CHAPTER 4 A Tour of the Cell Modules 4.1 – 4.5

The Art of Looking at Cells Artists are often inspired by biology and biology depends on art The paintings of Wassily Kandinsky (1866-1944) show the influence of cellular forms

Illustration is an important way to represent what scientists see through microscopes The anatomist Santiago Ramón y Cajal (1852-1934) was trained as an artist He drew these retina nerve cells

The microscope was invented in the 17th century INTRODUCTION TO THE WORLD OF THE CELL The microscope was invented in the 17th century Using a microscope, Robert Hooke discovered cells in 1665 All living things are made of cells (cell theory)

4.1 Microscopes provide windows to the world of the cell The light microscope enables us to see the overall shape and structure of a cell Image seen by viewer Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source Figure 4.1A

Electron microscopes were invented in the 1950s They use a beam of electrons instead of light The greater resolving power of electron microscopes allows greater magnification reveals cellular details

Scanning electron microscope (SEM) Scanning electron micrograph of cilia Figure 4.1B

Transmission electron microscope (TEM) Transmission electron micrograph of cilia Figure 4.1C

4.2 Cell sizes vary with their function Below is a list of the most common units of length biologists use (metric) Table 4.2

Cell size and shape relate to function Figure 4.2

4.3 Natural laws limit cell size At minimum, a cell must be large enough to house the parts it needs to survive and reproduce The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes

A small cell has a greater ratio of surface area to volume than a large cell of the same shape Surface area of one large cube = 5,400 µm2 Total surface area of 27 small cubes = 16,200 µm2 Figure 4.3

4.4 Prokaryotic cells are small and structurally simple There are two kinds of cells: prokaryotic and eukaryotic Prokaryotic cells are small, relatively simple cells They do not have a nucleus

A prokaryotic cell is enclosed by a plasma membrane and is usually encased in a rigid cell wall The cell wall may be covered by a sticky capsule Prokaryotic flagella Ribosomes Capsule Cell wall Inside the cell are its DNA and other parts Plasma membrane Nucleoid region (DNA) Pili Figure 4.4

4.5 Eukaryotic cells are partitioned into functional compartments All other life forms are made up of one or more eukaryotic cells These are larger and more complex than prokaryotic cells Eukaryotes are distinguished by the presence of a true nucleus

An animal cell Smooth endoplasmic reticulum Nucleus Rough endoplasmic reticulum Flagellum Not in most plant cells Lysosome Centriole Ribosomes Peroxisome Golgi apparatus Microtubule Plasma membrane Cytoskeleton Intermediate filament Microfilament Mitochondrion Figure 4.5A

The plasma membrane controls the cell’s contact with the environment The cytoplasm contains organelles Many organelles have membranes as boundaries These compartmentalize the interior of the cell This allows the cell to carry out a variety of activities simultaneously

A plant cell has some structures that an animal cell lacks: Chloroplasts A rigid cell wall

Rough endoplasmic reticulum Nucleus Ribosomes Smooth endoplasmic reticulum Golgi apparatus Microtubule Central vacuole Not in animal cells Intermediate filament Cytoskeleton Chloroplast Microfilament Cell wall Mitochondrion Peroxisome Plasma membrane Figure 4.5B

CHAPTER 4 A Tour of the Cell Modules 4.6 – 4.14

4.6 The nucleus is the cell’s genetic control center ORGANELLES OF THE ENDOMEMBRANE SYSTEM 4.6 The nucleus is the cell’s genetic control center The largest organelle is usually the nucleus The nucleus is separated from the cytoplasm by the nuclear envelope The nucleus is the cellular control center It contains the DNA that directs the cell’s activities

Two membranes of nuclear envelope NUCLEUS Chromatin Two membranes of nuclear envelope Nucleolus Pore ROUGH ENDOPLASMIC RETICULUM Ribosomes Figure 4.6

The endomembrane system is a collection of membranous organelles 4.7 Overview: Many cell organelles are related through the endomembrane system The endomembrane system is a collection of membranous organelles These organelles manufacture and distribute cell products The endomembrane system divides the cell into compartments Endoplasmic reticulum (ER) is part of the endomembrane system

4.8 Rough endoplasmic reticulum makes membrane and proteins The rough ER manufactures membranes Ribosomes on its surface produce proteins 1 2 3 4 Transport vesicle buds off Ribosome Sugar chain Glycoprotein Secretory (glyco-) protein inside transport vesicle ROUGH ER Polypeptide Figure 4.8

4.9 Smooth endoplasmic reticulum has a variety of functions Smooth ER synthesizes lipids In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

