A Tour of the Cell www.probes.com

History of the Cell  Cells were first discovered in 1665 by Robert Hooke From Micrographia  The accumulation of scientific evidence led to the ‘cell theory’ (1) All living things are composed of cells (2) All cells form from previously existing cells

Cells are the building blocks of all life forms Organisms are either:  Single-celled, such as most bacteria and protists  Multicelled, such as plants, animals, and most fungi

Cells are made up of MACROMOLECULES: Nucleic Acids (2) Proteins (3) Lipids (4) Carbohydrates

The Two Major Categories of Cells Prokaryotic cells  Eukaryotic cells

Prokaryotes Vs. Eukaryotes Prokaryotic cell Nucleoid region Eukaryotic cell Nucleus Organelles Figure 4.4

Prokaryotic cells: Are much smaller than eukaryotic cells Lack internal structures surrounded by membranes  Lack a nucleus

A Detailed View of Prokaryotic Cells flagella Nucleoid region (DNA) Plasma membrane Ribosomes Cell wall Capsule Pili Figure 4.5

A Detailed View of Eukaryotic Cells  An idealized animal cell Centriole Ribosomes Lysosome Not in most plant cells Flagellum Cytoskeleton Plasma membrane Mitochondrion Nucleus Rough endoplasmic reticulum (ER) Smooth endoplasmic reticulum (ER) Golgi apparatus Figure 4.6A

A Detailed View of Eukaryotic Cells  An idealized plant cell Not in animal cells Cytoskeleton Mitochondrion Central vacuole Nucleus Cell wall Rough endoplamsic reticulum (ER) Chloroplast Ribosomes Plasma membrane Smooth endoplasmic reticulum (ER) Plasmodesmata Golgi apparatus Figure 4.6B

Antony van Leeuwenhoek (1632-1723): Microscope Maker  Identified and termed ‘animalcules’

Microscopes as Windows to Cells  The light microscope is used by many scientists (1) Light passes through the specimen (2) Lenses enlarge, or magnify, the image (a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells Figure 4.2A

Microscope Terminology Magnification: An increase in the specimen’s apparent size Resolving power: The ability of an optical instrument to show two objects as separate

The Electron Microscope:  Uses a beam of electrons instead of light Has a higher resolving power than light microscopes (can magnify up to 100,000X)  The power of electron microscopy reveals many details of cellular components

Scanning Electron Microscopy (b) Scanning electron micrograph (SEM) of a white blood cell Figure 4.2B  for studying external cellular structures

Transmission Electron Microscopy (c) Transmission electron micrograph (TEM) of a white blood cell Figure 4.2C  for studying internal cellular structures

Power and Scale of Microscopy Human height Length of some nerve and muscle cells Chicken egg Unaided eye Frog eggs Plant and animal cells Light microscope Nucleus Most bacteria Mitochondrion Smallest bacteria Electron microscope Viruses Ribosomes Proteins Lipids Small molecules Atoms Figure 4.3

MEMBRANE STRUCTURE AND FUNCTION The plasma membrane separates the living cell from its nonliving surroundings and regulates what goes in and out. Organelles are surrounded by membranes to separate them as distinct compartments of the cell with specialized functions.

The Fluid Mosaic Model of Membranes:  Membranes are composed of lipids AND proteins and are highly dynamic (fluid)  Membranes of the cell have selective permeability (04-07a-MembraneStructure.mov): (1) They allow some substances to cross more easily than others (2) They block passage of some substances altogether (3) The traffic of some substances can only occur through transport proteins (like glucose)

The LIPID Component  The lipids belong to a special category called phospholipids  Phospholipids form a two-layered membrane, the phospholipid bilayer Outside cell Hydrophilic head Hydrophobic tail Cytoplasm (inside cell) (a) Phospholipid bilayer of membrane Figure 4.7A

Phospholipids in Membranes

The PROTEIN Component  Most membranes have specific proteins embedded in the phospholipid bilayer Hydrophilic region of protein Phospholipid bilayer Hydrophobic region of protein (b) Fluid mosaic model of membrane Figure 4.7B

FUNCTIONS of Membrane Proteins Cytoplasm Fibers of extracellular matrix c Enzymatic activity b Cell signaling a Attachment to cytoskeleton and extracellular matrix e Intercellular joining f Cell-cell recognition d Transport Cytoplasm Cytoskeleton Figure 4.8 04-08-ReceptorProtAnim.mov

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

THE NUCLEUS: GENETIC CONTROL OF THE CELL  The nucleus is the ‘manager’ of the cell Genes in the nucleus store the information necessary to produce proteins, which perform cellular functions

Structure and Function of the Nucleus  The nucleus is bordered by a double membrane called the nuclear envelope The nucleus contains chromatin and the nucleolus

