Mosby items and derived items © 2007, 2003 by Mosby, Inc. Chapter 3 I. Cells Slide 1

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 3

I. Cells

Slide 1

Mosby items and derived items © 2007, 2003 by Mosby, Inc. Slide 2

A. Functional Anatomy of Cells

• 1. Cell structures a. Plasma membrane—separates the cell from its

surrounding environment b. Cytoplasm—thick gel-like substance inside of

the cell composed of numerous organelles suspended in watery cytosol;

c. Nucleus—large membranous structure near the center of the cell




B. Cell Membranes

• 1. Fluid mosaic model—theory explaining how cell membranes are constructed

• 2. Chemical attractions are the forces that hold membranes together a. Groupings of membrane molecules form rafts,

each of which float as a unit in the membrane

b. Rafts may pinch inward, bringing material into the cell or organelle



• 3. Primary structure of a cell membrane is a double layer of phospholipid molecules a. Heads are hydrophilic (water-loving) b. Tails are hydrophobic (water-fearing) c. Molecules arrange themselves in bilayers in water d. Cholesterol molecules are scattered among the

phospholipids to allow the membrane to function properly at body temperature

e. Most of the bilayer is hydrophobic


II. Cytoplasm and Organelles

• A. Cytoplasm—gel-like internal substance of cells that includes many organelles suspended in watery intracellular fluid called cytosol


• B. Two major groups of organelles: 1. Membranous organelles

2. Nonmembranous organelles


C. Organelles

• 1. literally means “little organ”

• 2. 100’s to 1000’s in each cell

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3. Endoplasmic reticulum

a. Made of canals with membranous walls and flat, curving sacs arranged in parallel rows throughout the cytoplasm; extend from the plasma membrane to the nucleus

b. Proteins move through the canals


c. Two types of endoplasmic reticulum:

• 1. Rough endoplasmic reticulum

Ribosomes dot the outer surface of the membranous walls

Ribosomes synthesize proteins, which move toward the Golgi apparatus and then eventually leave the cell

Function in protein synthesis and intracellular transportation


• 2. Smooth endoplasmic reticulum

No ribosomes border membranous wall

Functions are less well established and probably more varied than for rough endoplasmic reticulum

Synthesizes certain lipids and carbohydrates and creates membranes for use throughout cell

Removes and stores Ca++ from cell’s interior.


4. Ribosomes

a. Many are attached to the rough endoplasmic reticulum and many lie free, scattered through the cytoplasm

b. Each ribosome is a nonmembranous structure made of two pieces, a large subunit and a small subunit; each subunit is composed of rRNA

c. Ribosomes in the endoplasmic reticulum make proteins for “export” or to be embedded in the plasma membrane; free ribosomes make proteins for the cell’s domestic use

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5. Golgi apparatus

a. Membranous organelle consisting of cisternae stacked on one another and located near the nucleus

b. Processes protein molecules from the endoplasmic reticulum

c. Processed proteins leave the final cisterna in a vesicle; contents may then be secreted to outside the cell


6. Lysosomes

a. Made of microscopic membranous sacs that have “pinched off” from Golgi apparatus

b. The cell’s own digestive system; enzymes in lysosomes digest the protein structures of defective cell parts, including plasma membrane proteins, and particles that have become trapped in the cell


7. Proteasomes

a. Hollow, protein cylinders found throughout the cytoplasm

b. Break down abnormal/misfolded proteins and normal proteins no longer needed by the cell

c. Break down protein molecules one at a time by tagging each one with a chain of ubiquitin molecules and unfolding it as it enters the proteasome, then breaking apart peptide bonds


8. Peroxisomes

a. Small membranous sacs containing enzymes that detoxify harmful substances that enter the cells

b. Often seen in kidney and liver cells


9. Mitochondria

a. Made up of microscopic sacs; wall composed of inner and outer membranes separated by fluid; thousands of particles make up enzyme molecules attached to both membranes

b. The “power plants” of cells; mitochondrial enzymes catalyze series of oxidation reactions that provide about 95% of cell’s energy supply

c. Each mitochondrion has a DNA molecule, allowing it to produce its own enzymes and replicate copies of itself


10. Nucleus

• a. Definition—spherical body in center of cell; enclosed by an envelope with many pores

• b. Structure- Consists of nuclear envelope (composed of two membranes each with essentially the same molecular structure as plasma membrane) surrounding nucleoplasm; nuclear envelope has holes called nuclear pores


c. Contains DNA (heredity molecules), which appear as the following:

• Chromatin threads or granules in nondividing cells

• Chromosomes in early stages of cell division

• Functions of nucleus are functions of DNA molecules; DNA determines both structure and function of cells and heredity


11. Cytoskeleton

• a. The cell’s internal supporting framework made up of rigid, rodlike pieces that provide support and allow movement and mechanisms that can move the cell or its parts


• b. Centrosome

An area of the cytoplasm near the nucleus that coordinates the building and breaking of microtubules in the cell

Plays an important role during cell division

The general location of the centrosome is identified by the centrioles


• c. Cell extensions Cytoskeleton forms projections that extend the

plasma membrane outward to form tiny, fingerlike processes

Microvilli—found in epithelial cells that line the intestines and other areas where absorption is important; they help to increase the surface area manyfold

Cilia and flagella—cell processes that have cylinders made of microtubules at their core; cilia are shorter and more numerous than flagella; flagella are found only on human sperm cells


III. Cell Connections

• A. Gap junctions—membrane channels of adjacent plasma membranes adhere to each other; have two effects: 1. Form gaps or “tunnels” that join the

cytoplasm of two cells

2. Fuse two plasma membranes into a single structure


• B. Tight junctions 1. Occur in cells that are joined by “collars” of

tightly fused material

2. Molecules cannot permeate the cracks of tight junctions

3. Occur in the lining of the intestines and other parts of the body, where it is important to control what gets through a sheet of cells

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Mosby items and derived items © 2007, 2003 by Mosby, Inc. Chapter 3 I. Cells Slide 1