© 2010 Pearson Education, Inc. CHAPTER 4: A TOUR OF THE CELL 6 SECTIONS: 1)Microscopic World of Cells 2) Membrane Structure 3) Nucleus & Ribosomes: Genetic control of the cell 4)Endomembrane System: Manufacturing & Distributing Cell Products 5) Chloroplasts & Mitochondria: Energy Production 6) Cytoskeleton: Cell shape & movement

Biology and Society: Drugs That Target Bacterial Cells Antibiotics were first isolated from mold in The widespread use of antibiotics drastically decreased deaths from bacterial infections. © 2010 Pearson Education, Inc. Most antibiotics kill bacteria while minimally harming the human host by binding to structures found only on bacterial cells. Some antibiotics bind to the bacterial ribosome, leaving human ribosomes unaffected. Other antibiotics target enzymes found only in the bacterial cells.

Colorized TEM Figure 4.00

© 2010 Pearson Education, Inc. THE MICROSCOPIC WORLD OF CELLS Organisms are either Single-celled, such as most prokaryotes and protists or Multicelled, such as plants, animals, and most fungi Light microscopes can be used to explore the structures and functions of cells, in living cells. When scientists examine a specimen on a microscope slide Light passes through the specimen Lenses enlarge, or magnify, the image

Light Micrograph (LM) (for viewing living cells) Light micrograph of a protist, Paramecium LM Colorized SEM Scanning Electron Micrograph (SEM) (for viewing surface features) Scanning electron micrograph of Paramecium TYPES OF MICROGRAPHS Transmission Electron Micrograph (TEM) (for viewing internal structures) Transmission electron micrograph of Paramecium Colorized TEM Figure 4.1

Light Micrograph (LM) (for viewing living cells) Light micrograph of a protist, Paramecium LM Figure 4.1a

Colorized SEM Scanning Electron Micrograph (SEM) (for viewing surface features) Scanning electron micrograph of Paramecium Figure 4.1b

Transmission Electron Micrograph (TEM) (for viewing internal structures) Transmission electron micrograph of Paramecium Colorized TEM Figure 4.1c

© 2010 Pearson Education, Inc. Magnification is an increase in the specimen’s apparent size. Resolving power is the ability of an optical instrument to show two objects as separate. Cells were first described in 1665 by Robert Hooke. The accumulation of scientific evidence led to the cell theory. All living things are composed of cells. All cells come from other cells. The electron microscope (EM) uses a beam of electrons, which results in better resolving power than the light microscope. Two kinds of electron microscopes reveal different parts of cells. Scanning electron microscopes examine cell surfaces. Transmission electron microscopes (TEM) are useful for internal details of cells. The electron microscope can Magnify up to 100,000 times Distinguish between objects 0.2 nanometers apart

Figure 4.2 An electron micrograph is formed by a beam of e- that is generated at the top of the column and travels through the specimen observed.

10 m 1 m 10 cm 1 cm 1 mm 100 mm 10 mm Human height Chicken egg Frog eggs Length of some nerve and muscle cells Unaided eye Light microscope Plant and animal cells Most bacteria Nucleus Mitochondrion 1 mm 100 nm 10 nm 1 nm 0.1 nm Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Electron microscope Figure 4.3

© 2010 Pearson Education, Inc. The Two Major Categories of Cells The countless cells on earth fall into two categories: Prokaryotic cells — Bacteria and Archaea Eukaryotic cells — plants, fungi, and animals All cells have several basic features. They are all bound by a thin outer membrane called plasma membrane, which regulates the traffic of molecules between the cell and its surroundings. All cells have DNA and ribosomes, tiny structures that build proteins. Prokaryotic and eukaryotic cells have important differences. Prokaryotic cells are older than eukaryotic cells. Prokaryotes appeared about 3.5 billion years ago. Eukaryotes appeared about 2.1 billion years ago.

© 2010 Pearson Education, Inc. Prokaryotes Are smaller than eukaryotic cells Lack internal structures surrounded by membranes Lack a nucleus Have a rigid cell wall Eukaryotes Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions. The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA.

