Development of the Light Microscope and the Cell Theory

• First compound light microscopes built in mid 1600s by Anton van Leeuwenhoek (Dutch) and Robert Hooke (English); discovered a previously unknown world

– Corresponded with each other (via letters)– Robert Hooke coined term “cell” (based on observations of cork)

and published the book Micrographia– van Leeuwenhoek first to see living, cellular “pond animalcules”

• The Cell Theory (mid 1800s; Schleiden, Schwann, and Verchow)

1) All organisms are composed of cells (one or many) • Matthais Schleiden (a botanist) and Theodor Schwann (a zoologist)

observed cells in plants and animals, respectively2) The cell is the basic unit of structure and function in living systems

(ex. movement of body results from movement of muscle cells)

3) All cells come from pre-existing cells (Rudolph Verchow)• Spontaneous generation disproved by Francisco Redi and Louis

Pasteur; today, oxygenated atmosphere and omnipresence of bacteria result in degradation and loss of free organic materials

Fig. 3.1

Modern Microscopes

• Compound Light Microscope– Magnification a product of the two lenses (eyepiece and objective

lens); lowest objective lens known as scanning lens (4X)– Images inverted; resolution limited by relatively large size of

photons– Parfocal: object placed in center of field of view prior to changing

objective lenses; field of view decreased but object will be there

• Dissecting Microscope (Stereomicroscope)– Image is not inverted (better for dissections)

• Electron Microscopes (in use by 1950s; incr. resolution)– Scanning Electron Microscope: images are of objects’ surfaces; up

to ~60,000x magnifications – Transmission Electron Microscope: images are of sections, internal

structures (such as organelles); up to ~200,000x magnifications

– Scanning Tunneling Microscopes (Atomic Force Microscopes): images of large molecules possible; multiple technologies; magnifications up to ~100 million x actual size

Fig. 3.2

Cell Types and Shared Structures

• Prokaryotic Cells (Prokaryotes: Eubacteria and Archaea)– Most 1-10 μm; seen in fossil record by 3.5 bya; lack a nucleus and

other membrane-bound organelles (DNA free in cell, in nucleoid region)

• Eukaryotic Cells (Eukaryotes: Fungi, Protists, Plants, and Animals)

– Most 10-100 μm; seen in fossil record by 2.2 bya; have a nucleus and other membrane-bound organelles

• All Cells Share (thus common ancestor had …)– Cell (plasma) membrane: a boundary; micelles can form naturally– Ribosomes: composed of proteins and RNA; bacterial ribosomes

have a different size and structure than those in eukaryotes– DNA, RNA, and the Genetic Code: bacterial chromosome a simple

ring of DNA; in eukaryotes, DNA is packaged with proteins – Other molecules / structures: membrane proteins (ex. ATP, ATP

synthase), metabolic enzymes, cytoskeletal tubules and filaments

Table 3.1

Fig. 3.4

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes

• Nucleus: bound by porous nuclear membrane; contains DNA (chromatin), nucleotides, and nucleolus

• Nucleolus: dense, protein-rich area in nucleus; ribosomes form• Ribosomes: in Rough ER and cytoplasm; site of protein

assembly (amino acids joined by peptide bonds)

– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol– Flagella and Cilia

Fig. 3.7

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes– Endoplasmic Reticulum (ER)

• Membranous extension from nuclear membrane; extends throughout cell; transports materials through cell

• Rough ER: studded with ribosomes; proteins assembled (esp. membrane and secretory proteins)

• Smooth ER: synthesis of lipids (incl. steroids), modification of proteins (incl. detoxification of poisons)

– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol– Flagella and Cilia

Fig. 3.8

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, nucleolus, and ribosomes– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles

• Products from ER modified (“tagged”) and transported (“shipped”) via vesicles

• In secretory cells, the cell’s main product sent to cell membrane, where vesicles fuse, and products enter blood or saliva

– Lysosomes and Vacuoles– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol– Flagella and Cilia

