Cell Structure and Function Chapter 4 2-

The Cell Theory All living things are made of cells. A cell The basic unit of all living things. 4-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Historical Context of the Cell Theory Robert Hooke coined the term “cell.” Look at cork cells under a simple microscope. Anton van Leeuwenhoek Made better microscopes Used them to look at a variety of substances and identified animalcules 4-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Historical Context of the Cell Theory Mathias Jakob Schleiden Concluded that all plants were made of cells Theodor Schwann Concluded that all animals were made of cells 4-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Initial Observations of Cells Cell wall Outer non-living part of plant cells Protoplasm Interior living portion of the cell Nucleus Contains the genetic information of the cell Cytoplasm Fluid part of the protoplasm Organelles “Little organs” within the protoplasm 4-5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Different Kinds of Cells Prokaryotic Structurally simple cells Lack a nucleus Lack most other organelles Bacteria Eukaryotic cells More complex Have a nucleus Have a variety of organelles Plants, animals, fungi, protozoa and algae Typically much larger than prokaryotic cells 4-6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Prokaryotic Cells Origin: ‘pro’-before; ‘karyote’ - nut Lack a membrane-bound nucleus. genetic material is present in the nucleoid Two types of prokaryotes: Bacteria Archaea

Prokaryotic Cell Characteristics: Simplest organisms - simple internal organization Very small (1 to 10 microns across) Genetic material in the nucleoid No membrane-bound organelles Capsules Cytoplasm

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Eukaryotic Cells Origin: ‘eu’ - true, good; ‘karyote’ - nut Possess a membrane-bound nucleus. genetic material is highly organized within double-layer nuclear envelope DNA never leaves the nuclear envelope Types of eukaryotes divided into 4 kingdoms:1. Plantae 2. Fungi 3. Animalia 4. Protista

Eukaryotic Cell Characteristics: More complex organisms highly organized structure Typically larger than prokaryote (10-100 microns) Genetic material in the membrane-bound nucleus Many membrane-bound organelles Cytoplasm Cytoskeleton

Prokaryotes vs. Eukaryotes 4-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Eukaryotic and Prokaryotic Characteristics: DNA, RNA Ribosomes Plasma membrane Cytoplasm Cell walls (plantae, fungi, protista, not present in animal cells) Flagella

Eukaryotic Cells 14

Prokaryotic Cells 15

Cell Size Prokaryotic cells Eukaryotic cells 1-2 micrometers in diameter Eukaryotic cells 10-200 micrometers in diameter 4-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.2

Cell Size is Limited Surface Area-to-Volume Ratio Cells must get all of their nutrients from their environment through their cell membranes. Volume increases more quickly than surface area. Surface area-to-volume ratio must remain small. 4-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Surface Area-to-Volume Ratio 19

The Structure of Cell Membranes Thin sheets composed of phospholipids and proteins Fluid-mosaic model Two layers of phospholipids Fluid Has an oily consistency Things can move laterally within the bilayer. Mosaic Proteins embedded within the phospholipid bilayer 4-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Phospholipids Phospholipid Structure (Chapter 3) glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid 2 fatty acids attached to the glycerol phosphate group attached to the glycerol

Nonpolar Hydrocarbon Tail Phospholipids Chapter 3: Phospholipids are Amphiphilic molecules Polar Head Group Nonpolar Hydrocarbon Tail 101

Phospholipids The fatty acids are nonpolar chains of carbon and hydrogen. Their nonpolar nature makes them hydrophobic (“water-fearing”). The phosphate group is polar and hydrophilic (“water-loving”).

The Phospholipid Bilayer Phospholipid structure Hydrophobic tails Hydrophilic heads Bilayer Hydrophobic tails of each layer associate with each other. Hydrophilic heads on the surface of the bilayer Cholesterol Hydrophobic Found within the hydrophobic tails Keeps the membrane flexible 4-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Phospholipids The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer: fatty acids are on the inside phosphate groups are on both surfaces of the bilayer

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Membrane Proteins Some are on the surface Some are partially embedded. Protrude from one side Some are completely embedded. Protrude from both sides Functions Transport molecules across the membrane Attachment points for other cells Identity tags for cells 4-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Organelles Composed of Membranes Plasma membrane (cell membrane) Different cellular membranous structures serve different functions Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Vacuoles and vesicles Nuclear membrane 4-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Plasma Membrane Composed of phospholipid bilayer Separates the contents of the cell from the external environment Important features Metabolic activities Moving molecules across the membrane Structurally different inside and outside Identification: Self vs. nonself Attachment sites Signal transduction 4-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Endoplasmic Reticulum (ER) Consists of folded membranes and tubes throughout the cell Provides a large surface area for important chemical reactions Because it is folded, it fits into a small space. Two types of ER Rough Smooth 4-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Endoplasmic Reticulum 35

