17 ge lecture presentation
TRANSCRIPT
![Page 1: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/1.jpg)
BIOLOGYA Global Approach
Campbell • Reece • Urry • Cain • Wasserman • Minorsky • Jackson
© 2015 Pearson Education Ltd
TENTH EDITION
Global Edition
Lecture Presentation by Nicole Tunbridge andKathleen Fitzpatrick
17Expression of
Genes
![Page 2: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/2.jpg)
© 2015 Pearson Education Ltd
The Flow of Genetic Information
a) The information content of genes is in the specific sequences of nucleotides
b) The DNA inherited by an organism leads tospecific traits by dictating the synthesis of proteins
c) Proteins are the links between genotype and phenotype
d)Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation
![Page 3: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/3.jpg)
© 2015 Pearson Education Ltd
Figure 17.1
![Page 4: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/4.jpg)
© 2015 Pearson Education Ltd
Figure 17.1a
An albino racoon
![Page 5: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/5.jpg)
© 2015 Pearson Education Ltd
Concept 17.1: Genes specify proteins via transcription and translation
a) How was the fundamental relationship between genes and proteins discovered?
![Page 6: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/6.jpg)
© 2015 Pearson Education Ltd
Evidence from the Study of Metabolic Defects
a) In 1902, British physician Archibald Garrod first suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions
b) He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme
c) Cells synthesize and degrade molecules in a series of steps, a metabolic pathway
![Page 7: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/7.jpg)
© 2015 Pearson Education Ltd
Nutritional Mutants in Neurospora: Scientific Inquiry
a) George Beadle and Edward Tatum exposed bread mold to X-rays, creating mutants that were unable to survive on minimal media
b) Using crosses, they and their coworkers identified three classes of arginine-deficient mutants, each lacking a different enzyme necessary for synthesizing arginine
c) They developed a one gene–one enzyme hypothesis, which states that each gene dictates production of a specific enzyme
![Page 8: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/8.jpg)
© 2015 Pearson Education Ltd
Figure 17.2
Precursor
Enzyme A
Enzyme B
Enzyme C
Ornithine
Citrulline
Arginine
No growth:Mutant cellscannot growand divide
Growth:Wild-typecells growingand dividing
Control: Minimal medium
Results Table
Wild type
Minimalmedium(MM)(control)
MM +ornithine
MM +citrulline
MM +arginine(control)
Summaryof results
Can grow withor without anysupplements
Gene(codes forenzyme) Wild type
Precursor
Ornithine
Gene A
Gene B
Gene C
Enzyme A
Enzyme B
Enzyme C
Enzyme A
Enzyme B
Enzyme C
Citrulline
Arginine
Precursor
Ornithine
Citrulline
Arginine
Precursor
Ornithine
Citrulline
Arginine
Precursor
Ornithine
Citrulline
Arginine
Enzyme A
Enzyme B
Enzyme C
Enzyme A
Enzyme B
Enzyme C
Class I mutants(mutation in
gene A)
Class II mutants(mutation in
gene B)
Class III mutants(mutation in
gene C)
Can grow onornithine,citrulline,or arginine
Can grow onlyon citrulline orarginine
Require arginineto grow
Class I mutants Class II mutants Class III mutants
Classes of Neurospora crassa
Con
ditio
n
![Page 9: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/9.jpg)
© 2015 Pearson Education Ltd
Figure 17.2a
Precursor
Enzyme A
Enzyme B
Enzyme C
Ornithine
Citrulline
Arginine
![Page 10: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/10.jpg)
© 2015 Pearson Education Ltd
Figure 17.2b
No growth:Mutant cellscannot growand divide
Growth:Wild-typecells growingand dividing
Control: Minimal medium
![Page 11: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/11.jpg)
© 2015 Pearson Education Ltd
Figure 17.2c
Results Table
Wild type
Minimalmedium(MM)(control)
MM +ornithine
MM +citrulline
MM +arginine(control)
Summaryof results
Can grow withor without anysupplements
Can grow onornithine,citrulline,or arginine
Can grow onlyon citrulline orarginine
Require arginineto grow