Fig. 3.9

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles

• Lysosomes: membrane-enclosed sacs of digestive enzymes found almost exclusively in animal cells

– Involved in digestion of food, programmed cell death, immunity, and destruction of cellular waste products

• Vacuoles: membranous sacs that bud from the ER, Golgi, or cell membrane

– Storage vacuoles store food or water (large central vacuole in plant cells), contractile vacuoles control water balance

in some Protists

– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol– Flagella and Cilia

Fig. 3.10

Fig. 11.15

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles– Plastids (chloroplast, chromoplast, and mitochondrion)

• Chloroplasts: found in many plant and algal cells; contain chlorophyll and perform photosynthesis

• Chromoplasts: contain other pigments (ex. melanin in dermis)• Mitochondria: found in all eukaryotes; site of cell respiration

(cell’s energy factories)

– The Cytoskeleton and the Cytosol– Flagella and Cilia

Fig. 3.11

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol

• Cytoskeleton: network of fibers in cell; supports organelles, maintains cell shape, controls movement of some cells; dynamic – can dismantle in one area and be re-assembled; consists of microtubules, intermediate filaments, and microfilaments

• Cytosol: the semi-fluid medium of the cell’s cytoplasm

– Flagella and Cilia

Figures 3.13 and 3.14

Eukaryotic Structures and Organelles

• Structures and Organelles– Nucleus, Nucleolus, and Ribosomes– Endoplasmic Reticulum– Golgi Apparatus (Complex) and Vesicles– Lysosomes and Vacuoles– Plastids (chloroplasts, chromoplasts, and mitochondria)– The Cytoskeleton and the Cytosol– Flagella and Cilia

• Motile appendages in Protists and sperm cells; used for food capture in some Protists; mechanosensory functions in “hair cells” of cochlea and lateral line; clean trachea and bronchi of mucus; found in lining of Fallopian tubes

• Ultrastructure includes internal and peripheral microtubules; rotor at base most studied in prokaryotic flagellum

• Flagellum: relatively long, often singular; move in undulatory whiplike motion

• Cilia: relatively short and found in groups, move in unison

Figures 11.4 and 11.9

Evolution of the Eukaryotic Cell• Serial Endosymbiotic Theory (Lynn Margulis)

– Evolution of new species by the acquisition and incorporation of other organisms’ genomes (a process)

• “I picture genes and their products flowing through a sea of cells” (Carl Woese, on early cellular life)

– An endosymbiont gradually (over generations) “loses identity” to become an organelle or structure of a larger cell

• Aerobic bacterium mitochondrion• Cyanobacterium (photosynthetic) chloroplast• Spirochaete (spirillum bacterium) flagellum

– Evidence very strong for origin of plastids• Approximate size of bacteria with structural similarities• Membrane bound, with bacterial proteins in membranes• Contain DNA in ring (bacterial chromosome)• Divide by binary fission• Progressive stages in the “loss of identity” have been observed in

various Protists

What is the Structure of the Cell Membrane?

• Constituents– Phospholipids: molecule consists of two hydrocarbon

chains (hydrophobic) and phosphate group (hydrophilic)

– Proteins• Integral proteins: embedded in lipids; some cross entire

membrane, often act like gates (allow substances into/out of cell)

• Peripheral proteins: along edge of membrane (inside or outside); often receptors for hormones; entire complex

moves into cell – Cholesterol: maintains fluidity of membrane – Carbohydrate Chains: found on outside of cell; involved

in cell to cell recognition and hormone reception• The Fluid-Mosaic Model: fluid bi-layer; lipids

internalized in membrane

Fig. 3.6

Fig. 3.15

Science 301: 361 (18 July 2003)

How do Substances Get Into or Out Of Cells?

