Toe-Tapping Transcription and Toe-Tapping Transcription and TranslationTranslation

From Gene to Protein...From Gene to Protein...

Chapter 17Chapter 17

I. Background Information I. Background Information

DNA contains information for how to DNA contains information for how to “build” an organism“build” an organism

Variations in genes make different Variations in genes make different phenotypesphenotypes

Proteins are the links between genotype Proteins are the links between genotype and phenotypeand phenotype

Proteins are one or more polypeptideProteins are one or more polypeptide One gene codes for one polypeptideOne gene codes for one polypeptide

II. The Big PictureII. The Big Picture

A.A. Flow of InformationFlow of Information

TranscriptionTranscription

Genes (DNA) Genes (DNA) mRNAmRNA

NucleusNucleus

II. The Big PictureII. The Big Picture

TranslationTranslation

mRNAmRNA Protein/(polypeptide)Protein/(polypeptide)

RibosomeRibosome

II. The Big PictureII. The Big Picture

B. Difference Between DNA and RNA B. Difference Between DNA and RNA

DNADNA RNARNA

SUGARSUGAR DeoxyriboseDeoxyribose RiboseRibose

BASESBASES A,T,C,GA,T,C,G A,U,C,GA,U,C,G

SIZESIZE Double StrandDouble Strand Single StrandSingle Strand

LOCATIONLOCATION NucleusNucleus Leaves nucleus Leaves nucleus

To cytoplasmTo cytoplasm

II. The Big PictureII. The Big Picture

C.C. Prokaryotic vs. EukaryoticProkaryotic vs. Eukaryotic Prokaryotic have no nucleus, so Prokaryotic have no nucleus, so

transcription and translation happen transcription and translation happen simultaneouslysimultaneously

Eukaryotic have processes separated, Eukaryotic have processes separated, one in nucleus and one in cytoplasmone in nucleus and one in cytoplasm

Genetic CodeGenetic Code

DNA contains only 4 basesDNA contains only 4 basesThere are 20 amino acidsThere are 20 amino acidsTo make all 20, you must have To make all 20, you must have

combinations of at least 3 nucleotide combinations of at least 3 nucleotide basesbases

Triplet Code: DNA contains 3 letter codes Triplet Code: DNA contains 3 letter codes = codon that make each amino acid= codon that make each amino acid

III. Transcription III. Transcription

A.A. The OverviewThe Overview1.1. DNA opens upDNA opens up

2.2. mRNA reads template side (only one mRNA reads template side (only one side of DNA is used)side of DNA is used)

3.3. Don’t forget that Uracil replaces TDon’t forget that Uracil replaces T

III. TranscriptionIII. Transcription

B.B. The DetailsThe Details1.1. RNA polymerase opens the two strands of DNA and RNA polymerase opens the two strands of DNA and

hooks RNA nucleotides as they base pair along the hooks RNA nucleotides as they base pair along the DNA templateDNA template

2.2. Works only in the 5’ to 3’ directionWorks only in the 5’ to 3’ direction3.3. Starts at a Starts at a promoterpromoter sequence. sequence.

Ends at a Ends at a terminatorterminator sequence sequenceTranscription UnitTranscription Unit = gene + promoter + terminator = gene + promoter + terminator

4.4. As it elongates, strand detaches from DNA template. As it elongates, strand detaches from DNA template. DNA closes behind it.DNA closes behind it.

III. TranscriptionIII. Transcription

InitiationInitiationPromoter – attachment point for RNA Promoter – attachment point for RNA

polymerase, determines which side of DNA is polymerase, determines which side of DNA is templatetemplate

In Eukaryotes – promoter includes a TATA In Eukaryotes – promoter includes a TATA box and transcription factors that help RNA box and transcription factors that help RNA polymerase to bindpolymerase to bind

III. TranscriptionIII. Transcription

ElongationElongationRNA polymerase moves along DNA and RNA polymerase moves along DNA and

unwinds itunwinds itBrings in correct RNA bases to match DNA Brings in correct RNA bases to match DNA

templatetemplateRNA peels away from DNA templateRNA peels away from DNA templateMore than one RNA strand can be made at More than one RNA strand can be made at

one timeone time

III. TranscriptionIII. Transcription

TerminationTerminationBacteria – when RNA polymerase reaches the Bacteria – when RNA polymerase reaches the

termination signal it detaches from DNA and termination signal it detaches from DNA and releases the transcript as mRNAreleases the transcript as mRNA

