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TRANSCRIPTION AND TRANSLATION The molecular basis of protein synthesis 1 Miniature machinery • We are now going to look at the molecular basis for protein synthesis • Just like in DNA synthesis, there are specific proteins and molecules that are responsible for carrying out the process of transcription and translation 2 Transcription • Remember that the first step in protein synthesis is copying the DNA into mRNA 3 How does it know where to start? • Specific genes encoded in DNA have a sequence at the start known as a PROMOTER 4 A brief overview • http://www.johnkyrk.com/DNAtranscription.h tml 5 New mRNA • Newly synthesized mRNA can then undergo modifications • These modifications include: 6 Controlling the copies • mRNA is not as stable a molecule as DNA – it has tendency to break down really easily • mRNAases – enzymes that break mRNA down help to accelerate this process to control protein production Copyright©2010 Companyname | Free template by Investintech PDF 7 Post-transcriptional modifications • To help control mRNA survival, a few modifications are made: • 5’ cap: made up of methyl guanosine that protects against enzymes that break down mRNA 8 Removal of Introns • Modification of mRNA after transcription may be necessary to remove redundant information found in DNA • Remember that DNA often contains excess information that is not necessary - these parts are called introns • http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter16/animati on_-_exon_shuffling.html 9 Translation • Once copied, mRNA leaves the nucleus through the nuclear pores in the nuclear membrane and moves into the cytoplasm 10 Corral and tie • Essentially, the ribosome is responsible for reading the mRNA and polymerizing (sticking together) the amino acids together to form the new protein 11 tRNA • Since tRNA is essentially RNA it contains the same base pairs and are used as the basis of translation 12 13 14 Ribosome structure: an overview • And a smaller “bottom” bun known as the 30S subunit • Multiple RNA can read one mRNA copy at once, creating bulk amounts of a given protein 15 Copyright©2010 Companyname | Free template by Investintech PDF Solution 16 E, P, A • The large 50S subunit has 3 active sites lodged into it known as the E, P, and A site Copyright©2010 Companyname | Free template by Investintech PDF Solution 17 Copyright©2010 Companyname | Free template by Investintech PDF Solution 18 Copyright©2010 Companyname | Free template by Investintech PDF Solution 19 All together now • Ribosome sandwiches the mRNA • tRNA with appropriate anti-codon attaches to the exposed codon in the A-site • Ribosome polymerizes the amino acid attached to the tRNA in the P-site to the new polypeptide chain • http://en.wikipedia.org/wiki/File:Translation.gif 20 Starting and ending • Special codons located at the beginning and end of an mRNA sequence help to indicate where the ribosome should attach and where it should separate • A start codon initiates the polypeptide sequence; it usually codes for the amino acid methionine 21 Energy needed! • Notice that this process requires energy – the hydrolysis of GTP (a molecule similar to ATP) provides the ribosome energy • GTP is needed to: – Polymerize the incoming amino acid to the polypeptide chain – Translocate (move) the tRNA to the next bonding site 22 Chance meeting • Remember that with numerous tRNA floating around a small cell, there is no mechanism that brings tRNAs to the ribosome • Nice to know the production of necessary components of your body is dependent on random movement! 23 • http://www.biostudio.com/demo_freeman_pr otein_synthesis.htm • Check this out at home: • http://www.learnerstv.com/animation/animat ion.php?ani=181&cat=biology 24