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Cell Structure and Function
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Impacts, Issues: Food For Thought
A strain of E. coli bacteria that causes severe illness or death occasionally contaminates foods such as ground beef and fresh vegetables
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4.1 The Cell Theory The cell theory, a foundation of modern biology, states that cells are the fundamental units of life
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Measuring Cells One micrometer (μm) is one-thousandth of a millimeter
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Animalcules and Beasties
Van Leeuwenhoek was the first to describe small organisms seen through a microscope, which he called animalcules and beasties Hooke was the first to sketch and name cells
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Development of the Microscope
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The Cell Theory Emerges
In 1839, Schleiden and Schwann proposed the basic concepts of the modern cell theory All organisms consists of one or more cells A cell is the smallest unit with the properties of life Each new cell arises from division of another, preexisting cell Each cell passes its hereditary material to its offspring
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4.2 What Is a Cell? Cell The smallest unit that shows the properties of life All cells have a plasma membrane and cytoplasm, and all start out life with DNA
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The Basics of Cell Structure
Eukaryotic cell Cell interior is divided into functional compartments, including a nucleus Prokaryotic cell Small, simple cells without a nucleus
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All Cells Have Three Things In Common
Plasma membrane Controls substances passing in and out of the cell DNA containing region Nucleus in eukaryotic cells Nucleoid region in prokaryotic cells Cytoplasm A semifluid mixture containing cell components
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Prokaryotic and Eukaryotic Cells
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Figure 4.4 General organization of prokaryotic and eukaryotic cells. If the prokaryotic cell were drawn at the same scale as the other two cells, it would be about this big: Fig. 4-4a, p. 56
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Figure 4.4 General organization of prokaryotic and eukaryotic cells. If the prokaryotic cell were drawn at the same scale as the other two cells, it would be about this big: Fig. 4-4b, p. 56
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Cells Have Large Surface Area-to-Volume Ratio
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Cell Size Surface-to-volume ratio restricts cell size by limiting transport of nutrients and wastes
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Preview of Cell Membranes
Lipid bilayer A double layer of phospholipids organized with their hydrophilic heads outwards and their hydrophobic tails inwards Many types of proteins embedded or attached to the bilayer carry out membrane functions
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Basic Structure of Cell Membranes
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A A phospholipid, the main type of lipid in cell membranes.
hydrophilic head two hydrophobic tails Figure 4.6 Basic structure of cell membranes. A A phospholipid, the main type of lipid in cell membranes. Fig. 4-6a, p. 57
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Figure 4.6 Basic structure of cell membranes. Fig. 4-6b, p. 57
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Figure 4.6 Basic structure of cell membranes. Fig. 4-6c, p. 57
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4.1-4.2 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 consist of cytoplasm and an innermost region of DNA
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4.3 How Do We See Cells? We use different types of microscopes to study different aspects of organisms, from the smallest to the largest
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Modern Microscopes Light microscopes Electron microscopes
Phase-contrast microscopes Reflected light microscopes Fluorescence microscopes Electron microscopes Transmission electron microscopes Scanning electron microscopes
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Light and Electron Microscopes
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Figure 4.7 Examples of microscopes. Fig. 4-7a, p. 58
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Figure 4.7 Examples of microscopes. Fig. 4-7b, p. 58
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Different Microscopes, Different Characteristics
a) Light micrograph. A phase-contrast micro-scope yields high-contrast images of transparent specimens, such as cells. b) Light micrograph. A reflected light micro-scope captures light reflected from opaque specimens. c) Fluorescence micro-graph. The chlorophyll molecules in these cells emitted red light (they fluoresced) naturally. d) A transmission electron micrograph reveals fantastically detailed images of internal structures. e) A scanning electron micro-graph shows surface details of cells and structures. Often, SEMs are artificially colored to highlight certain details. Figure 4.8 Different microscopes can reveal different characteristics of the same aquatic organism—a green alga (Scenedesmus). Try estimating the size of one of these algal cells by using the scale bar. Stepped Art Fig. 4-8, p. 59
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4.3 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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4.4 Introducing Prokaryotic Cells
Bacteria and archaea are the prokaryotes (“before the nucleus”), the smallest and most metabolically diverse forms of life Bacteria and archaea are similar in appearance and size, but differ in structure and metabolism
