1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 3 4 5 6 7 8 9 50 51 52 3 Cells and Tissues 42 Chapter Overview Cells are the basic units of any organism. Although the human body has many different types of cells, they have similar structures and some similar functions.The cell membrane forms the boundary of the cell and keeps the cell contents separated from the fluid outside the cell. This membrane is a thin, pliable film composed of two layers of phospholipids and cholesterol molecules.Two types of proteins are also components of the cell membrane. Integral proteins completely penetrate the cell membrane and serve diverse roles; some allow water and water-soluble substances to cross the cell membrane or, as receptors, bind specific substances to the cell. Peripheral proteins attach to lipids and proteins within the membrane.They attach the cell to other cells or structures or are involved in cell signaling. Carbohydrates combined with membrane lipids and proteins form a sugary outer coating, or glycocalyx, that protects the cell from damage and that helps identify one type of cell from others. In some specialized cells, the cell membrane forms hairlike or whiplike projections that have specific purposes. Within each cell are various structures called organelles that perform distinct functions. The nucleus of each cell controls all the cell’s activities. Deoxyribonucleic acid (DNA), a very long organic molecule within the nucleus, contains instructions to make proteins. Each segment of DNA that codes for making a specific protein is called a gene. When genes issue incorrect instructions, genetic defects result. Other organelles are involved in energy generation, protein and lipid synthesis, transport, and waste disposal. Cells reproduce, a process necessary for growth and also for normal functioning of the body, because cells age and die—either naturally, in a process called apoptosis, or due to injury or disease, a process called necrosis. Cells reproduce by producing duplicates of the organelles and DNA and then dividing into two, with half the organelles going to each new daughter cell. DNA synthesis is called replication. Mitosis describes the division of the nucleus; cytokinesis describes the division of the cytoplasm. Stem cells are unspecialized cells that can reproduce and give rise to more specialized cells. • Totipotent stem cells can give rise to an entire organism or to any particular type of cell in the body.A zygote, or fertilized egg, is totipotent.
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Chapter OverviewCells are the basic units of any organism. Although the human body has many differenttypes of cells, they have similar structures and some similar functions. The cell membraneforms the boundary of the cell and keeps the cell contents separated from the fluid outsidethe cell. This membrane is a thin, pliable film composed of two layers of phospholipids andcholesterol molecules. Two types of proteins are also components of the cell membrane.Integral proteins completely penetrate the cell membrane and serve diverse roles; someallow water and water-soluble substances to cross the cell membrane or, as receptors, bindspecific substances to the cell. Peripheral proteins attach to lipids and proteins within themembrane. They attach the cell to other cells or structures or are involved in cell signaling.Carbohydrates combined with membrane lipids and proteins form a sugary outer coating, orglycocalyx, that protects the cell from damage and that helps identify one type of cell fromothers. In some specialized cells, the cell membrane forms hairlike or whiplike projectionsthat have specific purposes.
Within each cell are various structures called organelles that perform distinct functions.The nucleus of each cell controls all the cell’s activities. Deoxyribonucleic acid (DNA), a verylong organic molecule within the nucleus, contains instructions to make proteins. Eachsegment of DNA that codes for making a specific protein is called a gene. When genes issueincorrect instructions, genetic defects result. Other organelles are involved in energygeneration, protein and lipid synthesis, transport, and waste disposal.
Cells reproduce, a process necessary for growth and also for normal functioning of thebody, because cells age and die—either naturally, in a process called apoptosis, or due toinjury or disease, a process called necrosis. Cells reproduce by producing duplicates of theorganelles and DNA and then dividing into two, with half the organelles going to each newdaughter cell. DNA synthesis is called replication. Mitosis describes the division of thenucleus; cytokinesis describes the division of the cytoplasm.
Stem cells are unspecialized cells that can reproduce and give rise to more specialized cells.
• Totipotent stem cells can give rise to an entire organism or to any particular type of cell in the body. A zygote, or fertilized egg, is totipotent.
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• Pluripotent stem cells can produce any type of tissue.
