cells and cell communication. components of all cells plasma membrane controls substances passing in...
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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
Figure 4-2 p54
A. A prokaryotic cell. cytoplasm DNA plasma membrane
nucleus
B. A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus.
Eukaryotic cellCell interior is divided into functional compartments, including a nucleus
Prokaryotic cellSmall, simple cells without a nucleus
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
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
CELL THEORY
• 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
• A cell is the smallest unit with the properties of life
• Each new cell arises from division of a preexisting cell
• Each cell passes its hereditary material to its offspring
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