CHAPTER 4 A Tour of the Cell

Biology and Society: Cells That Cure During a heart attack, Heart muscle cells die because they are starved for oxygen. Unfortunately, these kinds of cells do not regenerate. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

In recent years, a new treatment called “cell therapy” has emerged. In this procedure, cells are taken from other parts of the body And delivered to the ailing heart, facilitating healing.

Figure 4.1

The Microscopic World of Cells Organisms are either: Single-celled, such as most bacteria and protists Multicelled, such as plants, animals, and most fungi

The Microscopic World of Cells The human body is made up of trillions of cells many of which are specialized Muscle cells, Nerve cells, & blood cells…

Cells were first discovered in 1665 by Robert Hooke. The accumulation of scientific evidence led to the cell theory. All living things are composed of cells. All cells are formed from previously existing cells.

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

Microscopes as a Window on the World of Cells The light microscope is used by many scientists. Light passes through the specimen. Lenses enlarge, or magnify, the image. Magnification Is an increase in the specimen’s apparent size. Resolving power Is the ability of an optical instrument to show two objects as being separate.

The electron microscope (EM) uses a beam of electrons. It has a higher resolving power than the light microscope. The electron microscope can magnify up to 100,000X. Such power reveals the diverse parts within a cell.

Microscopes as a Window on the World of Cells The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell. Produces a 3D image Used to study cell surfaces

Microscopes as a Window on the World of Cells The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell. An electron beam is aimed through a thin section.

The Two Major Categories of Cells The countless cells on earth fall into two categories: Prokaryotic cells Eukaryotic cells Both cells Are surrounded by a plasma membrane Consist of cytoplasm and organelles and contain DNA Prokaryotic and eukaryotic cells differ in several respects.

Figure 4.4

Most cells are 10-100 micrometers in size Cell size and shape relate to function Figure 4.2

Natural laws limit cell size The lower limit of cell size is determined by the fact that 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. The ratio of surface are to volume imposes limits on cell size Muscle and nerve cells can be very long because they are thin and have more surface area compared to volume

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

Prokaryotic cells Are smaller than eukaryotic cells. Lack internal structures surrounded by membranes. Lack a nucleus.

The cell wall may be covered by a sticky capsule 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 Nucleoid Region (DNA) Capsule Cell wall Inside the cell are its DNA and other parts Plasma membrane Ribosome Pili Figure 4.4

Structures of Prokaryotic Cells Nucleoid region – area where DNA is coiled in the cytoplasm. DNA is in direct contact with the rest of the cell Plasmid – smaller circular DNA molecules Ribosomes – where proteins are made Plasma membrane – encloses the cytoplasm of the prokaryotic cell Cell wall – rigid, composed of lipids, carbohydrates and protein. Protects the cell and maintains its shape

Cell Wall components determine if bacteria is classified as gram positive (+) or gram negative In general more toxic and resistant to antibiotics http://www.bio.upenn.edu/computing/media/Instructional.Stain.Gram.php

Structures of the Prokaryotic Cell Capsule – sticky outer coat that surrounds some prokaryotes. Protects the cell surface. Helps bacteria attach to surfaces Pili – short surface projections found in some prokaryotes. Helps attach bacteria to surfaces Flagella – long whiplike extensions found in some prokaryotes. Propel cell through liquid environments

The Role of Bacteria in the Nitrogen Cycle

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

A Panoramic View of Eukaryotic Cells An idealized animal cell Cytoplasmic Streaming

Figure 4.6b

The Plasma Membrane Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function?

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins The plasma membrane separates the living cell from its nonliving surroundings. The membranes of cells are composed mostly of: Lipids Proteins Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

The plasma membrane The lipids belong to a special category called phospholipids. Phospholipids form a two-layered membrane, the phospholipid bilayer.

The plasma membrane Most membranes have specific proteins embedded in the phospholipid bilayer. Membranes also contain cholesterol wedged between the phospholipids. Carbohydrates are found on the external surface attached to phospholipids or protein.

Membrane phospholipids and proteins can drift about in the plane of the membrane. This behavior leads to the description of a membrane as a fluid mosaic: Molecules can move freely within the membrane. A diversity of proteins exists within the membrane.

Most cells secrete materials for coats of one kind or another Cell Surfaces Most cells secrete materials for coats of one kind or another That are external to the plasma membrane. These extracellular coats help protect and support cells And facilitate interactions between cellular neighbors in tissues.

Animal cells have an extracellular matrix, Which helps hold cells together in tissues and protects and supports them.

The Cell Wall Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function?

