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PROTEIN SYNTHESIS DNA and Genes DNA • DNA contains genes, sequences of nucleotide bases • These Genes code for polypeptides (proteins) • Proteins are used to build cells and do much of the work inside cells Genes & Proteins Proteins are made of amino acids linked together by peptide bonds 20 different amino acids exist Polypeptides • Amino acid chains are called polypeptides DNA Begins the Process • DNA is found inside the nucleus • Proteins, however, are made in the cytoplasm of cells by organelles called ribosomes • Ribosomes may be free in the cytosol or attached to the surface of rough ER Starting with DNA • DNA ‘s code must be copied and taken to the cytosol • In the cytoplasm, this code must be read so amino acids can be assembled to make polypeptides (proteins) • This process is called PROTEIN SYNTHESIS RNA Roles of RNA and DNA • DNA is the MASTER PLAN • RNA is the BLUEPRINT of the Master Plan RNA Differs from DNA • RNA has a sugar ribose DNA has a sugar deoxyribose Other Differences • • RNA contains the base uracil (U) DNA has thymine (T) RNA molecule is single-stranded DNA is doublestranded DNA Structure of RNA . 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 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 ) 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 Ribosomal RNA (rRNA) • rRNA is a single strand 100 to 3000 nucleotides long • Globular in shape • Made inside the nucleus of a cell • Associates with proteins to form ribosomes • Site of protein Synthesis 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 The Genetic Code •Use the code by reading from the center to the outside •Example: AUG codes for Methionine Name the Amino Acids • • • • • GGG? UCA? CAU? GCA? AAA? Remember the Complementary Bases On DNA: A-T C-G On RNA: A-U C-G 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 Transfer RNA amino acid attachment site U A C anticodon 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 Transcription and Translation Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein 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 DNA RNA Protein Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 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 Question: What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’ Answer: • DNA 5’-GCGTATG3’ • RNA 3’-CGCAUAC-5’ 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 mRNA Transcript •mRNA leaves the nucleus through its pores and goes to the ribosomes Translation • Translation is the process of decoding the mRNA into a polypeptide chain • Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins Transcription Translation 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 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 protein methionine codon 2 codon 3 glycine serine codon 4 isoleucine codon 5 codon 6 glycine alanine codon 7 stop codon Primary structure of a protein aa1 aa2 aa3 peptide bonds aa4 aa5 aa6