Eukaryotes – RNA polymerase reaches Eukaryotes – RNA polymerase reaches polyadenylation sequence AAUAAA and polyadenylation sequence AAUAAA and proteins cut off pre-mRNA from the DNA proteins cut off pre-mRNA from the DNA templatetemplate

III. TranscriptionIII. Transcription

C.C. Alteration of mRNA ends Alteration of mRNA ends (eukaryotes)(eukaryotes)

1.1. 5’ end gets a guanine cap (5’ cap) 5’ end gets a guanine cap (5’ cap) for protection and attach signal for for protection and attach signal for ribosome.ribosome.

2.2. 3’ end gets a poly(A) tail (50-250 3’ end gets a poly(A) tail (50-250 adenines). This protects, is used adenines). This protects, is used for attachment, and aides in for attachment, and aides in transport.transport.

III. TranscriptionIII. Transcription

D.D. RNA splicingRNA splicing1.1. IntronsIntrons = non-coding sections = non-coding sections

2.2. ExonsExons = coding sections = coding sections

Introns get spliced before the mRNA goes Introns get spliced before the mRNA goes to the cytoplasmto the cytoplasm

3.3. SpliceosomeSpliceosome, made up of small nuclear , made up of small nuclear ribonucleoproteins (snRNPs) and ribonucleoproteins (snRNPs) and proteins, cut out the introns.proteins, cut out the introns.

III. TranscriptionIII. Transcription

E.E. Why Introns?Why Introns? Different splicing patterns make different Different splicing patterns make different

polypeptidespolypeptides Introns may regulate gene activityIntrons may regulate gene activity Alternative splicing may make different Alternative splicing may make different

sections of a proteinsections of a protein

IV. Tricky TranslationIV. Tricky Translation

A.A. The BasicsThe Basics mRNA (all spliced and modified) goes out of mRNA (all spliced and modified) goes out of

nucleus to cytoplasm to make a protein in the nucleus to cytoplasm to make a protein in the ribosomeribosome

mRNA is read in groups of three bases called mRNA is read in groups of three bases called CODONSCODONS..

tRNAtRNA transfers amino acids from cytoplasm transfers amino acids from cytoplasm sea to the ribosomesea to the ribosome

the the ribosomeribosome connects the amino acids connects the amino acids togethertogether

B. Details on tRNA B. Details on tRNA

Each tRNA carries a specific Each tRNA carries a specific amino acidamino acid at one endat one end

At the other end is a nucleotide triplet At the other end is a nucleotide triplet called an called an anticodonanticodon. This base pairs with . This base pairs with the mRNA. the mRNA.

Made in nucleus, goes to cytoplasmMade in nucleus, goes to cytoplasmCan be used repeatedlyCan be used repeatedlyShort single strand of nucleotidesShort single strand of nucleotides

B. Details on tRNAB. Details on tRNA

Folds into 3D shape (we love H-bonds)Folds into 3D shape (we love H-bonds)WobbleWobble - some tRNA’s have anticodons - some tRNA’s have anticodons

that can recognize two or more codons, that can recognize two or more codons, these involve switches in the these involve switches in the thirdthird-position -position only.only.

Aminoacyl-tRNA synthetaseAminoacyl-tRNA synthetase - Enzyme - Enzyme that joins amino acid to tRNA. 20 that joins amino acid to tRNA. 20 varieties, 1 for each amino acid.varieties, 1 for each amino acid.

C. Rockin’ Ribosomes C. Rockin’ Ribosomes

1.1. Made up of a large and small subunit Made up of a large and small subunit which are made of proteins and which are made of proteins and ribosomal RNAribosomal RNA

2.2. Subunits are made in nucleolusSubunits are made in nucleolus

3.3. Place where mRNA codons and tRNA Place where mRNA codons and tRNA amino acids come together to make a amino acids come together to make a proteinprotein

C. Rockin’ RibosomesC. Rockin’ Ribosomes

4.4. P-site: holds the tRNA carrying the P-site: holds the tRNA carrying the growing polypeptide chaingrowing polypeptide chain

5.5. A-site: holds the tRNA carrying the A-site: holds the tRNA carrying the next amino acid to be added to the next amino acid to be added to the chainchain

