Contents Chapter Introduction The Genetic Code: Using
Information 9.1Genetic Material 9.2Importance of Proteins
Transcription 9.3RNA Synthesis 9.4RNA Processing Protein Synthesis
9.5Translation 9.6Transport and Modification of Proteins
9.7Translation Errors Viruses 9.8Genetic Information and Viruses
9.9Impact of Viruses Chapter Highlights Chapter Animations Chapter
Menu
Slide 4
Learning Outcomes 1 AExplain the connection between DNA and RNA
in protein synthesis; describe the genetic code and its role in
protein synthesis. Learning Outcomes By the end of this chapter you
will be able to: BExplain why proteins are important to biological
systems. CIdentify the stages of transcription and explain what
occurs during each stage. DSummarize the events that occur in RNA
processing.
Slide 5
Learning Outcomes 2 EIdentify the stages of translation and
explain what occurs during each stage. Learning Outcomes By the end
of this chapter you will be able to: FDescribe posttranslational
modification and transport of proteins. GInfer the consequences of
RNA translation errors. HExplain the relationship between viruses
and host cells and describe the impact of viruses on living
systems.
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Chapter Introduction 1 Does a cell express all of its genetic
information all the time? Expressing Genetic Information How does
an organism use the information stored in its genetic material? A
colored scanning electron micrograph of a group of human
chromosomes (x6,875)
Slide 7
Chapter Introduction 2 Expressing Genetic Information Living
organisms store information in their genetic material. In a process
called gene expression, organisms read and use the encoded
information by directing the synthesis of proteins. When a virus
infects a cell, the virus takes control of gene expression in the
cell. A colored scanning electron micrograph of a group of human
chromosomes (x6,875)
Slide 8
End of the Introduction
Slide 9
9.1 Genetic Material 1 Genetic material consists of two nucleic
acids DNA and RNAthat are involved in gene expression. The Genetic
Code: Using Information 9.1 Genetic Material Gene expression
depends on two features of their molecular structure: 1.nucleic
acids consist of a long strand of repeating subunits that act as
letters in a code 2.the subunit bases of one strand pair with the
bases of another strand
Slide 10
9.1 Genetic Material 2 Living cells store genetic information
in DNA which specifies the primary structures of proteins. 9.1
Genetic Material (cont.) By determining the primary structure of
each protein, DNA indirectly dictates protein function. Proteins,
in turn, carry out important cell activities. When a gene becomes
active, an enzyme makes a temporary RNA copy of the information the
DNA contains. The Genetic Code: Using Information
Slide 11
9.1 Genetic Material 3 Messenger RNA (mRNA) is the temporary
copy of a gene that encodes a protein. The process of making an
mRNA molecule is called transcription. 9.1 Genetic Material (cont.)
The Genetic Code: Using Information In translation, the mRNA
molecule provides the pattern that determines the order in which
amino acids are added to the protein being made. Protein synthesis
takes place on ribosomes which are made of proteins and ribosomal
RNA (rRNA). Each amino acid that will be used in making the protein
is attached to transfer RNA (tRNA).
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9.1 Genetic Material 4 Information stored in DNA is copied to
mRNA, which in turn directs the synthesis of a particular
protein.
Slide 13
9.1 Genetic Material 5 The genetic code describes how a
sequence of bases in DNA or RNA translates into the sequence of
amino acids in a protein. The nucleotides serve as the four letters
of the DNA alphabet. A genetic code requires at least 20 different
code wordsone for each amino acid. 9.1 Genetic Material (cont.) The
Genetic Code: Using Information
Slide 14
9.1 Genetic Material 6 Three nucleotides are grouped at a time
allowing 64 triplet combinations, such as CTG, TAC, and ACA. Each
nucleotide triplet in DNA directs a particular triplet to be formed
in mRNA during transcription. In translation, a second base-pairing
step is essential for reading the genetic code. 9.1 Genetic
Material (cont.) The Genetic Code: Using Information
Slide 15
9.1 Genetic Material 7 A triplet in mRNA, called a codon, pairs
with a triplet on a tRNA molecule, called an anticodon, carrying
the correct amino acid. 9.1 Genetic Material (cont.) The Genetic
Code: Using Information A molecule of transfer RNA (tRNA) with a
specific amino acid attached reads each codon of a messenger RNA
(mRNA) during protein synthesis (translation).
Slide 16
9.1 Genetic Material 8 The genetic code is written in
nucleotide triplets, or codons, in a strand of mRNA. Each triplet
codon specifies an amino acid. For example, UGG codes for the amino
acid tryptophan. Several amino acids have more than one codon. Some
triplets are punctuation telling the system to start or stop
translation.