• Multipotent stem cells can produce a limited range of specialized cell types. Small numbers ofmultipotent stem cells persist in adults and are used to make replacements for dead or dysfunctional cells.
Cells specialize to perform different tasks. Germ cells, the reproductive cells, found only in theovary or testis, develop into ova (eggs) or sperm. Somatic cells develop into specific types of cells—liver, muscle, brain, and so on—by focusing solely on those genes that perform a set of specializedfunctions and by turning off the genes that would lead them to manufacture other proteins, andthus perform other functions.To carry out these functions, cells must make proteins followinginstructions in the DNA. First, a messenger RNA (mRNA) copy is made of a particular gene by theprocess of transcription. Ribosomes and transfer RNA (tRNA) decode the mRNA transcript toform a protein, a process called translation.
For many cell processes to occur, substances must move from one part of the cell to another orbetween the inside and outside of the cell. Lipids and gases, which are lipid soluble, can pass easilythrough the phospholipids in the cell membrane to enter the cell. Any substances that are watersoluble, however, must be carried through the cell membrane by proteins. Some of these water-soluble substances pass through the cell membrane through channels, or watery tunnels. Channelshave different shapes, which permit the passage of specific substances. Glucose and some othersubstances diffuse across the membrane through carrier proteins, using a process called facilitateddiffusion. Some of the movement must take place up the concentration gradient, from low to highconcentration.This process is called active transport.Transport proteins called pumps use energyfrom ATP to force particles across a membrane from the low concentration side to the highconcentration side.
The concentration of all solutes in a particular compartment is called its osmolarity, measuredin particles of solute per liter of water. The osmolarity of most body cells and fluids is relativelyfixed, at about 300 mOsm (milliosmoles per liter).When substances moved into or out of thecell, they alter the relative osmolarity of the cytosol and the extracellular fluid.This action iscompensated for by osmosis, the movement of water across the cell membrane from the area ofhigh water concentration to the area of low water concentration.
Sometimes, the cell expels or accepts substances in large amounts at one time. The process ofexpelling such substances is called exocytosis and takes place through a vesicle. Taking in suchsubstances is called endocytosis, and this process often takes place when a specific receptor onthe cell membrane binds with a particular substance, usually a molecule too large to enter byother means. In phagocytosis, microbes are brought into specialized cells called phagocytes tobe destroyed.
Cells combine to form tissues, in which they work together to perform certain specificfunctions.The body is made of four kinds of tissue: muscle tissue, nervous tissue, connective tissue,and epithelial tissue. (The first two kinds of tissue are discussed in later chapters.) Epithelial tissue,also called epithelium, is a thin layer of cells lining the surface of the skin and hollow internalorgans.The cells making this tissue are packed closely together and function as a barrier. Epithelialtissues have three functions: to act as a barrier, to absorb substances, and to secrete substances. Asheet of these cells, the epithelial membrane, usually rests on a layer of connective tissue thatincludes blood vessels and nerve cells. Epithelial tissue also makes up glands, structures thatsecrete substances into blood (endocrine glands) or onto body surfaces (exocrine glands).Connective tissue is structural or supports the rest of the body, and most connective cells arespaced widely apart, separated by the extracellular matrix.There are five types of connectivetissue: loose connective tissue, which underlies the skin and other epithelial membranes; denseconnective tissue, which is tough and appears in tendons and ligaments; cartilage; bone; and blood.
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Addressing the Learning Outcomes
1. List the components of the cell membrane, and explain the function of each.
Exercise 3.1
Study the diagram of the cell membrane and its environment (Fig. 3.1). Choosing from the list ofterms below, write the name of the feature next to the number in the chart that corresponds to the number in the diagram that shows the feature. Then, in the right-hand column of the chart,explain the function of the feature.
cholesterol hydrophobic headextracellular fluid integral proteinglycolipid peripheral proteinglycoprotein phospholipidshydrophilic tail
1
6 7 8 9
2 3 4 5
Figure 3.1
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Chapter 3 Cells and Tissues 45
Feature Function
1.
2. and 3.
4. and 5.
6.
7.
8.
9.