Nuclear envelope Ribosomes Chromatic Nucleolus Pore Figure 4.9

How DNA Controls the Cell  Genes encoded by DNA are copied to another molecule, mRNA DNA 1 Synthesis of mRNA in the nucleus mRNA mRNA molecules representing genes are exported from the nucleus into the cytoplasm Nucleus Cytoplasm 2 Movement of mRNA into cytoplasm via nuclear pore mRNA  Ribosomes in the cytoplasm ‘read’ the mRNA and use the info to make a protein Ribosome 3 Synthesis of protein in the cytoplasm Protein Figure 4.10

The Central Dogma of Molecular Biology DNA RNA Protein   Transcription Translation

Exceptions to the Central Dogma DNA RNA Protein   Retroviruses

Chloroplasts and Mitochondria: Energy Conversion  Cells require a constant energy supply to do all the work of life

Chloroplasts Inner and outer membranes of envelope  Chloroplasts are the sites of photosynthesis: the conversion of light energy to chemical energy Space between membranes Granum Stroma (fluid in chloroplast) Figure 4.17

Mitochondria  Mitochondria are the sites of cellular respiration, the process of producing ATP from food molecules Outer membrane Inner membrane Cristae Matrix Space between membranes Figure 4.18

EVOLUTION CONNECTION: The Origin of Organelles  The Endosymbiont Theory: eukaryotic organelles evolved from prokaryotes that were engulfed by other cells

The Cytoskeleton: Cell Shape and Movement  The cytoskeleton is an infrastructure of the cell consisting of a network of fibers: (1) Actin Fibers (structure & movement OF the cell) (2) Microtubules (structure & movement WITHIN the cell)

Functions of the Cytoskeleton:  Provide mechanical support and structure to the cell to give it shape Figure 4.19A

Functions of the Cytoskeleton:  The cytoskeleton can change the shape of a cell for movement Figure 4.19B

Motile Appendages  Flagella propel the cell in a whiplike motion  Cilia move in a coordinated back-and-forth motion Figure 4.20A, B

Non-moving cells have cilia and flagella, too  The human windpipe is lined with cilia Figure 4.20C

The universal architecture of eukaryotic cilia (a) Paramecium (b) Cells from fallopian tube (c) Cross section of cilium Figure 1.9

CELL SURFACES: Protection, Support, and Cell-Cell Interactions  Most cells secrete materials that are external to the plasma membrane (except those that have cell walls!)

Plant Cell Walls and Cell Junctions  Plant cells are encased by cell walls Walls of two adjacent plant cells Vacuole Plasmodesmata (channels between cells) Figure 4.21

Animal Cell Surfaces and Cell Junctions  Animal cells lack cell walls: They secrete a sticky covering called the extracellular matrix (2) This layer helps hold cells together to form tissues and organs and so on.

Connections Between Animal Cells: Extracellular matrix (a) Tight junctions (b) Anchoring junctions (c) Communicating junctions Plasma membranes of adjacent cells Extracellular matrix Figure 4.22

The Secretory System: Manufacturing and Distributing Cellular Products  Many of the membranous organelles in the cell belong to the secretory, or endomembrane, system

The Endoplasmic Reticulum  The endoplasmic reticulum (ER): Nuclear envelope Produces an enormous variety of molecules (2) Is composed of smooth and rough ER Ribosomes Rough ER Smooth ER Figure 4.11

Rough ER  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: (1) Producing proteins (2) Producing new membrane

After the rough ER synthesizes a molecule it packages the molecule into transport vesicles 4 Transport vesicle buds off Secretory protein inside transport vesicle Ribosome 3 Protein 1 Rough ER 2 Polypeptide Figure 4.12

Smooth ER  The smooth ER lacks the surface ribosomes of ER and produces lipids, including steroids

The Golgi Apparatus  Works in partnership with the ER  Refines, stores, and distributes the products of cells Transport vesicle from ER “Receiving” side of Golgi apparatus Golgi apparatus New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Plasma membrane Figure 4.13

Lysosomes  A lysosome is a membrane-enclosed sac: It contains digestive enzymes (2) The enzymes break down macromolecules

Digestive Functions of the lysosome: To fuse with food vacuoles to digest the food Lysosome Digestive enzymes Plasma membrane Digestion Food Food vacuole (a) Lysosome digesting food Figure 4.14a

Digestive Functions of the lysosome: To break down damaged organelles Lysosome Digestion Damaged organelle (b) Lysosome breaking down damaged organelle Figure 4.14b

Vacuoles: Membranous Sacs  Two types are the contractile vacuoles of protists and the central vacuoles of plants Central vacuole Contractile vacuoles (a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell Figure 4.15

Summary of the Endomembrane System Rough ER Transport vesicle from ER Golgi apparatus Secretory vesicle from Golgi Secretory protein Vacuole Lysosome Plasma membrane Figure 4.16 04-16-EndomembraneSysAnim.mov

BIOLOGY AND SOCIETY: Drugs That Target CELLS  Antibiotics are one of the great marvels of modern medicine: (1)Treatment with these drugs will kill invading bacteria (2)The drugs don’t harm the human cells of the host Figure 4.1

BIOLOGY AND SOCIETY: Drugs That Target CELLS  Chemotherapy and Cancer: Targets cells that are growing rapidly (2) The drugs don’t affect most human cells, but…