Alt. Splicing and transcriptional regulation + Translation

• Alternative splicing is the production of different mRNA transcripts from the same gene
• The 5 main types of alt. splicing mechanisms are 1. alternative promoters, 2. exon skipping, 3. alternative splice sites, 4. retain intron, and 5. alternative poly-A sites
• Different physiological environments can lead to promoter 1 vs 2 being used for transcription
• Alternative splicing controls whether antibodies are secreted or membrane bound, with the inclusion or exclusion of the membrane-bound terminus
• Splicing enhancers can be activated and help the spliceosome splice the mRNA
• The splicing silencer site can be blocked by a repressor, which prevents the spliceosome from splicing the RNA
• Constitutive splicing removes all introns and leaves all exons, to make a transcript not regulated by external factors
• Regulated splicing is influenced by external factors and has regulatory factors that lead to different transcripts being created
• Sex determination in fruit flies is controled by alternative splicing
• In female fruit flies, the early promoter is used and makes the early female sxl protein. The sxl protein causes alternative splicing by omission of one exon which produces funtional sxl protein.
• the sxl gene is the sex lethal gene, named so because it inhibits male development
• In male embryos, the late promoter is used and causes a transcript that produces nonfunction sxl to be made.
• Sex determination in fruit flies is dose-dependent of x chromosome, which dictates if sxl protein will be made
• DNA is transcribed into mRNA which is translated into amino acids
• The 3 steps of translation are initiation, elongation, and termination
• Initiation involves recruitment of mRNA to the ribosome
• Elongation involves synthesis of a new polypeptide
• Termination involves the release of polypeptide from the ribosome
• An mRNA has multiple ribosome-binding sites (RBS), have complementary sequences to rRNA on ribosomal subunits. RBS help in initation and helps ribosomes associate
• Translation components include: ribosomes, mRNA, tRNA, initiation factors, and elongation factors
• The ribosome is made up a small subunit with a P and A site, and a large subunit with a E, P, and A site.
• The 16s rRNA is a component of the ribosome that helps align the mRNA codons to tRNA anticodons for correct amino acid addition
• the 16s rRNA is in the small ribosomal subunit in prokaryotes
• There are 4 nTs and 64 codon combos
• tRNA is composed of an anticodon, which lets it interact with mRNA, and an amino acid attachment site, which lets it bring AAs
• tRNA is an adapter molecule, like a middleman
• tRNAs can be found in 3 possible states: 1. deacylated tRNA, 2. aminoacyl tRNA, and 3. peptidyl tRNA
• deacylated tRNA has no AA attached
• aminoacyl tRNA has one AA attached
• peptidyl tRNA has a growing AA chain attached
• Only eukaryotes have ribosome binding sites
• Eukaryotes have kozak consensus sequences that help the ribosome initiate translation in the place. it is made of Gs and As upstream of AUG and one G after AUG
• tRNA reads mRNA and brings it the correct AA to the ribosome to add it
• The ribosome E site is the exit site. It's where the spent tRNA leaves the ribosome after its amino acid is transferred to the growing polypeptide chain
• The P site is the peptidyl tRNA binding site. This is where the tRNA holds the growing polypeptide chain.
• the A site is the amino acyl tRNA binding site.The A site is where the incoming aminoacyl-tRNA pairs with the mRNA codon
• AAs are covalently linked together to make proteins, and form a peptide bond when their fusion releases h2o
• AAs are made of an amino group (NH2), a carboxyl group (COOH) and a side chain (R group)
• tRNA charging is a process where tRNA are charged with their amino acid cargos. AAs are added by aminoacyl-tRNA synthetase enzymes.
• tRNA charging is also known as aminoacylation