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46 Study Guide to Accompany Human Form, Human Function
2. Explain how DNA is organized in dividing and nondividing cells.
Exercise 3.2
Choosing from the words in the list below, write the correct terms in the spaces to complete the paragraph.
The nucleus contains the long organic molecule called (1) ___________________. This molecule
appears in both dividing and nondividing cells. In nondividing cells, it takes the form of
(2) ___________________, a dense tangle of DNA strands. These dark regions of matter are mixed with
(3) ___________________, a semiliquid substance that fills the nucleus. Long threads of the organic
molecule are wound around nuclear organizing proteins called (4) ___________________. In the
nucleus of dividing cells, the molecule is visible as 46 distinct units called (5) ___________________.
These organic molecules contain the instructions—the code—the body must follow to make
(6) ___________________. Each distinct segment of material that encodes a particular protein is
called a(n) (7) ___________________.
3. List the organelles of the cell, and briefly describe the function of each.
Exercise 3.3
Study Figure 3.2, a diagram of a cell. Choosing from the list below, write the name of the featurenext to the number in the chart that corresponds to the number in the diagram. Then, in the right-hand column of the chart, explain the function of the feature. Finally, use a colored pen or pencilto circle the names of the organelles that are surrounded by a membrane. Use a different color tocircle the names of the organelles that are not surrounded by a membrane. Draw a rectanglearound the name of any features that are not organelles.
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Chapter 3 Cells and Tissues 49
4. Briefly describe the form and function of three types ofcytoskeletal filaments.
Exercise 3.4
Match the correct description of a filament in the cytoskeleton in the right column with thecorrect name for the filament in the left column by writing the letter of the appropriatedescription in the space next to the name.
Feature Function
11.
12.
13.
(continued)
________ 1. Intermediate filament
________ 2. Microfilament
________ 3. Microtubule
a. hollow tubes that attach to certain cell parts and act as pulleysto move the parts around in the cell
b. long string, much like a beaded necklace, which forms anetwork supporting the cell membrane, participating in thecontraction of muscle cells, and aiding the movement of somecells that move
c. long, interwoven protein fibers that stabilize the placement oforganelles and strengthen the nuclear envelope
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5. Compare apoptosis and necrosis.
Exercise 3.5
Use the lines below to describe apoptosis and necrosis and give an example of each.
6. Name the four phases of the cell cycle and the four stages of mitosis,and describe events that occur in each.
Exercise 3.6
Describe the process of cell division in the chart below. For each phase and subphase of theprocess listed in the chart, write the correct letter or number from Figure 3.3 illustrating that partin the process. Then, in the third column of the chart, describe the phase or subphases.
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3
2
A
4
5
67
8
B
1
Figure 3.3
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Chapter 3 Cells and Tissues 51
Letter or Number Phase or Subphase Description
anaphase
DNA synthesis phase (S phase)
first growth phase (G1 phase)
interphase
metaphase
mitosis
prophase
second growth phase (G2 phase)
telophase
cytokinesis
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7. Use a diagram to explain how DNA replication works.
Exercise 3.7
Use the lines below to describe the process by which DNA replicates itself. Refer to Figure 3.4 asyou write your description.
1 Chromatid
Template strand
Sense strand
Centromere
Free nucleotide
Direction of replication
Direction of replication
1 Chromatid
T
AT
ATA
A
G
G
CG
C
C
G
T
T
A
T
A
T
A
AT
GC
GC
GC
C
G
G
C
T
A
TC
1 Chromosome:before the S phase
1 Chromosome:after the S phase
Figure 3.4
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Chapter 3 Cells and Tissues 53
8. Compare and contrast multipotent, pluripotent, and totipotent stem cells.
Exercise 3.8
Match the correct description of a type of stem cell in the right column with the correct name forthat type of cell in the left column by writing the letter of the appropriate description in the spacenext to the name.
________ 1. Multipotent
________ 2. Pluripotent
________ 3. Totipotent
a. can produce any type of tissue—heart, brain, liver, skin, youname it—but cannot form an entire new human being
b. can give rise to an entire organism or to any particular type ofcell in the body
c. specialized stem cells that can produce only a limited range ofcell types
9. Name the four types of RNA and the function of each.
Exercise 3.9
Complete the chart by describing the function of the four kinds of RNA found in cells.
