PROTEIN SYNTHESIS (thuyết trình)

PROTEIN SYNTHESIS Protein Synthesis  The production (synthesis) of polypeptide chains (proteins)  Two phases: Transcription & Translation  mRNA must be processed before it leaves the nucleus of eukaryotic cells DNA → RNA → Protein DNA Transcription mRNA Ribosome Translation Protein Prokaryotic Cell DNA → RNA → Protein Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein Nucleic Acids DNA or Protein?  Walter Sutton discovered chromosomes were made of DNA and Protein  However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell DNA!  Frederick Griffith in 1928 showed the DNA was the cell’s genetic material  Watson & Crick in the 1950’s built the 1st model of DNA Structure of DNA  DNA is made of subunits called nucleotides  DNA nucleotides are composed of a phosphate, deoxyribose sugar, and a nitrogen-containing base  The bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C) DNA Nucleotide 10 Ribosomes • Made of a large and small subunit • Composed of rRNA (40%) and proteins (60%) • Have two sites for tRNA attachment - P and A 45 Ribosomes Large subunit P Site A Site mRNA Small subunit A U G C U A C U U C G 46 Translation • Synthesis of proteins in the cytoplasm • Involves the following: mRNA (codons) tRNA (anticodons) ribosomes amino acids 47 Translation • Three steps: initiation: start codon (AUG) elongation: amino acids linked termination: stop codon (UAG, UAA, or UGA) Let’s Make a Protein ! 48 mRNA Codons Join the Ribosome Large subunit P Site A Site mRNA A U G Small subunit C U A C U U C G 49 Initiation aa1 1-tRNA anticodon hydrogen bonds U A C A U G codon aa2 2-tRNA G A U C U A C U U C G A mRNA 50 Elongation peptide bond aa1 aa3 aa2 3-tRNA 1-tRNA anticodon hydrogen bonds U A C A U G codon 2-tRNA G A A G A U C U A C U U C G A mRNA 51 aa1 peptide bond aa3 aa2 1-tRNA 3-tRNA U A C (leaves) 2-tRNA A U G G A A G A U C U A C U U C G A mRNA Ribosomes move over one codon 52 aa1 peptide bonds aa2 aa4 aa3 4-tRNA 2-tRNA A U G 3-tRNA G C U G A U G A A C U A C U U C G A A C U mRNA 53 aa1 peptide bonds aa4 aa2 aa3 2-tRNA 4-tRNA G A U (leaves) 3-tRNA A U G G C U G A A C U A C U U C G A A C U mRNA Ribosomes move over one codon 54 aa1 peptide bonds aa5 aa2 aa3 aa4 5-tRNA U G A 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A A C U mRNA 55 peptide bonds aa1 aa5 aa2 aa3 aa4 5-tRNA U G A 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 56 aa4 aa5 Termination aa199 aa3 primary structure aa2 of a protein aa200 aa1 200-tRNA A C U terminator or stop codon C A U G U U U A G mRNA 57 End Product –The Protein! • The end products of protein synthesis is a primary structure of a protein • A sequence of amino acid bonded together by peptide bonds aa2 aa1 aa3 aa4 aa5 aa199 aa200 58 59 [...]... (rRNA), along with protein, makes up the ribosomes • Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized 22 Making a Protein 23 Genes & Proteins  Proteins are made of amino acids linked together by peptide bonds  20 different amino acids exist  Amino acids chains are called polypeptides  Segment of DNA that codes for the amino acid sequence in a protein are called... together by peptide bonds  20 different amino acids exist  Amino acids chains are called polypeptides  Segment of DNA that codes for the amino acid sequence in a protein are called genes 24 Two Parts of Protein Synthesis  Transcription makes an RNA molecule complementary to a portion of DNA  Translation occurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a polypeptide 25