Chapter 6 Part A A tour of The Cell

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 light microscope is used by many scientists. Light passes through the specimen. Lenses enlarge, or magnify, the image.

Microscopes as a Window on the World of Cells glena

Magnification Resolving power 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 accumulation of scientific evidence since the cell discovery (1665) led to the cell theory. All living things are composed of cells. All cells are formed from previously existing cells.

The electron microscope (EM) uses a beam of electrons. It has a higher resolving power than the light microscope (200 nm vs 2 nm). The electron microscope can magnify up to 100,000X. Such power reveals the diverse parts within a cell.

Figure 4.3

The scanning electron microscope (SEM) is used: To study the detailed architecture of the surface of a cell.

The transmission electron microscope (TEM) is: useful for exploring the internal structure of a cell.

The Two Major Categories of Cells The countless cells on earth fall into two categories: Prokaryotic cells Eukaryotic cells Prokaryotic and eukaryotic cells differ in several respects.

Figure 4.4

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

(b) A thin section through the bacterium Bacillus coagulans (TEM) Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes Flagella: locomotion organelles of some bacteria (a) A typical rod-shaped bacterium 0.5 µm Bacterial chromosome Figure 6.6 A, B

Animal & Plant (Eukaryotic) Cells A animal cell Rough ER Smooth ER Centrosome CYTOSKELETON Microfilaments Microtubules Microvilli Peroxisome Lysosome Golgi apparatus Ribosomes In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Nucleolus Chromatin NUCLEUS Flagelium Intermediate filaments ENDOPLASMIC RETICULUM (ER) Mitochondrion Nuclear envelope Plasma membrane Figure 6.9

Ribosomes (small brwon dots) A plant cell Ribosomes (small brwon dots) Central vacuole Microfilaments Intermediate filaments Microtubules Rough endoplasmic reticulum Smooth Chromatin NUCLEUS Nuclear envelope Nucleolus Chloroplast Plasmodesmata Wall of adjacent cell Cell wall Golgi apparatus Peroxisome Tonoplast Centrosome Plasma membrane Mitochondrion CYTOSKELETON In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Figure 6.9

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins Plasma membrane separates cell living & nonliving surroundings. Membranes composed mostly of lipids & proteins Lipids belong to a special category (phospholipids) Phospholipids form a two-layered membrane, the phospholipid bilayer. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 4.7a

Figure 4.7b

Membrane phospholipids and proteins: Can drift about in the plane of the membrane. Behavior why membrane described as a fluid mosaic: Fluid: Molecules freely moving w/in membrane. Mosaic: Diversity of proteins w/in membrane.

These extracellular coats help: Cell Surfaces Most cells secrete: Coating materials of one kind or another Coats are external to the plasma membrane. These extracellular coats help: Protect cells Support cells Facilitate cellular interactions in tissues.

Plant cells have the cell walls, which: Help protect the cells Maintain their shape Keep the cells from absorbing too much water. Animal cells have an extracellular matrix, which: Helps hold cells together in tissues Protects cells Supports cells.

Structure and Function of the Nucleus Is bordered by a double membrane (nuclear envelope) containing communication pores Contains chromatin fibers (DNA molecule & proteins; each fiber is a chromosome). Chromosomes are visible during cell division Contains a nucleolus (mass of fibers & granules)

Structure and Function of the Nucleus The nucleus is the manager of the cell. Genes are stretches of DNA Genes store information for protein production Nucleolus make ribosome components Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 4.8

How DNA Controls the Cell DNA transfers its coded information into mRNA mRNA moves to cytoplasm mRNA information is used to make protein Ribosomes are responsible for protein synthesis

Figure 4.9

Many of the membranous organelles in the cell belong to: The Endomembrane System: Manufacturing and Distributing Cellular Products Many of the membranous organelles in the cell belong to: The endomembrane system, which includes: Endoplasmic reticulum Golgi appraatus Lysosomes Vacuoles Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

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

Figure 4.10

The “roughness” of the rough ER is due to: Ribosomes studding the outside membrane. The functions of the rough ER include: Producing two types of proteins Membrane protein (new membrane) Secretory protein (salivary glands) Packages synthesized molecules into transport vesicles

Figure 4.11