Chapter 14: Genetic Transcription and Translation

1. Chapter 14: Genetic Transcription and Translation

2. 14.1 The Structure of Proteins • Recall: Proteins • Biological molecule • Building blocks amino acids • String of amino acids polypeptide chain • Folding of a polypeptide chain functional protein

3. Synthesizing Many Proteins from 20 Amino Acids • Analogy • 20 Amino Acids 26 Letters in the Alphabet • The order and number of amino acid determines a protein the order and number of the letters determines a word • Fig. 14.1 • Insulin

4. 14.2 Protein Synthesis Overview • Transcription the process by which the genetic information encoded in DNA is copied into mRNA • DNA Unwinds • Nucleotides form base pairs Creating a mRNA • mRNA leaves the nucleus and enters the cytoplasm to find a ribosome • Translation information encoded in mRNA is used to assemble a protein at a ribosome • mRNA attaches to the ribosome • Corresponding Amino acids are paired with nucleotide sequences • When the entire chain is translated a protein is produced

5. 14.3 A Closer Look at Transcription Recall: Difference between RNA and DNA • RNA • Single strand • Nucleotide Uracil • Sugar ribose • DNA • Double stranded • Nucleotide  Thymine • Sugar deoxyribose *Both Uracil and Thymine pair up with Adenine

6. Transcription • RNA polymerase unwinds a region of the DNA double helix • RNA polymerase enzyme it unwinds the DNA double helix and adds nucleotides to the DNA strand • RNA polymerase begins assembling RNA nucleotides on the DNA template • Completed portions of the RNA transcript separates from the gene, meanwhile RNA polymerase continues transcribing • The RNA transcript is released and the DNA is rewound • Later the RNA molecule is modified to become mRNA • mRNA a type of RNA that encodes, and carries to ribosomes, information for the synthesis of proteins

7. Messenger RNA Processing • RNA molecule (rough draft) mRNA (final draft) • In Eukaryotes non-coding regions are interspersed with coding regions • Exons “expressed” region of the gene that is expressed or read for protein synthesis • Introns are regions that are not expressed

8. A Triplet Code Triplet Code • Codon every three nucleotides of mRNA  codes for one Amino acid • 3 nucleotides 1 Amino Acid • Genetic code the inventory of linkages between nucleotide triplets and the amino acids they code for

11. A Closer Look at Translation • tRNA transfer RNA a form of RNA that, in protein synthesis , bonds with amino acids, transfers them to ribosomes, and then bonds with a mRNA • Anticodon the part of tRNA that bonds with the codon of mRNA • rRNA ribosomal RNA  a type of RNA that, along with proteins, forms ribosomes.

13. Translation Overview • tRNA and amino acids occur in the cytoplasm • tRNA links to an Amino Acid and transfers it to a ribosome • tRNA carries the anticodon that will link up to the mRNA codon • A polypeptide chain is produced

14. Translation • First Step • mRNA binds to the small ribosomal subunit • The first tRNA arrives • mRNA  first codon AUG= Start codon • Codon AUG= Anticodon UAC • Second Step • The large ribosomal subunit joins to the ribosome • The second tRNA arrives at the A site

16. Translation cont. • Third step • A bond is formed between leu and met= forming the polypeptide chain • The mRNA codons are shifted to the right • The tRNA moves along with the mRNA • Fourth Step • One tRNA exits the E site while another tRNA enters the A site • This process of elongation continues • Several codons at the end of the mRNA do not code for any amino acid but are termination codons where the ribosome dissembles and the polypeptide chain is released • http://www.youtube.com/watch?v=NJxobgkPEAo\