Transcript Chapter 17 notes

Chapter 17
From Gene to Protein
Central Dogma of Molecular
Biology
DNA
RNA
Protein
Metabolic control
• Gene to protein relationship 1st proposed by
Garrod: inherited diseases reflect inability to
make a particular enzyme
“inborn errors of metabolism”
Beadle & Tatum’s experiment
• Studying Neurospora (fungus) supported
“one gene – one enzyme” & modified to
“one gene – one polypeptide”
• Nucleic acids & proteins are informational
polymers assembled from linear sequences of
nucleotides & amino acids, respectively
Figure 17.1 Beadle and Tatum’s evidence for the one gene-one enzyme hypothesis
Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic
information
Figure 17.3 The triplet code
Transcription
(mRNA synthesis)
• Catalyzed by RNA polymerase
• (Initiation, Elongation, Termination)
• DNA portion (one gene in length) unwinds,
unzips
• Free RNA nucleotides pair up on 1 of the DNA
strands
• Promoters signal initiation of transcription until
terminator sequence is reached, then it breaks
off & DNA rejoins & rewinds
• Modified, then mRNA travels to cytoplasm
Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer
1)
Figure 17.6 The stages of transcription: initiation, elongation, and termination
Figure 17.6 The stages of transcription: initiation, elongation, and termination
Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer
4)
Figure 17.6 The stages of transcription: elongation
Figure 17.7 The initiation of transcription at a eukaryotic promoter
Translation
(Protein synthesis)
• (Initiation, Elongation, Termination)
• tRNA’s pick up specific AA’s based on
anticodon & carry AA’s to mRNA attached to a
ribosome
• ATP driven process catalyzed by many AA
activating enzymes
• P and A sites of ribosome help hold mRNA &
tRNA together; peptide bond forms, mRNA
moves down the ribosome (made of protein &
rRNA)
Figure 17.12 Translation: the basic concept
Figure 17.13a The structure of transfer RNA (tRNA)
Figure 17.13b The structure of transfer RNA (tRNA)
Figure 17.15 The anatomy of a functioning ribosome
Figure 17.17 The initiation of translation
Translation
• mRNA is freed from ribosome & AA chain
• Proteins functioning on membranes or exported
from cell are synthesized on ribosomes on
rough ER
Figure 17.18 The elongation cycle of translation
Figure 17.19 The termination of translation
Figure 17.20 Polyribosomes
Figure 17.21 The signal mechanism for targeting proteins to the ER
Figure 17.22 Coupled transcription and translation in bacteria
The Genetic Code
• Determined in early 1960’s
• codon – 3-base unit (triplet) that codes for 1 AA
• anticodon – 3-base unit on tRNA which is
complementary to codon on mRNA
• All codons don’t code for AA (43 codons)
• Most genes are interrupted by introns – long
noncoding regions
Figure 17.4 The dictionary of the genetic code
Eukaryotic RNA processing
• Removing (excising) introns & joining exons by
RNA splicing triggered by sets of nucleotides at
either end of intron
• Splicing catalyzed by small nuclear
ribonucleoproteins (snRNP’s) consisting of
small nuclear RNA (snRNA) & proteins
operating within larger groups called
spliceosomes
Figure 17.8 RNA processing; addition of the 5 cap and poly(A) tail
Figure 17.9 RNA processing: RNA splicing
Figure 17.10 The roles of snRNPs and spliceosomes in mRNA splicing
Eukaryotic RNA processing
• Eukaryotic mRNA receives a modified GTP cap
at the 5’ end and a poly-A tail (stretch of
nucleotides) at the 3’ end (protects from
degradation & enhance translation)
• 30 – 200 adenine nucleotides (poly–A)
Figure 17.11 Correspondence between exons and protein domains
Mutations
1) base pair substitutions - point mutations
2) base pair insertions/deletions - frameshift
3) conditional mutations – harmful under certain
environmental conditions (high/low temp. if
temp. sensitive)
4) spontaneous mutations – may occur during
replication or repair
Figure 17.23 The molecular basis of sickle-cell disease: a point mutation
Figure 17.24 Categories and consequences of point mutations: Base-pair
substitution
Figure 17.24 Categories and consequences of point mutations: Base-pair insertion
or deletion
Figure 17.25 A summary of transcription and translation in a eukaryotic cell