Slide 17
9.2 Importance of Proteins 1 Many proteins, such as keratin,
collagen, and myosin, serve as the material that makes up cell
structures or tissues. 9.2 Importance of Proteins The Genetic Code:
Using Information The feathers responsible for the appearance of
this Raggiana bird of paradise, Poradisaea raggiana, are composed
mostly of the protein keratin.
Slide 18
9.2 Importance of Proteins 2 Some proteins are enzymes,
essential catalysts that make the chemical reactions of living
systems happen fast enough to be useful. Proteins, such as
hemoglobin, bind to specific molecules. 9.2 Importance of Proteins
(cont.) The Genetic Code: Using Information
Slide 19
9.2 Importance of Proteins 3 Protein hormones, such as insulin,
play a key role in communication within an organism. Hormones are
chemical signals given off by cells in one part of an organism that
regulate behavior of cells in another part of the organism. 9.2
Importance of Proteins (cont.) The Genetic Code: Using
Information
Slide 20
9.2 Importance of Proteins 4 A proteins structure determines
its function, and information expressed from the code in DNA
determines the structures of proteins. Collagen exists as long
fibers that bind cells together in tissues. 9.2 Importance of
Proteins (cont.) The Genetic Code: Using Information A scanning
electron micrograph of human pancreatic connective tissue
(collagen), x39,000. Many enzymes, such as lysozyme, have cavities
or pockets that bind only specific substrate molecules.
Slide 21
End of Section 1
Slide 22
9.3 RNA Synthesis 1 Gene expression begins with RNA synthesis
when the transcription enzyme RNA polymerase joins RNA nucleotides
according to the base sequence in DNA. Transcription 9.3 RNA
Synthesis Prokaryotes have one type of RNA polymerase. Eukaryotes
have three RNA polymerases, each responsible for making different
types of RNA.
Slide 23
9.3 RNA Synthesis 2 In eukaryotes, protein synthesis takes
place outside the nucleus; however, mRNA, tRNA, and rRNA are built
in the nucleus. 9.3 RNA Synthesis (cont.) During protein synthesis,
two ribosomal subunits bind to each other and an mRNA to form an
intact ribosome. Transcription
Slide 24
9.3 RNA Synthesis 3 Each type of RNA carries out a different
function in protein synthesis. This figure uses a linear symbol for
mRNA to emphasize that its sequence corresponds to the linear
sequence of amino acids in a protein. In reality, the mRNA is
folded and twisted rather than being straight or rigid.
Slide 25
9.3 RNA Synthesis 4 Only one strand of the DNA, the coding or
template strand, directs the synthesis of RNA. 9.3 RNA Synthesis
(cont.) Transcription Each DNA nucleotide pairs with a particular
RNA nucleotide. This pairing is the basis of the genetic code. Note
that in RNA, uracil (U) replaces the thymine (T) of DNA.
Slide 26
9.3 RNA Synthesis 5 Transcription takes place in three stages:
1.Initiationthe enzyme RNA polymerase attaches to a specific region
of the DNA 2.Elongation of the RNARNA polymerase partially unwinds
the DNA, exposing the coding strand of the gene 3.TerminationRNA
polymerase reaches the terminator region, or the end of the DNA to
be transcribed and the enzyme and primary transcript are released
from the DNA 9.3 RNA Synthesis (cont.) Transcription
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9.3 RNA Synthesis 6 The three stages in transcription of RNA
from a DNA template Click the image to view an animated
version.
Slide 28
9.4 RNA Processing 1 In prokaryotes, new mRNA is translated and
broken down by enzymes within a few minutes. 9.4 RNA Processing In
eukaryotes, mRNA can last from minutes to days, depending partly on
how the primary transcript is processed. Transcription A
transmission electron micrograph of an unidentified operon of the
bacterium Escherichia coli, x72,600. Ribosomes attach to mRNA, and
protein synthesis begins even before transcription is
complete.
Slide 29
9.4 RNA Processing 2 All three types of RNA are processed in
the nucleus of eukaryotes before they leave the nucleus. Enzymes
add additional nucleotides and chemically modify or remove others.
9.4 RNA Processing (cont.) Transcription
Slide 30
9.4 RNA Processing 3 9.4 RNA Processing (cont.) Transcription
Enzymes attach a cap of chemically modified guanine nucleotides
(methyl-guanine, or mG) to the starting end of the mRNA
molecule.