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General Prokaryote Body Plan
Cell wall surrounds the plasma membrane Made of peptidoglycan (in bacteria) or proteins (in archaea) and coated with a sticky capsule Flagellum for motion Pili help cells move across surfaces Sex pilus aids in sexual reproduction
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cytoplasm, with ribosomes
flagellum capsule cell wall plasma membrane Figure 4.10 Generalized body plan of a prokaryote. cytoplasm, with ribosomes DNA in nucleoid pilus Fig. 4-10, p. 60
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Archaeans
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Bacteria
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4.5 Microbial Mobs Although prokaryotes are all single-celled, few live alone Biofilm Single-celled organisms sharing a secreted layer of polysaccharides and glycoproteins May include bacteria, algae, fungi, protists, and archaeans
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A Biofilm
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4.4-4.5 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
Eukaryotic (“true nucleus”) cells carry out much of their metabolism inside membrane-enclosed organelles Organelle A structure that carries out a specialized function within a cell
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Organelles of Eukaryotic Cells
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Eukaryotes: Animal and Plant Cells
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(a) Human white blood cell. 1 µm
vacuole plasma membrane mitochondrion nucleus Figure 4.14 Transmission electron micrographs of eukaryotic cells. (a) Human white blood cell. (b) Photosynthetic cell from a blade of timothy grass. (a) Human white blood cell. 1 µm Fig. 4-14a, p. 62
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(b) Photosynthetic cell from a blade of timothy grass.
cell wall central vacuole plasma membrane chloroplast mitochondrion nucleus Figure 4.14 Transmission electron micrographs of eukaryotic cells. (a) Human white blood cell. (b) Photosynthetic cell from a blade of timothy grass. 1 µm (b) Photosynthetic cell from a blade of timothy grass. Fig. 4-14b, p. 62
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4.7 Visual Summary of Eukaryotic Cells
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4.7 Visual Summary of Eukaryotic Cells
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4.8 The Nucleus The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm The nuclear envelope controls when DNA is accessed
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The Nuclear Envelope Nuclear envelope
Two lipid bilayers pressed together as a single membrane surrounding the nucleus Outer bilayer is continuous with the ER Nuclear pores allow certain substances to pass through the membrane
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The Nucleoplasm and Nucleolus
Viscous fluid inside the nuclear envelope, similar to cytoplasm Nucleolus A dense region in the nucleus where subunits of ribosomes are assembled from proteins and RNA
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The Chromosomes Chromatin Chromosome
All DNA and its associated proteins in the nucleus Chromosome A single DNA molecule with its attached proteins During cell division, chromosomes condense and become visible in micrographs Human body cells have 46 chromosomes
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Chromosome Condensation
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4.9 The Endomembrane System
A series of interacting organelles between the nucleus and the plasma membrane Makes lipids, enzymes, and proteins for secretion or insertion into cell membranes Other specialized cell functions
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The Endoplasmic Reticulum
Endoplasmic reticulum (ER) An extension of the nuclear envelope that forms a continuous, folded compartment Two kinds of endoplasmic reticulum Rough ER (with ribosomes) folds polypeptides into their tertiary form Smooth ER (no ribosomes) makes lipids, breaks down carbohydrates and lipids, detoxifies poisons
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Vesicles Vesicles Peroxisomes Vacuoles
Small, membrane-enclosed saclike organelles that store or transport substances Peroxisomes Vesicles containing enzymes that break down hydrogen peroxide, alcohol, and other toxins Vacuoles Vesicles for waste disposal
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Golgi Bodies and Lysosomes
Golgi body A folded membrane containing enzymes that finish polypeptides and lipids delivered by the ER Packages finished products in vesicles that carry them to the plasma membrane or to lysosomes Lysosomes Vesicles containing enzymes that fuse with vacuoles and digest waste materials
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The Endomembrane System
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The Endomembrane System
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The Endomembrane System
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4.10 Lysosome Malfunction When lysosomes do not work properly, some cellular materials are not properly recycled, which can have devastating results Different kinds of molecules are broken down by different lysosomal enzymes One lysosomal enzyme breaks down gangliosides, a kind of lipid
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Tay Sachs Disease In Tay Sachs disease, a genetic mutation alters the lysosomal enzyme that breaks down gangliosides, which accumulate in nerve cells Affected children usually die by age five
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4.11 Other Organelles Eukaryotic cells make most of their ATP in mitochondria Plastids function in storage and photosynthesis in plants and some types of algae
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Mitochondria Mitochondrion
