BISC 1112 Chapter Notes - Chapter 17: Nonsense Mutation, Endomembrane System, Start Codon
Quiz 3 (3) Chapter 17 Notes: Gene Expression BISC 1115
1
• Gene expression is the process by which DNA directs the synthesis of proteins. 2 stages
o 1) Transcription
o 2) Translation
• Alternative splicing- process for a eukaryotic gene can code for a set of closely related
polypeptides.
• RNA- The bridge between DNA and protein synthesis; contains ribose instead of
deoxyribose as its sugar and has the nitrogenous base uracil rather than thymine, and is
usually single stranded.
• Triplet code- the genetic instructions for a polypeptide chain are written in the DNA as
a series of non-overlapping, three nucleotide-words
• Template strand provides the pattern, or template, for the sequence of nucleotides in
an RNA transcript.
• An mRNA molecule is complementary to its DNA template, not identical.
• Transcription is the synthesis of RNA using information in the DNA. DNA strand acts as
a template for assembling a complementary sequence of RNA nucleotides.
o Messenger RNA (mRNA)- carries a genetic message from the DNA to the
protein-synthesizing machinery of the cell.
o Transcription occurs in the nucleus; and mRNA is transported to the cytoplasm
where translation occurs
o The transcription of a protein-coding eukaryotic gene results in pre-mRNA, and
further processing yields the finished mRNA.
o Primary transcript- The initial RNA transcript from any gene, including those
specifying RNA that is not translated into protein
• Translation is the synthesis of a polypeptide using the information in the mRNA. The
cell must translate the nucleotide sequence of an mRNA molecule into the amino acid
sequence of a polypeptide.
o The sites of translation are ribosomes- molecular complexes that facilitate the
orderly linking of amino acids into polypeptide chains.
o During translation, the sequence of codons along an mRNA molecule is decoded,
or translated, into a sequence of amino acids making up a polypeptide chain.
o codons- mRNA nucleotide triplets, and they are customarily written in the 5’
’ direction.
▪ AUG is a common start codon (methionine)
find more resources at oneclass.com
find more resources at oneclass.com
Quiz 3 (3) Chapter 17 Notes: Gene Expression BISC 1115
2
Transcription
• An enzyme called RNA polymerase pries the two strands of DNA apart and joins
together RNA nucleotides complementary to the DNA template strand, thus elongating
the RNA polynucleotide.
o Can only assemble a polynucleotide in its 5’ 3’ direction.
o Don’t need a primer like DNA polymerase.
• Promoter- The DNA sequence where RNA polymerase attaches and initiates
transcription (TATA box is crucial)
• In bacteria, the sequence that signals the end of transcription is called the terminator.
• The stretch of DNA downstream from the promoter that is transcribed into an RNA
molecule is called a transcription unit.
o Promoter sequence is upstream from the terminator.
• The 3 stages of transcription
o 1) Initiation
o 2) Elongation
o 3) Termination
• In eukaryotes, a collection of proteins called transcription factors mediate the binding
of RNA polymerase and the initiation of transcription.
o Only after transcription factors are attached to the promoter does RNA
polymerase II bind to it to form a transcription initiation complex.
• As RNA polymerase II moves along the DNA, it untwists the double helix for pairing
with RNA nucleotides.
• The mechanism of termination differs between bacteria and eukaryotes.
o In bacteria, transcription proceeds through a terminator sequence in the DNA.
The terminator functions as the termination signal, causing the polymerase to
detach from the DNA and release the transcript, which requires no further
modification before translation.
o In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the
polyadenylation signal sequence- which specifies a polyadenylation signal in
the pre-mRNA.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Bisc 1115: gene expression is the process by which dna directs the synthesis of proteins. Bisc 1115: an enzyme called rna polymerase pries the two strands of dna apart and joins. Transcription together rna nucleotides complementary to the dna template strand, thus elongating the rna polynucleotide: promoter- the dna sequence where rna polymerase attaches and initiates transcription (tata box is crucial) In bacteria, transcription proceeds through a terminator sequence in the dna. The terminator functions as the termination signal, causing the polymerase to detach from the dna and release the transcript, which requires no further modification before translation. In eukaryotes, rna polymerase ii transcribes a sequence on the dna called the polyadenylation signal sequence- which specifies a polyadenylation signal in the pre-mrna. Bisc 1115: each end of a pre-mrna molecule is modified in a particular way. Introns- noncoding segments; these are cut out of the molecule.
