CHAPTER 4 A Tour of the Cell: History, Tools, Parts and Function

CHAPTER 4CHAPTER 4

A Tour of the Cell:

History, Tools, Parts and Function

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

History

Cells couldn’t be discovered until the microscope was invented

Anton von Leeuwenhoek 1673

Simple Microscopes

• Basically a hand lens

• Looked at water, poop, muscle tissue, bacteria, mold, bees, lice


History

Robert Hooke – 1665 – Cork cells• First to use the word ‘cell’ to describe

the boxes he saw in cork, a plant


• The accumulation of scientific evidence led to the cell theory.

– All living things are composed of cells.

– All cells are formed from previously existing cells.


The compound microscope


The compound microscope

• Resolving power

– Is the ability of an optical instrument to show two objects as being separate.

• Magnification

– Is an increase in the specimen’s apparent size.



Magnification

Total Magnification is:

• ocular lens x the objective

– 10x X 4x = 40 times magnified

– The object should look 40x larger than normal

Field of view – the size of the area you can see

Which picture has a larger field of view?

Figure 4.3


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

– It has a higher resolving power than the light microscope.

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

– Such power reveals the diverse parts within a cell.


• 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.



Cells are different

Can be big, little, flat, round

• A nerve cell can be 2 meters long!



The Two Major Categories of Cells• The countless cells on earth fall into two

categories:

– Prokaryotic cells

– Eukaryotic cells

Figure 4.4

The Plasma Membrane:A Fluid Mosaic of Lipids and Proteins

• The membranes of cells are composed mostly of:

– Lipids

– Proteins

• The lipids belong to a special category called phospholipids.

• Phospholipids form a two-layered membrane, the phospholipid bilayer.

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 4.7b


• Membrane phospholipids and proteins can drift about in the plane of the membrane.

• This behavior leads to the description of a membrane as a fluid mosaic:

– Molecules can move freely within the membrane.

– A diversity of proteins exists within the membrane.


Cell Surfaces

• Most cells secrete materials for coats of one kind or another

– That are external to the plasma membrane.

• These extracellular coats help protect and support cells

– And facilitate interactions between cellular neighbors in tissues.


• Plant cells have cell walls,

– Which help protect the cells, maintain their shape, and keep the cells from absorbing too much water.

• Animal cells have an extracellular matrix,

– Which helps hold cells together in tissues and protects and supports them.

The Nucleus and Ribosomes:Genetic Control of the Cell

• The nucleus controls the cell

– Genes in the nucleus (DNA) store information necessary to produce proteins.



Structure and Function of the Nucleus

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

– It contains chromatin.

– It contains a nucleolus.

• Ribosomes are responsible for protein synthesis.

– Made in the nucleolus


How DNA Controls the Cell

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

– The information in the RNA is used to make proteins.

The Endomembrane System: Manufacturing and Distributing Cellular Products

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



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:

– Producing proteins to be sent out of the cell

– Producing new membrane lipids


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


Smooth ER

• The smooth ER lacks the surface ribosomes of RER

– produces lipids, including steroids

– detoxifies poisons


The Golgi Apparatus

• The Golgi apparatus

– Works in partnership with the ER.

– Refines, stores, and distributes ( SHIPS OUT ) the chemical products of cells.


Lysosomes

• A lysosome is a membrane-enclosed sac.

– It contains digestive enzymes.

– The enzymes break down macromolecules from the food you eat.

• Break down old organelles

Figure 4.13a


Vacuoles

• Vacuoles are membranous sacs.

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

Paramecium Vacuole


Chloroplasts

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


Mitochondria

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


• Mitochondria and chloroplasts share another feature unique among eukaryotic organelles.

– They contain their own DNA.

• The existence of separate “mini-genomes” is believed to be evidence that

– Mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past.


Cytoskeleton: Microtubules and Microfilaments

• functions of the cytoskeleton

– Both structure and movement

• Skeleton and muscles

– Protect cell from breaking

– Help move organelles into place

– Organize DNA for cell division

Figure 4.18a


Cilia and Flagella

• Cilia and flagella are motile appendages.


• Flagella propel the cell in a whiplike motion.

• Cilia move in a coordinated back-and-forth motion.

Paramecium Cilia

Cilia and Flagella


• Some cilia or flagella extend from nonmoving cells.

– The human windpipe is lined with cilia.

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CHAPTER 4 A Tour of the Cell: History, Tools, Parts and Function