Class I mutants Class II mutants Class III mutants
Classes of Neurospora crassaC
ondi
tion
![Page 12: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/12.jpg)
© 2015 Pearson Education Ltd
Figure 17.2d
Gene(codes forenzyme) Wild type
Precursor
Ornithine
Gene A
Gene B
Gene C
Enzyme A
Enzyme B
Enzyme C
Citrulline
Arginine
Class I mutants(mutation in
gene A)
Class II mutants(mutation in
gene B)
Class III mutants(mutation in
gene C)Precursor
Ornithine
Enzyme A
Enzyme B
Enzyme C
Citrulline
Arginine
Precursor
Ornithine
Enzyme A
Enzyme B
Enzyme C
Citrulline
Arginine
Precursor
Ornithine
Enzyme A
Enzyme B
Enzyme C
Citrulline
Arginine
![Page 13: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/13.jpg)
© 2015 Pearson Education Ltd
The Products of Gene Expression:A Developing Story
a) Some proteins aren’t enzymes, so researchers later revised the hypothesis: one gene–one protein
b) Many proteins are composed of several polypeptides, each of which has its own gene
c) Therefore, Beadle and Tatum’s hypothesis is now restated as the one gene–one polypeptide hypothesis
d) It is common to refer to gene products as proteins rather than polypeptides
![Page 14: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/14.jpg)
© 2015 Pearson Education Ltd
Basic Principles of Transcription and Translation
a) RNA is the bridge between genes and the proteins for which they code
b)Transcription is the synthesis of RNA using information in DNA
c) Transcription produces messenger RNA (mRNA)
d)Translation is the synthesis of a polypeptide, using information in the mRNA
e) Ribosomes are the sites of translation
![Page 15: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/15.jpg)
© 2015 Pearson Education Ltd
a) In prokaryotes, translation of mRNA can begin before transcription has finished
b) In a eukaryotic cell, the nuclear envelope separates transcription from translation
c) Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA
![Page 16: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/16.jpg)
© 2015 Pearson Education Ltd
Figure 17.3
Nuclear envelope
CYTOPLASM
DNA
Pre-mRNA
mRNA
RibosomeTRANSLATION
(b) Eukaryotic cell
NUCLEUS
RNA PROCESSING
TRANSCRIPTION
(a) Bacterial cell
Polypeptide
DNA
mRNARibosome
CYTOPLASM
TRANSCRIPTION
TRANSLATION
Polypeptide
![Page 17: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/17.jpg)
© 2015 Pearson Education Ltd
Figure 17.3a-1
(a) Bacterial cell
DNA
mRNACYTOPLASM
TRANSCRIPTION
![Page 18: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/18.jpg)
© 2015 Pearson Education Ltd
Figure 17.3a-2
(a) Bacterial cell
Polypeptide
DNA
mRNARibosome
CYTOPLASM
TRANSCRIPTION
TRANSLATION
![Page 19: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/19.jpg)
© 2015 Pearson Education Ltd
Figure 17.3b-1
Nuclear envelope
CYTOPLASM
DNA
Pre-mRNA
(b) Eukaryotic cell
NUCLEUS
TRANSCRIPTION
![Page 20: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/20.jpg)
© 2015 Pearson Education Ltd
Figure 17.3b-2
Nuclear envelope
CYTOPLASM
DNA
Pre-mRNA
mRNA
(b) Eukaryotic cell
NUCLEUS
RNA PROCESSING
TRANSCRIPTION
![Page 21: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/21.jpg)
© 2015 Pearson Education Ltd
Figure 17.3b-3
Nuclear envelope
CYTOPLASM
DNA
Pre-mRNA
mRNA
RibosomeTRANSLATION
(b) Eukaryotic cell
NUCLEUS
RNA PROCESSING
TRANSCRIPTION
Polypeptide
![Page 22: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/22.jpg)
© 2015 Pearson Education Ltd
a) A primary transcript is the initial RNA transcript from any gene prior to processing
b) The central dogma is the concept that cells are governed by a cellular chain of command: DNA → RNA → protein
![Page 23: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/23.jpg)
© 2015 Pearson Education Ltd
Figure 17.UN01
DNA RNA Protein
![Page 24: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/24.jpg)
© 2015 Pearson Education Ltd
The Genetic Code
a) How are the instructions for assembling amino acids into proteins encoded into DNA?
b) There are 20 amino acids, but there are only four nucleotide bases in DNA
c) How many nucleotides correspond to anamino acid?
