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Chapter 3
Anatomy of Cells
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CASE STUDY
Ben and Louise Carpenter have come to the clinic to discuss family
planning. They decided to stop birth control methods in an attempt to
begin a family. Both Ben and Louise are concerned because Louise is
older than 35 years. They worry that she will have difficulty conceiving
or that something may “go wrong” with the pregnancy or fetus.
1. As part of the routine examination, Mr. and Mrs. Carpenter were
checked for sexually transmitted diseases and a Gram stain test
was completed. Which one of the following statements is the
BEST description of the Gram stain test?
A. Each cell produces its own pigment that gives color to the
specimen.
B. The specimen is stained to identify structural differences.
C. The specimen is stained to study the cell as it functions.
D. The specimen is stained to study the macroscopic anatomy of
the cell.
3. Ben and Louise ask about tests to determine genetic problems
because there is a previous history within their families of some
genetically transmitted diseases. The practitioner’s response
would include information about which part of the cell?
A.
B.
C.
D.
Golgi apparatus
Lysosome
Mitochondria
Nucleus
4. In discussing how fertilization occurs, which is the BEST
description of movement of the sperm and ovum?
A. Sperm move by means of a flagellum; ova are moved by cilia.
B. Sperm move by means of a flagellum; ova are moved by
microvilli.
C. Ova move by means of a flagellum; sperm are moved by cilia.
D. Both sperm and ova have flagella.
2. Studies are completed as part of the prenatal evaluation to
ascertain that Mrs. Carpenter is in good health. Which of the
following cells would be the most critical to evaluate?
A.
B.
C.
D.
Nerve cells
Muscle cells
Gland cells
Blood cells
CHAPTER SUMMARY
FUNCTIONAL ANATOMY OF CELLS
A. The typical cell (Figure 3-1)
1. Also called composite cell
2. Vary in size; all are microscopic (Table 3-1)
3. Vary in structure and function (Table 3-2)
B. Cell structures
1. Plasma membrane—separates the cell from its surrounding
environment
2. Cytoplasm—thick gel-like substance inside the cell composed of numerous organelles suspended in watery cytosol;
each type of organelle is suited to perform particular functions (Figure 3-2)
3. Nucleus—large membranous structure near the center of
the cell
CELL MEMBRANES
A. Each cell contains a variety of membranes
1. Plasma membrane (Figure 3-3)
2. Membranous organelles—sacs and canals made of the
same material as the plasma membrane
B. Fluid mosaic model—theory explaining how cell membranes
are constructed
1. Molecules of the cell membrane are arranged in a sheet
2. The mosaic of molecules is fluid; that is, the molecules are
able to float around slowly
3. This model illustrates that the molecules of the cell membrane form a continuous sheet
C. Chemical attractions are the forces that hold membranes together
D. Groupings of membrane molecules form rafts that float as a
unit in the membrane (Figure 3-4)
1. Rafts may pinch inward to bring material into the cell or organelle
2. Primary structure of a cell membrane is a double layer of
phospholipid molecules
3. Heads are hydrophilic (water loving)
4. Tails are hydrophobic (water fearing)
5. Arrange themselves in bilayers in water
6. Cholesterol molecules are scattered among the phospholipids to allow the membrane to function properly at body
temperature
7. Most of the bilayer is hydrophobic; therefore water or
water-soluble molecules do not pass through easily
E. Membrane proteins (Table 3-4)
1. A cell controls what moves through the membrane by
means of membrane proteins embedded in the phospholipid bilayer
2. Some membrane proteins have carbohydrates attached to
them and as a result form glycoproteins that act as identification markers
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3. Some membrane proteins are receptors that react to specific chemicals, sometimes permitting a process called signal transduction
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 (Table 3-3)
1. Membranous organelles are specialized sacs or canals
made of cell membranes
2. Nonmembranous organelles are made of microscopic filaments or other nonmembranous materials
C. Endoplasmic reticulum (Figure 3-5)
1. Made of membranous-walled canals and flat, curving sacs
arranged in parallel rows throughout the cytoplasm; extend
from the plasma membrane to the nucleus
2. Proteins move through the canals
3. Two types of endoplasmic reticulum
a. Rough endoplasmic reticulum
(1) Ribosomes dot the outer surface of the membranous walls
(2) Ribosomes synthesize proteins, which move toward
the Golgi apparatus and then eventually leave the
cell
(3) Function in protein synthesis and intracellular
transportation
b. Smooth endoplasmic reticulum
(1) No ribosomes border the membranous wall
(2) Functions are less well established and probably
more varied than for the rough endoplasmic reticulum
(3) Synthesizes certain lipids and carbohydrates and
creates membranes for use throughout the cell
(4) Removes and stores Ca from the cell’s interior.
