CELLS AND CELL
COMMUNICATION
COMPONENTS OF ALL CELLS
• Plasma membrane
• Controls substances passing in and out of the cell
• DNA containing region
• Nucleus in eukaryotic cells
• Nucleoid region in prokaryotic cells
• Cytoplasm
• A semifluid mixture containing cell components
A. A prokaryotic
cell.
cytoplasm
Eukaryotic cell
Cell interior is divided into functional
compartments, including a nucleus
DNA
plasma membrane
nucleus
Prokaryotic cell
Small, simple cells without a nucleus
B. A eukaryotic
(plant) cell. Only
eukaryotic cells
have a nucleus.
Figure 4-2 p54
ANIMATED FIGURE: OVERVIEW OF CELLS
PREVIEW OF CELL MEMBRANES
• Lipid bilayer
• A double layer of phospholipids
organized with their hydrophilic heads
outwards and their hydrophobic tails
inwards
• Many types of proteins embedded or
attached to the bilayer carry out
membrane functions
CONSTRAINTS ON CELL SIZE
• Surface-to-volume ratio restricts cell size by limiting transport of nutrients and
wastes
OSMOSIS AND TONICITY
• Osmosis is the
movement of water
along its gradient
through a
semipermeable
membrane. Since other
substances cannot go
through the membrane
tonicity results.
THE CELL THEORY
CELL THEORY
THE CELL THEORY EMERGES
•
•
•
Van Leeuwenhoek was the first to describe
small organisms seen through a microscope,
which he called animalcules and beasties
Hooke was the first to sketch and name cells
Brown was the first to identify a cell nucleus
•
The cell theory, a foundation of modern biology,
states that cells are the fundamental units of life
•
In 1839, Schleiden and Schwann proposed the
basic concepts of the modern cell theory
•
•
All organisms consists of one or more cells
•
Each new cell arises from division of a
preexisting cell
•
Each cell passes its hereditary material to its
offspring
A cell is the smallest unit with the properties of
life
TAKE-HOME MESSAGE:
HOW ARE ALL CELLS ALIKE?
• All cells start life with a plasma membrane, cytoplasm, and a region of DNA, which, in eukaryotic cells only, is
enclosed by a nucleus
• The surface-to-volume ratio limits cell size and influences cell shape
• Observations of cells led to the cell theory: All organisms consist of one or more cells; the cell is the smallest unit
of life; each new cell arises from another cell; and a cell passes hereditary material to its offspring
CELL JUNCTIONS
•
Cell junctions allow cells to interact
with each other and the environment
•
In plants, plasmodesmata extend
through cell walls to connect the
cytoplasm of two cells
•
Animals have three types of cell
junctions: tight junctions, adhering
junctions, gap junctions
CELL JUNCTIONS IN ANIMAL TISSUES
free surface of
epithelial tissue
tight junctions
adhering
junction
gap junction
basement membrane
ANIMATED FIGURE: ANIMAL CELL JUNCTIONS