Protein Synthesis Summary
Central Dogma - FLOW IS FROM DNA TO RNA TO PROTEIN
Transcription
• Purpose: To copy a segment of DNA into mRNA.
• Location: Inside the nucleus.
• Process:
– RNA polymerase: an enzyme that unwinds DNA helix and uses base pairing
rules to make mRNA from a DNA template or coding strand.
– Promoter: a specific sequence
of DNA that RNA polymerase
binds to begin making mRNA
(TATAATA box)
Transcription
• Transcribe the DNA sequence below:
http://www.youtube.com/watch?v=8nQH0GqFn6k
http://www.youtube.com/watch?v=SMtWvDbfHLo
Transcription
RNA Editing (occurs between transcription and translation)
• 2% of the DNA in the nucleus is used to make proteins.
• Gene: sequences of DNA that code for proteins.
• Before the mRNA can leave the nucleus the DNA that is
used to make proteins must be separated from the DNA
that does not make proteins.
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Introns: Segments of DNA that do
not code for proteins. These are
removed before mRNA leaves the
nucleus
Exons: the segments of
DNA that code for a protein.
These are spliced together
once introns are removed
Transcription
RNA Editing
•Poly-A tail is added to the 3’ end of the mRNA.
– Allows the mRNA to leave through pores in the
nuclear membrane.
– Protects the mRNA from enzymes as it leaves
the nucleus.
• Guanine cap is added to the 5’ end of the mRNA.
– The guanine cap allows the mRNA to be recognized by the ribosome.
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm