Protein Synthesis PDF

PROTEIN SYNTHESIS 1  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 2 ...

PROTEIN SYNTHESIS 1  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 2 DNA RNA Protein DNA Transcription mRNA Ribosome Translation Protein Prokaryotic Cell 3  DNA RNA Protein Nuclear DNA membrane Transcription Pre-mRNA Eukaryotic RNA Processing Cell mRNA Ribosome Translation Protein 4 Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein 5 Nucleic Acids 6  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 7  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 8  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 4 bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C) 9 DNA Nucleotide 10  Base Pairing Rule Watson and Crick showed that DNA is a double helix A (adenine) pairs with T (thymine) C (cytosine) pairs with G (guanine) 11  Nitrogen Rings Purines have single rings of carbon-nitrogen (G, A) Pyrimidines have double carbon-nitrogen rings (C, T) This is called complementary base pairing because a purine is always paired with a pyrimidine 12  5’ to 3’ Sugars. When the DNA double helix unwinds, it resembles a ladder The sides of the ladder are the sugar- phosphate backbones The rungs of the ladder are the complementary paired bases The two DNA strands are anti-parallel (they run in opposite directions) 13 Anti-Parallel Strands of DNA 14  DNA Replication 15  Steps in DNA Replication Occurs when chromosomes duplicate (make copies) An exact copy of the DNA is produced with the aid of the enzyme DNA polymerase Hydrogen bonds between bases break and enzymes “unzip” the molecule Each old strand of nucleotides serves as a template for each new strand New nucleotides move into complementary positions are joined by DNA polymerase 16  Two New, Identical DNA Strands Result from Replication 17 Another View of Replication 18 RNA 19  RNA Differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains the base uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded 20 Structure of RNA 21. Three Types of RNA Messenger RNA (mRNA) carries 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 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 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  Genetic Code  DNA contains a triplet code  Every three bases on DNA stands for ONE amino acid  Each three-letter unit on mRNA is called a codon  Most amino acids have more than one codon!  There are 20 amino acids with a possible 64 different triplets  The code is nearly universal among living organisms 26 27 Transcription Translation 28  Overview of Transcription  During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for mRNA formation  RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the triplet code in DNA 29  Steps in Transcription  The transfer of information in the nucleus from a DNA molecule to an RNA molecule  Only 1 DNA strand serves as the template  Starts at promoter DNA (TATA box)  Ends at terminator DNA (stop)  When complete, pre-RNA molecule is released 30 Transcription 31 32  What is the enzyme responsible for the production of the mRNA molecule? 33  RNA Polymerase  Enzyme found in the nucleus  Separates the two DNA strands by breaking the hydrogen bonds between the bases  Then moves along one of the DNA strands and links RNA nucleotides together 34 DNA RNA Polymerase pre-mRNA 35  Question:  What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’ 36  Answer: DNA 5’-GCGTATG-3’ RNA 3’-CGCAUAC-5’ 37  Processing Pre-mRNA Also occurs in the nucleus Pre-mRNA made up of segments called introns & exons Exons code for proteins, while introns do NOT! Introns spliced out by splicesome-enzyme and exons re-join End product is a mature RNA molecule that leaves the nucleus to the cytoplasm 38  RNA Processing pre-RNA molecule exon intro exon intron exon n intron intron exon exon exon splicesome splicesome exon exon exon Mature RNA molecule 39  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 40  Messenger RNA (mRNA) start codon mRNA A U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds 41  Transfer RNA (tRNA) Made up of 75 to 80 nucleotides long Picks up the appropriate amino acid floating in the cytoplasm Transports amino acids to the mRNA Have anticodons that are complementary to mRNA codons Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds 42  Transfer RNA (tRNA) amino acid attachment site methionine amino acid U A C 43 anticodon  Ribosomal RNA (rRNA) Made up of rRNA is 100 to 3000 nucleotides long Made inside the nucleus of a cell Associates with proteins to form ribosomes 44  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 A Site Site mRNA A U G C U A C U U C G Small subunit 46  Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. ribosomes 4. amino acids 47  Translation Three steps: 1. initiation: start codon (AUG) 2. elongation: amino acids linked 3. termination: stop codon (UAG, UAA, or UGA). Let’s Make a Protein ! 48  mRNA Codons Join the Ribosome Large subunit P A Site Site mRNA A U G C U A C U U C G Small subunit 49  Initiation aa2 aa1 2-tRNA 1-tRNA G A U anticodon U A C hydrogen A U G C U A C U U C G A bonds codon mRNA 50  Elongation peptide bond aa3 aa1 aa2 3-tRNA 1-tRNA 2-tRNA G A A anticodon U A C G A U hydrogen A U G C U A C U U C G A bonds codon mRNA 51  aa1 peptide bond aa3 aa2 1-tRNA U A C 3-tRNA (leaves) 2-tRNA G A A G A U A U G C U A C U U C G A mRNA 52 Ribosomes move over one codon  peptide bonds aa1 aa4 aa2 aa3 4-tRNA 2-tRNA 3-tRNA G C U G A U G A A A U G C U A C U U C G A A C U mRNA 53  peptide bonds aa1 aa4 aa2 aa3 2-tRNA 4-tRNA G A U (leaves) 3-tRNA G C U G A A A U G C U A C U U C G A A C U mRNA 54 Ribosomes move over one codon  peptide bonds aa5 aa1 aa2 aa4 aa3 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  aa1 peptide bonds aa5 aa2 aa3 aa4 5-tRNA 3-tRNA U G A G A A 4-tRNA G C U G C U A C U U C G A A C U mRNA 56 Ribosomes move over one codon  aa5 aa4 aa199 Termination aa3 primary aa200 structure aa2 of a protein aa1 terminator 200-tRNA or stop codon A C U 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 aa5 aa3 aa4 aa2 aa199 aa1 aa200 58 59