AP Bio Ch 10 Power Point

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Chapter 10Chapter 10

Gene ExpressionGene Expressionand Regulationand Regulation

Chapter 10 2 11 22 The Link Between DNA and ProteinThe Link Between DNA and Protein

DNA contains the molecular blueprint of every DNA contains the molecular blueprint of every cellcell

Proteins are the “molecular workers” of the Proteins are the “molecular workers” of the cellcell

Proteins control cell shape, function, Proteins control cell shape, function, reproduction, and synthesis of reproduction, and synthesis of biomoleculesbiomolecules

The information in DNA The information in DNA genesgenes must therefore must therefore be linked to the proteins that run the cellbe linked to the proteins that run the cell

Chapter 10 3 11 22 One Gene Encodes One ProteinOne Gene Encodes One Protein

Synthesis of new molecules inside the cell Synthesis of new molecules inside the cell occurs through occurs through biochemical pathwaysbiochemical pathways

Each step in a biochemical pathway is Each step in a biochemical pathway is catalyzed by a catalyzed by a proteinprotein enzymeenzyme

George Beadle and Edward Tatum showed George Beadle and Edward Tatum showed that that one DNA geneone DNA gene encodes the information encodes the information for for one enzyme (protein)one enzyme (protein) in a biochemical in a biochemical pathwaypathway

• There are exceptions to the one gene/one There are exceptions to the one gene/one protein relationship, as discussed laterprotein relationship, as discussed later

Chapter 10 4 11 22 RNA IntermediariesRNA Intermediaries

DNA in eukaryotes is kept in the nucleusDNA in eukaryotes is kept in the nucleusProtein synthesis occurs at ribosomes in the Protein synthesis occurs at ribosomes in the

cytoplasmcytoplasmDNA information must be carried by an DNA information must be carried by an

intermediaryintermediary ( (RNARNA) from nucleus to cytoplasm) from nucleus to cytoplasm

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Chapter 10 6 11 22

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catalytic site

tRNA docking sites

Attached amino acidtRNAtransfer

Smallsubunit

rRNAribosomal

Largesubunit

CC

AA

GG

AA

UU

GG

GG

AA

GG

UU

UU

AA

UU

GG

GG

mRNAmRNAmessengermessenger

AA GG UU

Met

anticodon

Three Types of RNAThree Types of RNA

Chapter 10 7 11 22 Transcription and TranslationTranscription and Translation

DNA directs protein synthesis in a two-step DNA directs protein synthesis in a two-step processprocess

1.1. Information in a DNA gene is copied into Information in a DNA gene is copied into mRNA in the process of mRNA in the process of transcriptiontranscription

2. mRNA, together with tRNA, amino acids, and a 2. mRNA, together with tRNA, amino acids, and a ribosomeribosome, synthesize a protein in the process , synthesize a protein in the process of of translationtranslation

Chapter 10 8 11 22

Information Information Flow:Flow:

DNA DNA

RNA RNA

ProteinProtein

Chapter 10 9 11 22 The Genetic CodeThe Genetic Code

The base sequence in a DNA gene dictates The base sequence in a DNA gene dictates the sequence and type of amino acids in the sequence and type of amino acids in translationtranslation

Bases in mRNA are read by the ribosome in Bases in mRNA are read by the ribosome in triplets called triplets called codonscodons

Each codon specifies a unique amino acid in Each codon specifies a unique amino acid in the the genetic codegenetic code

Each mRNA also has a Each mRNA also has a startstart and a and a stop codonstop codon

Chapter 10 10 11 22

Chapter 10 11 11 22

Cracking the Cracking the genetic codegenetic code

a.

b.

c.

d.

Chapter 10 12 11 22 Overview of TranscriptionOverview of Transcription

Transcription of a DNA gene into RNA has Transcription of a DNA gene into RNA has three stagesthree stages

• InitiationInitiation• ElongationElongation• TerminationTermination

Chapter 10 13 11 22 InitiationInitiation

Initiation phase of transcriptionInitiation phase of transcription1.1. DNA molecule is unwound and strands are DNA molecule is unwound and strands are

separated at the beginning of the gene sequenceseparated at the beginning of the gene sequence2.2. RNA polymeraseRNA polymerase binds to binds to promoterpromoter region at region at

beginning of a gene on beginning of a gene on template strandtemplate strand

Chapter 10 14 11 22

Chapter 10 15 11 22 ElongationElongation

Elongation phase of transcriptionElongation phase of transcription1.1. RNA polymerase synthesizes a sequence of RNA polymerase synthesizes a sequence of