![Page 25: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/25.jpg)
© 2015 Pearson Education Ltd
Codons: Triplets of Nucleotides
a) The flow of information from gene to protein is based on a triplet code: a series of nonoverlapping, three-nucleotide words
b) The words of a gene are transcribed into complementary nonoverlapping three-nucleotide words of mRNA
c) These words are then translated into a chain of amino acids, forming a polypeptide
![Page 26: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/26.jpg)
© 2015 Pearson Education Ltd
Figure 17.4
A C C A A A C C G A G T
ACTTTT CGGGGT
U G G U U U G G C CU A
SerGlyPheTrp
CodonTRANSLATION
TRANSCRIPTION
Protein
mRNA 5′
5′
3′
Amino acid
DNAtemplatestrand
5′
3′
3′
![Page 27: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/27.jpg)
© 2015 Pearson Education Ltd
a) During transcription, one of the two DNA strands, called the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
b) The template strand is always the same strandfor a given gene
![Page 28: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/28.jpg)
© 2015 Pearson Education Ltd
a) During translation, the mRNA base triplets, called codons, are read in the 5′ → 3′ direction
b) Each codon specifies the amino acid (one of 20)to be placed at the corresponding position alonga polypeptide
![Page 29: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/29.jpg)
© 2015 Pearson Education Ltd
Cracking the Code
a) All 64 codons were deciphered by the mid-1960s
b) Of the 64 triplets, 61 code for amino acids; 3 triplets are “stop” signals to end translation
c) The genetic code is redundant (more than one codon may specify a particular amino acid) butnot ambiguous; no codon specifies more thanone amino acid
d) Codons must be read in the correct reading frame (correct groupings) in order for the specified polypeptide to be produced
![Page 30: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/30.jpg)
© 2015 Pearson Education Ltd
Figure 17.5Second mRNA base
Third
mR
NA
base
(3′
end
of c
odon
)
Firs
t mR
NA
base
(5′
end
of c
odon
)
UUU
UUC
UUA
UUG
Phe
Leu
Leu
Ile
Val
CUU
CUC
CUA
CUG
AUU
AUC
AUA
AUG
GUU
GUC
GUA
GUG
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG GAG
GAA
GAC
GAU
AAG
AAA
AAC
AAU
CAG
CAA
CAC
CAU
Ser
Pro
Thr
AlaGlu
Asp
Lys
Asn
Gln
His
Tyr Cys
Trp
Arg
Ser
Arg
Gly
GGG
GGA
GGC
GGU
AGG
AGA
AGC
AGU
CGG
CGA
CGC
CGU
UGG
UGA
UGC
UGUUAU
UAC
UAA
UAG Stop
Stop Stop
Met orstart
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
U C A G
G
A
C
U
![Page 31: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/31.jpg)
© 2015 Pearson Education Ltd
Evolution of the Genetic Code
a) The genetic code is nearly universal, shared by the simplest bacteria to the most complex animals
b) Genes can be transcribed and translated after being transplanted from one species to another
![Page 32: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/32.jpg)
© 2015 Pearson Education Ltd
Figure 17.6
Pig expressing a jellyfishgene
(b)Tobacco plant expressinga firefly gene
(a)
![Page 33: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/33.jpg)
© 2015 Pearson Education Ltd
Figure 17.6a
Tobacco plant expressinga firefly gene
(a)
![Page 34: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/34.jpg)
© 2015 Pearson Education Ltd
Figure 17.6b
Pig expressing a jellyfishgene
(b)
![Page 35: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/35.jpg)
© 2015 Pearson Education Ltd
Concept 17.2: Transcription is the DNA-directed synthesis of RNA: A closer look
a) Transcription is the first stage of gene expression
![Page 36: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/36.jpg)
© 2015 Pearson Education Ltd
Molecular Components of Transcription
a) RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and joins together the RNA nucleotides
b) The RNA is complementary to the DNA template strand
c) RNA polymerase does not need any primer
d) RNA synthesis follows the same base-pairing rules as DNA, except that uracil substitutes for thymine
![Page 37: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/37.jpg)
© 2015 Pearson Education Ltd
Figure 17.7-1Promoter Transcription unit
RNA polymeraseStart point
1
Template strand of DNARNAtranscript
UnwoundDNA
Initiation
5′3′
5′3′
5′3′
5′3′
![Page 38: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/38.jpg)
© 2015 Pearson Education Ltd
Figure 17.7-2Promoter Transcription unit
RNA polymeraseStart point
1
Template strand of DNARNAtranscript
UnwoundDNA
RewoundDNA
RNAtranscript
Direction oftranscription(“downstream”)
Initiation
Elongation2
5′3′
5′
5′3′
5′3′
5′3′ 3′
5′3′
5′3′
![Page 39: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/39.jpg)
© 2015 Pearson Education Ltd
Figure 17.7-3Promoter Transcription unit
RNA polymeraseStart point
1
Template strand of DNARNAtranscript
UnwoundDNA
RewoundDNA
RNAtranscript
Direction oftranscription(“downstream”)
Completed RNA transcript
Initiation
Elongation
Termination
2
3
5′3′
5′
5′3′
5′3′
5′3′
5′
5′3′ 3′
5′3′
3′
5′3′
5′3′
![Page 40: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/40.jpg)
© 2015 Pearson Education Ltd
Animation: Transcription
![Page 41: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/41.jpg)
© 2015 Pearson Education Ltd
a) The DNA sequence where RNA polymerase attaches is called the promoter; in bacteria, the sequence signaling the end of transcription is called the terminator
b) The stretch of DNA that is transcribed is called a transcription unit
![Page 42: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/42.jpg)
© 2015 Pearson Education Ltd
Synthesis of an RNA Transcript
a) The three stages of transcription
a)Initiation
b)Elongation
c)Termination
![Page 43: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/43.jpg)
© 2015 Pearson Education Ltd
Figure 17.8 Promoter Nontemplate strand
15′3′
5′3′
Start point
RNA polymerase II
Templatestrand
TATA box
Transcriptionfactors
DNA3′5′
3′5′
3′5′
2
3
Transcription factors
RNA transcript
Transcription initiation complex
3′5′5′3′
A eukaryoticpromoter
Severaltranscriptionfactors bindto DNA.
Transcriptioninitiationcomplexforms.
T A T AAAATA A T T T T
![Page 44: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/44.jpg)
© 2015 Pearson Education Ltd
Elongation of the RNA Strand
a) As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time
b) Transcription progresses at a rate of 40 nucleotides per second in eukaryotes
c) A gene can be transcribed simultaneously by several RNA polymerases
d) Nucleotides are added to the 3′ end of thegrowing RNA molecule
![Page 45: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/45.jpg)
© 2015 Pearson Education Ltd
Figure 17.9
Nontemplatestrand of DNA
5′
3′3′ end
5′
3′
5′
Direction of transcription
RNApolymerase
Templatestrand of DNA
Newly madeRNA
RNA nucleotides
A
A
AA
A AA
AA
CC
G G T TT
C C CU
U
C CT
TC
A
TT
GG
U
![Page 46: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/46.jpg)
© 2015 Pearson Education Ltd
Concept 17.3: Eukaryotic cells modify RNA after transcription
a) Enzymes in the eukaryotic nucleus modify pre-mRNA (RNA processing) before the genetic messages are dispatched to the cytoplasm
b) During RNA processing, both ends of the primary transcript are usually altered
c) Also, usually certain interior sections of the molecule are cut out, and the remaining parts spliced together
![Page 47: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/47.jpg)
© 2015 Pearson Education Ltd
Alteration of mRNA Ends
a) Each end of a pre-mRNA molecule is modified in a particular way
a)The 5′ end receives a modified nucleotide 5′ cap
b)The 3′ end gets a poly-A tail
b) These modifications share several functions
a)They seem to facilitate the export of mRNA to the cytoplasm
