A Tour of the Cell

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Cells were first discovered in 1665 by Robert Hooke

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

History of the Cell

From Micrographia

• 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:

(1) Nucleic Acids

(2) Proteins

(3) Lipids

(4) Carbohydrates

The Two Major Categories of Cells

Prokaryotic cells

Eukaryotic cells

Figure 4.4

Prokaryotic cell Nucleoid region

Eukaryotic cell Nucleus Organelles

Prokaryotes Vs. Eukaryotes

Prokaryotic cells:

Are much smaller than eukaryotic cells

Lack internal structures surrounded by membranes

Lack a nucleus

Figure 4.5

Prokaryoticflagella

Nucleoid region (DNA)

RibosomesPlasmamembrane

Cell wall

Capsule

Pili

A Detailed View of Prokaryotic Cells

An idealized animal cell

A Detailed View of Eukaryotic Cells

Figure 4.6A

Cytoskeleton

RibosomesCentriole

LysosomeFlagellum

Not in mostplant cells

Nucleus

Smoothendoplasmicreticulum (ER)Golgi

apparatus

Roughendoplasmicreticulum (ER)

Mitochondrion

Plasmamembrane

An idealized plant cell

Figure 4.6B

Cytoskeleton

Mitochondrion

Nucleus

Rough endoplamsicreticulum (ER)

Ribosomes

Smoothendoplasmicreticulum (ER)

Golgi apparatus

Plasmodesmata

Plasmamembrane

Chloroplast

Cell wall

Centralvacuole

Not in animal cells

A Detailed View of Eukaryotic Cells

Antony van Leeuwenhoek (1632-1723): Microscope Maker

Identified and termed ‘animalcules’

The light microscope is used by many scientists

Microscopes as Windows to Cells

(1) Light passes through the specimen

(2) Lenses enlarge, or magnify, the image

Figure 4.2A

(a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells

Magnification: An increase in the specimen’s apparent size

Resolving power: The ability of an optical instrument to show two objects as separate

Microscope Terminology

Uses a beam of electrons instead of light

The Electron Microscope:

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

Figure 4.2B

(b) Scanning electron micrograph (SEM) of a white blood cell

Scanning Electron Microscopy

for studying external cellular structures

Figure 4.2C(c) Transmission electron micrograph (TEM) of a white blood cell

Transmission Electron Microscopy

for studying internal cellular structures

Figure 4.3

Human height

Length of somenerve andmuscle cells

Frogeggs

Chickenegg

Plant andanimalcells

NucleusMost bacteriaMitochondrion

Smallest bacteria

Viruses

Ribosomes

Proteins

Lipids

Smallmolecules

Atoms

Un

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Lig

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mic

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Ele

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Power and Scale of Microscopy

The plasma membrane separates the living cell from its nonliving surroundings and

regulates what goes in and out.

MEMBRANE STRUCTURE AND FUNCTION

Organelles are surrounded by membranes to separate them as distinct compartments

of the cell with specialized functions.

Membranes are composed of lipids AND proteins and are highly dynamic (fluid)

The Fluid Mosaic Model of Membranes:

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 lipids belong to a special category called phospholipids

Phospholipids form a two-layered membrane, the phospholipid bilayer

Figure 4.7A

Hydrophilichead

Hydrophobictail

Outside cell

Cytoplasm(inside cell)

(a) Phospholipid bilayer of membrane

The LIPID Component

Phospholipids in Membranes

Most membranes have specific proteins embedded in the phospholipid bilayer

Figure 4.7B

Hydrophilicregion ofprotein

Phospholipidbilayer

Hydrophobicregion of protein

(b) Fluid mosaic model of membrane

The PROTEIN Component

Figure 4.8

Fibers ofextracellularmatrix

Cytoskeleton Cytoplasm

Attachment tocytoskeleton andextracellularmatrix

a

b Cell signaling

c

d

Enzymatic activity

Transport

e Intercellularjoining f Cell-cell

recognition

Cytoplasm

FUNCTIONS of Membrane Proteins

04-08-ReceptorProtAnim.mov

Phospholipids were probably among the organic molecules on the early Earth

EVOLUTION CONNECTION:The Origin of Membranes

When mixed with water, phospholipids spontaneously form membranes

The nucleus is the ‘manager’ of the cell

THE NUCLEUS:GENETIC CONTROL OF THE CELL

Genes in the nucleus store the information necessary to produce proteins, which perform cellular functions

The nucleus is bordered by a double membrane called the nuclear envelope

Structure and Function of the Nucleus

The nucleus contains chromatin and

the nucleolus

Figure 4.9

Ribosomes Chromatic Nuclearenvelope

Nucleolus Pore

Genes encoded by DNA are copied to another molecule, mRNA

How DNA Controls the Cell

Figure 4.10

Synthesis ofmRNA in thenucleus

1

2 Movement ofmRNA intocytoplasm vianuclear pore

3 Synthesis ofprotein in thecytoplasm

DNA

mRNA

Nucleus

Cytoplasm

mRNA

Ribosome

Protein

mRNA molecules representing genes are exported from the nucleus into the cytoplasm

Ribosomes in the cytoplasm ‘read’ the mRNA and use the info to make a protein

The Central Dogma of Molecular Biology

DNA RNA Protein

①Transcription②Translation

Exceptions to the Central Dogma

DNA RNA Protein

Retroviruses

Cells require a constant energy supply to do all the work of life

Chloroplasts and Mitochondria: Energy Conversion

Chloroplasts are the sites of photosynthesis: the conversion of light energy to chemical energy

Chloroplasts

Figure 4.17

Inner and outermembranes ofenvelope

Space betweenmembranes

Stroma (fluid inchloroplast)

Granum

Mitochondria are the sites of cellular respiration, the process of producing ATP from food molecules

Mitochondria

Figure 4.18

Outermembrane

Innermembrane

Cristae

Matrix

Space betweenmembranes

EVOLUTION CONNECTION:The Origin of Organelles

The Endosymbiont Theory: eukaryotic organelles evolved from prokaryotes that were engulfed by other cells

The cytoskeleton is an infrastructure of the cell consisting of a network of fibers:

The Cytoskeleton:Cell Shape and Movement

(1) Actin Fibers (structure & movement OF the cell)

(2) Microtubules (structure & movement WITHIN the cell)

Functions of the Cytoskeleton:

Figure 4.19A

Provide mechanical support and structure to the cell to give it shape

The cytoskeleton can change the shape of a cell for movement

Figure 4.19B

Functions of the Cytoskeleton:

Flagella propel the cell in a whiplike motion

Cilia move in a coordinated back-and-forth motion

Figure 4.20A, B

Motile Appendages

The human windpipe is lined with cilia

Figure 4.20C

Non-moving cells have cilia and flagella, too

The universal architecture of eukaryotic cilia

Figure 1.9

(a) Paramecium (b) Cells from fallopian

tube

(c) Cross section of cilium

Most cells secrete materials that are external to the plasma membrane (except those that have cell walls!)

CELL SURFACES:Protection, Support, and Cell-Cell

Interactions

Plant cells are encased by cell walls

Plant Cell Walls and Cell Junctions

Figure 4.21

Walls of two adjacentplant cells

Vacuole

Plasmodesmata(channels between cells)

Animal cells lack cell walls:

Animal Cell Surfaces and Cell Junctions

(1) 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:

Figure 4.22

Extracellular matrix

(a) Tight junctions

(b) Anchoring junctions

(c) Communicating junctions

Plasma membranesof adjacent cells

Extracellular matrix

Many of the membranous organelles in the cell belong to the secretory, or endomembrane, system

The Secretory System: Manufacturing and Distributing Cellular Products

The endoplasmic reticulum (ER):

The Endoplasmic Reticulum

(1) Produces an enormous variety of molecules

(2) Is composed of smooth and rough ER

Figure 4.11

Nuclearenvelope

Ribosomes

Rough ERSmooth ER

The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

Rough ER

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

Figure 4.12

Transport vesiclebuds off

Ribosome Secretoryprotein insidetransportvesicle

ProteinRough ER

Polypeptide

12

3

4

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

Smooth ER

The Golgi Apparatus

Works in partnership with the ER

Refines, stores, and distributes the products of cells

Figure 4.13

Transportvesiclefrom ER

“Receiving” side ofGolgi apparatus

Golgi apparatus

New vesicle forming

Transport vesiclefrom the Golgi

“Shipping” side ofGolgi apparatus

Plasma membrane

A lysosome is a membrane-enclosed sac:

Lysosomes

(1) It contains digestive enzymes

(2) The enzymes break down macromolecules

Digestive Functions of the lysosome:

To fuse with food vacuoles to digest the food

Plasmamembrane

Digestive enzymesLysosome

Food Food vacuole

Digestion

(a) Lysosome digesting food

Figure 4.14a

To break down damaged organelles

Figure 4.14b

(b) Lysosome breaking down damaged organelle

Lysosome

Damagedorganelle

Digestion

Digestive Functions of the lysosome:

Vacuoles: Membranous Sacs

Two types are the contractile vacuoles of protists and the central vacuoles of plants

Figure 4.15

Contractilevacuoles

Centralvacuole

(a) Contractile vacuoles in a protist (b) Central vacuole in a plant cell

Summary of the Endomembrane System

Figure 4.16

Rough ER

Transportvesicle from ER

Golgiapparatus

Secretoryvesicle from Golgi

Secretoryprotein

Vacuole Lysosome

Plasma membrane

04-16-EndomembraneSysAnim.mov

Antibiotics are one of the great marvels of modern medicine:

BIOLOGY AND SOCIETY: Drugs That Target CELLS

(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:

(1) Targets cells that are growing rapidly

(2) The drugs don’t affect most human cells, but…