RNA nucleotides along DNA template strandRNA nucleotides along DNA template strand2. Bases in newly synthesized RNA strand are 2. Bases in newly synthesized RNA strand are

complementary to the DNA template strandcomplementary to the DNA template strand3.3. RNA strand peels away from DNA template RNA strand peels away from DNA template

strand as DNA strands repair and wind upstrand as DNA strands repair and wind up

Chapter 10 16 11 22

Chapter 10 17 11 22 ElongationElongation

As elongation proceeds, one end of the RNA As elongation proceeds, one end of the RNA drifts away from the DNA; RNA polymerase drifts away from the DNA; RNA polymerase keeps the other end temporarily attached to keeps the other end temporarily attached to the DNA template strand the DNA template strand

Figure 10-5Figure 10-5, p. 174, shows many RNA molecules , p. 174, shows many RNA molecules undergoing elongationundergoing elongation

Chapter 10 18 11 22

Chapter 10 19 11 22 TerminationTermination

Termination phase of transcriptionTermination phase of transcription• RNA polymerase reaches a termination RNA polymerase reaches a termination

sequence and releases completed RNA strandsequence and releases completed RNA strand

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Chapter 10 21 11 22

Chapter 10 22 11 22 mRNAmRNA

An intermediate molecule is required to An intermediate molecule is required to convey DNA gene sequence to the convey DNA gene sequence to the ribosomeribosome

Messenger RNA (mRNA)Messenger RNA (mRNA) performs this function performs this function by serving as the complementary copy of a by serving as the complementary copy of a DNA gene that is read by a ribosomeDNA gene that is read by a ribosome


• In prokaryotesIn prokaryotes• The chromosomes are not contained within The chromosomes are not contained within

a nucleusa nucleus• All of the nucleotides in a gene encode for All of the nucleotides in a gene encode for

the amino acids of a proteinthe amino acids of a protein• Genes for a related function are adjacent and Genes for a related function are adjacent and

are transcribed togetherare transcribed together• Transcription and translation occur Transcription and translation occur

simultaneously within the same simultaneously within the same compartmentcompartment

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• In eukaryotesIn eukaryotes• The DNA is in the nucleus and the The DNA is in the nucleus and the

ribosomes are in the cytoplasmribosomes are in the cytoplasm• The genes that encode the proteins for a The genes that encode the proteins for a

biochemical pathway are not clustered biochemical pathway are not clustered together on the same chromosometogether on the same chromosomeEach gene consists of multiple segments of Each gene consists of multiple segments of

DNA that encode for protein, called DNA that encode for protein, called exonsexonsExons are interrupted by other segments that Exons are interrupted by other segments that

are not translated, called are not translated, called intronsintrons

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IntronsIntrons

snipped out

snipped out

Introns

Introns

snipped out

snipped out

exonsexonsDNADNA

intronsintronspromoterpromoter

Transcription from DNA to RNATranscription from DNA to RNAInitialInitial

transcripttranscript

SplicingSplicing

completedcompletedmRNA transcriptmRNA transcript


• In eukaryotes (continued)In eukaryotes (continued)• Transcription of a gene produces a very long Transcription of a gene produces a very long

RNA strand that contains introns and exons RNA strand that contains introns and exons • Enzymes in the nucleus cut out the introns Enzymes in the nucleus cut out the introns

and splice together the exons to make true and splice together the exons to make true mRNAmRNA

• mRNA exits the nucleus through a mRNA exits the nucleus through a membrane pore and associates with a membrane pore and associates with a ribosomeribosome

Chapter 10 30 11 22 RibosomesRibosomes

Ribosomes are large complexes of proteins Ribosomes are large complexes of proteins and rRNAand rRNA

Chapter 10 31 11 22 RibosomesRibosomes

Ribosomes are composed of two subunitsRibosomes are composed of two subunits• Small subunit has binding sites for mRNA and Small subunit has binding sites for mRNA and

a tRNAa tRNA• Large subunit has binding sites for two tRNA Large subunit has binding sites for two tRNA

molecules and catalytic site for peptide bond molecules and catalytic site for peptide bond formationformation

Chapter 10 32 11 22 Transfer RNAsTransfer RNAs

Transfer RNAs hook up to and bring amino Transfer RNAs hook up to and bring amino acids to the ribosomeacids to the ribosome

There is at least one type of tRNA assigned to There is at least one type of tRNA assigned to carry each of the twenty different amino carry each of the twenty different amino acidsacids

Each tRNA has three exposed bases called an Each tRNA has three exposed bases called an anticodonanticodon

