Learning objectives Understand the basic tenets of the cell theory Contrast the general features of prokaryotic and eukaryotic cells Be able to distinguish the organelles and structures typical of eukaryotic plant and animal cells. Know the functions associated with these organelles and structures.

4.2 Cell Structure The cell is the smallest unit that shows the properties of life All cells have a plasma membrane and cytoplasm, and all start out life with DNA

Components of All Cells 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

Organelles Organelles are structures that carry out special metabolic functions inside a cell Membrane-enclosed organelles compartmentalize tasks such as building, modifying, and storing substances

Prokaryotic and Eukaryotic Cells Cell interior is divided into functional compartments, including a nucleus Prokaryotic cell Small, simple cells without a nucleus

B A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus. A A prokaryotic cell. cytoplasm DNA plasma membrane nucleus Figure 4.2 Animated Overview of the general organization of a cell.Archaea are similar to bacteria in overall structure; both are generally much smaller than eukaryotic cells. If the two cells depicted here had been drawn to the same scale, the prokaryotic cell would be about this big: B A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus. Figure 4-2 p54 6

ANIMATED FIGURE: Overview of cells To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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

cell’s exterior plasma membrane cell’s interior Figure 4.3 Preview of cell membranes. A plasma membrane separates a cell from its external environment. Proteins (in color) embedded in the lipid bilayer (gray) carry out special membrane functions. Chapter 5 returns to membrane structure and function. plasma membrane cell’s interior Figure 4-3 p54

The Cell Theory Emerges 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 Brown was the first to identify a cell nucleus

Cell Theory The cell theory, a foundation of modern biology, states that cells are the fundamental units of life 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 a preexisting cell Each cell passes its hereditary material to its offspring

Take-Home Message: How are all cells alike? All cells start life with a plasma membrane, cytoplasm, and a region of DNA, which, in eukaryotic cells only, is enclosed by a nucleus The surface-to-volume ratio limits cell size and influences cell shape Observations of cells led to the cell theory: All organisms consist of one or more cells; the cell is the smallest unit of life; each new cell arises from another cell; and a cell passes hereditary material to its offspring

4.3 How Do We See Cells? Most cells are 10–20 micrometers in diameter, about fifty times smaller than the unaided human eye can perceive One micrometer (μm) is one-thousandth of a millimeter, which is one-thousandth of a meter We use different types of microscopes to study different aspects of organisms, from the smallest to the largest

Table 4-1 p56

Modern Microscopes Light microscopes Phase-contrast microscopes Reflected light microscopes Fluorescence microscopes Electron microscopes Transmission electron microscopes Scanning electron microscopes

path of light rays (bottom to top) to eye prism that directs rays to ocular lens ocular lens objective lenses specimen stage Figure 4.5 Animated Examples of microscopes. a A compound light microscope. condenser lens illuminator light source (in base) focusing knob Figure 4-5a p56

incoming electron beam condenser lens specimen on grid objective lens Figure 4.5 Animated Examples of microscopes. b A transmission electron microscope (TEM). projective lens phosphor screen Figure 4-5b p56

Different Microscopes, Different Characteristics

Relative Sizes human eye (no microscope) largest organisms small animals frog eggs 100 m 10 m 1 m 10 cm 1 cm 1 mm 100 µm Figure 4.7 Relative sizes. Below, the diameter of most cells is in the range of 1 to 100 micrometers. Table 4.1 shows conversions among units of length; also see Units of Measure, Appendix VIII.

mitochondria, chloroplasts Relative Sizes electron microscopes light microscopes most eukaryotic cells viruses most bacteria mitochondria, chloroplasts molecules of life small molecules DNA carbohydrates proteins lipids Figure 4.7 Relative sizes. Below, the diameter of most cells is in the range of 1 to 100 micrometers. Table 4.1 shows conversions among units of length; also see Units of Measure, Appendix VIII. 10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm

Take-Home Message: How do we see cells? Most cells are visible only with the help of microscopes Different types of microscopes reveal different aspects of cell structure

4.4 Introducing “Prokaryotes” 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

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

General Prokaryote Body Plan Ribosomes Organelles upon which polypeptides are assembled Nucleoid An irregularly shaped region of cytoplasm containing a single, circular DNA molecule Plasmids Small circles of DNA carry a few genes that can provide advantages, such as resistance to antibiotics

General Prokaryote Body Plan 7 flagellum 1 cytoplasm, with ribosomes plasma membrane 3 5 capsule 6 pilus Figure 4.8 Animated Generalized body plan of a “prokaryote” (a bacterium or archaeon). DNA in nucleoid cell wall 2 4

Bacteria Figure 4.9 A sampling of bacteria (this page) and archaea (facing page).