• Passive Transport – Diffusion: spread of substance along a concentration gradient (from

high to low concentrations)• Only small, neutral molecules can pass through membrane (ex. O2, CO2)• Osmosis: diffusion of water across a cell membrane

– Facilitated Transport• Molecule or ion crosses membrane via carrier/gate protein, following a

concentration gradient (no energy expenditure required)

• Active Transport– Molecule or ion crosses membrane via carrier/gate protein, against a

concentration gradient (energy expenditure)

• Endocytosis/Exocytosis (requires energy expenditure)– Endo: molecules enveloped by cell membrane vesicle into cell – Exo: molecules produced in cell excreted via vesicle

Fig. 3.18

Fig. 3.20

Fig. 3.21

How is Energy Involved in Cellular Metabolism?

• ATP and Metabolism– Energy required for many cellular reactions, including

active transport, endo- and exocytosis, biosynthesis, and mechanical work/movement

– Energy transferred from exothermic to endothermic reactions via adenosine triphosphate (ATP), the universal energy currency

• Overview of Catabolic Processes– Stage I: Hydrolysis of Dietary Macromolecules into

Small Subunits • Starch maltose glucose, catalyzed by amylase and

maltase• Proteins denatured by stomach acid, digested by pepsin and

various protease enzymes• Emulsion of fats by bile salts; hydrolysis by lipase

– Stage II: Conversion of Monomers to Forms That Can Be Fully Oxidized

• Monomers enter either glycolysis or the Krebs Cycle– Stage III: Complete Oxidation of Compounds and the

Production of ATP

Fig. 4.6

How are Enzymes Involved in Cellular Metabolism?

• Importance of Shape and Structure with Proteins– Cellular functions related to shape and intact

structures of proteins– Denaturation: loss of 3° and/or 4° structures; can

be caused by excess temperature, pH changes, chemicals, or mechanical stress

• Enzymes: biological catalysts; most are proteins– Increase rates of chemical reactions; reduce

activation energy; each molecule recycled– IUPAC names derive from substrates and actions;

end with –ase – Substrate(s) fit in active site(s); induced-fit model

favored over lock-and-key model– Often require cofactors (metals, organics) and/or

coenzymes

Fig. 4.3

Fig. 4.4

What Factors Affect Enzyme Function?

• Effect of pH Levels– Enzymes are only active within narrow pH ranges, and

work best at specific pH optima– Most cytoplasmic enzymes require pH of 7; pepsin works

best at pH ~2 (in stomach acid)– Some bacteria have evolved to live at extreme pH levels

• Effect of Temperature– Enzymes are only active within narrow temperature

ranges, and work best at their temperature optima (humans ~37 C)

– If too hot, can become denatured; if too cold, reaction rates can be reduced below critical rates

• Enzyme Inhibition: compounds block active sites– Irreversible Inhibitors: include arsenic, snake venoms,

nerve gases– Competitive Inhibitors: compounds are structural

analogues to enzymes’ substrates (the dose makes the poison)

How do Cells Obtain Energy from Food?

• Cellular Respiration: the breakdown of glucose for the production of energy (ATP molecules)

– In eukaryotes, occurs in the mitochondria– Anaerobic respiration (without oxygen): efficiency = 2.1%

1. Glycolysis: glucose (C6) split into two pyruvate (C3) molecules; net production of two ATP molecules

2. Pyruvate reduced to either lactate or ethyl alcohol (fermentation); CO2 byproduct

– Aerobic respiration (with oxygen): efficiency = 39%• General Reaction: glucose + O2 CO2 + H2O + ATP 1. Glycolysis: in cytoplasm; oxygen not required2. Transition reaction: pyruvate converted to acetyl co-enzyme A as

enters mitochondrion; CO2 released3. Kreb’s cycle: oxygen required, some ATP produced and CO2 results4. Electron transport (oxidative phosphorylation): oxygen required;

major production of ATP

• Catabolism of fats: form glycerol (involved in glycolysis) and fatty acids (break down into acetyl Co-A)

Figures 4.10 and 4.14

Fig. 4.17

Fig. 4.18