The World of Cells
4.1
Cells
1.
The human body is made up of cells, most of which are too small to be seen with the
naked eye.
2.
The Cell Theory
3.
Robert Hooke first described cells in 1665 and coined the term that eventually came
to be “cells.”
4.
Modern cell theory includes three principles, as follows:
1.
All living or ganisms are composed of cells.
2.
Nothing smaller than a cell is considered to be alive.
3.
Cells arise only from preexisting cells, and all living or ganisms have descended from
the earliest cells.
1.
Most Cells Are Very Small.
2.
Cells vary in size, most of which are 5 to 20 micrometers in diameter .
3.
Why Aren’ t Cells Lar ger?
4.
Cells are small because lar ger cells do not function ef ficiently .
5.
Cell size is limited by two factors: (1) surface area-to-volume relationships that make
distribution of materials throughout a lar ge cell dif ficult, and (2) the volume of
cytoplasm the nucleus can control.
6.
An Overview of Cell Structure
7.
Cells are filled with a semifluid matrix, called cytoplasm, surrounded by a membrane
that controls the permeability of the cell.
8.
Visualizing Cells
9.
Cells can be made visible by the use of microscopes.
10.
Certain cell structures can be made more visible by staining specific molecules in a
cell.
4.2
The Plasma Membrane
1.
All cells are surrounded by a plasma membrane composed of a bilayer of
phospholipids, according to the fluid mosaic model.
2.
The polar ends of these phospholipids interact with the fluid interior and exterior
environments of the cell, while the nonpolar fatty acid chains form the interior of the
membrane.
3.
The phospholipids are arranged in a bilayer , with nonpolar tails extending to the
inside.
4.
Proteins Within the Membrane
5.
Floating within the lipid bilayer are a variety of membrane proteins. Some of these
proteins function to transport materials across the membrane (transmembrane proteins), and others serve as identification markers in cell communication (cell
surface proteins).
6.
Membrane Defects Can Cause Disease.
7.
Cystic fibrosis is a deadly genetic disorder caused by a defective transmembrane
protein that does not properly admit chloride ions into the body's cells.
Kinds of Cells
4.3
Prokaryotic Cells
1.
Cells can be divided into prokaryotic cells or eukaryotic cells based on whether or not
the cytoplasm of the cells is divided into compartments by internal membranes.
2.
Prokaryotic cells lack internal membranes and are evolutionarily more primitive.
3.
Prokaryotes include the bacteria and the archaea. Prokaryotic cells contain ribosomes
and DNA but no internal membrane-bounded or ganelles. Most prokaryotic cells are
surrounded by a cell wall.
4.4
Eukaryotic Cells
1.
Eukaryotic cells are more complex and can compartmentalize dif ferent chemical
reactions into membrane-bounded interior compartments and a variety of or ganelles.
2.
Eukaryotic cells, as their name implies, have a true nucleus, while prokaryotes lack
one.
3.
Plant cells also have storage vacuoles and protective cell walls.
Tour of a Eukaryotic Cell
4.5
The Nucleus: The Cell’ s Contr ol Center
1.
The nucleus is the command and control center of the eukaryotic cell, directing all of
its activities.
2.
Nuclear Membrane
3.
The nucleus is enclosed by a double membrane, the nuclear envelope, which contains
pores to regulate the passage of materials into and out of the nucleus.
4.
Chromosomes
5.
The DNA of eukaryotes is divided into segments associated with protein, forming
chromosomes.
6.
When the cell is not under going division, the DNA is uncoiled into threadlike strands
called chromatin.
7.
Nucleolus
8.
A darker staining area inside the nucleus is the nucleolus, which contains information
for the construction of ribosomes that are needed for protein synthesis.
4.1
Cells
1.
The human body is made up of cells, most of which are too small to be seen with the
naked eye.
2.
The Cell Theory
3.
Robert Hooke first described cells in 1665 and coined the term that eventually came
to be “cells.”
4.
Modern cell theory includes three principles, as follows:
1.
All living or ganisms are composed of cells.
2.
Nothing smaller than a cell is considered to be alive.
3.
Cells arise only from preexisting cells, and all living or ganisms have descended from
the earliest cells.
1.
Most Cells Are Very Small.
2.
Cells vary in size, most of which are 5 to 20 micrometers in diameter .
3.
Why Aren’ t Cells Lar ger?
4.
Cells are small because lar ger cells do not function ef ficiently .
5.
Cell size is limited by two factors: (1) surface area-to-volume relationships that make
distribution of materials throughout a lar ge cell dif ficult, and (2) the volume of
cytoplasm the nucleus can control.
6.
An Overview of Cell Structure
7.
Cells are filled with a semifluid matrix, called cytoplasm, surrounded by a membrane
that controls the permeability of the cell.
8.
Visualizing Cells
9.
Cells can be made visible by the use of microscopes.
10.
Certain cell structures can be made more visible by staining specific molecules in a
cell.
4.2
The Plasma Membrane
1.
All cells are surrounded by a plasma membrane composed of a bilayer of
phospholipids, according to the fluid mosaic model.
2.
The polar ends of these phospholipids interact with the fluid interior and exterior
environments of the cell, while the nonpolar fatty acid chains form the interior of the
membrane.
3.
The phospholipids are arranged in a bilayer , with nonpolar tails extending to the
inside.
4.
Proteins Within the Membrane
5.
Floating within the lipid bilayer are a variety of membrane proteins. Some of these
proteins function to transport materials across the membrane (transmembrane proteins), and others serve as identification markers in cell communication (cell
surface proteins).
6.
Membrane Defects Can Cause Disease.
7.
Cystic fibrosis is a deadly genetic disorder caused by a defective transmembrane
protein that does not properly admit chloride ions into the body's cells.
Kinds of Cells
4.3
Prokaryotic Cells
1.
Cells can be divided into prokaryotic cells or eukaryotic cells based on whether or not
the cytoplasm of the cells is divided into compartments by internal membranes.
2.
Prokaryotic cells lack internal membranes and are evolutionarily more primitive.
3.
Prokaryotes include the bacteria and the archaea. Prokaryotic cells contain ribosomes
and DNA but no internal membrane-bounded or ganelles. Most prokaryotic cells are
surrounded by a cell wall.
4.4
Eukaryotic Cells
1.
Eukaryotic cells are more complex and can compartmentalize dif ferent chemical
reactions into membrane-bounded interior compartments and a variety of or ganelles.
2.
Eukaryotic cells, as their name implies, have a true nucleus, while prokaryotes lack
one.
3.
Plant cells also have storage vacuoles and protective cell walls.
Tour of a Eukaryotic Cell
4.5
The Nucleus: The Cell’ s Contr ol Center
1.
The nucleus is the command and control center of the eukaryotic cell, directing all of
its activities.
2.
Nuclear Membrane
3.
The nucleus is enclosed by a double membrane, the nuclear envelope, which contains
pores to regulate the passage of materials into and out of the nucleus.
4.
Chromosomes
5.
The DNA of eukaryotes is divided into segments associated with protein, forming
chromosomes.
6.
When the cell is not under going division, the DNA is uncoiled into threadlike strands
called chromatin.
7.
Nucleolus
8.
A darker staining area inside the nucleus is the nucleolus, which contains information
for the construction of ribosomes that are needed for protein synthesis.
