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Cell Structure and Function
Chapter 4
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4.1 What is a Cell? Each cell has a plasma membrane, cytoplasm, and a nucleus (in eukaryotic cells) or a nucleoid (in prokaryotic cells)
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a Bacterial cell (prokaryotic)
cytoplasm DNA plasma membrane a Bacterial cell (prokaryotic) Fig. 4.3, p. 52
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b Plant cell (eukaryotic)
cytoplasm DNA in nucleus plasma membrane b Plant cell (eukaryotic) Fig. 4.3, p. 52
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c Animal cell (eukaryotic)
cytoplasm DNA in nucleus plasma membrane c Animal cell (eukaryotic) Fig. 4.3, p. 52
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Components of Cell Membranes
Lipid bilayer
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“head” two “tails” Fig. 4.4, p. 53
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fluid lipid bilayer fluid Fig. 4.4, p. 53
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extracellular environment one layer of lipids one layer of lipids
membrane protein cytoplasm Fig. 4.4, p. 53
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Cell Size and Shape Surface-to-volume ratio limits cell size
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Key Concepts: WHAT ALL CELLS HAVE IN COMMON
Each cell has a plasma membrane, a boundary between its interior and the outside environment The interior consists of cytoplasm and an innermost region of DNA
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4.2 How Do We See Cells? Three key points of the cell theory:
All organisms consist of one or more cells The cell is the smallest unit that retains the capacity for life A cell arises from the growth and division of another cell
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Relative Sizes
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Fig. 4.6, p. 54
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Microscopes Different microscopes use light or electrons to reveal details of cell shapes or structures
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path of light rays (bottom to top) to eye
Ocular lens enlarges primary image formed by objective lenses. prism that directs rays to ocular lens Objective lenses (those closest to specimen) form the primary image. Most compound light microscopes have several. stage supports microscope slide Condenser lenses focus light rays through specimen. illuminator light source (in base) Fig. 4.7, p. 55
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incoming electron beam
condenser lens (focuses a beam of electrons onto specimen) specimen objective lens intermediate lens projector lens viewing screen (or photographic film) Fig. 4.7, p. 55
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Five Different Views
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Key Concepts: MICROSCOPES
Microscopic analysis supports three generalizations of the cell theory: Each organism consists of one or more cells and their products A cell has a capacity for independent life Each new cell is descended from a living cell
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4.3 Membrane Structure and Function
Each cell membrane is a boundary (lipid bilayer) that controls the flow of substances across it Fluid mosaic model Membrane is composed of phospholipids, sterols, proteins, and other components Phospholipids drift within the bilayer
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Membrane Proteins Many proteins are embedded in or attached to cell membrane surfaces Receptors, transporters, communication proteins, and adhesion proteins Plasma (outer) membrane also incorporates recognition proteins
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Common Membrane Proteins
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A glucose transporter allows glucose to cross the membrane through a channel in its interior. An ATP synthase, which makes ATP when H+ crosses a membrane through its interior. A calcium pump moves calcium ions across the membrane; requires ATP energy. EXTRACELLULAR FLUID LIPID BILAYER B cell receptor. It binds to bacteria, other foreign agents. Recognition protein that identifies a cell as belonging to one’s own body. phospholipid protein filaments of the cytoskeleton CYTOPLASM Fig. 4.9, p. 57
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Membrane Structure Studies
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fusion into hybrid cell proteins from both cells in fused membrane
human cell mouse cell fusion into hybrid cell proteins from both cells in fused membrane Fig. 4.10, p. 57
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Key Concepts: COMPONENTS OF CELL MEMBRANES
All cell membranes are mostly a lipid bilayer (two layers of lipids) and a variety of proteins The proteins have diverse tasks, including control over which water-soluble substances cross the membrane at any given time
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4.4 Introducing Prokaryotic Cells