SMOOTH ER ROUGH ER Nuclear envelope Ribosomes SMOOTH ER ROUGH ER Figure 4.9

4.10 The Golgi apparatus finishes, sorts, and ships cell products The Golgi apparatus consists of stacks of membranous sacs These receive and modify ER products, then send them on to other organelles or to the cell membrane

The Golgi apparatus Golgi apparatus Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming “Shipping” side of Golgi apparatus Transport vesicle from the Golgi Figure 4.10

4.11 Lysosomes digest the cell’s food and wastes Lysosomes are sacs of digestive enzymes budded off the Golgi LYSOSOME Nucleus Figure 4.11A

Lysosomal enzymes digest food destroy bacteria recycle damaged organelles function in embryonic development in animals

Transport vesicle (containing inactive hydrolytic enzymes) Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus Engulfment of particle Lysosome engulfing damaged organelle “Food” LYSOSOMES Digestion Food vacuole Figure 4.11B

4.12 Connection: Abnormal lysosomes can cause fatal diseases Lysosomal storage diseases are hereditary They interfere with other cellular functions Examples: Pompe’s disease, Tay-Sachs disease

4.13 Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole The vacuole has lysosomal and storage functions Central vacuole Nucleus Figure 4.13A

Protists may have contractile vacuoles These pump out excess water Nucleus Contractile vacuoles Figure 4.13B

4.14 A review of the endomembrane system The various organelles of the endomembrane system are interconnected structurally and functionally Transport vesicle from Golgi Transport vesicle from ER Rough ER Plasma membrane Vacuole Nucleus Lysosome Golgi apparatus Smooth ER Nuclear envelope Figure 4.14

CHAPTER 4 A Tour of the Cell Modules 4.15 – 4.21

4.15 Chloroplasts convert solar energy to chemical energy ENERGY-CONVERTING ORGANELLES 4.15 Chloroplasts convert solar energy to chemical energy Chloroplasts are found in plants and some protists Chloroplasts convert solar energy to chemical energy in sugars Chloroplast Stroma Inner and outer membranes Granum Intermembrane space Figure 4.15

4.16 Mitochondria harvest chemical energy from food Mitochondria carry out cellular respiration This process uses the chemical energy in food to make ATP for cellular work

MITOCHONDRION Outer membrane Intermembrane space Inner membrane Cristae Matrix Figure 4.16

THE CYTOSKELETON AND RELATED STRUCTURES 4.17 The cell’s internal skeleton helps organize its structure and activities A network of protein fibers makes up the cytoskeleton Figure 4.17A

Microfilaments of actin enable cells to change shape and move Intermediate filaments reinforce the cell and anchor certain organelles Microtubules give the cell rigidity provide anchors for organelles act as tracks for organelle movement

INTERMEDIATE FILAMENT Tubulin subunit Actin subunit Fibrous subunits 25 nm 7 nm 10 nm MICROFILAMENT INTERMEDIATE FILAMENT MICROTUBULE Figure 4.17B

4.18 Cilia and flagella move when microtubules bend Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells A cilia or flagellum is composed of a core of microtubules wrapped in an extension of the plasma membrane

Electron micrograph of sections: FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasma membrane Flagellum Central microtubules Outer microtubule doublet Plasma membrane Basal body Basal body (structurally identical to centriole) Figure 4.18A

Clusters of microtubules drive the whipping action of these organelles Microtubule doublet Sliding force Dynein arm Figure 4.18B

4.19 Cell surfaces protect, support, and join cells EUKARYOTIC CELL SURFACES AND JUNCTIONS 4.19 Cell surfaces protect, support, and join cells Cells interact with their environments and each other via their surfaces Plant cells are supported by rigid cell walls made largely of cellulose They connect by plasmodesmata, channels that allow them to share water, food, and chemical messages

Walls of two adjacent plant cells Vacuole PLASMODESMATA Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.19A

Animal cells are embedded in an extracellular matrix It is a sticky layer of glycoproteins It binds cells together in tissues It can also have protective and supportive functions

Tight junctions can bind cells together into leakproof sheets Anchoring junctions link animal cells Communicating junctions allow substances to flow from cell to cell TIGHT JUNCTION ANCHORING JUNCTION COMMUNICATING JUNCTION Plasma membranes of adjacent cells Extracellular matrix Figure 4.19B

4.20 Eukaryotic organelles comprise four functional categories Eukaryotic organelles fall into four functional groups Table 4.20

Table 4.20 (continued)

4.21 Connection: Extraterrestrial life-forms may share features with life on Earth It is almost certain that Earth is the only life-bearing planet in our solar system But it is conceivable that conditions on some of the moons of the outer planets or on planets in other solar systems have allowed the evolution of life Figure 4.21