CELLS AND CELL COMMUNICATION. COMPONENTS OF ALL CELLS Plasma membrane Controls substances passing in and out of the cell Controls substances passing in.

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