The bases of the tRNA anticodon pair with an The bases of the tRNA anticodon pair with an mRNA codon within a ribosome binding mRNA codon within a ribosome binding sitesite

Chapter 10 33 11 22 TranslationTranslation

Ribosomes, tRNA, and mRNA cooperate in Ribosomes, tRNA, and mRNA cooperate in protein synthesis, which begins with protein synthesis, which begins with initiation:initiation:

1.1. The mRNA binds to the small ribosomal The mRNA binds to the small ribosomal subunitsubunit

2. The mRNA slides through the subunit until 2. The mRNA slides through the subunit until the first AUG (start codon) is exposed in the the first AUG (start codon) is exposed in the first tRNA binding site…first tRNA binding site…

Chapter 10 34 11 22 TranslationTranslation

3. 3. The first tRNA carrying methionine (and The first tRNA carrying methionine (and anticodon UAC) binds to the mRNA start anticodon UAC) binds to the mRNA start codon completing the codon completing the initiation complexinitiation complex

4. The large ribosomal subunit joins the 4. The large ribosomal subunit joins the complexcomplex

Chapter 10 35 11 22

A tRNA with an A tRNA with an attached methionine attached methionine amino acid binds to a amino acid binds to a small ribosomal small ribosomal subunit, forming an subunit, forming an initiation complex. initiation complex.

Translation:Translation:Initiation (1)Initiation (1)

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The initiation The initiation complex binds to complex binds to end of mRNA and end of mRNA and travels down until it travels down until it encounters an AUG encounters an AUG codon in the mRNA. codon in the mRNA.

The anticodon of the The anticodon of the tRNA in the initiation tRNA in the initiation complex forms base complex forms base pairs with the AUG pairs with the AUG codon.codon.


Chapter 10 37 11 22

The large The large ribosomal subunit ribosomal subunit binds to the small binds to the small subunit, with the subunit, with the mRNA between the mRNA between the two subunits.two subunits.

The methionine The methionine tRNA is in the first tRNA is in the first tRNA site on the tRNA site on the large subunit. large subunit.


Chapter 10 38 11 22

The second tRNA enters the The second tRNA enters the second tRNA site on the second tRNA site on the large ribosomal subunit.large ribosomal subunit.

Which tRNA binds depends Which tRNA binds depends on the ability of its anticodon on the ability of its anticodon (CAA in this example) to base (CAA in this example) to base pair with the codon (GUU in pair with the codon (GUU in this example) in the mRNA.this example) in the mRNA.

tRNAs with a CAA anticodon tRNAs with a CAA anticodon carry an attached valine carry an attached valine amino acid, which was added amino acid, which was added to it by enzymes in the to it by enzymes in the cytoplasm.cytoplasm.

Translation:Translation:Elongation 1Elongation 1

Chapter 10 39 11 22

The "empty" tRNA is The "empty" tRNA is released and the ribosome released and the ribosome moves down the mRNA, moves down the mRNA, one codon to the right.one codon to the right.

The tRNA that is attached The tRNA that is attached to the two amino acids is to the two amino acids is now in the first tRNA now in the first tRNA binding site and the binding site and the second tRNA binding site second tRNA binding site is empty.is empty.


Chapter 10 40 11 22

The catalytic site on The catalytic site on the large subunit the large subunit catalyzes the catalyzes the formation of a peptide formation of a peptide bond linking the bond linking the amino acids amino acids methionine to valine.methionine to valine.

The two amino acids The two amino acids are now attached to are now attached to the tRNA in the the tRNA in the second binding second binding position.position.


Chapter 10 41 11 22

Another tRNA enters the Another tRNA enters the second tRNA binding site second tRNA binding site carrying its attached carrying its attached amino acid.amino acid.

The tRNA has an The tRNA has an anticodon that pairs with anticodon that pairs with the codon. (Here, the CAU the codon. (Here, the CAU mRNA codon pairs with a mRNA codon pairs with a GUA tRNA anticodon.)GUA tRNA anticodon.)

The tRNA molecule carries The tRNA molecule carries the amino acid histidine the amino acid histidine (his).(his).


Chapter 10 42 11 22


Binding of tRNAs, & Binding of tRNAs, & formation of peptide formation of peptide bonds continues.bonds continues.

Ribosome reaches Ribosome reaches STOP codon (UAG).STOP codon (UAG).

Protein "release Protein "release factors" signal the factors" signal the ribosome to release ribosome to release the protein.the protein.

The mRNA is also The mRNA is also released and large & released and large & small subunits small subunits separate.separate.

