Copyright © 2005 Pearson Prentice Hall, Inc. How Are Genes & Proteins Related? GENETIC INFO: DNA’s Nucleotide Sequence EXPRESSED AS: Protein’s Amino Acid

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


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


translation

transcription

modification

degradation

mRNA tRNA

tRNA

rRNA+ proteins

ribosomes

amino acids

THECENTRALDOGMA:

DNA

RNA

PROTEIN



• 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)



• 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)


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


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)


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.


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.


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


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


Mutations: What They Are & How They Affect Gene

Function

• Mutations: Provide Variability for Evolution


Figure 21.13 Homeotic mutations and abnormal pattern formation in Drosophila


Figure 21.x5 Normal and double winged Drosophila


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


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)

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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