Plasma membrane (encloses cytoplasm) Cell wall (provides Rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) Colorized TEM Figure 4.4

© 2010 Pearson Education, Inc. An Overview of Eukaryotic Cells Eukaryotic cells are fundamentally similar. The region between the nucleus and plasma membrane is the cytoplasm. The cytoplasm consists of various organelles suspended in fluid. Unlike animal cells, plant cells have Protective cell walls Chloroplasts, which convert light energy to the chemical energy of food

Cytoskeleton RibosomesCentriole Lysosome Flagellum Nucleus Plasma membrane Mitochondrion Rough endoplasmic reticulum (ER) Golgi apparatus Smooth endoplasmic reticulum (ER) Idealized animal cell Idealized plant cell Cytoskeleton Mitochondrion Nucleus Rough endoplasmic reticulum (ER) Ribosomes Smooth endoplasmic reticulum (ER) Golgi apparatus Plasma membrane Channels between cells Not in most plant cells Central vacuole Cell wall Chloroplast Not in animal cells Figure 4.5

Cytoskeleton Ribosomes Centriole Lysosome Flagellum Nucleus Plasma membrane Mitochondrion Rough endoplasmic reticulum (ER) Golgi apparatus Smooth endoplasmic reticulum (ER) Idealized animal cell Not in most plant cells Figure 4.5a

Idealized plant cell Cytoskeleton Mitochondrion Nucleus Rough endoplasmic reticulum (ER) Ribosomes Smooth endoplasmic reticulum (ER) Golgi apparatus Plasma membrane Channels between cells Central vacuole Cell wall Chloroplast Not in animal cells Figure 4.5b

© 2010 Pearson Education, Inc. MEMBRANE STRUCTURE The plasma membrane separates the living cell from its nonliving surroundings. The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins The membranes of cells are composed mostly of Lipids Proteins The lipids belong to a special category called phospholipids. They are related to dietary fats but have only two fatty acid tails instead of three. In place of the 3 rd fatty acid tail, there is a phosphate group (PO4-). The phosphate is electrically charged, making it hydrophilic, but the 2 fatty acid tails are hydrophobic. Phospholipids form a two-layered membrane, the phospholipid bilayer.

© 2010 Pearson Education, Inc. Animation: Tight Junctions Animation: Gap Junctions Animation: Desmosomes

(a) Phospholipid bilayer of membrane (b) Fluid mosaic model of membrane Outside of cell Hydrophilic head Hydrophobic tail Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Phospholipid bilayer Phospholipid Proteins Cytoplasm (inside of cell) Figure 4.6

(a) Phospholipid bilayer of membrane Outside of cell Hydrophilic head Hydrophobic tail Phospholipid Cytoplasm (inside of cell) Figure 4.6a

(b) Fluid mosaic model of membrane Outside of cell Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Phospholipid bilayer Proteins Cytoplasm (inside of cell) Figure 4.6b

© 2010 Pearson Education, Inc. Most membranes have specific proteins embedded in the phospholipid bilayer. These proteins help regulate traffic across the membrane and perform other functions. The plasma membrane is a fluid mosaic: Fluid because molecules can move freely past one another A mosaic because of the diversity of proteins in the membrane

© 2010 Pearson Education, Inc. The Process of Science: What Makes a Superbug? Some bacteria cause disease by rupturing the PM of human cells. Example: Staphylococcus, found on the skin/nose; usually harmless but can multiply into an infection. Most staph infections are treated w/antibiotics, but some are resistant: MRSA (Methicillin-resistant Staph). Observation: Bacteria use a protein called PSM to disable human immune cells by forming holes in the plasma membrane. Question: Does PSM play a role in MRSA infections? Hypothesis: MRSA bacteria lacking the ability to produce PSM would be less deadly than normal MRSA strains.

© 2010 Pearson Education, Inc. Experiment: Researchers infected Seven mice with normal MRSA Eight mice with MRSA that does not produce PSM Results: All seven mice infected with normal MRSA died. Five of the eight mice infected with MRSA that does not produce PSM survived. Conclusions: MRSA strains appear to use the membrane-destroying PSM protein, but Factors other than PSM protein contributed to the death of mice

MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) Colorized SEM Figure 4.7-1

MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) Colorized SEM PSM proteins forming hole in human immune cell plasma membrane Plasma membrane PSM protein Pore Figure 4.7-2

MRSA bacterium producing PSM proteins Methicillin-resistant Staphylococcus aureus (MRSA) Colorized SEM PSM proteins forming hole in human immune cell plasma membrane Plasma membrane PSM protein Pore Cell bursting, losing its contents through the pores Figure 4.7-3

© 2010 Pearson Education, Inc. Cell Surfaces Plant cells have rigid cell walls surrounding the membrane. Plant cell walls Are made of cellulose Protect the cells Maintain cell shape Keep the cells from absorbing too much water Animal cells Lack cell walls Have an extracellular matrix, which Helps hold cells together in tissues Protects and supports them The surfaces of most animal cells contain cell junctions, structures that connect to other cells.