Plant cells have cell walls, Which help protect the cells, maintain their shape, and keep the cells from absorbing too much water. Made of Cellulose and other components in plant cells Prokaryotes’ cell wall performs the same function, though it is composed of different organic molecules

Cell Junctions “Tunnels” that Connects the cytoplasm of one plant cell with the cytoplasm of another plant cell, thus allowing small substances to move from cell to cell. There are other types of junctions, but that is for Advanced bio I Ex: cell Junctions

Would this organelle/ structure also be found in prokaryotes? The Nucleus Would this organelle/ structure also be found in prokaryotes?

The Nucleolus

Figure 4.8

The Nucleus and Ribosomes: Genetic Control of the Cell The nucleus is the manager of the cell Genes in the nucleus store information necessary to produce proteins which direct the cell’s activities It is usually the largest organelle. It contains chromatin (DNA) The nucleus is separated from the cytoplasm by the nuclear envelope. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Structure and Function of the Nucleolus The nucleolus is found within the nucleus It is a mass of fibers and granules It is where ribosomes are made

Ribosomes Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function?

Ribosomes Ribosomes are responsible for protein synthesis. DNA controls the cell by transferring its coded information into RNA. The information in the RNA is used by ribosomes to make proteins.

The endomembrane system is a collection of membranous organelles The Endomembrane System: Manufacturing and Distributing Cellular Products The endomembrane system is a collection of membranous organelles These organelles manufacture and distribute cell products The endomembrane system divides the cell into compartments Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 4.10

The Endoplasmic Reticulum The endoplasmic reticulum (ER) Produces an enormous variety of molecules. Is composed of smooth and rough ER.

Rough Endoplasmic Reticulum

Rough ER makes membrane and proteins The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane. The functions of the rough ER include: Producing two types of membrane proteins Producing new membrane

Rough Endoplasmic REticulum After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles. 1 2 3 4 Transport vesicle buds off Ribosome Sugar chain Glycoprotein Secretory (glyco-) protein inside transport vesicle ROUGH ER Polypeptide

Smooth Endoplasmic Reticulum

Smooth ER Continuous with the rough ER Lacks the surface ribosomes of ER Produces lipids, including steroids. For example how cells in your ovaries or testes produce steroid based sex hormones like estrogen and testosterone In some cells, it regulates carbohydrate metabolism In liver cells breaks down toxins and drugs Antibiotics, barbiturates, alcohol In other cells- especially muscle cells it stores calcium ions.

The Golgi Complex

Figure 4.12

The Golgi Apparatus The Golgi apparatus Works in partnership with the ER. It consists of stacks of membranous sacs Refines, stores, and distributes the chemical products of cells.

Vesicles

Lysosomes A lysosome is a membrane-enclosed sac. It contains digestive enzymes. The enzymes break down macromolecules.

Figure 4.13a

Figure 4.13b

Lysosomes have several types of digestive functions. They fuse with food vacuoles to digest the food. They break down damaged organelles. Lysosome Formation

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

Vacuoles Vacuoles are membranous sacs. Two types are the contractile vacuoles of protists and the central vacuoles of plants. Paramecium Vacuole

The Central Vacuole

Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole The vacuole absorbs water, stores vital chemicals, stores waste products Central vacuole Nucleus Figure 4.13A

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

Figure 4.15

Chloroplasts and Mitochondria: Energy Conversion Cells require a constant energy supply to do all the work of life. This function is carried out by the chloroplasts and the mitochondria Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Chloroplasts

Chloroplasts Chloroplasts are found in plants and some protists. Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy in sugars.

Mitochondria

Mitochondria Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules.

Mitochondria and chloroplasts share another feature unique among eukaryotic organelles. They contain their own DNA. The existence of separate “mini-genomes” is believed to be evidence that Mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.

Cytoskeleton

The Cytoskeleton: Cell Shape and Movement The cytoskeleton is an infrastructure of the cell consisting of a network of fibers. One function of the cytoskeleton is to provide mechanical support to the cell and maintain its shape. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

The Cytoskeleton The cytoskeleton can change the shape of a cell. This allows cells like amoebae to move.

Flagella Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function?

Cilia and Flagella Cilia and flagella are motile appendages. Flagella propel the cell in a whiplike motion. Cilia move in a coordinated back-and-forth motion.

Cilia and Flagella Some cilia or flagella extend from nonmoving cells. The human windpipe is lined with cilia.

Evolution Connection: The Origin of Membranes Phospholipids were probably among the organic molecules on the early Earth. When mixed with water, phospholipids spontaneously form membranes. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings