copyright © 2005 pearson prentice hall, inc. how are genes & proteins related? genetic info:...
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Copyright © 2005 Pearson Prentice Hall, Inc.
How Are Genes & Proteins Related?
• GENETIC INFO: DNA’s Nucleotide Sequence
• EXPRESSED AS: Protein’s Amino Acid Sequence
• AN EXAMPLE: 2 DNA Base Sequences– GTG CAC CTG ACT CCT GAG GAG normal Hb– GTG CAC CTG ACT CCT GTG GAG sickle Hb
Cell Movies 102/SikldCellsInCapQTmovie
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translation
transcription
modification
degradation
mRNA tRNA
tRNA
rRNA+ proteins
ribosomes
amino acids
THECENTRALDOGMA:
DNA
RNA
PROTEIN
DNA
messenger RNA
protein
Transcription
(cytoplasm)(nucleus)
gene
Translation
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translation
transcription
modification
degradation
mRNA tRNA
tRNA
rRNA+ proteins
ribosomes
amino acids
THECENTRALDOGMA:
DNA
RNA
PROTEIN
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How Are Genes & Proteins Related?
• Genetic Information Is– Transcribed into RNA– Then Translated into Protein
• Genetic info: from DNA to RNA to protein(F10.3 p. 166)
• Processes Involved in the Use and Inheritance of Genetic Information
(T10.2 p. 167)
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How Are Genes & Proteins Related?
• DNA’s Nucleotide Sequence Expressed as Protein’s Amino Acid Sequence
• Most Genes Contain the Information for the Synthesis of a Single Protein
• DNA Provides Instructions for Protein Synthesis via RNA Intermediaries– DNA & RNA Comparison (T10.1 p. 165) – Cells make 3 major types of RNA (F10.2 p. 166)
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Transcription• Transcription: (F10.4 p. 168)
– RNA synthesis from DNA instructions– 3 Steps
• Initiation: – RNA Polymerase Binds to the Promoter of a Gene
• Elongation:– Proceeds Until RNA Polymerase Reaches a
Termination Signal
• Termination:– RNA Polymerase “Falls Off” the DNA
• Transcription in Action (F10.5 p. 169)
RNA
RNApolymerase
Initiation
Elongation
Termination
Conclusion of transcription
gene 1 gene 2 gene 3
DNA
At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase detaches from the DNA and releases the RNA molecule.
RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA molecule. The nucleotides in the RNA are complementary to the template strand of the DNA.
RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near the promoter.
After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcriptiononce again.
DNA
RNA DNA template strand
gene
DNA
RNAmolecules
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Translation• The Process of Protein Synthesis
– mRNA Base Sequence into Protein Amino Acid Sequence (F10.6 p. 171)
• mRNA:– Carries Information for Protein Synthesis from the Nucleus to the
Cytoplasm
• Ribosomes :– “Dumb” Workbench Where Amino Acids Are Hooked Together– 2 Subunits, Each Composed of rRNA & Protein
• tRNA: – Decodes mRNA Base Sequence into Protein Amino Acid Sequence– Complementary Base Pairing of tRNA Anticodon to mRNA Codon– The Genetic Code (Codons of mRNA) (T10.3 p. 167)
Ribosome: containsribosomal RNA(rRNA)
Transfer RNA (tRNA)
largesubunit
1 2
tRNA/amino acidbinding sites
catalytic site
attachedamino acid
anticodon
smallsubunit
Messenger RNA (mRNA)
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0.05 micrometers
mRNA
ribosomes
F5.7 P85
template DNA strand
complementaryDNA strand
DNA
gene
codons
anticodons
amino acids
etc.
etc.
etc.
etc.
mRNA
tRNA
protein
etc.
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Translation• Translation: ACTIVITY
– Protein Synthesis from mRNA Information– 3 steps
• Initiation: – mRNA & tRNA Bind to a Ribosome
• Elongation : – tRNA Anticodons Form Complementary Base Pairs to mRNA Anticodons– tRNA Brings In Next Amino Acid– rRNA Transfers This Amino Acid from tRNA to Growing Amino Acid
Polymer– Protein Synthesis Proceeds One Amino Acid at a Time Until ……………..
• Termination:– A Stop Codon Is Reached– mRNA & Ribosome Fall Apart– Completed Protein is Released
small ribosomal subunit
tRNAmethioninetRNA
amino acid
first tRNAbindingsite
large ribosomalsubunit
catalytic sitesecond tRNA binding site
initiator tRNA detaches
catalytic sitecatalytic site
peptide bond
ribosome moves one codon to right
catalytic site
completedpeptide
stop codon
Elongation:
Initiation:
Termination:
initiationcomplex
A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, formingan initiation complex
The large ribosomal subunit bindsto the small subunit. The methioninetRNA binds to the first tRNA site onthe large subunit.
The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty.
The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine and valine. The two amino acids are now attached to the tRNA in the second binding position.
mRNA
The second codon of mRNA (GUU) base-pairs with the anticodon (CAA) of a second tRNA carrying the amino acid valine (val). This tRNA binds to the second tRNA site on the large subunit.
The initiation complex binds to an mRNA molecule. The methionine (met) tRNA anticodon (UAC) base-pairs with the start codon (AUG) of the mRNA.
The third codon of mRNA (CAU) base-pairs with the anticodon (GUA) of a tRNA carrying the amino acid histidine (his). This tRNA enters the second tRNA binding site on the large subunit.
The catalytic site forms a new peptide bond between valine and histidine. A three-amino-acid chain is now attached to the tRNA in the second binding site. The tRNA in the first site leaves, and the ribosome moves one codon over on the mRNA.
This process repeats until a stop codon is reached; the mRNA and the completed peptide are released from the ribosome, and the subunits separate.
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THE CENTRAL DOGMAIN ACTION
• Recap:– Convert DNA Base Sequence mRNA Base
Sequence into Protein Amino Acid Sequence– 2 Processes: Transcription & Translation
• Complementary Base Pairing:– Critical to Decode Genetic Information (F10.7 p.
172) – Occurs Twice
• Transcription: DNA Base Sequence Converted to mRNA Base Sequence
• Translation: mRNA Codons Match to tRNA Anticodons
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Mutations: What They Are & How They Affect Gene
Function• Mutation = A Change in DNA Base Sequence
– Nucleotide Substitutions, Insertions, or Deletions– External Agents – Chemicals, Radiation– Uncorrected Replication Errors– “Jumping Genes” Burkitt’s Lymphoma
• May Affect Protein Structure & Function– Sickle Cell Anemia = 1 BP Mutation in Hemoglobin Gene
(T10.4 p. 173)
• GTG CAC CTG ACT CCT GAG GAG normal Hb• GTG CAC CTG ACT CCT GTG GAG sickle Hb
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Mutations: What They Are & How They Affect Gene
Function
• Mutations: Provide Variability for Evolution
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Figure 21.13 Homeotic mutations and abnormal pattern formation in Drosophila
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Figure 21.x5 Normal and double winged Drosophila
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Regulation of Gene Expression
• Regulation of Gene Expression – Critical for an Organism’s Development & Health– Eukaryotic Cells May Regulate the Transcription of Individual
Genes, Regions of Chromosomes, or Entire Chromosomes– Regulatory Proteins: Bind to Gene’s Promoter Alter the
Transcription of Individual Genes– Some Regions of Chromosomes Are Condensed & Not
Transcribed– Entire Chromosomes May Be Inactivated, Preventing
Transcription• Barr bodies (F10.9 p. 177) • X chromosome inactivation (F10.10 p. 179)
translation
transcription
modification
degradation
mRNA tRNA
tRNA
rRNA+ proteins
ribosomes
amino acids
RNA polymerase transcribes both the exons and introns, producing a long RNA molecule. Enzymes in the nucleus then cut out the RNA introns and splice together the exons to form the true mRNA,which moves out of the nucleus and is translated on the ribosomes.
Eukaryotic gene structure
DNA
promoter
exons
introns
RNA synthesis and processing in eukaryotes
A typical eukaryotic gene consists of sequences of DNA called exons, which code for the aminoacids of a protein (medium blue), and intervening sequences called introns (dark blue), which donot. The promoter determines where RNA polymerase will begin transcription.
DNA
completed mRNA
initialRNA transcript
transcription
RNA splicing
to cytoplasmfor translation
introns cut out and broken down
Eukaryotic gene structure
DNA
promoter
exons
introns
A typical eukaryotic gene consists of sequences of DNA called exons, which code for the aminoacids of a protein (medium blue), and intervening sequences called introns (dark blue), which donot. The promoter determines where RNA polymerase will begin transcription.
RNA polymerase transcribes both the exons and introns, producing a long RNA molecule.Enzymes in the nucleus then cut out the RNA introns and splice together the exons to formthe true mRNA, which moves out of the nucleus and is translated on the ribosomes.
RNA synthesis and processing in eukaryotes
DNA
completed mRNA
initialRNA transcript
transcription
RNA splicing
to cytoplasmfor translation
introns cut out and broken down
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10.5 How Are Genes Regulated?
• 10.5.2 Eukaryotic Cells May Regulate the Transcription of Individual Genes, Regions of Chromosomes, or Entire Chromosomes– 10.5.2.1 Regulatory Proteins That Bind to the Gene’s Promoter Alter
the Transcription of Individual Genes– 10.5.2.2 Some Regions of Chromosomes Are Condensed and Not
Normally Transcribed– 10.5.2.3 Entire Chromosomes May Be Inactivated, Thereby Preventing
Transcription• Figure 10.9 Barr bodies (p. 177) • Figure E10.2 Androgen insensitivity leads to female features • Figure E10.3 A 48-year-old woman with Werner syndrome• Figure 10.10 Inactivation of the X chromosome regulates gene expression (p.
179)