Bacteria and archaeans The simplest cells The groups with greatest metabolic diversity Biofilms Shared living arrangements of prokaryotes
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Prokaryote Structure Cell wall Flagella Pili Surrounds plasma membrane
Used for motion Pili Protein filaments used for attachment “Sex” pilus transfers genetic material
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Prokaryote Structure
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Prokaryote Structure
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Most prokaryotic cells have a cell wall outside the plasma membrane,
cytoplasm, with ribosomes bacterial flagellum Most prokaryotic cells have a cell wall outside the plasma membrane, and many have a thick, jellylike capsule around the wall. cell wall plasma membrane DNA in nucleoid pilus capsule Fig. 4.11, p. 58
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4.5 Microbial Mobs Biofilm formation
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Key Concepts: PROKARYOTIC CELLS
Archaeans and bacteria are prokaryotic cells which have few, if any, internal membrane-enclosed compartments In general, they are the smallest and structurally the simplest cells
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4.6 Introducing Eukaryotic Cells
Start with a nucleus and other organelles Carry out specialized functions inside a cell
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plasma membrane nucleus mitochondria Fig. 4.14, p. 60
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cell wall plasma membrane central vacuole nucleus chloroplast
Fig. 4.14, p. 60
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Components of Eukaryotic Cells
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4.7 Components of The Nucleus
Nucleus separates DNA from cytoplasm Chromatin (all chromosomal DNA with proteins) Chromosomes (condensed) Nucleolus assembles ribosome subunits Nuclear envelope encloses nucleoplasm Pores, receptors, transport proteins
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Nucleus and Nuclear Envelope
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Nucleus and Nuclear Envelope
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Nucleus and Nuclear Envelope
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nuclear envelope chromatin nucleolus cytoplasm Fig. 4.15, p. 61
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nucleus pore across the nuclear envelope nucleoplasm nucleolus
chromatin nuclear envelope’s outer lipid bilayer merging with an ER membrane Fig. 4.15, p. 61
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nuclear pore nuclear envelope (two lipid bilayers) cytoplasm
Fig. 4.15, p. 61
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4.8 The Endomembrane System
Endoplasmic reticulum (ER) An extension of the nuclear envelope RER modifies new polypeptide chains SER makes lipids; other metabolic functions Golgi bodies Further modify polypeptides Assemble lipids
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The Endomembrane System
Vesicles Endocytic and exocytic: Transport or store polypeptides and lipids Peroxisomes: Digest fatty acids and amino acids; break down toxins and metabolic by-products Lysosomes: Intracellular digestion (animals) Central vacuole: Storage; fluid pressure (plants)
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Endomembrane System
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Endomembrane System
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Endomembrane System
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nucleus rough ER smooth ER Golgi body vesicles Fig. 4.16, p. 62
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the cell nucleus rough ER chromatin pore cytoplasm nucleolus
nuclear envelope (two lipid bilayers) ribosome vesicle the cell nucleus rough ER Fig. 4.16, p. 62
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plasma membrane smooth ER Golgi body smooth ER channel, cross-section
budding vesicle plasma membrane smooth ER Golgi body Fig. 4.16, p. 62
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4.9 Mitochondria and Chloroplasts
Break down organic compounds by aerobic respiration (oxygen-requiring) Produce ATP Chloroplasts Produce sugars by photosynthesis
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Mitochondria and Chloroplasts
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two outer membranes stroma thylakoids (inner membrane
system folded into flattened disks) Fig. 4.18, p. 63
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4.10 Visual Summary: Plant Cells
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Visual Summary: Animal Cells
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a Typical plant cell components.
CELL WALL CHLOROPLAST CENTRAL VACUOLE NUCLEUS nuclear envelope nucleolus DNA in nucleoplasm CYTOSKELETON microtubules microfilaments intermediate filaments (not shown) RIBOSOMES ROUGH ER MITOCHONDRION SMOOTH ER PLASMODESMA GOLGI BODY PLASMA MEMBRANE LYSOSOME-LIKE VESICLE a Typical plant cell components. Fig. 4.19, p.65
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b Typical animal cell components.