b)They protect mRNA from hydrolytic enzymes
c)They help ribosomes attach to the 5′ end
![Page 48: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/48.jpg)
© 2015 Pearson Education Ltd
Figure 17.10
A modified guaninenucleotide added tothe 5′ end
Region that includesprotein-coding segments
5′
5′ Cap
5′ UTR Startcodon
Stopcodon
G P P P
3′ UTR
3′AAUAAA AAA AAA
Poly-A tail
Polyadenylationsignal
50–250 adeninenucleotides addedto the 3′ end
…
![Page 49: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/49.jpg)
© 2015 Pearson Education Ltd
Split Genes and RNA Splicing
a) Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions
b) These noncoding regions are called intervening sequences, or introns
c) The other regions are called exons because they are eventually expressed, usually translated into amino acid sequences
d)RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
![Page 50: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/50.jpg)
© 2015 Pearson Education Ltd
Figure 17.11
Pre-mRNA Intron Intron
Introns cut outand exonsspliced together
Poly-A tail5′ Cap
5′ Cap Poly-A tail
1–30 31–104 105–146
1–1463′ UTR5′ UTR
Codingsegment
mRNA
![Page 51: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/51.jpg)
© 2015 Pearson Education Ltd
Figure 17.12
Spliceosome Small RNAs
Exon 2
Cut-outintron
Spliceosomecomponents
mRNA
Exon 1 Exon 2
Pre-mRNA
Exon 1
Intron
5′
5′
![Page 52: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/52.jpg)
© 2015 Pearson Education Ltd
Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide: A closer look
a) Genetic information flows from mRNA to protein through the process of translation
![Page 53: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/53.jpg)
© 2015 Pearson Education Ltd
Molecular Components of Translation
a) A cell translates an mRNA message into protein with the help of transfer RNA (tRNA)
b) tRNAs transfer amino acids to the growing polypeptide in a ribosome
c) Translation is a complex process in terms of its biochemistry and mechanics
![Page 54: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/54.jpg)
© 2015 Pearson Education Ltd
Figure 17.14
PolypeptideAminoacids
tRNA withamino acidattached
Ribosome
tRNA
Anticodon
Codons
mRNA
5′
U U U UG G G G C
A C C
A A A
CC
G
Phe
Trp
3′
Gly
![Page 55: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/55.jpg)
© 2015 Pearson Education Ltd
The Structure and Function of Transfer RNA
a) Molecules of tRNA are not identical
a)Each carries a specific amino acid on one end
b)Each has an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA
![Page 56: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/56.jpg)
© 2015 Pearson Education Ltd
a) A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long
b) Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf
![Page 57: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/57.jpg)
© 2015 Pearson Education Ltd
a) Because of hydrogen bonds, tRNA actually twists and folds into a three-dimensional molecule
b) tRNA is roughly L-shaped
![Page 58: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/58.jpg)
© 2015 Pearson Education Ltd
Figure 17.15
Amino acidattachmentsite Amino acid
attachment site5′
3′ACCACGCUUA
G
GC
GAUUUA
AGAA CC
CU*
**CG
G U UGC*
**
*C CUA G
GGGA
GAGC
CC
*U* G A
GGU**
*A
A
AG
CU
GAA
Hydrogenbonds
Hydrogenbonds
Anticodon Anticodon
Symbol usedin this book
Three-dimensionalstructure
(a) Two-dimensional structure (b) (c)Anticodon
5′3′A A G
3′5′
![Page 59: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/59.jpg)
© 2015 Pearson Education Ltd
Figure 17.15a
Amino acidattachmentsite 5′
3′
Hydrogenbonds
(a) Two-dimensional structureAnticodon
ACCAC
CG
GCUUAA
GGAUUUAA GCC
CA * C CU
A G **G
GGAGAGC
***
*
*
U
GC
CCAGA
CU
GAA
A*
**
U U
U
G GC
* G AGGU
![Page 60: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/60.jpg)
© 2015 Pearson Education Ltd
Figure 17.15b
