BIOL230W Weeks 3, 4, & 5 Material Fall 2013
Week 3 Material: Genome Organization
• Epigenetics studies changes in gene expression that occur without changes in the
nucleotide sequence of DNA.
• A gene is a region of DNA or RNA that codes for a specific protein or functional RNA
chain. Alleles are different forms of a gene.
• The genetic code defines how sequences of nucleotides specify for certain amino acids.
• A group of 3 nucleotides that encodes an amino acid is referred to a codon.
• DNA includes promoter and enhancer regions, while the mRNA contains a 5' cap, a
coding sequence, and a poly(A) tail at the 3’ end.
o Promoter regions signal where the transcription of a gene starts. They are usually
located upstream (toward the 5' end of a DNA strand) before the genes they
o Both promoters and enhancers are regulatory regions of DNA where transcription
factors bind. Promoters are usually adjacent to the genes they transcribe while
enhancers can act from long distances.
• An operon is a group of genes that code for proteins with similar functions and that are
transcribed together in a unit. Operons are usually found in prokaryotes.
• Gene expression is how information encoded by genes is used to produce biologically
functional gene products.
• The possible products of gene expression are RNA or protein.
• Post-Transcriptional Modification involves three main mechanisms.
1. The 5’ end of the pre-mRNA is modified with the addition of 7-methylguanosine
(m G). This 5’ capping protects the 5’ end of the primary RNA transcript from being
degraded by ribonucleases.
2. At the 3’ end, around 250 adenine residues are added to form a poly(A) tail. This
occurs if the polyadenylation signal 5'- AAUAAA-3', CA cleavage sequence, and
GU-rich sequences are found.
3. Non-coding regions of RNA known as introns are removed by splicesomes while the
remaining exons (coding regions) are joined together.
Week 4 Material: Transcription and Translation
Transcription – Key Concepts
• A splicesome is a small nuclear ribonucleoprotein (snRNP) complex that modifies pre-
mRNA by removing introns.
• The nucleotide sequences GU and AG within an intron are especially important in post-
transcriptional processing because they mark the beginning and end of the intron regions
respectively. The GU sequence is located at the 5’ end of the intron while the AG
sequence is located at the 3’ end.
• A point mutation (i.e., a change in a single nucleotide) in pre-mRNA can lead to a major
change in the transcript and final protein product by causing splicing to occur where it BIOL230W Weeks 3, 4, & 5 Material Fall 2013
normally isn’t supposed to. This change can cause a mature mRNA transcript to be
produced that is missing part of an exon, thereby affecting the final protein product.
Protein Translation – Key Concepts
• One end of a tRNA contains the anticodon while the other contains an amino acid.
• The function of aminoacyl-tRNA synthetase is to catalyze the reaction that covalently
bonds the amino acid to the 3’ end of the tRNA, forming an aminoacyl-tRNA molecule.
• The three major stages of translation are: initiation, elongation, and termination
• The initiation factors recognize the 5’ cap of the mRNA to