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Template strand
- Transcription is done by RNA polymerase enzyme.
- -Copies only one strand of the DNA double helix to make RNA.
- -This strand is now a template
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Gene Structure
- -Genes have three parts.
- -Promoter
- -Transcribed region
- -Terminator
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Promoter
- -Controls the transcription
- -The enzyme (RNA polymerase) that makes RNA binds to the promoter with the help of other proteins known as transcription factors.
- -transcription complex formed.
- -Starts copying gene
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What two regions are important in the prokaryotes?
- -Around -10 region
- -Around the -35 region
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Numbering of Nucleotides
- Nucleotides downstream get + numbers and upstream get - numbers.
- -Promoters get - numbers.
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Sigma Factor
- Binds to the promoter, and opens the double helix
- -RNA polymerase copies the template strand of DNA
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Terminator
-RNA polymerase reaches terminator, the transcription ends.
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TATA Box
- -Its around the -30 region
- -transcription factor protein called TATA binding protein binds to the box.
- -Helps RNA polymerase to bind to the promoter.
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mRNA in Eukaryotes
- -Included in the nucleus
- -vefore mRNA comes out of the nucleus, they remove introns and rejoins exons by splicing .
- -makes mRNA shorter than the gene it was copied from.
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Cap
- -cap is added to the 5' end of the mRNA.
- -protects it from damage
- -directs ribosomes towards the 5' end
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poly (A) tail
- -added to the 3' end
- -protects the 3' end from damage.
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Translation
- -Once mRNA comes to the cytoplasm, ribosomes start translating them.
- -3 steps of translation
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Initiation of Translation
- -small subunit of ribosome finds the mRNA, binds to a region close to the first ATG with the help of initiation factor proteins.
- -tRNA arrives to start the AUG codon
- -Binds to the AUG start codon with help of more initiation factors.
- -large subunit of ribosomes binds to this complex
- -Use energy from GTP to help these processes.
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Elongation of Translation
- -start moving down the mRNA
- -there are 3 sites for tRNA binding
- -A site, P site, and E site
- -
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A-site
binds the incoming tRNA that brings the amino acid
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P-site
The amino acid carried by it makes the peptide bond with the amino acid that is attached to the tRNA at the P site.
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E-site
- When the ribosomes movies, the tRNAs shift positions.
- -The first tRNA is now pused to the E-site, where it exits the ribosomes.
- -A site opens up, next amino acid binds .
- -process continues until ribosome reaches a stop codon.
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Termination of Translation
- -When ribosome reaches the stop codon, there is no tRNA for that.
- -protein called release factor vinds to the A-site.
- -This dissociated the mRNA from the ribosome, the two subunits separate, and the protein chain is released.
- -This terminates the translation
- -More ribosomes bind to the 5' side of the mRNA
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