Chapter 10 43 11 22

The catalytic site forms The catalytic site forms a new peptide bond, in a new peptide bond, in this example, between this example, between the valine and the the valine and the histidine.histidine.

A three-amino acid A three-amino acid chain is now attached chain is now attached to the tRNA in the to the tRNA in the second tRNA binding second tRNA binding site.site.

The empty tRNA in the The empty tRNA in the first site is released first site is released and the ribosome and the ribosome moves one codon to moves one codon to the right.the right.

Translation:Translation:TerminationTermination

Chapter 10 44 11 22

GG GG GG AA GG CC GG AA UU UU UU

CC AA AA CC AA UU CC CC UU

Methionine Glycine Valine etc.

GG GG GG AA GG TT TT CC TT GG AA

templateDNA strand

(a) complementaryDNA strand

(b) mRNA

(c) tRNA

(d) protein

amino acids

anticodons

codons

gene

etc.

etc.

etc.

etc.

GG TT CC CC CC CC AA AA AA TT CC

Complementary Base PairingComplementary Base Pairing

Chapter 10 45 11 22

AminoAminoAcidsAcids

ActiveActiveProteinProtein

Overview ofOverview ofInformation FlowInformation Flow

InactiveInactiveProteinProtein

(Cytoplasm)(Cytoplasm)

DNADNA(Nucleus)(Nucleus)

rRNArRNA tRNAtRNA1 TranscriptionTranscription

+ Proteins+ Proteins

RibosomesRibosomestRNAtRNA

tRNA-AAtRNA-AA

mRNAmRNA

mRNAmRNA

2 TranslationTranslation

3 ModificationModification

ProductProductSubstrateSubstrate4 DegradationDegradation

Chapter 10 46 11 22 Effects of Mutations on ProteinsEffects of Mutations on Proteins

Recall that mutations are changes in the base Recall that mutations are changes in the base sequence of DNAsequence of DNA

Most mutations are categorized asMost mutations are categorized as• SubstitutionsSubstitutions• DeletionsDeletions• InsertionsInsertions• Inversions Inversions • Translocations Translocations


Inversions and translocationsInversions and translocations• When pieces of DNA are broken apart and When pieces of DNA are broken apart and

reattached in different orientation or locationreattached in different orientation or location• Not problematic if entire gene is moved Not problematic if entire gene is moved • If gene is split in two it will no longer code for If gene is split in two it will no longer code for

a complete, functional proteina complete, functional protein


Insertions or deletionsInsertions or deletions• Nucleotides are added or subtracted from a Nucleotides are added or subtracted from a

genegene• Reading frame of RNA codons is changedReading frame of RNA codons is changed

– THEDOGSAWTHECATTHEDOGSAWTHECAT is changed by deletion of is changed by deletion of the letter “S” to the letter “S” to THEDOGAWTHECATTHEDOGAWTHECAT

• Resultant protein has very different amino Resultant protein has very different amino acid sequence; almost always is non-acid sequence; almost always is non-functionalfunctional


Nucleotide substitutions (point mutations)Nucleotide substitutions (point mutations)• An incorrect nucleotide takes the place of a An incorrect nucleotide takes the place of a

correct onecorrect one• Protein structure and function is unchanged Protein structure and function is unchanged

because many amino acids are encoded by because many amino acids are encoded by multiple codonsmultiple codons

• Protein may have amino acid changes that Protein may have amino acid changes that are unimportant to function (are unimportant to function (neutral mutationsneutral mutations))


Effects of nucleotide substitutionsEffects of nucleotide substitutions• Protein function is changed by an altered Protein function is changed by an altered

amino acid sequence (as in gly amino acid sequence (as in gly val in val in hemoglobin in sickle cell anemia)hemoglobin in sickle cell anemia)

• Protein function is destroyed because DNA Protein function is destroyed because DNA mutation creates a premature stop codonmutation creates a premature stop codon

Chapter 10 51 11 22

Chapter 10 52 11 22 Mutations Fuel EvolutionMutations Fuel Evolution

Mutations are heritable changes in the DNAMutations are heritable changes in the DNAApprox. 1 in 10Approx. 1 in 1055-10-1066 eggs or sperm carry a eggs or sperm carry a

mutationmutationMost mutations are harmful or neutralMost mutations are harmful or neutralMutations create new gene sequences and are Mutations create new gene sequences and are

the ultimate source of genetic variationthe ultimate source of genetic variationMutant gene sequences that are beneficial Mutant gene sequences that are beneficial

may spread through a population and may spread through a population and become commonbecome common

Chapter 10 53 11 22 How Are Genes Regulated?How Are Genes Regulated?