Slide 31
9.4 RNA Processing 4 Other enzymes then replace part of the
opposite end with a tail of 100200 adenine nucleotides called a
poly-A tail. 9.4 RNA Processing (cont.) Transcription
Slide 32
9.4 RNA Processing 5 The final step in mRNA processing involves
removal of some internal segments of the RNA that do not code for
protein called introns. The parts of the transcript that remain
(and code for protein) are called exons. 9.4 RNA Processing (cont.)
Transcription
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9.4 RNA Processing 6 The process of removing introns and
rejoining cut ends is called splicing. 9.4 RNA Processing (cont.)
Transcription If introns are left in RNA, the consequences can be
serious.
Slide 34
9.4 RNA Processing 7 An important step in the processing of
tRNA is the chemical modification of several nucleotides and
folding into a cloverleaf shape. 9.4 RNA Processing (cont.)
Transcription Mature tRNA resembles a cloverleaf (a), with the
amino- acid binding site at the end of a stem and the anticodon at
the loop on the opposite end. Base pairing between parallel parts
of the tRNA molecule stabilizes the cloverleaf shape. The
three-dimensional structure of the molecule is roughly L-shaped
(b).
Slide 35
9.4 RNA Processing 8 Ribosomal RNA is not involved in coding.
The primary rRNA transcript is spliced and modified to produce
mature rRNA molecules. 9.4 RNA Processing (cont.)
Transcription
Slide 36
End of Section 2
Slide 37
9.5 Translation 1 On ribosomes, protein synthesis translates
the codon sequence of mRNA into the amino-acid sequence of a
protein. Protein Synthesis 9.5 Translation tRNA anticodons pair
with the mRNA codons that encodes a particular amino acid.
Attachment of the correct amino acid to its tRNA molecule is called
tRNA charging. A molecule of ATP provides the energy to form this
bond.
Slide 38
9.5 Translation 2 Charged tRNA, mRNA, and the growing
polypeptide chain come together at specific binding sites on a
ribosome. 9.5 Translation (cont.) At these sites, tRNA anticodons
base-pair with mRNA codons, positioning the amino acids they carry
so that they can bond to the growing polypeptide chain. Protein
Synthesis
Slide 39
9.5 Translation 3 One of the binding sites, the P site, holds
the tRNA carrying the growing polypeptide chain. The A site holds
the tRNA carrying the next amino acid to be added to the chain.
Next to the P site is the exit site, or E site. An uncharged tRNA
leaves the E site after its amino acid is added to the growing
chain. 9.5 Translation (cont.) Protein Synthesis
Slide 40
9.5 Translation 4 9.5 Translation (cont.) Protein Synthesis A
charged tRNA sits in the A site of the ribosome, bound to the
correct mRNA codon by base pairing. A second tRNA, carrying a
growing polypeptide, is in the P site, bound to the previous mRNA
codon. The E site is not shown. A groove between the large and
small subunits of the ribosome accommodates mRNA and the growing
polypeptide chain.
Slide 41
9.5 Translation 5 Translation involves initiation, elongation,
and termination, the same three stages as transcription. Initiation
and elongation require energy supplied by GTP (guanosine
triphosphate), a molecule closely related to ATP. 9.5 Translation
(cont.) Protein Synthesis
Slide 42
9.5 Translation 6 During initiation of translation, the
ribosome attaches at a specific site on the mRNA. 9.5 Translation
(cont.) Protein Synthesis
Slide 43
9.5 Translation 7 During elongation, peptide bonds join each
amino acid with the next in the sequence. A charged tRNA whose
anticodon matches the next codon on the message enters the A site
of the ribosome. 9.5 Translation (cont.) Protein Synthesis
Slide 44
9.5 Translation 8 This positions the amino acid it carries to
form a peptide bond with the amino acid attached to the tRNA at the
P site. 9.5 Translation (cont.) Protein Synthesis
Slide 45
9.5 Translation 9 9.5 Translation (cont.) Protein Synthesis
When the bond forms, the polypeptide chain transfers to the tRNA at
the A site
Slide 46
9.5 Translation 10 The entire ribosome moves down the mRNA to
position the next codon at the A site and the uncharged tRNA leaves
the E site. The A site is now open and available for the next
matching tRNA to bring in an amino acid. 9.5 Translation (cont.)