Eukaryotic organelle that makes the energy molecule ATP through aerobic respiration Contains two membranes, forming inner and outer compartments; buildup of hydrogen ions in the outer compartment drives ATP synthesis Has its own DNA and ribosomes Resembles bacteria; may have evolved through endosymbiosis
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Mitochondrion
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Plastids Plastids Chloroplasts
Organelles that function in photosynthesis or storage in plants and algae; includes chromoplasts, amyloplasts, and chloroplasts Chloroplasts Plastids specialized for photosynthesis Resemble photosynthetic bacteria; may have evolved by endosymbiosis
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The Chloroplast
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The Central Vacuole Central vacuole
A plant organelle that occupies 50 to 90 percent of a cell’s interior Stores amino acids, sugars, ions, wastes, toxins Fluid pressure keeps plant cells firm
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4.12 Cell Surface Specializations
A wall or other protective covering often intervenes between a cell’s plasma membrane and the surroundings
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Eukaryotic Cell Walls Animal cells do not have walls, but plant cells and many protist and fungal cells do Primary cell wall A thin, pliable wall formed by secretion of cellulose into the coating around young plant cells Secondary cell wall A strong wall composed of lignin, formed in some plant stems and roots after maturity
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Plant Cell Walls
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Figure 4.22 Some characteristics of plant cell walls. Fig. 4-22a, p. 70
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Figure 4.22 Some characteristics of plant cell walls. Fig. 4-22b, p. 70
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Figure 4.22 Some characteristics of plant cell walls. Fig. 4-22c, p. 70
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Plant Cuticle Cuticle A waxy covering that protects exposed surfaces and limits water loss
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Matrixes Between Animal Cells
Extracellular matrix (ECM) A nonliving, complex mixture of fibrous proteins and polysaccharides secreted by and surrounding cells; structure and function varies with the type of tissue Example: Bone is mostly ECM, composed of collagen (fibrous protein) and hardened by mineral deposits
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ECM A bone cell surrounded by extracellular matrix
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Cell Junctions Cell junctions allow cells to interact with each other and the environment In plants, plasmodesmata extend through cell walls to connect the cytoplasm of two cells Animals have three types of cell junctions: tight junctions, adhering junctions, gap junctions
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Cell Junctions in Animal Tissues
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4.6-4.12 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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4.13 The Dynamic Cytoskeleton
Eukaryotic cells have an extensive and dynamic internal framework called a cytoskeleton Cytoskeleton An interconnected system of many protein filaments – some permanent, some temporary Parts of the cytoskeleton reinforce, organize, and move cell structures, or even a whole cell
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Components of the Cytoskeleton
Microtubules Long, hollow cylinders made of tubulin Form dynamic scaffolding for cell processes Microfilaments Consist mainly of the globular protein actin Make up the cell cortex Intermediate filaments Maintain cell and tissue structures
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Figure 4.26 Components of the cytoskeleton. Below, a fluorescence micrograph shows microtubules (yellow) and actin microfilaments (blue) in the growing end of a nerve cell. These cytoskeletal elements support and guide the cell’s lengthening. Fig (a-c), p. 72
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Figure 4.26 Components of the cytoskeleton. Below, a fluorescence micrograph shows microtubules (yellow) and actin microfilaments (blue) in the growing end of a nerve cell. These cytoskeletal elements support and guide the cell’s lengthening. Fig. 4-26d, p. 72
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Motor Proteins Motor proteins
Accessory proteins that move molecules through cells on tracks of microtubules and microfilaments Energized by ATP Example: kinesins
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Motor Proteins: Kinesin
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Cilia, Flagella, and False Feet
Eukaryotic flagella and cilia Whiplike structures formed from microtubules organized into arrays Grow from a centriole which remains in the cytoplasm as a basal body Psueudopods “False feet” used by amoebas and other eukaryotic cells to move or engulf prey
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Moving Cells Flagellum of the human sperm, and pseudopods of a predatory amoeba
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Eukaryotic Flagella and Cilia
Figure 4.29 Eukaryotic flagella and cilia. Eukaryotic Flagella and Cilia Fig. 4-29a, p. 73
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Figure 4.29 Eukaryotic flagella and cilia. Fig. 4-29b, p. 73
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Figure 4.29 Eukaryotic flagella and cilia. Fig. 4-29c, p. 73
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4.13 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 cell structures or the whole cell
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Summary: Components of Prokaryotic and Eukaryotic Cells
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