic Cell: no true nucleus Eukaryotic Cell: true nucleus
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Similarities in Prokaryotic Cell and Eukaryotic Cells
All cells share certain characteristics. Cells tend to be microscopic. All cells are enclosed by a membrane called a cell membrane. All cells are filled with cytoplasm – jellylike substance that contains organelles. All cells contain organelles – tiny organs within the cell
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Prokaryotic Cells These cells lack internal structures that are surrounded by membranes. They do not have a true nucleus Most are single-celled and microscopic Example: Bacteria
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Basic Parts of the Prokaryotic Cell
Basic Organelles: Nucleoid Region Cytoplasm Capsule Cell Wall Ribosomes Pili Flagella
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Eukaryotic Cells Cells contain a Nucleus that acts as the control center of the cell and is the largest organelle in the cell Can be an Animal Cell or Plant Cell Can be either single cellular , or multicellular
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Cell Organelles The membrane-bound structures within eukaryotic cells are called organelles. Each organelle has a specific function that contributes to cell survival.
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Cytoskeleton A flexible network of proteins that provide structural support for cells. Made of small protein subunits that form long threads or fibers that crisscross the entire cell
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3 Main Types of Cytoskeleton
1. Microtubules: long hollow tubes that gives the cell its shape and acts like tracks for organelle movement. 2. Intermediate Filaments: smaller than microtubules and gives the cell strength 3. Microfilaments (Actin Filament): smallest and are tiny threads that enable the cell to move and divide
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Cytoskeleton
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Nucleus 2 Major Demands of the Nucleus: 1. DNA must be carefully protected 2. DNA must be available for use at the right time Nucleus is the storehouse for most of the genetic information or DNA in your cell Is the Brain of the cell-controls all cell functions Is the largest organelle in the cell
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Parts of the Nucleus Nucleolus: makes DNA; makes proteins from ribosomes Chromatin: Turns into chromosomes before Cell Division Nuclear Envelope: Allows RNA to pass out of the nucleus Nuclear Pore: allows Proteins into & out of the nucleus, and allows RNA out of the nucleus
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Endoplasmic Reticulum
Is an interconnected network of thin folded membranes that transport Proteins to the Nucleus Numerous processes take place inside the lumen and on the surface: production of proteins and lipids ER membranes for a maze called lumen
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2 Types of Endoplasmic Reticulum
1. ER studded with ribosomes are called Rough ER 2. ER without ribosomes are called Smooth ER
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Ribosomes Ribosomes link amino acids together to form proteins
Ribosomes are made of proteins and RNA After assembly in the nucleolus they pass through the nuclear pores into the cytoplasm; this is where most protein synthesis occurs
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Golgi Apparatus Consist of closely stacked layers of membranes that processes, packages, and delivers proteins. Some proteins are stored for later use, some transported to other organelles, some are carried to the membrane and secreted outside the cell
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Vesicles Small membrane-bound sacs that divide some material from the rest of the cytoplasm and transport these materials throughout the cell Are usually short lived and are formed & recycled as needed -After a protein has been made, part of the ER pinches off to form a vesicle surrounding the protein. -The protein can be transferred to the Golgi Apparatus with a vesicle
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Mitochondria Energy maker; are bean shaped membrane-bound organelles in plant and animal cells that transform energy for the cell Mitochondria have their own ribosomes, DNA & can divide
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Inner & Outer Membranes
Mitochondria have an inner and outer membrane The outer one is smooth while the inner one is shaped into folds called cristae The matrix (fluid) is inside the inner membrane
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Vacuole Vacuole A fluid filled sac used for storage
Water, food molecules, inorganic ions, and enzymes Animal cells have small vacuoles Plant cells have a single large vacuole Vacuole
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Lysosome Membrane bound organelle that contains digestive enzymes; Suicide Sac They defend cells from invading bacteria and viruses They break down damaged or worn-out cells Animal cells-numerous Plant cells-none
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Centrioles Barrel- shaped organelles found in animals & protists
Occur in pairs: usually at right angles to one another Usually near the nucleus Replicate and move to opposite ends of the cell during mitosis (cell division) Centrosome is a small region of cytoplasm that produces microtubules