The human genome contains ~ 30,000 genesThe human genome contains ~ 30,000 genesA given cell “expresses” (transcribes) only a A given cell “expresses” (transcribes) only a

small number of genessmall number of genesSome genes are expressed in all cellsSome genes are expressed in all cellsOther genes are expressed onlyOther genes are expressed only

• In certain types of cellsIn certain types of cells• At certain times in an organism’s lifeAt certain times in an organism’s life• Under specific environmental conditionsUnder specific environmental conditions

Chapter 10 54 11 22 Gene Regulation in ProkaryotesGene Regulation in Prokaryotes

Prokaryotic DNA is organized into units Prokaryotic DNA is organized into units called called operons, operons, which contain functionally which contain functionally related genesrelated genes


Each operon consists ofEach operon consists of• A A regulatory generegulatory gene, which controls the , which controls the

transcription of other genestranscription of other genes• A A promoterpromoter, which RNA polymerase recognizes , which RNA polymerase recognizes

as the place to start transcribingas the place to start transcribing• An An operatoroperator, which governs access of RNA , which governs access of RNA

polymerase to the promoterpolymerase to the promoter• The The structural genesstructural genes, which encode for related , which encode for related

proteinsproteins


Whole operons are regulated as units, so that Whole operons are regulated as units, so that functionally related proteins are synthesized functionally related proteins are synthesized simultaneously when the need arises simultaneously when the need arises


The intestinal bacterium The intestinal bacterium Escherichia coli Escherichia coli (E.coli) (E.coli) lives on what its host eatslives on what its host eats

Specific enzymes are needed to metabolize Specific enzymes are needed to metabolize the type of food that comes alongthe type of food that comes along

e.g. in newborn mammals, e.g. in newborn mammals, E.coliE.coli are bathed are bathed in milk, containing the milk sugar lactosein milk, containing the milk sugar lactose

The The lactose operonlactose operon contains three structural contains three structural genes, each coding for an enzyme that aids genes, each coding for an enzyme that aids in lactose metabolismin lactose metabolism


Figure 10-10Figure 10-10, p. 181, illustrates regulation of , p. 181, illustrates regulation of the lactose operon…the lactose operon…

Chapter 10 59 11 22

Chapter 10 60 11 22

Chapter 10 61 11 22

Chapter 10 62 11 22 Gene Regulation in EukaryotesGene Regulation in Eukaryotes

Eukaryotic gene regulationEukaryotic gene regulation• DNA is in a membrane-bound nucleusDNA is in a membrane-bound nucleus• Variety of cell types in multicelluar eukaryotesVariety of cell types in multicelluar eukaryotes• The genome is organized differentlyThe genome is organized differently• RNA transcripts undergo complex processing RNA transcripts undergo complex processing


Expression of genetic information by a Expression of genetic information by a eukaryotic cell is a multistep process, eukaryotic cell is a multistep process, beginning with transcription of DNA, and beginning with transcription of DNA, and ending with a protein that performs a ending with a protein that performs a particular functionparticular function


Gene expression is regulated in a number of Gene expression is regulated in a number of waysways

• The frequency of transcription of a gene can The frequency of transcription of a gene can be controlledbe controlled

• Different mRNAs may be translated at Different mRNAs may be translated at different ratesdifferent rates

• Proteins may be synthesized in an inactive Proteins may be synthesized in an inactive form and require modification for activationform and require modification for activation

• Life span of a protein can be regulatedLife span of a protein can be regulated

Chapter 10 65 11 22


In eukaryotic cells, transcriptional regulation In eukaryotic cells, transcriptional regulation occurs on at least three levelsoccurs on at least three levels

• The individual geneThe individual gene• Regions of chromosomesRegions of chromosomes• Entire chromosomesEntire chromosomes


Regulatory proteins can bind to a gene’s Regulatory proteins can bind to a gene’s promoter region and alter transcriptionpromoter region and alter transcription

• The protein hormone estrogen causes binding The protein hormone estrogen causes binding of a protein to certain gene promoters, of a protein to certain gene promoters, activating transcriptionactivating transcription


Condensed or tightly wound DNA can make Condensed or tightly wound DNA can make genes inaccessible to RNA polymerasegenes inaccessible to RNA polymerase

Whole chromosomes can be condensed and Whole chromosomes can be condensed and inactivated (e.g. Barr bodies in female inactivated (e.g. Barr bodies in female mammals)mammals)

Chapter 10 69 11 22

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Chapter 10Chapter 10

The EndThe End

Technology

AP Bio Ch 10 Power Point