CELLS AND CELL COMMUNICATION

COMPONENTS OF ALL CELLS Plasma membrane Controls substances passing in and out of the cell Controls substances passing in and out of the cell DNA containing region DNA containing region in eukaryotic cells Nucleus in eukaryotic cells region in prokaryotic cells Nucleoid region in prokaryotic cells Cytoplasm A semifluid mixture containing cell components A semifluid mixture containing cell components

Figure 4-2 p54 A. A prokaryotic cell. cytoplasmDNA plasma membrane nucleus B. A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus. Eukaryotic cell Cell interior is divided into functional compartments, including a nucleus Prokaryotic cell Small, 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 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 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 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. 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 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 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 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 allow cells to interact with each other and the environment Cell junctions allow cells to interact with each other and the environment In plants, extend through cell walls to connect the cytoplasm of two cells In plants, plasmodesmata extend through cell walls to connect the cytoplasm of two cells Animals have three types of cell junctions 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