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Ribonucleic Acid

Ribonucleic Acid. RNA. The structure of ribonucleic acid. Learning Objectives: Describe the structure of ribonucleic acid (RNA) Describe the structure and role of messenger RNA (mRNA) Describe the structure and role of transfer RNA (tRNA). RNA. RNA = ribonucleic acid

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Ribonucleic Acid

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  1. Ribonucleic Acid RNA

  2. The structure of ribonucleic acid • Learning Objectives: • Describe the structure of ribonucleic acid (RNA) • Describe the structure and role of messenger RNA (mRNA) • Describe the structure and role of transfer RNA (tRNA)

  3. RNA • RNA = ribonucleic acid • RNA is a single -stranded polymer • Each RNA nucleotide consists of: • A pentose sugar (ribose) • A phosphate group • A base – adenine, cytosine, guanine, uracil (instead of thymine) • RNA used in protein synthesis is messenger RNA (mRNA) or transfer RNA (tRNA).

  4. RNA contains the pentose sugar ribose. DNA contains the pentose sugar deoxyribose. DNA RNA

  5. The Genetic Code(recap of unit 2) • 3 nucleotide bases on mRNA (a codon) codes for each amino acid in a protein (DNA = triplet code). • A few amino acids have a single codon. • The code is degenerate – most amino acids have more than one codon. • 3 codons code for no amino acids – they are stop codons and mark the end of the polypeptide chain. • Non-overlapping – each nucleotide is read only once. • Universal – same codon codes for the same amino acid in all organisms (few minor exceptions).

  6. mRNA (m = messenger)

  7. tRNA (t = transfer) Amino acid joins here Anticodon

  8. Complete the worksheet…

  9. Messenger RNA (mRNA) • Used to transfer the DNA code from the nucleus to the cytoplasm, 1 gene at a time. • Complementary to the DNA code. • Small enough to leave the nuclear pores. • Once in the cytoplasm, mRNA associates with the ribosomes. • Easily broken down and only exists whilst it is needed to manufacture a protein.

  10. Transfer RNA (tRNA) • Small molecule (~80 nucleotides). • Single stranded and folded into a clover leaf shape with one end of the chain slightly longer. • This longer section is attached to an amino acid. • Each tRNA carries a different amino acid. • 3 bases at the opposite end of the tRNA are called an anticodon. • Each amino acid has a different anticodon. • The anticodon pairs with the complementary codon on the mRNA.

  11. Go to boardworks ppt…

  12. Polypeptide synthesis – transcription and splicing • Learning Objectives: • How is pre-mRNA produced from DNA in the process called transcription? • How is pre-mRNA modified to form mRNA?

  13. Transcription • Helicase (enzyme) acts on a region of DNA to break the hydrogen bonds between the bases. • RNA polymerase moves along one of the two DNA strands – template strand • RNA polymerase matches up complementary RNA nucleotides. • C matches G and G matches C U matches A and A matches T • As the RNA nucleotides join together the pre-mRNA is formed. • The DNA behind the RNA polymerase rejoins into a double helix. • When the RNA polymerase reaches a “stop” codon, the chain is terminated and the pre-mRNA detaches.

  14. Splicing of mRNA to form mRNA • Once the introns (non-functional DNA) have been removed, the remaining exon sections join together.

  15. RNA Splicing Spliceosome snRNPs

  16. Transcription Animation http://www.johnkyrk.com/DNAtranscription.html http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/mRNA_synthesis.swf::mRNA_synthesis.swf mRNA splicing http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/spliceosomes.swf::spliceosomes.swf

  17. Polypeptide synthesis – translation • Learning Objectives: • How is a polypeptide synthesised during the process of translation? • What are the roles of mRNA and tRNA in translation?

  18. Amino acids tRNA mRNA Translation (Protein Synthesis)

  19. Synthesising the polypeptide (translation) • mRNA attaches to the ribosome at the “start” codon – AUG. • tRNA with a complementary anticodon attaches to the mRNA – UAC. • This tRNA is attached to an amino acid – methionine • The ribosome moves along the mRNA bringing in 2 tRNA molecules at any one time. • An enzyme and ATP are used to join the amino acids with a peptide bond. • The first tRNA is released and can collect another amino acid. • The process is repeated until a “stop” codon is reached. • Many ribosomes can travel along the mRNA at the same time – polysome.

  20. Translation Animation http://www.johnkyrk.com/DNAtranslation.html http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/protein_synthesis.swf::protein_synthesis.swf

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