- The word cell means a small chamber
- Proteins have a unique shape or conformation that enables them to bind specific molecules on
portions of their surfaces known as binding
- To form an image with an electron beam, most of the electrons must pass through the
specimen, just as light passes through a specimen in a light microscope.
Pg 44 is an image
- Two classes of cells, eukaryotic cells and prokaryotic cells, can be distinguished by their
- The cells of the human body, as well as those of other multicellular animals and plants, are
eukaryotic (true-nucleus) cells. These cells contain a nuclear membrane surrounding the cell
nucleus, and also contain numerous other membrane-bound structures.
- Prokaryotic cells, such as bacteria, lack these membranous structures.
- Plasma membrane surrounds cells with a limited barrier and covers the cell surface
- These membrane-bound compartments, along with some particles and filaments, are known as
- The interior of a cell is divided into two regions: (1) the nucleus, a spherical or oval structure
usually near the center of the cell, and (2) the cytoplasm, the region outside the nucleus (Figure
- The cytoplasm contains cell organelles and fluid surrounding the organelles, known as the
- The term intracellular fluid refers to nil the fluid inside a cell—in other words, cytosol plus the
fluid inside all the organelles, including the nucleus
- Their most universal role is to act as a selective barrier to the passage of molecules, allowing
some molecules to cross while excluding others.
Figure 3-4 cell structures found in humans
Membrane Structure - All membranes consist of a double layer of lipid molecules containing embedded proteins (figure
- The major membrane lipids are phospholipids, which are amphipathic molecules.
- One end has a charged or polar region, and the remainder of the molecule, which consists of
two long fatty acid chains, is nonpolar.
- There are two classes of membrane proteins: integral and peripheral.
- Integral membrane proteins are closely associated with the membrane lipids and cannot be
extracted from the membrane without disrupting the lipid bilayer.
- Most integral proteins span the entire membrane and are referred to as transmembrane
proteins. Most of these transmembrane proteins cross the lipid bilayer several times
- Peripheral membrane proteins are not amphipathic and do not associate with the nonpolar
regions of the lipids in the interior of the membrane. They are located at the membrane surface
where they are bound to the polar regions of the integral membrane proteins (see Figure 3-7).
- These carbohydrates consist of short, branched chains of monosaccharides that extend from the
cell surface into the extracellular fluid, where they form a layer known as the glycocalyx.
- These surface carbohydrates play important roles in enabling cells to identify and interact with
- All membranes have the general structure just described, which is known as the fluid-mosaic
- Most cells are packaged into tissues and are not free to move around the body. But even in
tissues, there is usually a space between the plasma membranes of adjacent cells.
- This space, filled with extracellular (interstitial) fluid, provides a pathway for substances to pass
between cells on their way to and from the blood.
- integrins, to bind to specific proteins in the extracellular matrix and link them to membrane
proteins on adjacent cells.
- Desmosomes (Figure 3-I0a) consist of a region between two adjacent cells where the apposed
plasma membranes are separated by about 20 nm.
- Cadherins are proteins that extend from the cell into the extracellular space, where they link up
and bind with cadherins from an adjacent cell.
- Desmosomes hold adjacent cells firmly together in areas that are subject to considerable
stretching, such as the skin.
- usually disk-shaped
- A second type of membrane junction, the tight junction (Figure 3-10b), forms when the
extracellular surfaces of two adjacent plasma membranes join together so that no extracellular
space remains between them. - the gap junction, consists of protein channels linking the cytosols of adjacent cells
- Cell organelles of different sizes and density settle out at various rates, so by controlling the
speed and time of centrifugation, various fractions can be separated. We can then study these
isolated cell organelles to learn their chemical composition and metabolic functions.
- The primary function of the nucleus is the storage and transmission of genetic information to
the next generation of cells
- Surrounding the nucleus is a barrier, the nuclear envelope, composed of two membranes.