Amino acidattachment site
Hydrogenbonds
Anticodon Anticodon
Symbol usedin this book
Three-dimensionalstructure
(b) (c)
5′3′
3′5′
A A G
![Page 61: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/61.jpg)
© 2015 Pearson Education Ltd
Video: Stick and Ribbon Rendering of a tRNA
![Page 62: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/62.jpg)
© 2015 Pearson Education Ltd
Ribosomes
a) Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
b) The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)
c) Bacterial and eukaryotic ribosomes are somewhat similar but have significant differences: some antibiotic drugs specifically target bacterial ribosomes without harming eukaryotic ribosomes
![Page 63: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/63.jpg)
© 2015 Pearson Education Ltd
Figure 17.17
Exit tunnel
Largesubunit
Smallsubunit
mRNA 3′5′
E P A
tRNAmolecules
Growingpolypeptide
(a) Computer model of functioning ribosome
Growingpolypeptide Next amino
acid to beadded topolypeptidechain
tRNA3′
5′
mRNA
Amino end
Codons
E
(c) Schematic model with mRNA and tRNA(b) Schematic model showing binding sites
Smallsubunit
Largesubunit
Exit tunnel
A site (Aminoacyl-tRNA binding site)
P site (Peptidyl-tRNA binding site)
E site(Exit site)
mRNAbinding site
E P A
![Page 64: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/64.jpg)
© 2015 Pearson Education Ltd
Figure 17.17a
Exit tunnel
Largesubunit
Smallsubunit
mRNA 3′5′
E P A
tRNAmolecules
Growingpolypeptide
(a) Computer model of functioning ribosome
![Page 65: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/65.jpg)
© 2015 Pearson Education Ltd
Figure 17.17b
(b) Schematic model showing binding sites
Smallsubunit
Largesubunit
Exit tunnel
A site (Aminoacyl-tRNA binding site)
P site (Peptidyl-tRNA binding site)
E site(Exit site)
mRNAbinding site
E P A
![Page 66: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/66.jpg)
© 2015 Pearson Education Ltd
Figure 17.17c
Growingpolypeptide
Next aminoacid to beadded topolypeptidechain
tRNA
3′
5′
mRNA
Amino end
Codons
E
(c) Schematic model with mRNA and tRNA
![Page 67: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/67.jpg)
© 2015 Pearson Education Ltd
Elongation of the Polypeptide Chain
a) During elongation, amino acids are added oneby one to the C-terminus of the growing chain
b) Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation
c) Energy expenditure occurs in the first andthird steps
d) Translation proceeds along the mRNA in a5′ → 3′ direction
![Page 68: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/68.jpg)
© 2015 Pearson Education Ltd
Figure 17.19-1Amino endof polypeptide
Codonrecognition
13′
5′
E
P Asitesite
E
P A
mRNA
GTP
P iGDP +
![Page 69: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/69.jpg)
© 2015 Pearson Education Ltd
Figure 17.19-2Amino endof polypeptide
Codonrecognition
13′
5′
E
P Asitesite
E
P A
mRNA
GTP
P i
2
GDP +
E
P A
Peptide bondformation
![Page 70: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/70.jpg)
© 2015 Pearson Education Ltd
Figure 17.19-3Amino endof polypeptide
Codonrecognition
13′
5′
E
P Asitesite
E
P A
mRNA
GTP
P i
23 GTP
P i
GDP +
GDP +
Translocation
E
P A
Peptide bondformation
E
P A
Ribosome ready fornext aminoacyl tRNA
![Page 71: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/71.jpg)
© 2015 Pearson Education Ltd
Termination of Translation
a) Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
b) The A site accepts a protein called a release factor
c) The release factor causes the addition of a water molecule instead of an amino acid
d) This reaction releases the polypeptide, and the translation assembly comes apart
![Page 72: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/72.jpg)
© 2015 Pearson Education Ltd
Figure 17.20-1
1
Releasefactor
3′5′
Stop codon(UAG, UAA, or UGA)
Ribosome reaches astop codon on mRNA.