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Cell Wall Is a fairly ridged structure located outside the plasma membrane that provides additional support and protection Only cells with a cell wall: Plant cell Bacteria Cells (prokaryotic) Fungi Cells
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Chloroplasts are cell organelles that capture light energy and produce food to store for a later time. Carry out photosynthesis Has a double membrane Have their own DNA & Ribosomes Chloroplasts & Energy granum 2 membranes stroma thylakoid
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Structure of the Chloroplast
Thylakoid: trap energy from sunlight. Coin-like structure Granum: The inner membranes are arranged in stacks; resembles stacks of coins Stroma: The fluid that surrounds the stacks of granum
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Plastids The chloroplasts belong to a group of plant organelles called plastids, which are used for storage. Some store starch or lipids, some contain pigments, molecules that give color Plastids are named according to their color or the pigment they contain Chlorophyll traps light energy and gives the leaves and stems their green color
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Cell Movement Some cell surfaces have cilia and flagella, which are structures that aid in locomotion or feeding. Cilia and flagella can be distinguished by their structure and by the nature of their action.
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Cilia Cilia are short, numerous, hair-like projections that move in a wavelike motion Cilia
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Flagella Flagella are long projections that move in a whip-like motion. Flagella and cilia are the major means of locomotion in unicellular organisms Flagella
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Unicellular: One celled organisms
Multi-cellular: Organisms with many cells
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Is a barrier that separates a cell from the external conditions
The Cell Membrane Is a barrier that separates a cell from the external conditions
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Maintaining a Balance All living cells must maintain a balance regardless of internal and external conditions. Survival depends on the cell’s ability to maintain the proper conditions within itself
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Cell Membrane AKA: Plasma Membrane
The cell membrane is the boundary between the cell and its environment It controls the passage of materials into and out of a cell This process of maintaining the cell’s environment is called homeostasis
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Cell Membrane’s Job Description
1. Allow a steady supply of glucose, amino acids, and lipids to come into the cell no matter what the external conditions are. 2. Remove excess amounts of these nutrients when levels get so high that they are harmful 3. Allow waste and other products to leave the cell.
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Phospholipid Is a molecule composed of 3 parts 1: Glycerol (polar end)
2: a Charged Phosphate Group (PO4) 3: Two Fatty Acid Chains (non-polar)
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Phospholipids Bilayer
The cell membrane/ plasma membrane is composed of two layers of phospholipids back-to-back. Phospholipids are lipids with a phosphate attached to them
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Cell Membrane Water
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Properties & Characteristics
They give the membrane properties & characteristics they would not have 1. Cholesterol molecules strengthen the cell membrane 2. some proteins extend through one or both phospholipid layers & help materials cross Other proteins are key components of the cytoskeleton 3. carbohydrates attached to membrane proteins serve as identification tags to distinguish one cell from another
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Other components of the Plasma Membrane
Cholesterol plays the important role of preventing the fatty acid chains of the phospholipids from sticking together Transport proteins allow needed substances or waste materials to move through the plasma membrane Cholesterol Molecule
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Fluid Mosaic Model Describes the arrangement of the molecules that make up a cell membrane The Fluid Mosaic Model states: that the phospholipid bilayer behaves like a fluid more than it behaves like a solid
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It was Named from 2 Characteristics
1. The cell membrane is flexible, not rigid The phospholipids in each layer can move from side to side and slide past each other ~so it behaves like a liquid 2. the molecules in the membrane are arranged like colorful tiles with different textures & patterns that make up a mosaic
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Cell membranes are composed of two phospholipid layers.
The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.
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Selective Permeable Membrane
Selective permeability is a process used to maintain homeostasis in which the plasma membrane allows some molecules into the cell while keeping others out
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Chemical signals are transmitted across the cell membrane.