The Endoplasmic Reticulum Rough Endoplasmic Reticulum (RER) System of cytoplasmic membranes that create a network of channels throughout the cytoplasm Ribosomes are attached to the outside of the RER membrane giving it a rough appearance under the microscope Synthesis of proteins to be secreted out of the cell, or packaged and sent to lysosomes or plasma membrane Proteins are synthesized into the RER channels (cisternal space)

The Endoplasmic Reticulum Smooth Endoplasmic Reticulum (SER) Relatively few associated ribosomes Functions: Synthesis of membrane lipids Detoxification of foreign substances

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The Golgi Apparatus Stacks of flattened membrane sacs Functions Modifies molecules that were made in other places Manufactures some polysaccharides and lipids Packages and ships molecules 4-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.12

Traffic Through the Golgi Vesicles bring molecules from the ER that contain proteins. Vesicles fuse with the Golgi apparatus. The Golgi finishes the molecules and ships them out in other vesicles. Some are transported to other membrane structures. Some are transported to the plasma membrane. Some vesicles become lysosomes. 4-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Lysosomes Vesicles containing enzymes that digest macromolecules Carbohydrates Proteins Lipids Nucleic acids Interior contains low pH These enzymes only work at pH=5. The cytoplasm is pH=7. If the lysosome breaks open, these enzymes will inactivate and will not damage the cell. 4-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Functions of Lysosomes Digestion Of food taken into the cell Destruction Disease-causing organisms Old organelles 4-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Peroxisomes Not formed from golgi membrane, but from ER membrane Contain the enzyme catalase Breaks down hydrogen peroxide Breaks down long-chain fatty acids Synthesizes cholesterol and bile salts Synthesizes some lipids 4-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.15

Vacuoles and Vesicles Membrane-enclosed sacs Vacuoles Vesicles Larger sacs Contractile vacuoles found in many protozoa Forcefully expel excess water from the cytoplasm Vesicles Smaller vesicles 4-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Vacuoles and Vesicles 4-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.16

The Nuclear Membrane Separates the genetic material from the rest of the cell Filled with nucleoplasm Composed of two bilayers Contains holes called nuclear pore complexes Allow large molecules like RNA to pass through the membrane into the cytoplasm 4-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Endomembrane System ̶ Interconversion of Membranes Membranes are converted from one membranous organelle to another. 4-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Mitochondria Energy Converting Organelles Mitochondrion A small bag with a large bag stuffed inside Larger internal bag is folded into cristae Cristae contain proteins for cellular respiration. Releases the energy from food Requires oxygen Uses the energy to make ATP 4-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Mitochondria 53

Chloroplasts Energy Converting Organelles Chloroplasts 4-26 Sac-like organelle Contain chlorophyll Perform photosynthesis Uses the energy in light to make sugar Contain folded membranes called thylakoids Thylakoids stacked into grana Thylakoids contain chlorophyll and other photosynthetic proteins. Thylakoids surrounded by stroma 4-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chloroplasts 55

Nonmembranous Organelles Ribosomes Cytoskeleton Centrioles Cilia flagella Inclusions 4-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Ribosomes Made of RNA and proteins Composed of two subunits Large Small Are the sites of protein production Found in two places Free floating in the cytoplasm Attached to endoplasmic reticulum 4-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.10 Ribosomes

Cytoskeleton Network of protein fibers found in all eukaryotic cells Made up of Microtubules Microfilaments (actin filaments) Intermediate filaments 4-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cytoskeleton Functions: Supports the shape of the cell Keeps organelles in fixed locations Helps move materials within the cell

Cytoskeleton 61

Centrioles Two sets of microtubules arranged at right angles to each other Located in a region called the centrosome Microtubule-organizing center near nucleus Organize microtubules into spindles used in cell division 4-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 4.21

Cilia and Flagella Hair-like projections extending from the cell Composed of microtubules covered by plasma membrane Flagella Long and few in number Move with an undulating whip-like motion Cilia Small and numerous Move back and forth like oars on a boat 9 + 2 arrangement of microtubules Cell can control their activity 4-31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cilia and Flagella 4-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Fig. 4.24b http://www.youtube.com/watch?v=2SoSvup6bGI&feature=related

Inclusions Collections of miscellaneous materials Can be called granules Temporary sites for the storage of nutrients and waste 4-33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glycogen Inclusions Stryer's Biochemistry Fig. 23-2 82

Nuclear Components Contains chromatin DNA + proteins Becomes condensed during cell division into chromosomes Surrounded by double layer of membrane Nuclear membrane contains pores to control transport of materials in and out of nucleus Contains one or more nucleoli Site of ribosome synthesis Contains nucleoplasm Water, nucleic acids, etc. 4-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Nuclear Components 71

Getting Through Membranes Membrane Transport Motion of substances in and out of the cell Cell membranes are Selectively Permeable Two Types of Transport Mechanisms: Passive Transport Active Transport