Biofilms Although prokaryotes are all single-celled, few live alone Single-celled organisms sharing a secreted layer of polysaccharides and glycoproteins May include bacteria, algae, fungi, protists, and archaeans

Dental Plaque: A Biofilm Figure 4.10 Oral bacteria in dental plaque, a biofilm. Three species of bacteria (tan, green) and a yeast (red) stick to one another and to teeth via a gluelike mass of shared, secreted polysaccharides (pink). Other secretions of these organisms cause cavities and periodontal disease.

Take-Home Message: How are bacteria and archaea alike? Bacteria and archaea do not have a nucleus. Most kinds have a cell wall around their plasma membrane; the permeable wall reinforces and imparts shape to the cell body The structure of bacteria and archaea is relatively simple, but as a group these organisms are the most diverse forms of life; they inhabit nearly all regions of the biosphere Some metabolic processes occur at the plasma membrane of bacteria and archaea; they are similar to complex processes that occur at certain internal membranes of eukaryotic cells

4.5 Introducing Eukaryotic Cells All protists, fungi, plants, and animals are eukaryotes 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

Importance of Organelles Membranes around eukaryotic organelles control the types and amounts of substances that enter and exit them Such control maintains a special internal environment that allows the organelle to carry out its particular function Some metabolic pathways take place in a series of different organelles

Components of Eukaryotic Cells

Components of Eukaryotic Cells

Cell Wall Central Vacuole Chloroplast nuclear envelope Cytoskeleton nucleolus Nucleus DNA in nucleoplasm microtubules microfilaments intermediate filaments (not shown) Ribosomes Rough ER Mitochondrion Plasmodesma Smooth ER Figure 4.12 Animated Organelles and structures typical of (a) plant cells and (b) animal cells. A Typical plant cell components. Golgi Body Plasma Membrane Lysosome-Like Vesicle Figure 4-12a p61 34

Modifies proteins made by ribosomes attached to it Rough ER Makes lipids, breaks down carbohydrates and fats, inactivates toxins Smooth ER Finishes, sorts, ships lipids, enzymes, and proteins Golgi Body Digests, recycles materials Lysosome Stepped Art p64

Prepare to be amazed…. http://www.youtube.com/watch?v=wJyUtbn0O5Y

Take-Home Message: What do eukaryotic cells have in common? All eukaryotic cells start life with a nucleus and other membrane-enclosed organelles

4.6 The Nucleus All of a eukaryotic cell’s DNA is in its nucleus The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm The nuclear envelope controls when DNA is accessed

Table 4-2 p60

nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER Figure 4.13 Animated The cell nucleus. TEM at right, nucleus of a mouse pancreas cell. ER Figure 4-13a p62

nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER Figure 4.13 Animated The cell nucleus. TEM at right, nucleus of a mouse pancreas cell. ER Figure 4-13b p62

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

Structure of the Nuclear Envelope

B Each nuclear pore is an organized cluster of membrane proteins that selectively allows certain substances to cross it on their way into and out of the nucleus. nuclear pore Figure 4.14 Animated Structure of the nuclear envelope. A The outer surface of this nuclear envelope was split apart to reveal the pores that span the two lipid bilayers. Figure 4-14ab p63

nuclear envelope (two lipid bilayers) nuclear pore nuclear envelope (two lipid bilayers) Figure 4.14 Animated Structure of the nuclear envelope. cytoplasm Figure 4-14b p63

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

Chromosomes Chromatin 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

A Condensed Chromosome

Take-Home Message: What is the function of the cell nucleus? A nucleus protects and controls access to a eukaryotic cell’s DNA The nuclear envelope is a double lipid bilayer. Proteins embedded in it control the passage of molecules between the nucleus and the cytoplasm