THE NUCLEUS AND RIBOSOMES: GENETIC CONTROL OF THE CELL The nucleus is the chief executive of the cell. Genes in the nucleus store information necessary to produce proteins. Proteins do most of the work of the cell. © 2010 Pearson Education, Inc. The nucleus is bordered by a double membrane called the nuclear envelope. Pores in the envelope allow materials to move between the nucleus and cytoplasm. The nucleus contains a nucleolus where ribosomes are made.

Ribosomes Chromatin Nucleolus Pore Nuclear envelope Surface of nuclear envelopeNuclear pores TEM Figure 4.8

Ribosomes ChromatinNucleolus Pore Nuclear envelope Figure 4.8a

Surface of nuclear envelope TEM Figure 4.8b

Nuclear pores TEM Figure 4.8c

© 2010 Pearson Education, Inc. Stored in the nucleus are long DNA molecules and associated proteins that form fibers called chromatin. Each long chromatin fiber constitutes one chromosome. The number of chromosomes in a cell depends on the species.

DNA molecule Chromosome Proteins Chromatin fiber Figure 4.9

© 2010 Pearson Education, Inc. Ribosomes Ribosomes are responsible for protein synthesis. Ribosome components are made in the nucleolus but assembled in the cytoplasm. Ribosomes may assemble proteins: Suspended in the fluid of the cytoplasm or Attached to the outside of an organelle called the endoplasmic reticulum

Ribosome Protein mRNA Figure 4.10

Ribosomes in cytoplasm Ribosomes attached to endoplasmic reticulum TEM Figure 4.11

© 2010 Pearson Education, Inc. How DNA Directs Protein Production DNA directs protein production by transferring its coded information into messenger RNA (mRNA). Messenger RNA exits the nucleus through pores in the nuclear envelope. mRNA carries the genetic message from a gene (DNA) to ribosomes that translate it into a protein. A ribosome moves along the mRNA translating the genetic message into a protein with a specific amino acid sequence. CENTRAL DOGMA!

Synthesis of mRNA in the nucleus Nucleus DNA mRNA Cytoplasm Figure

Synthesis of mRNA in the nucleus Nucleus DNA mRNA Cytoplasm mRNA Movement of mRNA into cytoplasm via nuclear pore Figure

Synthesis of mRNA in the nucleus Nucleus DNA mRNA Cytoplasm mRNA Movement of mRNA into cytoplasm via nuclear pore Ribosome Protein Synthesis of protein in the cytoplasm Figure

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS Many membranous organelles forming the endomembrane system in a cell are interconnected either Directly or Through the transfer of membrane segments between them © 2010 Pearson Education, Inc.

The Endoplasmic Reticulum The endoplasmic reticulum (ER) is one of the main manufacturing facilities in a cell. The ER Produces an enormous variety of molecules The ER membrane separates its internal compartment from the surrounding fluid in the cytoplasm. (* The nucleus is contiguous with the ER) Is composed of smooth and rough ER, which are physically connected but differ in structure and function

Nuclear envelope Smooth ER Rough ER Ribosomes TEM Figure 4.13

Nuclear envelope Smooth ER Rough ER Ribosomes Figure 4.13a

Ribosomes TEM Rough ER Smooth ER Figure 4.13b

© 2010 Pearson Education, Inc. Rough ER The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane. These ribosomes produce membrane proteins and secretory proteins. After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles.

Proteins are often modified in the ER. Secretory proteins depart in transport vesicles. Vesicles bud off from the ER. A ribosome links amino acids into a polypeptide. Ribosome Transport vesicle Polypeptide Protein Rough ER Figure 4.14

© 2010 Pearson Education, Inc. Smooth ER The smooth ER Lacks surface ribosomes Produces lipids, including steroids Helps liver cells detoxify circulating drugs

© 2010 Pearson Education, Inc. The Golgi Apparatus The Golgi apparatus Works in partnership with the ER Receives, refines, stores, and distributes chemical products of the cell

“Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from rough ER “Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from the Golgi Plasma membrane “Shipping” side of Golgi apparatus Colorized SEM Figure 4.15

Transport vesicle from rough ER “Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from the Golgi Plasma membrane “Shipping” side of Golgi apparatus Figure 4.15a

“Receiving” side of Golgi apparatus New vesicle forming Colorized SEM Figure 4.15b

© 2010 Pearson Education, Inc. Lysosomes A lysosome is a sac of digestive enzymes found in animal cells. Enzymes in a lysosome can break down large molecules such as Proteins Polysaccharides Fats Nucleic acids Lysosomes have several types of digestive functions. Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles. These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food. Small molecules from digestion leave the lysosome and nourish the cell. Lysosomes can also Destroy harmful bacteria Break down damaged organelles