Type of RNA Function
Messenger RNAs (mRNAs)
Transfer RNAs (tRNAs)
Ribosomal RNAs (rRNAs)
Small nuclear RNAs (snRNAs)
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10. Draw a diagram illustrating the steps of transcription and translation of a very short gene.The sense strand of this gene is TTT CCC TTT.
Exercise 3.10
Listed below, out of sequence, are the 10 steps describing the process of transcription andtranslation of the gene TTT CCC TTT. Place the steps in the correct order by writing each step in the correct box in the diagram.
Steps:
• The proline tRNA with its CCC anticodon attaches to the mRNA’s GGG, and the ribosome transfers the phenylalanine to bind to this proline.
• RNA polymerase joins uracils and guanines into a complementary mRNA codons: UUU CCC UUU.
• When the ribosome reaches a stop codon, it releases both the mRNA and the new protein.
• The ribosome reads the next codon, GGG, and signals for its tRNA carrying proline.
• The DNA helix separates, exposing the DNA triplet AAA GGG AAA on the antisense strand.
• The second phenylalanine tRNA attaches to the mRNA, and the growing polypeptide chain isattached to this phenylalanine.
• The tRNA anticodon attaches and binds to the first UUU codon on the mRNA.
• The ribosome moves right again and signals for a second phenylalanine-carrying tRNA.
• The mRNA carries the full coded message from the nucleus into a ribosome.
• Reading the mRNA code, the ribosome signals for a tRNA that carries the amino acidphenylalanine.
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Step 1
Step 2
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Chapter 3 Cells and Tissues 55
Step 3
Step 4
Step 5
Step 6
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Step 7
Step 8
Step 9
Step 10
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Chapter 3 Cells and Tissues 57
13. Draw a diagram showing how the normal CFTR protein moves fromthe Golgi apparatus to the cell membrane by exocytosis.
Exercise 3.12
Study Figure 3.5 below showing the formation and transport of the normal CFTR protein. Usingthe list below, label the structures in the diagram. Then use the lines that follow to describe eachof the six numbered steps shown in the diagram.
11. Identify the mutation that is the cause of Julia’s cystic fibrosis.
Note: Objective 11 is covered in Exercise 3.13.
12. Prepare a table comparing simple diffusion, facilitated diffusion,osmosis, and active transport under the following categories:Relation to gradient; Energy requirement; Membrane proteinrequirement; Transported substance; Example.
Exercise 3.11
Fill in the missing information in the chart below to describe the four types of transport across the cell membrane.
MembraneRelation to Energy Protein Transported
Type of Transport Gradient Requirement Requirement Substance Example
Simple diffusion
Facilitated diffusion
Osmosis
Active transport
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14. Explain why the deletion of three nucleotides of the CFTR gene canresult in viscous mucus; and 11. Identify the mutation that is thecause of Julia’s cystic fibrosis.
Exercise 3.13
Study Figure 3.6 below, and then read the two paragraphs that follow. Use the words from the listto fill in the missing words from the explanations of the genetic cause of Julia’s cystic fibrosis andof why this mutation produces its particular effect.
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The gene involved is called the cystic fibrosis transmembrane conductance regulator, or the CFTR
gene, found on chromosome 7. In a(n) (1) ___________________ CFTR gene (left side of figure), the
DNA sense strand reads “ATC TTT GGT” and the (2) ___________________ reads “AUC AAA GGU.”
