APK 2105C Lecture Notes - Lecture 7: Sense Strand, Nuclear Pore, Transfer Rna
23 May 2018
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Chapter 2, Part 5
The Cell: Structure & Function
• Protein synthesis
o How does the nucleus control/regulate cellular activity?
▪ DNA
o How does DNA control/regulate cellular activity
▪ DNA codes for proteins
o If DNA is only in nucleus, how can it control cellular activity outside of the nucleus?
▪ RNA
o Contributes to cellular communication with other cells
• Gene = segment of DNA within a very specific order of linked nucleotides that codes for a specific
protein
o Codes for specific order of AAs
o Triplets = nucleotide bases code for different AAs in DNA
o Codons = 3 nucleotide bases that code for different AAs in RNA
o Gene expression
▪ DNA → proteins
▪ Transcription = RNA synthesized from the sense strand of DNA
• Starts with double helix DNA
o 2 strands
▪ Sense strand
• Starts at 3’ end and goes to 5’ end
▪ Anti-sense strand = strand with complimentary base pairs
o Beginning of gene = promoter sequence
• RNA polymerase initiates unzipping of DNA by binding to promoter sequence
• DNA uncoils and separates
• Free RNA nucleotide (from cytosol) aligns with complimentary base pair and is
added to new RNA strand
• RNA synthesis begins
• RNA polymerase moves down DNA
• RNA elongates
• Transcription goes from 5’ to 3’ end
▪ Post transcriptional modification
• Remove introns (don’t code for anything)
o Exons code for AA
• Add 5’ cap to help with binding of small ribosomal subunit to RNA (signals to
subunit)
• Adds poly A tail to 3’ end of mRNA
o Signals to enzymes that they should not degrade mRNA (shows it’s not a
foreign material)
• Now have functional mRNA which is transported through nuclear pore into
cytoplasm
▪ Translation = polypeptides are synthesized from RNA codons as a template for
assembly of the correct order of AAs
• Small ribosomal subunit binds to mRNA
o Helped by 5’ cap from post transcription modification
• tRNA with methionine (first AA) is loaded into small ribosomal subunit
o Has complimentary codon for on mRNA
• Initiation factors are released
• Large ribosomal subunit binds
o 2 sites that are place holders within unit (P and A site)
• Now have active ribosome—must have small and large together
• Then another tRNA comes in with another AA and binds to the mRNA
o Base pairs on tRNA are complimentary to mRNA
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