CHAPTER 4

A Tour of the Cell

• If you stacked up 8000 cell membranes, they would be only as thick as a page in this book

• An electron microscope can visualize objects a million times smaller than the head of a pin

BIOLOGY AND SOCIETY:
DRUGS THAT TARGET CELLS

• Antibiotics are one of the great marvels of modern medicine

Microscopes as Windows to Cells

• The light microscope is used by many scientists

• Cells were first discovered in 1665 by Robert Hooke

THE MICROSCOPIC WORLD OF CELLS

• Cells are the building blocks of all life

• The electron microscope (EM) uses a beam of electrons

• The electron microscope can magnify up to 100,000X

• The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell

• The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell

Cell Theory

– Biogenesis was proved by Pasteur. He used straight neck and bent neck flasks. Bent neck flasks trapped airborne, microbe laden particles so that no life would be found in flask. Straight neck flasks allowed entrance of these particles and the rapid formation of colonies of bacteria.

Surface area to volume ratio limits the maximum size of a cell

• Organisms are either

The Two Major Categories of Cells

• The countless cells on earth fall into two categories

• Prokaryotic and eukaryotic cells differ in several respects

• Prokaryotic cells

A Panoramic View of Eukaryotic Cells

• contain membrane bound organelles example: mitochondria or true nucleus

MEMBRANE STRUCTURE AND FUNCTION

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

A Fluid Mosaic of Lipids and Proteins

• The membranes of cells are composed of

• The lipids belong to a special category called phospholipids

• Most membranes have specific proteins embedded in the phospholipid bilayer

• Some functions of membrane proteins

THE NUCLEUS AND RIBOSOMES:
GENETIC CONTROL OF THE CELL

• The nucleus is the manager of the cell

Structure and Function of the Nucleus

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

How DNA Controls the Cell

• DNA controls the cell by transferring its coded information into RNA

• Ribosomes build all the cell’s proteins

THE ENDOMEMBRANE SYSTEM: MANUFACTURING AND DISTRIBUTING CELLULAR PRODUCTS

• Many of the membranous organelles in the cell belong to the endomembrane system

The Endoplasmic Reticulum

• The endoplasmic reticulum (ER)

• After the rough ER synthesizes a molecule it packages the molecule into transport vesicles

The Golgi Apparatus

Lysosomes

• A lysosome is a membrane-enclosed sac

– They break down damaged organelles

• Lysosomes have several types of digestive functions

• A review of the endomembrane system

Cellular energy conversion

• Mitochondria –

• This organelle converts the chemical energy in ingested food to a chemical energy form used by all cellular processes [ATP]

Mitochondria

• Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules

• An idealized plant cell

Vacuoles

• Vacuoles are membranous sacs

CHLOROPLASTS

• Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy

THE CYTOSKELETON:
CELL SHAPE AND MOVEMENT

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

Maintaining Cell Shape

• One function of the cytoskeleton

• The cytoskeleton can change the shape of a cell

Cilia and Flagella

• Cilia and flagella are motile appendages

• Some cilia or flagella extend from nonmoving cells

CELL SURFACES:
PROTECTION, SUPPORT, AND CELL-CELL INTERACTIONS

• Most cells secrete materials that are external to the plasma membrane

Plant Cell Walls and Cell Junctions

• Plant cells are encased by cell walls

SUMMARY OF KEY CONCEPTS

• The Two Major Categories of Cells