These three (3) ___________________ encode the (4) ___________________ isoleucine (Ile),
phenylalanine (Phe), and glycine (Gly). In the (5) ___________________ that causes cystic fibrosis,
the short DNA sequence “C TT” is (6) ___________________ (right side of figure), making the DNA
U U GG G UAUUG GU UU UA C
U
Ile Phe Gly Ile Gly Val
Chromosome 7
CFTR gene
Deletion site
DNA template
DNA sense strand (triplets)
Deleted
FPO FPO
mRNA (codons)
Translation
Folding
Amino acid# 508
(a) NORMAL (b) CYSTIC FIBROSIS
T
A
T
A
T
A
T
A
G
C
G
C
G
C
G
C
G
C
T
A
A
T
T
A
T
A
T
A
T
A
T
A
A
T
C
G
Figure 3.6
Au: Pls.conformFig. 3.6
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Chapter 3 Cells and Tissues 61
sequence now read “ATT GGT GTT.” Enzymes (7) ___________________ this sequence into RNA
with the sequence “AUU GGU GUU,” producing the amino acid (8) ___________________
“Ile-Gly-Val.” As a result, one amino acid—Phe—is deleted.Because an amino acid is missing, the
(9) __________________ coded by the defective CFTR gene has a surface different from normal and
it is destroyed by barrel-shaped organelles called (10) __________________. Because of this, the
protein cannot take its normal place in the cell membrane or do its normal job, which is to
(11) __________________ chloride molecules out of the cell across the cell membrane. Without the
integral protein to make a channel for them, however, they remain in the cell, increasing the
(12) __________________ of these molecules inside the cell. Just as less chloride moves out
of the airway cells to the airway lumen, so less water moves out of the cell through
(13) __________________. The lack of water means respiratory secretions cannot be diluted,
so they become (14) __________________, or thick.
15. Prepare a chart describing the form and function of six types of epithelial membranes and five types of connective tissue.
Exercise 3.14
Complete the chart to identify the six types of epithelial tissue, describe the form of each, andindicate a location where such cells are typically found.
Type Form Location (Example)
Simple squamous epithelium
Flat, many layers
Lining the ducts of glands, e.g., pancreas
(continued)
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Exercise 3.15
Complete the chart to identify the five types of connective tissue and to describe the contents andform and the function of each.
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Type Contents and Form Function
_____________ connective Contains a few _____________ and Loosely binds _____________ to
tissue _____________, some fat cells, and a thin _____________ _____________, fills gaps
mixture of _____________ and elastin; between _____________ bundles and
lacy and _____________ between some _____________, forms a
layer of the _____________ and large arteries
Dense _____________ Packed with _____________ _____________ Withstands strong forces in _____________,
_____________ woven into thick parallel bundles _____________, the capsules that encase
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Testing Your Knowledge
Building Understanding
I. Multiple Choice
Select the best answer and circle the letter of your choice.
1. What type of organic molecule provides the bulk of the cell membrane?
a. carbohydratesb. lipidsc. nucleotidesd. proteins
2. How do the cilia promote health in the airways?
a. They attack foreign bodies that enter the airways.b. They help identify molecules as belonging to the body or not.c. Their movement sweeps mucus that holds trapped particles out of the airways.d. They attach to foreign particles and by whiplike motion carry them away.
3. The functions of cells are carried out by specialized structures that collectively are called what?
a. cytoplasmb. cytosolc. inclusionsd. organelles
4. In RNA, the nucleotide uracil replaces what nucleotide in DNA to bond with adenine?
a. adenineb. cytosinec. guanined. thymine
5. What activity takes place in ribosomes?
a. DNA replicationb. protein synthesisc. RNA transcriptiond. zygote formation
6. Which of these is not a characteristic of integral proteins that allows them to support facilitated diffusion?
a. ability to change from being channels to carriersb. being both lipid soluble and water solublec. combined protein–carbohydrate makeupd. position extending across the entire cell membrane
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Chapter 3 Cells and Tissues 65
7. In which environment would water leave the cell?
a. atonicb. hypertonicc. hypotonicd. isotonic
8. What is the name of the process by which the cell destroys invading microbes and cleans updead cell debris in diseased or injured tissue?
a. endocytosisb. exocytosisc. phagocytosisd. transcytosis
9. Which of these is not a function of epithelial cells?
a. serving as a barrierb. secreting substancesc. destroying substancesd. absorbing substances
10. Which of these is not a description of connective tissue?
a. is structural or supportiveb. connects body systems through the nervous systemc. derived from a kind of tissue called mesodermd. has a large amount of extracellular matrix
II. Completion
Write the word or phrase that correctly completes each sentence.
