Advanced BiologyAdvanced Biology
Transcription and TranslationTranscription and Translation
RNA differs from DNA RNA differs from DNA
12.1
DNA DNA Protein Protein
An organisms DNA codes for specific traits by An organisms DNA codes for specific traits by dictating the synthesis of proteinsdictating the synthesis of proteins
The process by which DNA directs protein The process by which DNA directs protein synthesis, synthesis, gene expressiongene expression includes two includes two stages, called transcription and translationstages, called transcription and translation
DNA DNA RNA RNA proteinprotein
12.2
Eukaryotes vs. ProkaryotesEukaryotes vs. Prokaryotes
12.3
CodonsCodons
12.4
CodonsCodons
12.4
Codon Reading FrameCodon Reading FrameAUG is always the AUG is always the “start” codon so all “start” codon so all polypeptides begin with polypeptides begin with Methionine when they Methionine when they are synthesizedare synthesized
Having a consistent start Having a consistent start codon is necessary so codon is necessary so that the reading frame is that the reading frame is always the same.always the same.
12.5
TranscriptionTranscription
The synthesis of RNA from The synthesis of RNA from DNADNA
Promoters and TerminatorsPromoters and Terminators
Are sequences of DNAAre sequences of DNA
Promoters signal the initiation of RNA Promoters signal the initiation of RNA synthesis synthesis (TATA)(TATA)
Terminators signal the end of RNA synthesis Terminators signal the end of RNA synthesis (AAUAAA in eukaryotes)(AAUAAA in eukaryotes)
12.6
Three StepsThree Steps
12.7
Alteration of mRNA EndsAlteration of mRNA Ends
Each end of a pre-mRNA molecule is Each end of a pre-mRNA molecule is modified in a particular waymodified in a particular way– The 5The 5 end receives a modified nucleotide end receives a modified nucleotide
capcap– The 3The 3 end gets a poly-A tail end gets a poly-A tail
Figure 17.9
A modified guanine nucleotideadded to the 5 end
50 to 250 adenine nucleotidesadded to the 3 end
Protein-coding segment Polyadenylation signal
Poly-A tail3 UTRStop codonStart codon5 Cap 5 UTR
AAUAAA AAA…AAA
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
mRNA
TRANSLATIONRibosome
Polypeptide
G P P P
5 3
12.8
Split Genes and RNA SplicingSplit Genes and RNA Splicing
RNA splicingRNA splicing– Removes introns and joins exons Removes introns and joins exons
Figure 17.10
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
mRNA
TRANSLATION
Ribosome
Polypeptide
5 CapExon
Intron
1
5
30 31Exon Intron
104 105 146Exon
3Poly-A tail
Poly-A tail
Introns cut out andexons spliced together
Codingsegment
5 Cap1 146
3 UTR3 UTR
Pre-mRNA
mRNA
12.8
Proteins often have a modular Proteins often have a modular architecturearchitecture
Consisting of discrete structural and functional Consisting of discrete structural and functional regions called domainsregions called domains
In many cases In many cases different exons code for the ifferent exons code for the different domains in a proteindifferent domains in a protein
GeneDNA
Exon 1 Intron Exon 2 Intron Exon 3
Transcription
RNA processing
Translation
Domain 3
Domain 1
Domain 2
Polypeptide12.8
TranslationTranslation
The RNA directed synthesis The RNA directed synthesis of a polypeptideof a polypeptide
Translation - Translation - an overviewan overview
tRNAtRNA
12.9
RibosomesRibosomes
12.10
InitiationInitiation
12.11
12.11
ElongationElongation
TerminationTermination
12.11
PolyribosomesPolyribosomes
12.12
Post TranslationPost Translation
Protein structure is determined by amino Protein structure is determined by amino acid sequence and modificationsacid sequence and modifications
Modifications includeModifications include– The attachment of certain sugars, lipids, or The attachment of certain sugars, lipids, or
phosphate groupsphosphate groups– Joining different subunits of the protein to Joining different subunits of the protein to
create the quaternary structurecreate the quaternary structure
12.13
Point MutationsPoint MutationsThe change of a single nucleotide in the DNA’s template strand
12.14
Two TypesTwo Types
SubstitutionsSubstitutions– Replacing one or more base with othersReplacing one or more base with others
Insertions or DeletionsInsertions or Deletions– Adding or removing one or more baseAdding or removing one or more base
12.14