D. Ribosomes (Figure 3-6)
1. Many are attached to the rough endoplasmic reticulum
and many lie free, scattered through the cytoplasm
2. Each ribosome is a nonmembranous structure made of two
pieces, a large subunit and a small subunit; each subunit is
composed of rRNA
3. 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
E. Golgi apparatus
1. Membranous organelle consisting of cisternae stacked on
one another and located near the nucleus (Figure 3-7)
2. Processes protein molecules from the endoplasmic reticulum (Figure 3-8)
3. Processed proteins leave the final cisterna in a vesicle; contents may then be secreted to outside the cell
F. Lysosomes (Figure 3-9)
1. Made of microscopic membranous sacs that have “pinched
off” from Golgi apparatus
2. 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
G. Proteasomes (Figure 3-10)
1. Hollow, protein cylinders found throughout the cytoplasm
2. Break down abnormal/misfolded proteins and normal proteins no longer needed by the cell (and which may cause
disease)
3. Break down protein molecules one at a time by tagging
each one with a chain of ubiquitin molecules, unfolding it
as it enters the proteasome, and then breaking apart peptide bonds
H. Peroxisomes
1. Small membranous sacs containing enzymes that detoxify
harmful substances that enter the cells
2. Often seen in kidney and liver cells
I. Mitochondria (Figure 3-11)
1. 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
2. The “power plants” of cells; mitochondrial enzymes catalyze series of oxidation reactions that provide about 95%
of a cell’s energy supply
3. Each mitochondrion has a DNA molecule, which allows it
to produce its own enzymes and replicate copies of itself
NUCLEUS
A. Definition—spherical body in center of cell; enclosed by an
envelope with many pores
B. Structure
1. Consists of a nuclear envelope (composed of two membranes each with essentially the same molecular structure
as the plasma membrane) surrounding nucleoplasm; the
nuclear envelope has holes called nuclear pores (Figure
3-12)
2. Contains DNA (heredity molecules), which appear as
a. Chromatin threads or granules in nondividing cells
b. Chromosomes in early stages of cell division
C. Functions of the nucleus are functions of DNA molecules;
DNA determines both the structure and function of cells and
heredity
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 (Figure 3-13)
B. Cell fibers
1. Intricately arranged fibers of varying length that form a
three-dimensional, irregularly shaped lattice
2. Fibers appear to support the endoplasmic reticulum, mitochondria, and “free” ribosomes
3. Smallest cell fibers are microfilaments (Figure 3-14)
a. “Cellular muscles”
b. Made of thin, twisted strands of protein molecules that
lie parallel to the long axis of the cell
c. Microfilaments can slide past each other and cause
shortening of the cell
4. Intermediate filaments are twisted protein strands slightly
thicker than microfilaments; form much of the supporting
framework in many types of cells
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5. Microtubules are tiny, hollow tubes that are the thickest of
the cell fibers; they are made of protein subunits arranged
in a spiral fashion; their function is to move things around
in the cell
C. Centrosome
1. An area of the cytoplasm near the nucleus that coordinates
the building and breaking of microtubules in the cell
2. Nonmembranous structure also called the microtubuleorganizing center (MTOC)
3. Plays an important role during cell division
4. The general location of the centrosome is identified by the
centrioles
D. Cell extensions
1. Cytoskeleton forms projections that extend the plasma
membrane outward to form tiny, fingerlike processes
2. There are three types of these processes; each has specific
functions (Figure 3-15)
a. Microvilli—found in epithelial cells that line the intestines and other areas where absorption is important;
they help increase the surface area manyfold
b. 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
CELL CONNECTIONS
A. Cells are held together by fibrous nets that surround groups of
cells (e.g., muscle cells), or cells have direct connections to
each other
B. There are three types of direct cell connections (Figure 3-16)
1. Desmosome
a. Fibers on the outer surface of each desmosome interlock with each other; anchored internally by intermediate filaments of the cytoskeleton
b. Spot desmosomes are like “spot welds” at various points
connecting adjacent membranes
c. Belt desmosomes encircle the entire cell like a collar
2. Gap junctions—membrane channels of adjacent plasma
membranes adhere to each other; have two effects:
a. Form gaps or “tunnels” that join the cytoplasm of two
cells
b. Fuse two plasma membranes into a single structure
Anatomy of Cells
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3. Tight junctions
a. Occur in cells that are joined by “collars” of tightly
fused material
b. Molecules cannot permeate the cracks of tight junctions
c. 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
REVIEW QUESTIONS
1. What is the range in human cell diameters?
2. List the three main cell structures.
3. Describe the location, molecular structure, and width of the
plasma membrane.
4. Explain the communication function of the plasma membrane, its transportation function, and its identification function.
5. Briefly describe the structure and function of the following
cellular structures/organelles: endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria, lysosomes, proteasomes, peroxisomes, cytoskeleton, cell fibers, centrosome,
centrioles, and cell extensions.
6. Describe the three types of intercellular junctions. What are
the special functional advantages of each?
7. Describe briefly the functions of the nucleus and the nucleoli.
8. Name three kinds of micrography used in this book to illustrate cell structures. What perspective does each give that the
other two do not?
CRITICAL THINKING QUESTIONS
1. Using the complementarity principle that cell structure is related to its function, discuss how the shapes of the nerve cell
and muscle cell are specific to their respective functions.
2. What is the relationship among ribosomes, endoplasmic reticulum, Golgi apparatus, and plasma membrane? How do they
work together as a system?