![Page 73: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/73.jpg)
© 2015 Pearson Education Ltd
Figure 17.20-2
1 2
Releasefactor
3′5′5′
3′
Stop codon(UAG, UAA, or UGA)
Ribosome reaches astop codon on mRNA.
Release factorpromotes hydrolysis.
Freepolypeptide
![Page 74: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/74.jpg)
© 2015 Pearson Education Ltd
Figure 17.20-3
31 2
Releasefactor
3′5′5′
3′
Stop codon(UAG, UAA, or UGA)
Ribosome reaches astop codon on mRNA.
Release factorpromotes hydrolysis.
Ribosomal subunitsand other componentsdissociate.
Freepolypeptide
3′
5′
2 GTP
2 GDP +2 P i
![Page 75: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/75.jpg)
© 2015 Pearson Education Ltd
Completing and Targeting the Functional Protein
a) Often translation is not sufficient to make a functional protein
b) Polypeptide chains are modified after translation or targeted to specific sites in the cell
![Page 76: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/76.jpg)
© 2015 Pearson Education Ltd
Protein Folding and Post-Translational Modifications
a) During its synthesis, a polypeptide chain begins to coil and fold spontaneously to form a protein with a specific shape—a three-dimensional molecule with secondary and tertiary structure
b) A gene determines primary structure, and primary structure in turn determines shape
c) Post-translational modifications may be required before the protein can begin doing its particular job in the cell
![Page 77: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/77.jpg)
© 2015 Pearson Education Ltd
Targeting Polypeptides to Specific Locations
a) Two populations of ribosomes are evident in cells: free ribosomes (in the cytosol) and bound ribosomes (attached to the ER)
b) Free ribosomes mostly synthesize proteins that function in the cytosol
c) Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell
d) Ribosomes are identical and can switch from free to bound
![Page 78: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/78.jpg)
© 2015 Pearson Education Ltd
a) In eukaryotes, the nuclear envelop separates the processes of transcription and translation
b) RNA undergoes processes before leavingthe nucleus
![Page 79: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/79.jpg)
© 2015 Pearson Education Ltd
Figure 17.24DNA
RNApolymerase
RNA transcript(pre-mRNA)Intron
Exon
Aminoacyl-tRNAsynthetase
AminoacidtRNA
Aminoacyl(charged)tRNA
mRNA
CYTOPLASM
NUCLEUS
RNAtranscript
3′
5′ Poly-
A
5′ Cap
5′ Cap
TRANSCRIPTION
RNAPROCESSING
Poly-A
Poly-A
AMINO ACIDACTIVATION
TRANSLATION
Ribosomalsubunits
E PA
E AA C C
U U U U U GGGA A A Anticodon
CodonRibosome
CAU
3′
A
![Page 80: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/80.jpg)
© 2015 Pearson Education Ltd
Figure 17.24a
TRANSCRIPTION DNA
Poly-A
Poly-A
5′ Cap
RNApolymerase
RNA transcript(pre-mRNA)Intron
Exon
Aminoacyl-tRNAsynthetase
AminoacidtRNA
AMINO ACIDACTIVATION
Aminoacyl(charged)tRNA
mRNA
CYTOPLASM
NUCLEUS
RNAPROCESSING
RNAtranscript
3′
5′
![Page 81: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/81.jpg)
© 2015 Pearson Education Ltd
Figure 17.24b
mRNA Growingpolypeptide
Ribosomalsubunits
Aminoacyl(charged)tRNA
Anticodon
TRANSLATION
Poly-A
5′ Cap
AE
U U U U U GGG AAAA
A C CC
UA
CodonRibosome
5′ Cap
E PA 3′
![Page 82: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/82.jpg)
© 2015 Pearson Education Ltd
BioFlix: Protein Synthesis
![Page 83: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/83.jpg)
© 2015 Pearson Education Ltd
Animation: Translation
![Page 84: 17 ge lecture presentation](https://reader036.vdocuments.co/reader036/viewer/2022062310/587d239a1a28ab1c2f8b60bf/html5/thumbnails/84.jpg)
© 2015 Pearson Education Ltd
Figure 17.UN10