LQB182 Exam:( Only this content will be on the multiple choice)2022/2023

Storage of DNA info -in the sequence of bases -5' to 3' -chromosomes= 51 million to 245 million base pairs -information in DNA used for replication of chromosomes, production of proteins and regulation -average gene = 1400 bp The central dogma replication DNA → RNA → protein (transcription and translation replication only occurs when the cell needs to divide, not when it needs to encode a message Nucleus: replication, transcription Cytosol: translation intron= non-coding sequence stop codon does not create an amino acid, isn't involved in the translation polyA signal = a long chain of adenine nucleotides added to a mRNA molecule to make a 5' to 3' end mRNA, the 3' to 5' DNA template strand must be copied intron sequences removed during splicing so finished transcription product contains only exons. it is then translated, goes through post-translational modification and results in a finished protein 00:01 01:24 Gene transcription Step 1: making a message eukaryote promoters: upstream of gene, contains TATA box approximately 25 nucleotides upstream of transcriptional start that will be recognised by transcription factors and will attach to it and will bring in the RNA polymerase. (enzyme that makes polymer of RNA) gene transcription: one one strand is copied into a complementary RNA transcript called the template strand. No T in RNA this transcript travels to the cytoplasm where its information into amino acid Step 2: removing introns and protecting ends Spliceosome Ribonucleoprotein: protein and RNA, sn= small nuclear the spliceosome recognises the intron boundary, forms a loops called a lariat and the introns excised and exons joined together. GT and AG are usually between the exon and intron which is how the spliceosome recognizes it. Protecting the mRNA ends 5' methyl cap added to 5' end PolyA tail protects 3' prime end: transcription continues past final end of RNA, polyA signal sequence (AAuAA), identifies cleavage site PolyA polymerase adds PolyA tail to 3' prime end From gene to mRNA to protein Ribosomes are 60% rRNA and 40% protein. large unit (60s) and small unit (40s) codons are made of 3 bases, 64 codons in the genetic code (64 different options), 3 stop codons tRNA: transcribed from tandem gene arrays,70-90 nucleotides in length tRNA structure: at the 3' prime end is the amino acid attachment sites (same in all tRNA), adaptor molecules (bind to codons in mRNA, donate 1 of 20 amino acids to protein synthesis at the ribosome during translation) aminoacyl-tRNA synthetases -link specific tRNA with correct amino acid -enzymes that catalyse a two step reaction requiring energy (from ATP) -20 of them -one for each amino acid making tRNA step1- amino acid and ATP bind in AMinoacyl-tRNA synthetase (2 pyrophosphate is lost, energy is transferred) step2- tRNA is recruited into another active site (AMP is displaced, energy used to attach tRNA to amino acid)