There are three main classes of RNA involved in gene expression: messenger RNA (mRNA) which carries genetic information from DNA to the ribosomes, ribosomal RNA (rRNA) which makes up the ribosomes, and transfer RNA (tRNA) which transfers amino acids to the ribosomes. Gene expression requires two main steps - transcription of DNA to mRNA and translation of mRNA to produce a protein. During transcription, RNA polymerase uses DNA as a template to produce mRNA which carries the code for a protein. Translation then occurs as ribosomes use the mRNA code to link amino acids in the correct sequence to form a protein.

1. Protein SynthesisProtein Synthesis
Section 2.7Section 2.7
Thank you Mr. Taylor for the use of several slidesThank you Mr. Taylor for the use of several slides

2. Gene ExpressionGene Expression
 RNA (ribonucleic acid)RNA (ribonucleic acid)

3. Gene ExpressionGene Expression
 Three Classes of RNAThree Classes of RNA
– Messenger RNA (mRNA)Messenger RNA (mRNA)
 Takes a message from DNA to the ribosomesTakes a message from DNA to the ribosomes
 CodonCodon
 TranscriptionTranscription
– Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)
 Makes up ribosomes (along with proteins)Makes up ribosomes (along with proteins)
– Transfer RNA (tRNA)Transfer RNA (tRNA)
 Transfers amino acids to ribosomesTransfers amino acids to ribosomes
 AnticodonAnticodon
 TranslationTranslation

4. Gene ExpressionGene Expression
 Gene Expression Requires Two Steps:Gene Expression Requires Two Steps:
– TranscriptionTranscription
– TranslationTranslation

5. Overview: the roles of transcription and translation in the flow of genetic informationOverview: the roles of transcription and translation in the flow of genetic information
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6. Overview: the roles of transcription and translation in the flow of genetic informationOverview: the roles of transcription and translation in the flow of genetic information
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7. Overview: the roles of transcription and translation in the flow of genetic informationOverview: the roles of transcription and translation in the flow of genetic information
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8. Overview: the roles of transcription and translation in the flow of genetic informationOverview: the roles of transcription and translation in the flow of genetic information
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9. Overview: the roles of transcription and translation in the flow of genetic informationOverview: the roles of transcription and translation in the flow of genetic information
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11. ITIT’S ANN’Y TIME’S ANN’Y TIME

13. TranscriptionTranscription

14. Gene ExpressionGene Expression
 TranscriptionTranscription
– During transcription, a segment of the DNADuring transcription, a segment of the DNA
serves as a template for the production of anserves as a template for the production of an
RNA moleculeRNA molecule
– Formation of Messenger RNA (mRNA)Formation of Messenger RNA (mRNA)
 DNA helix is opened so complementary baseDNA helix is opened so complementary base
pairing can occur – HELICASE!pairing can occur – HELICASE!
 RNA polymeraseRNA polymerase binds to a promoterbinds to a promoter
 RNA polymerase joins new RNA nucleotidesRNA polymerase joins new RNA nucleotides
in a sequence complementary to that on thein a sequence complementary to that on the
DNADNA
– Messenger RNA formed - CODONMessenger RNA formed - CODON
 Strand carries code for proteinStrand carries code for protein
 Is complementary to the section of DNAIs complementary to the section of DNA

15. Transcription of DNA to form mRNATranscription of DNA to form mRNA

16. TranslationTranslation

17. ANNY TIMEANNY TIME

19. Gene ExpressionGene Expression
 Transfer RNA - ANTICODONTransfer RNA - ANTICODON
– tRNA transports amino acids to the ribosomestRNA transports amino acids to the ribosomes
– Single stranded nucleic acid that correlates aSingle stranded nucleic acid that correlates a
specific nucleotide sequence with a specificspecific nucleotide sequence with a specific
amino acidamino acid
– Amino acid binds to one end, the opposite endAmino acid binds to one end, the opposite end
has an anticodonhas an anticodon
– the order of mRNA codons determines thethe order of mRNA codons determines the
order in which tRNA brings in amino acidsorder in which tRNA brings in amino acids

20. Transfer RNA: Amino Acid CarrierTransfer RNA: Amino Acid Carrier

21. Gene ExpressionGene Expression
 Translation (overview)Translation (overview)
– In cytoplasm/ribosomeIn cytoplasm/ribosome
– mRNA - Triplet codon: AUG initiates translationmRNA - Triplet codon: AUG initiates translation
– tRNA – attached to certain amino acids –tRNA – attached to certain amino acids –
corresponds to anticodon --- complementary tocorresponds to anticodon --- complementary to
codoncodon
– mRNA bonds to tRNA – H bondsmRNA bonds to tRNA – H bonds
– 20 different enzymes for each amino acid20 different enzymes for each amino acid
– Needs ATPNeeds ATP
– 2 amino acids make peptide bond – continues2 amino acids make peptide bond – continues
– Stop codon: UAA, UAG, UGA – nonsense codonStop codon: UAA, UAG, UGA – nonsense codon
– mRNA fragment – returns to nucleusmRNA fragment – returns to nucleus

22. TranslationTranslation

23. TranslationTranslation

24. TranslationTranslation

25. The Genetic CodeThe Genetic Code

26. Overview of Gene ExpressionOverview of Gene Expression

27. Genetic CodeGenetic Code
-- The Genetic CodeThe Genetic Code
 Triplet code- each 3-nucleotide unit of a mRNATriplet code- each 3-nucleotide unit of a mRNA
molecule is called a CODONmolecule is called a CODON
 There are 64 different mRNA codonsThere are 64 different mRNA codons
– 61 code for particular amino acids61 code for particular amino acids
 Redundant code-some amino acids have numerousRedundant code-some amino acids have numerous
code wordscode words
 Provides some protection against mutationsProvides some protection against mutations
– 1 start codon – AUG – also codes for a.a. - MET1 start codon – AUG – also codes for a.a. - MET
– 3 are stop codons signal polypeptide termination3 are stop codons signal polypeptide termination

28. Messenger RNA CodonsMessenger RNA Codons

30. Gene ExpressionGene Expression
Degenerate – two or more codonsDegenerate – two or more codons
code for the same amino acidcode for the same amino acid
Universal – all living organisms use theUniversal – all living organisms use the
same code (including viruses)same code (including viruses)
(Transcribe and Translate a Gene)(Transcribe and Translate a Gene)

37. One Gene, One PolypeptideOne Gene, One Polypeptide
 One gene will always make one enzyme.One gene will always make one enzyme.
 Became – One Gene, One Polypeptide HypothesisBecame – One Gene, One Polypeptide Hypothesis
 (Beadle and Tatum)(Beadle and Tatum)
 One Allele, One Protein (many different versions of a gene)One Allele, One Protein (many different versions of a gene)
– ExceptionsExceptions
 Some genes do not produce polypeptidesSome genes do not produce polypeptides
 Some genes code for RNA which does not produce aSome genes code for RNA which does not produce a
polypeptide. - (no start codon)polypeptide. - (no start codon)

38. Summary of GeneSummary of Gene ExpressionExpression

39. ENDEND