6.6. E-site: Discharged tRNA’s leave the E-site: Discharged tRNA’s leave the ribosome from ribosome from here.here.

D. Building a Polypeptide D. Building a Polypeptide

1.1. InitiationInitiation small ribosomal subunit binds to molecule of small ribosomal subunit binds to molecule of

mRNA at 5’ endmRNA at 5’ end An initiator tRNA (methionine-AUG) binds to P-An initiator tRNA (methionine-AUG) binds to P-

sitesite large subunit attaches to make functional large subunit attaches to make functional

ribosome. A-site is ready to get next amino ribosome. A-site is ready to get next amino acidacid

GTP, form of energy, is expended to put the GTP, form of energy, is expended to put the ribosome togetherribosome together

D. Building a PolypeptideD. Building a Polypeptide

2.2. ElongationElongation Codon recognition occurs as mRNA in the A-site Codon recognition occurs as mRNA in the A-site

of ribosome bonds with anticodon of tRNA (with of ribosome bonds with anticodon of tRNA (with amino acid). amino acid). This requires GTP.This requires GTP.

Amino acid in P-site binds to amino acid in A-site Amino acid in P-site binds to amino acid in A-site with a peptide bond to build the with a peptide bond to build the protein.protein.

Translocation - ribosome moves tRNA in A-site Translocation - ribosome moves tRNA in A-site to P-site. tRNA in P-site is released. Building to P-site. tRNA in P-site is released. Building continues.continues.

D. Building a PolypeptideD. Building a Polypeptide

3.3. TerminationTermination Keeps going until stop codon in mRNA Keeps going until stop codon in mRNA

reaches A-site of ribosomereaches A-site of ribosome UAA, UAG, UGA are stop codonsUAA, UAG, UGA are stop codons Release factor binds to stop codon in A-Release factor binds to stop codon in A-

site. Water added instead of an amino site. Water added instead of an amino acidacid

E. Other Fun Stuff E. Other Fun Stuff

1.1. PolyribosomesPolyribosomes Many ribosomes can work one strand of Many ribosomes can work one strand of

mRNA to make bulk proteinmRNA to make bulk protein

2.2. Becoming Functional by FoldingBecoming Functional by Folding Folds into secondary, tertiary, and Folds into secondary, tertiary, and

quaternary structuresquaternary structures Post translational modifications include Post translational modifications include

attachment of sugars, attachment of sugars, lipids, phosphates, lipids, phosphates, etc.etc.

V. Mucky MutationsV. Mucky Mutations

A.A. OverviewOverview1.1. Changes in genetic make-up of a cellChanges in genetic make-up of a cell

2.2. Point mutations-Chemical change in Point mutations-Chemical change in just one base pairjust one base pair

3.3. In gametes, it can go to offspring (sickle-In gametes, it can go to offspring (sickle-cell anemia)cell anemia)

B. Substitution B. Substitution

1.1. Replacement of one nucleotide and its Replacement of one nucleotide and its partner in the complementary DNA partner in the complementary DNA strand with another pair of nucleotidesstrand with another pair of nucleotides

2.2. Missense Mutation-altered codon still Missense Mutation-altered codon still codes for an amino acid, so it makes codes for an amino acid, so it makes sense, just wrong sensesense, just wrong sense

3.3. Nonsense Mutation-changes amino acid Nonsense Mutation-changes amino acid codon to a stop signal – almost codon to a stop signal – almost always makes nonfunctional proteinalways makes nonfunctional protein

C. Insertions or DeletionsC. Insertions or Deletions

1.1. Additions or losses of nucleotide pairs in Additions or losses of nucleotide pairs in a genea gene

2.2. Throws off the triplet reading (frame shift)Throws off the triplet reading (frame shift)

3.3. Produces nonfunctional proteinsProduces nonfunctional proteins

D. Why/How Mutations?D. Why/How Mutations?

1.1. Errors during DNA replication or repair Errors during DNA replication or repair (Spontaneous mutations)(Spontaneous mutations)

2.2. Mutagens, like physical and chemical Mutagens, like physical and chemical stuff, can interact with DNA and mutate itstuff, can interact with DNA and mutate it

3.3. Mutagens include UV light, X-rays, and Mutagens include UV light, X-rays, and chemicalschemicals

What is a Gene?What is a Gene?

A gene is a region of DNA that can be A gene is a region of DNA that can be expressed to produce a final functional expressed to produce a final functional product that is either a polypeptide or an product that is either a polypeptide or an RNA moleculeRNA molecule