Plasma membraneDigestive enzymes Lysosome Digestion Food vacuole (a) Lysosome digesting food Figure 4.16a

Lysosome Digestion (b) Lysosome breaking down the molecules of damaged organelles Vesicle containing damaged organelle Figure 4.16b

Vesicle containing two damaged organelles Organelle fragment TEM Figure 4.16c

© 2010 Pearson Education, Inc. Vacuoles Vacuoles are membranous sacs that bud from the ER Golgi Plasma membrane Contractile vacuoles of protists pump out excess water in the cell. Central vacuoles of plants Store nutrients Absorb water May contain pigments or poisons

Figure 4.17a Vacuole filling with water Vacuole contracting (a) Contractile vacuole in Paramecium TEM

(b) Central vacuole in a plant cell Central vacuole Colorized TEM Figure 4.17b

© 2010 Pearson Education, Inc. To review, the endomembrane system interconnects the Nuclear envelope ER Golgi Lysosomes Vacuoles Plasma membrane

Golgi apparatus Transport vesicle Plasma membrane Secretory protein Vacuoles store some cell products. Lysosomes carrying digestive enzymes can fuse with other vesicles. Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Some products are secreted from the cell. Rough ER Vacuole Lysosome Transport vesicle Figure 4.18a

New vesicle forming Transport vesicle from the Golgi Golgi apparatus TEM Figure 4.18b

CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION Cells require a constant energy supply to perform the work of life. © 2010 Pearson Education, Inc. Chloroplasts Most of the living world runs on the energy provided by photosynthesis. Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar. Chloroplasts are the organelles that perform photosynthesis. Chloroplasts have three major compartments: The space between the two membranes The stroma, a thick fluid within the chloroplast The space within grana, the structures that trap light energy and convert it to chemical energy

Inner and outer membranes Space between membranes Stroma (fluid in chloroplast) Granum TEM Figure 4.19

© 2010 Pearson Education, Inc. Mitochondria Mitochondria are the sites of cellular respiration, which produce ATP from the energy of food molecules. Mitochondria are found in almost all eukaryotic cells. An envelope of two membranes encloses the mitochondrion. These consist of An outer smooth membrane An inner membrane that has numerous infoldings called cristae

Outer membrane Inner membrane Cristae Matrix Space between membranes TEM Figure 4.20

© 2010 Pearson Education, Inc. Mitochondria and chloroplasts contain their own DNA, which encodes some of their proteins. This DNA is evidence that mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.

THE CYTOSKELETON: CELL SHAPE AND MOVEMENT The cytoskeleton is a network of fibers extending throughout the cytoplasm. © 2010 Pearson Education, Inc. Maintaining Cell Shape The cytoskeleton Provides mechanical support to the cell Maintains its shape The cytoskeleton contains several types of fibers made from different proteins: Microtubules Are straight and hollow Guide the movement of organelles and chromosomes Intermediate filaments and microfilaments are thinner and solid. The cytoskeleton is dynamic. Changes in the cytoskeleton contribute to the amoeboid motion of an Amoeba.

(a) Microtubules in the cytoskeleton (b) Microtubules and movement LM Figure 4.21

© 2010 Pearson Education, Inc. Cilia and Flagella Cilia and flagella aid in movement. Flagella propel the cell in a whiplike motion. Cilia move in a coordinated back-and-forth motion. Cilia and flagella have the same basic architecture. Cilia may extend from nonmoving cells. On cells lining the human trachea, cilia help sweep mucus out of the lungs.

(a) Flagellum of a human sperm cell Colorized SEM (b) Cilia on a protist (c) Cilia lining the respiratory tract Colorized SEM Figure 4.22

Evolution Connection: The Evolution of Antibiotic Resistance Many antibiotics disrupt cellular structures of invading microorganisms. Introduced in the 1940s, penicillin worked well against such infections. But over time, bacteria that were resistant to antibiotics were favored. The widespread use and abuse of antibiotics continues to favor bacteria that resist antibiotics. © 2010 Pearson Education, Inc.

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Prokaryotic CellsEukaryotic Cells Smaller Simpler Most do not have organelles Found in bacteria and archaea Larger More complex Have organelles Found in protists, plants, fungi, animals CATEGORIES OF CELLS Figure 4.UN12

Outside of cell Cytoplasm (inside of cell) Protein Phospholipid Hydrophilic Hydrophobic Figure 4.UN13

Light energy Chloroplast Mitochondrion Chemical energy (food) ATP PHOTOSYNTHESIS CELLULAR RESPIRATION Figure 4.UN14