Membrane Transport Passive transport is movement of molecules through the membrane in which no energy is required from the cell Active transport requires energy expenditure by the cell

1. Passive Transport Passive transport is movement of molecules through the membrane in which no energy is required from the cell Molecules move in response to a concentration gradient A concentration gradient is a difference between the concentration on one side of the membrane and that on the other side Passive transport mechanisms only movement substances along the concentration gradient From a higher concentration to a lower concentration

Types of Passive Transport: Diffusion movement of solute molecules from high solute concentration to low solute concentration Osmosis movement of solvent water from high solvent concentration to low solvent concentration

1. Diffusion Molecules are in constant, random motion. Molecules move from where they are most concentrated to where they are less concentrated. Involves a concentration gradient (diffusion gradient) No concentration gradient=dynamic equilibrium 4-36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Rate of Diffusion Depends on The size of the molecule Smaller molecules diffuse faster. The size of the concentration gradient The greater the concentration difference, the faster the diffusion. 4-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Diffusion in Cells Diffusion can only happen if there is no barrier to the movement of molecules. Can only happen across a membrane if the membrane is permeable to the molecule Membranes are semi-permeable; they only allow certain molecules through. Membrane permeability depends on the molecules size, charge, and solubility. 4-38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Diffusion There are two types of diffusion Simple (Direct) Diffusion Facilitated Diffusion

Simple Diffusion Substances pass directly through the cell membrane The cell membrane has limited permeability to small polar molecules, water, and ions Determined solely by the concentration gradient http://www.youtube.com/watch?v=s0p1ztrbXPY&feature=related

Simple Diffusion Example: Oxygen diffusion 4-39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Simple Diffusion The rate (molecules/sec.) of simple diffusion depends on the degree of concentration gradient As the gradient reaches equilibrium, diffusion slows At equilibrium, substances pass in and out of the membrane at equal rates

Rate of Simple Diffusion vs Concentration 83

Facilitated Diffusion Substances must pass through transport proteins to get through the cell membrane Facilitated diffusion is movement of a molecule from high to low concentration with the help of a carrier protein. Facilitated Diffusion: is specific is passive saturates when all carriers are occupied

Facilitated Diffusion Some molecules have to be carried across the membrane. Accomplished by carrier proteins Still involves diffusion Follows a concentration gradient Is passive transport 4-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Facilitated Diffusion Is Specific - a carrier protein transports only certain molecules or ions Is Passive - the direction of net movement is determined by the relative concentrations on the substances inside an outside the cell Has a Saturation Point - rate of facilitated diffusion (molecules/sec.) increases with gradient until all protein carriers are in use - saturation point

Saturation of Facilitated Diffusion Rate Concentration 87

2. Osmosis Osmosis is the movement of water from an area of high to low concentration of water Movement of water toward an area of high solute concentration In osmosis, only water is able to pass through the membrane

Osmosis 4-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Osmosis vs. Diffusion The difference between osmosis and diffusion is the semipermeable membrane between the two solutions If the membrane is permeable to the solute, then diffusion occurs If the membrane is impermeable to the solute, but permeable to water (solvent) only, then osmosis occurs

Osmosis Osmotic concentration is determined by the the concentration of all solutes in solution All solutes displace water Relative Osmotic Concentrations Hypertonic solutions: have a higher relative solute concentration Hypotonic solutions: have a lower relative solute concentration Isotonic Solutions: have equal relative solute concentrations

Osmotic Influences on Cells If a cell has less water (thus more solute) than its environment It is hypertonic to its surroundings. If a cell has more water (thus less solute) than its environment It is hypotonic to its surroundings. If a cell has equal amounts of water (and solute) as its environment It is isotonic to its surroundings. 4-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Osmotic Influences on Cells http://www.youtube.com/watch?v=XclGRjnilsk&feature=channel http://www.youtube.com/watch?v=dHc05E7BijQ http://www.youtube.com/watch?v=crpeX8nBgJE 4-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Active transport Able to moves substances against the concentration gradient - from low to high concentration Requires energy – ATP is used directly or indirectly to fuel active transport allows cells to store concentrated substances Requires the use of carrier proteins

Active Transport 4-45 http://www.youtube.com/watch?v=STzOiRqzzL4&NR=1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Endocytosis Moves large molecules or sets of molecules into the cell Phagocytosis Cell eating Food engulfed by the membrane Material enters the cell in a vacuole. Pinocytosis Cell drinking Just brings fluid into the cell Receptor-mediated endocytosis Molecules entering the cell bind to receptor proteins first. 4-46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Exocytosis Moves large molecules or sets of molecules out of the cell Vesicles containing the molecules to be secreted fuse with the plasma membrane. Contents are dumped outside the cell. 4-47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Endocytosis and Exocytosis 4-48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.