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From DNA to Protein: How Cells
Genetic Flow Controls the Synthesis of Proteins Read the Genome
Basic Principles of Transcription and Translation
Transcription: synthesis of RNA under the direction of DNA; produces mRNA.
Translation: synthesis of a polypeptide, using info in the mRNA.
Chemical Structure of RNA
RNA uses ribose as its sugar and uracil as a base. DNA uses deoxyribose as its sugar and thymine as a base.
During transcription uracil will complementary base pair with
Transcription generates an RNA strand that is complementary to one
Coding strand: non-template strand; equivalent to the RNA product.
Template strand: guided synthesis of the RNA molecules; strand from which RNA is made.
RNA Polymerase directs transcription of RNA polymerase: enzyme that unwinds DNA and adds RNA bases individually to the chain using DNA as the template; directs transcription of DNA into RNA. Types of RNA produced in cells ribosomal RNA’s (rRNA’s):Form the core of the ribosome’s structure and catalyze protein synthesis. transfer RNA's Serve as adaptors between mRNA and amino acids during protein synthesis.
Transcription in Prokaryotes Signals are Required to Tell RNA Polymerase where to start/stop transcription (Prokaryotes) Bacterial RNA polymerase: binds subunit called sigma factor that binds to promoter of gene; initiates transcription.
Promoter: region of DNA that leads
Terminator: sequence of DNA recognized by RNA polymerase that cause it to be released from DNA template, thus stopping transcription. Transcription in Eukaryotes RNA Polymerase Binding and Initiation of
A promoter called a TATA box is crucial in
forming the initiation complex in eukaryotes.
Eukaryotic RNA Polymerase Require Assembly of
Transcription Factors
The 3 RNA polymerases in eukaryotic
**- RNA polymerase I → Transcribes most rRNA genes
- RNA polymerase II → transcribes all protein- coding genes, miRNA genes, plus genes for other noncoding RNA's ( those of the spliceosome).
- RNA polymerase III→ transcribes tRNA genes, 5S rRNA gene, genes for many other small RNA’s.**
Export of mRNA from the nucleus
Alternative splicing produces different mRNAs and proteins
Summary of Transcription
Translation
Codons: a set of three nucleotides along an mRNA molecule are read by translation machinery in the 5’ to 3’ direction.
- each one correlates to 1 of the 20 amino acids.
mRNA can be translated into three potential open
Reading frame: dividing of nucleotide sequences into consecutive, non overlapping triplets.
tRNAs match amino acids to
tRNA: reads the RNA "message" and translates it into protein; functions at the ribosome.
Anticodon: sequence of 3 nucleotides that base-pair w/ codons in
mRNA.
Two steps required in translation:
a correct joining between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase a correct match between the tRNA anticodon and an mRNA codon
wobble: Flexible pairing at the third base of a codon; allows some tRNAs to
bind to more than one codon.
Specific Enzymes Couple tRNAs to the Aminoacyl-tRNA synthetase: joins an amino acid to its appropriate tRNA. 3 binding sites for tRNA in -The P site (Peptidyl-tRNA site) holds the tRNA that carries the growing polypeptide chain -The A site (Aminoacyl-tRNA site)holds the tRNA that carries the next amino acid to be added to the chain -The E site (Exit site) is the exit site, where discharged tRNAs leave the ribosome
Building a Polypeptide
The three stages of translation:
- Initiation
- Elongation
- Termination