NUCLEUS nuclear envelope nucleolus DNA in nucleoplasm CYTOSKELETON microtubules microfilaments intermediate filaments RIBOSOMES ROUGH ER MITOCHONDRION SMOOTH ER CENTRIOLES GOLGI BODY LYSOSOME PLASMA MEMBRANE b Typical animal cell components. Fig. 4.19, p. 64
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b Typical animal cell components.
NUCLEUS nuclear envelope nucleolus DNA in nucleoplasm CYTOSKELETON microtubules microfilaments intermediate filaments RIBOSOMES ROUGH ER MITOCHONDRION CENTRIOLES SMOOTH ER GOLGI BODY PLASMA MEMBRANE LYSOSOME Stepped Art b Typical animal cell components. Fig. 4-19, p. 64
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4.11 Cell Surface Specializations
Most prokaryotes, protists, fungi, all plant cells have a cell wall around their plasma membrane Protects, supports, maintains cell shape Primary and secondary cell walls Plasmodesmata across cell walls connect plant cells
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Plant Cell Walls
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Plant Cell Walls
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plasma membrane middle cytoplasm lamella primary cell wall secondary
(added in layers) primary cell wall pipeline made of abutting cell walls Fig. 4.20, p. 66
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middle lamella Plasmodesmata plasmodesma middle lamella
Fig. 4.20, p. 66
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Plant Cuticle Protective surface secretion, limits water loss
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thick, waxy cuticle at leaf surface cell of leaf epidermis
photosynthetic cell inside leaf Fig. 4.21, p. 67
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Extracellular Matrixes
Surrounds cells of specific tissues
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Animal Cell Junctions Connect cells of animals
Adhering junctions, tight junctions, gap junctions
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(extracellular matrix) adhering junction
free surface of epithelial tissue different kinds of tight junctions gap junction basement membrane (extracellular matrix) adhering junction Fig. 4.23, p. 67
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Key Concepts: EUKARYOTIC CELLS
Cells of protists, plants, fungi, and animals are eukaryotic; they have a nucleus and other membrane-enclosed compartments They differ in internal parts and surface specializations
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4.12 The Dynamic Cytoskeleton
Components of the cytoskeleton Microtubules Microfilaments Intermediate filaments (in most)
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Fig. 4.12, p. 59
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Fig. 4.12, p. 59
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Fig. 4.12, p. 59
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Components of the Cytoskeleton
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tubulin subunit 25 nm Fig. 4.24, p. 68
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actin subunit 5–7 nm Fig. 4.24, p. 68
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one polypeptide chain 8–12 nm Fig. 4.24, p. 68
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Cytoskeleton Function
Organizes and moves cell parts Reinforces cell shape Interactions between motor proteins and microtubules in cilia, flagella, and pseudopods can move the whole cell
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Motor Protein: Kinesin
Moves vesicles along microtubules
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Flagellum and Pseudopods
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Eukaryotic Flagella and Cilia: Dynein
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Eukaryotic Flagella and Cilia: Dynein
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basal body pair of microtubules in a central sheath protein spokes
plasma membrane pair of microtubules dynein arms dynein arms basal body Fig. 4.27, p. 69
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Key Concepts: A LOOK AT THE CYTOSKELETON
Diverse protein filaments reinforce a cell’s shape and keep its parts organized As some filaments lengthen and shorten, they move chromosomes or other structures to new locations
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Animation: Animal cell junctions
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Animation: Cell membranes
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Animation: Common eukaryotic organelles
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Animation: Cytoskeletal components
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Animation: Flagella structure
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Animation: How a light microscope works
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Animation: How an electron microscope works
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Animation: Lipid bilayer organization
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Animation: Motor proteins
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Animation: Nuclear envelope
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Animation: Overview of cells
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Animation: Plant cell walls
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Animation: Structure of a chloroplast
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Animation: Structure of a mitochondrion
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Animation: Surface-to-volume ratio
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Animation: The endomembrane system
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Animation: Typical prokaryotic cell
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