Receptors is a protein that detects a signal and changes as a response Receptors bind with ligands and change shape. There are two types of receptors. intracellular receptor: Within or Inside a cell ~ hormones membrane receptor: Cannot cross the membrane
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Materials move across membranes because of concentration differences
Diffusion and Osmosis Materials move across membranes because of concentration differences
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Connect to your world A water dam or pump allows water to pass through the same way a cell membrane allows fluids (water) to pass into and out of the cell This process is called osmosis and requires a plasma membrane to work
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The cell membrane is the boundary between the cell and its environment
It allows water and other molecules to pass into and out of the cell
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2 Types of Transport: Passive Transport the movement of particles across a membrane from high concentration to low concentration without ENERGY. Active Transport: The movement of particles across a membrane from low concentration to high concentration with ENERGY
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Passive Transport Some molecules (like water) can pass through the plasma membrane by simple diffusion The cell uses no energy to move these particles so they are classified as passive transport
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What is diffusion Diffusion is when molecules move from an area of high concentration (there are many) to an area of low concentration (there are few) This happens in liquids and gas Ex: spraying perfume Is a form of passive transport
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Concentration Gradient
Difference in the concentration between two different areas Particles slide along the concentration gradient to help the cell reach equilibrium. Equilibrium is equal portions of solute inside and outside the cell
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3 types of Passive Transport
1. Simple Diffusion 2. Facilitated Diffusion 3. Osmosis
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Simple Diffusion of Particles
Simple Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration In a cell, water always moves to reach an equal concentration on both sides of the membrane Examples: Oxygen Carbon Dioxide
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Facilitated Diffusion
Facilitated diffusion helps molecules passing through the membrane that may not be soluble in lipids or too large to pass through the pores in the cell Assistance is given by specific proteins called Protein Carrier
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Protein Carriers Transport molecules from an area of higher concentration on one side of the membrane to an area of lower concentration on the other side
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What is Osmosis? The movement of water across a selectively permeable membrane from an area of higher concentration to an area of lower concentration is called osmosis Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell
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Concentration Gradient of Osmosis
After Osmosis Before Osmosis Water molecule Sugar molecule Selectively permeable membrane
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3 Types of Osmosis Isotonic Solution Hypotonic Solution
Hypertonic Solution
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Hypotonic Solution In hypotonic solution, the concentration gradient outside the cell is lower than inside the cell This movement causes cells to swell
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Cells in Hypotonic Solution
In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2O H2O Water Molecule Dissolved Molecule
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Examples of Hypotonic Solution
Grocers keep produce fresh by misting with water Beans have to be soaked for hours before cooking Rice swells-do not throw at weddings Red blood cells swell until they burst
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Hypertonic Solution In a hypertonic solution, the concentration gradient of dissolved substances outside the cell is higher than inside the cell This movement causes cells to shrink
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Cells in Hypertonic Solution
In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink H2O H2O Water Molecule Dissolved Molecule
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Example of Hypertonic Solution
Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. Causes flowers to wilt Animal cells shrivel: beef jerky
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Isotonic Solution In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. Water moves into and out at the same rate and cells obtain their normal shape
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Cells in an Isotonic Solution
Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. H2O H2O Water Molecule Dissolved Molecule
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Examples of Isotonic Solution
A plant cell has its normal shape and pressure in an isotonic solution.
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Active Transport Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell.
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Active Transport
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2 Types of Active Transport
1. Endocytosis 2. Exocytosis
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Transport of Large Particles
Endocytosis is a process by which a cell surrounds and takes in material from its environment Nucleus Wastes Digestion
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The material is makes a pocket the pocket breaks off inside the cell, forms vesicles and fuses with a lysosome Phagocytosis - “Cell Eating” Pinocytosis – “Cell Drinking” Nucleus Endocytosis Wastes Digestion
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Exocytosis Exocytosis is the release or secretion of materials from a cell. Happens in your body with every movement
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