© 2010 Pearson Education, Inc. Cells  Cells are the smallest unit of living substance  Cell theory is one of the premier foundations of biology. The theory states that all living things are made of cells.  Think about this. Is it true?

© 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 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

© 2010 Pearson Education, Inc. 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.

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 plasma membrane. –All cells have DNA and ribosomes, tiny structures that build proteins.

© 2010 Pearson Education, Inc. Prokaryotes –Are smaller than eukaryotic cells –Lack internal structures surrounded by membranes –Lack a nucleus –Have a rigid cell wall

© 2010 Pearson Education, Inc. 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) Figure 4.4a

Colorized TEM Figure 4.4b

© 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.  KNOW THIS!

© 2010 Pearson Education, Inc. Unlike animal cells, plant cells have –Protective cell walls –Chloroplasts, which convert light energy to the chemical energy of food –Watch This:

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 Centrosome

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.  Plant cells have cell walls and a plasma membrane  Animal cells have only a plasma membrane

© 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 © 2010 Pearson Education, Inc.

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

(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.

© 2010 Pearson Education, Inc. 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. 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

© 2010 Pearson Education, Inc. 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.  REALLY? Think about it. If you cut out the nucleus of the cell does it die? NO! In reality, the nucleus is ONLY a repository of the blueprints for the proteins of the body. –Genes in the nucleus store information necessary to produce proteins. –Proteins do most of the work of the cell. © 2010 Pearson Education, Inc.

Structure and Function of the Nucleus 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

© 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.

Ribosome Protein mRNA Figure 4.10

© 2010 Pearson Education, Inc. Ribosomes may assemble proteins: –Suspended in the fluid of the cytoplasm or –Attached to the outside of an organelle called the endoplasmic reticulum

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. A ribosome moves along the mRNA translating the genetic message into a protein with a specific amino acid sequence.

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 –Is composed of smooth and rough ER

Nuclear envelope Smooth ER Rough ER Ribosomes TEM Figure 4.13

© 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

© 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

© 2010 Pearson Education, Inc. 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.

Plasma membraneDigestive enzymes Lysosome Digestion Food vacuole Lysosome Digestion (a) Lysosome digesting food (b) Lysosome breaking down the molecules of damaged organelles Vesicle containing damaged organelle Vesicle containing two damaged organelles Organelle fragment TEM Figure 4.16

© 2010 Pearson Education, Inc. Lysosomes can also –Destroy harmful bacteria –Break down damaged organelles

© 2010 Pearson Education, Inc. Vacuoles Vacuoles are membranous sacs that bud from the –ER –Golgi –Plasma membrane

© 2010 Pearson Education, Inc. Contractile vacuoles of protists pump out excess water in the cell. Central vacuoles of plants –Store nutrients –Absorb water –May contain pigments or poisons

Vacuole filling with water Vacuole contracting (a) Contractile vacuole in Paramecium (b) Central vacuole in a plant cell Central vacuole Colorized TEM LM Figure 4.17

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

© 2010 Pearson Education, Inc. Centrosomes vs centrioles  A centrosome is an organelle that is found close to the nucleus within the cytoplasm of cells. Centrosomes are key to the division of cells and produce the spindle fibers that are required during metaphase of mitosis. Each centrosome consists of two centrioles that are orientated at right-angles to each other. Each centriole is a cylindrical array of 9 microtubules.

Golgi apparatus Transport vesicle Plasma membrane Secretory protein New vesicle forming Transport vesicle from the Golgi 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. Golgi apparatus Rough ER Vacuole Lysosome Transport vesicle TEM Figure 4.18

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.

© 2010 Pearson Education, Inc. 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.

© 2010 Pearson Education, Inc. 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

© 2010 Pearson Education, Inc. 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.

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

© 2010 Pearson Education, Inc. The cytoskeleton is dynamic. Changes in the cytoskeleton contribute to the amoeboid motion of an Amoeba.

© 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.

(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

© 2010 Pearson Education, Inc. Cilia may extend from nonmoving cells. On cells lining the human trachea, cilia help sweep mucus out of the lungs.

© 2010 Pearson Education, Inc. The Remaining Slides  Are for your review only

© 2010 Pearson Education, Inc.  Know the organelles and their functions  What is the name of the area between the nuclear envelope and the plasma membrane?  Functions and anatomy of the plasma membrane  Why do phospholipids form a good barrier?  The nuclear is a double membrane  DNA is wound up with histones, a protein  Protein synthesis takes place on ribosomes, either free or on the RER  Information travels from nucleus to ribosomes via mRNA  Hormones are made on ribosomes on RER  Functions of SER?  Transport vesicles move ER products to Golgi apparatus  The golgi app. Modifies proteins for transport

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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