Protein Synthesis
Slide 47
9.5 Translation 11 Translation terminates when a stop codon
reaches the A site of the ribosome. A special protein known as a
release factor binds to the stop codon in the A site. At this
point, the ribosome lets go of the mRNA, the tRNA, and the release
factor. 9.5 Translation (cont.) Protein Synthesis
Slide 48
9.5 Translation 12 9.5 Translation (cont.) Protein Synthesis
Transcription produces mRNA, tRNA, and rRNA. All three participate
in translation.
Slide 49
9.6 Transport and Modification of Proteins 1 Many proteins must
be chemically modified and folded into an active tertiary structure
to be functional. 9.6 Transport and Modification of Proteins
Helper, or chaperone, proteins often help stabilize the polypeptide
as it is folded. After translation, the protein must be transported
to where it will function. Protein Synthesis
Slide 50
9.6 Transport and Modification of Proteins 2 Transport can
start while the protein is still being translated. The process uses
a signal that is part of the protein sequence, called the signal
sequence. 9.6 Transport and Modification of Proteins (cont.)
Protein Synthesis When translation is complete, the new protein is
released from the ribosome into the inner ER. Proteins to be
released from the cell pass from the ER to the vesicles of the
Golgi apparatus.
Slide 51
9.6 Transport and Modification of Proteins 3 Synthesis of
proteins for secretion or insertion in a membrane Click the image
to view an animated version.
Slide 52
9.7 Translation Errors 1 Errors sometimes occur during
translation although most are caught and corrected. 9.7 Translation
Errors The most common translation error results from misreading
the nucleotide sequence. A frame shift occurs when the start of
translation is shifted by one or two nucleotides in either
direction. The frame changes causing a different sequence of codons
and amino acids will result. Protein Synthesis
Slide 53
9.7 Translation Errors 2 9.7 Translation Errors (cont.) Protein
Synthesis Each time the reading frame shifts, a different
amino-acid sequence results.
Slide 54
9.7 Translation Errors 3 Some errors are due to splicing
mistakes or changes in the DNA. Insufficient amounts of a
particular amino acid also can disrupt translation. In some cases,
translational frame shifts or alternate initiation sites appear to
be normal ways in which one mRNA can specify more than one
polypeptide. 9.7 Translation Errors (cont.) Protein Synthesis
Slide 55
End of Section 3
Slide 56
9.8 Genetic Information and Viruses 1 Viruses are tiny
particles that have no cells, yet they replicate and evolve.
Viruses 9.8 Genetic Information and Viruses Discovered in 1892 by
Russian botanist Dmitri Ivanovsky, viruses depend on the
gene-expression machinery of the host cells they infect.
Slide 57
9.8 Genetic Information and Viruses 2 Most viruses consist of
little more than a small amount of genetic material and a
protective protein coat. 9.8 Genetic Information and Viruses
(cont.) Some, such as the familiar viruses that cause colds and the
T 2 bacteriophage that infects bacterial cells, contain DNA.
Viruses Other viruses, such as the influenza virus, contain
RNA.
Slide 58
9.8 Genetic Information and Viruses 3 9.8 Genetic Information
and Viruses (cont.) Viruses Bacteriophage T 2, which infects
bacterial cells, contains DNA surrounded by a protein coat. The
elongated structure attaches to bacterial cells and injects DNA.
HIV (human immunodeficiency virus), which infects human cells, is
surrounded by a protein and lipid membrane envelope. The genetic
material is RNA. HIV also carries two molecules of the enzyme
reverse transcriptase, ready to copy the RNA after entry into a
host cell.
Slide 59
9.8 Genetic Information and Viruses 4 The method of replication
varies among types of viruses, but the general principle of copying
stored genetic information is the same as for cells. Viral
replication falls into two patterns: 9.8 Genetic Information and
Viruses (cont.) Viruses In lytic infections, the host cells enzymes
replicate the viral DNA. In lysogenic infections, the viral DNA (or
a DNA copy of the viral RNA) inserts into the cellular DNA which is
then copied when the cell replicates.
Slide 60
9.8 Genetic Information and Viruses 5 Lytic and lysogenic viral
reproduction Click the image to view an animated version.
Slide 61
9.9 Impact of Viruses 1 Viruses live at the expense of the host
organism and pose a serious threat to cellular life. 9.9 Impact of
Viruses Antibiotics are useless against viruses. Modern
technologies such as air travel have, in some cases, made the
threat of viral diseases much greater. Viruses The Ebola virus
(x26,400). This deadly virus occurs in isolated parts of East
Africa, but air travel and human migration may cause it to spread
to new regions of the world.