1. Water cannot pass from extracellular fluid into the cell because the outer-facing side of
phospholipids and cholesterol molecules is .
2. Water and water-soluble molecules are able to pass through the cell membrane by way of the
, channels, or carriers.
3. In helping identify cells as structures that belong to the body, glycocalyx prevents the cell
from being attacked by the body’s .
4. The cytosol, in which organelles are embedded, is a viscous, solution containing salts,
bicarbonate, oxygen, CO2, and minerals in which the solvent is .
5. The DNA in a cell’s nucleus is organized into 23 pairs of structures, with one structure from each
pair inherited from each biological parent.Those structures are called .
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6. Unlike the smooth endoplasmic reticulum, the rough endoplasmic reticulum is covered by
. The two structures differ in function as well. The rough endoplasmic
reticulum modifies ; the smooth endoplasmic reticulum makes
.
7. Because cells die and must be replaced, cells must .
8. The phase of cell reproduction in which the chromosomes condense into visible structures
is called .
9. Cells manufacture most of the ATP required for cellular activities in organelles called
.
10. When people discuss embryonic stem cells, they are referring to the powerful but slightly
limited type of stem cells called .
11. In the process of transcription, RNA forms a sequence of nucleotides complementary to the
strand of DNA so that it is a copy of the strand of
DNA, which is the strand that carries the permanent code.
12. The chain of amino acids that indicates a protein’s destination is its
, which usually occurs at the beginning of the protein .
13. Because of a certain characteristic of cells and the composition of cell membranes, some, but
not all, substances can pass into and out of the cell. That characteristic is called
.
14. The proteins that facilitate diffusion of substances into cells by changing shape are called
.
15. When an intestinal cell absorbs glucose, it also absorbs water, in a demonstration of the
principle that .
16. Both endocytosis and exocytosis are processes that require energy supplied by
.
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Chapter 3 Cells and Tissues 67
17. The walls of capillaries and the air sacs of the lungs have a simple squamous epithelium
because this structure makes it easier to exchange oxygen and carbon dioxide between the
lungs and .
18. Exocrine glands, like the mammary glands that produce milk, make substances and secrete
them into .
19. The thick, parallel bundles that make up tendons and ligaments are rich in the protein
called .
20. Three locations where cartilage is found include , ,
and .
Understanding Concepts
I. True/False
For each question, write T for true or F for false in the blank to the left of each number. If astatement is false, correct it by replacing the underlined term and writing the correct statement inthe blank below the question.
________ 1. The two functions of the glycocalyx are to protect the cell from damage and to serveas an identifier.
________ 2. The interphase stage of cell reproduction, when structures other than the nucleusare prepared for duplication, lasts much less time than the mitosis phase.
________ 4. Translation refers to the process by which the nucleotide sequence of mRNA is readto produce the right amino acid sequence for a particular protein.
1. The body has trillions of cells, and many of them reproduce by cell division every day, whichmeans that mutations—defective copies of the cell’s DNA—happen frequently. Why are mostof these mutations not dangerous?
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Chapter 3 Cells and Tissues 71
2. Joe, a 50-year-old man, suffers a stroke that leaves his right arm paralyzed. With physical ther-apy, Joe is able to recover some, but not all, of his motor function. Why?
Expanding Your HorizonsThe buildup of free radicals in cells is potentially dangerous. These free electrons can seek toform a bond with the first available molecule, no matter if the cell is damaged in the process. Freeradicals are a product of normal cellular metabolism, but they must be kept in low concentrationbecause they can damage any part of the cell. The body has natural defenses against free radicals,enzymes in the peroxisome that combine the free radicals with oxygen, which neutralizes them and produces a nontoxic molecule. Popular writings on diet and nutrition, and manyadvertisements, warn of links between free radicals and serious diseases, such as cancer andheart disease. Many reports and ads tout the benefits of eating foods with antioxidants orconsuming supplements with these substances.
Critical ThinkingAs you read more about this issue, consider these questions:
1. To what extent are free radicals connected to serious diseases such as cancer and heart disease?
2. How effective are consuming large amounts of antioxidants, or taking supplements with antioxidants, toward preventing disease?