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PROTEIN SYNTHESIS

Learn about DNA, genes, and protein synthesis in eukaryotic cells. Understand the roles of mRNA, rRNA, and tRNA in the process. Explore the transcription and translation pathway to protein production.

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PROTEIN SYNTHESIS

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  1. PROTEIN SYNTHESIS

  2. DNA and Genes

  3. DNA • DNA contains genes, sequences of nucleotide bases • Genes have different alleles. • These genes code for polypeptides (proteins)

  4. Genes & Proteins • Proteins are made of amino acids linked together by covalent bonds called peptide bonds • Dehydration synthesis or condensation reactions form the bonds • 20 different amino acids exist

  5. Amino Acid Structure

  6. Polypeptides • Amino acid chains are called polypeptides

  7. DNA Begins the Process • DNA is found inside the nucleus • Proteins, however, are made in the cytosol of cells by organelles called ribosomes • Ribosomes may be free in the cytosol or attached to the surface of rough ER

  8. Starting with DNA • DNA ‘s code must be copied and taken to the cytosol • In the cytosol, this code must be read so amino acids can be assembled to make polypeptides (proteins) • This process is called PROTEIN SYNTHESIS

  9. RNA

  10. Roles of RNA and DNA • DNA is the MASTER PLAN • RNA is the copy of the Master Plan

  11. RNA Differs from DNA • RNA has a sugar ribose DNA has a sugar deoxyribose

  12. Other Differences • RNA contains the base uracil (U) DNA has thymine (T) • RNA molecule is single-stranded DNA is double-stranded DNA

  13. Structure of RNA

  14. . Three Types of RNA • Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes • Ribosomal RNA (rRNA), along with protein, makes up the ribosomes • Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

  15. Messenger RNA • Long Straight chain of Nucleotides • Made in the Nucleus • Copies DNA & leaves through nuclear pores • Contains the Nitrogen Bases A, G, C, U ( no T )

  16. Messenger RNA (mRNA) • Carries the information for a specific protein • Made up of 500 to 1000 nucleotides long • Sequence of 3 bases called codon • AUG – methionine or start codon • UAA, UAG, or UGA – stop codons

  17. Ribosomal RNA (rRNA) • rRNA is a single strand 100 to 3000 nucleotides long • Globular in shape • Made inside the nucleus of a cell in the nucleolus • Associates with proteins to form ribosomes • Site of protein Synthesis

  18. Transfer RNA (tRNA) • Clover-leaf shape • Single stranded molecule with attachment site at one end for an amino acid • Opposite end has three nucleotide bases called the anticodon

  19. amino acid attachment site U A C anticodon Transfer RNA

  20. Codons and Anticodons • The 3 bases of an anticodon are complementary to the 3 bases of a codon • Example: Codon ACU Anticodon UGA UGA ACU

  21. The Genetic Code • A codon designates an amino acid • An amino acid may have more than one codon • There are 20 amino acids, but 64 possible codons • Some codons tell the ribosome to stop translating

  22. The Genetic Code • Use the code by reading from the center to the outside • Example: AUG codes for Methionine

  23. Name the Amino Acids • GGG? • UCA? • CAU? • GCA? • AAA?

  24. Transcription and Translation

  25. Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein

  26. Protein Synthesis • The production or synthesis of polypeptide chains (proteins) • Two phases:Transcription & Translation • mRNA must be processed before it leaves the nucleus of eukaryotic cells

  27. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein DNA RNAProtein Eukaryotic Cell

  28. Transcription • The process of copying the sequence of one strand of DNA, the template strand • mRNA copies the template strand • Requires the enzyme RNA Polymerase

  29. Question: • What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

  30. Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’

  31. Transcription • During transcription, RNA polymerase binds to DNA and separates the DNA strands • RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA

  32. Transcription • Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA • Called the TATA box • Specific base sequences act as signals to stop • Called the termination signal

  33. RNA Polymerase

  34. mRNA Processing • After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional • Introns, non-functional segments of DNA are snipped out of the chain

  35. mRNA Editing • Exons, segments of RNA that code for proteins, are then rejoined by the enzyme ligase • A guanine triphosphate cap is added to the 5” end of the newly copied mRNA • A poly A tail is added to the 3’ end of the RNA • The newly processed mRNA can then leave the nucleus

  36. Result of Transcription New Transcript Tail CAP

  37. mRNA Transcript • mRNA leaves the nucleus through its pores and goes to the ribosomes

  38. Translation • Translation is the process of of decoding the mRNA into a polypeptide chain • Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

  39. Transcription Translation

  40. Ribosomes • Made of a large and small subunit • Composed of rRNA (40%) and proteins (60%) • Have two sites for tRNA attachment --- P and A

  41. Step 1- Initiation • mRNA transcript start codon AUG attaches to the small ribosomal subunit • Small subunit attaches to large ribosomal subunit mRNA transcript

  42. mRNA A U G C U A C U U C G Ribosomes Large subunit P Site A Site Small subunit

  43. Step 2 - Elongation • As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome • Peptide bonds join the amino acids

  44. aa2 aa1 2-tRNA 1-tRNA G A U U A C Initiation anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA

  45. aa3 3-tRNA G A A Elongation peptide bond aa1 aa2 1-tRNA 2-tRNA anticodon U A C G A U A U G C U A C U U C G A hydrogen bonds codon mRNA

  46. aa3 3-tRNA G A A aa1 peptide bond aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon

  47. aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA

  48. aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

  49. aa5 5-tRNA U G A peptide bonds aa1 aa2 aa4 aa3 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A A C U mRNA

  50. aa5 5-tRNA U G A peptide bonds aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

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