Slide 62
9.9 Impact of Viruses 2 Mechanical harvesting and international
shipment of agricultural products can spread viruses that infect
valuable crops and animals. Disabled viruses are exploited by
advanced technologies, such as for delivering DNA in cloning
experiments. 9.9 Impact of Viruses (cont.) Viruses
Slide 63
End of Section 4
Slide 64
Chapter Highlights 1 Summary Much of the genetic information
encodes the primary structure for proteins. Proteins carry out
numerous functions, including structural roles, cell signaling as
hormones or cell-surface receptors, regulators of gene activity,
and many catalytic functions. Genetic information is stored in DNA
or, in the case of some viruses, as RNA. As the information is
needed, it is expressed through transcription and translation.
Regulation of gene expression is essential for different cells to
carry out their particular activities. In transcription, the coding
strand of DNA is read as a template by RNA polymerases to build
matching RNA molecules. Genetic information serves as a master
program to direct cell activities.
Slide 65
Chapter Highlights 2 Summary (cont.) Proteins combine with rRNA
to form ribosomes. Amino acids are carried by their matching tRNAs
to the ribosomes. Protein synthesis occurs as the sequence of
codons in mRNA is translated into the sequence of amino acids in a
protein. Newly transcribed proteins must fold into the appropriate
three-dimensional structure in order to be functional. Often they
are chemically modified, too. Proteins must travel to the
appropriate location in order to do their job. Errors in
transcription, RNA processing, or translation can result in poor
function or absence of a particular protein. Primary RNA
transcripts are processed into tRNA, rRNA, or mRNA in the
nucleus.
Slide 66
Chapter Highlights 3 Summary (cont.) One group of RNA viruses,
the retroviruses, enter the host cell and make a DNA copy of their
RNA genes. Viruses pose a serious threat to cellular life. They are
exploited in biological research and for their potential as agents
of gene therapy and vaccination. A special exception to the usual
flow of genetic information is found in RNA viruses which use RNA
as the long-term storage of information.
Slide 67
Chapter Highlights 4 Reviewing Key Terms Match the term on the
left with the correct description. ___transcription ___translation
___codons ___introns ___exons ___RNA polymerase a.the
enzyme-catalyzed assembly of an RNA molecule b.the basic unit of
the genetic code c.a segment of RNA that is removed before mRNA
leaves the nucleus d.the assembly of a protein on ribosomes using
mRNA e.an enzyme that catalyzes the assembly of an RNA molecule f.a
segment of RNA that remains after mRNA leaves the nucleus a d b c f
e
Slide 68
Chapter Highlights 5 Reviewing Ideas 1.Describe the lytic viral
reproductive cycle. In lytic infections, the host cells enzymes
replicate the viral DNA. Viral genes are transcribed and translated
on the hosts ribosomes to make proteins for the outer capsule. New
viral particles assemble. When there are many new viruses, the cell
lyses (breaks open) and releases them to infect other cells.
Slide 69
Chapter Highlights 6 Reviewing Ideas 2.How will the
complementary segment of RNA be coded if the DNA is coded: GCT TGA
AAT GAC? Which amino acids do these codons represent? The RNA
codons would be: CGA ACU UUA CUG These codons represent the
following amino acids (in order): arginine, threonine, leucine,
leucine
Slide 70
Chapter Highlights 7 Using Concepts 3.What could happen if an
intron is left in RNA? If introns are left in RNA, the consequences
can be serious. For example, a change in one splice site of an
intron in betaglobin, a component of the oxygen-carrying blood
protein hemoglobin, results in defective hemoglobin.
Slide 71
Chapter Highlights 8 Using Concepts 4.Why are viruses
considered nonliving? Among the most important basic properties of
life is the ability to replicate and to evolve which viruses cannot
do without help. Viruses depend on the gene-expression machinery of
the host cells they infect. Most viruses consist of little more
than a bit of DNA or RNA and a protective protein coat. Some
viruses that infect animal cells have a membrane envelope, but they
do not carry out metabolism or respond to stimuli, as cells
do.
Slide 72
Chapter Highlights 9 Synthesize 5.What makes viruses,
particularly lysogenic infections, attractive for genetic research?
Viruses are designed to insert DNA or RNA into host cells.
Scientists can disarm viruses by removing the genes that cause
disease. Lysogenic infection, since it inserts the viral DNA into
the hosts DNA is useful in cloning experiments as well as in
vaccine research.
Slide 73
End of Chapter Presentation
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Slide 75
Chapter Animations Menu Chapter Animations The three stages in
transcription of RNA from a DNA template Synthesis of proteins for
secretion or insertion in a membrane Lytic and lysogenic viral
reproduction
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