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Hemophilia1. Caused by a defect in a single gene cannot produce all the proteins necessary for blood clotting 2. Depend on expensive injections of clotting proteins to prevent uncontrolled bleeding nuclear pore chromatin (DNA) nucleus nucleolus nuclear envelope flagellum rough endoplasmic reticulum cytoplasm intermediate filaments plasma membrane ribosome lysosome microtubules smooth endoplasmic reticulum Golgi complex free ribosome vesicle mitochondrion vesicle Protein Synthesis Gene Expression DNA, Genes & Proteins The relationship of Chromosomes, Genes, DNA & Proteins Franklin's Legacy | PBS DNA to Protein Genes and Proteins Genes provide information to make proteins Genetic information for protein synthesis is carried by RNA (ribonucleic acid) intermediates The genetic code and codons A sequence of nucleotide bases in DNA is translated into a sequence of amino acids in a protein. Protein Synthesis Two-step process Transcription and Translation 1. Transcription—nucleotide message sent from nucleus to cytoplasm a. DNA nucleotide sequence "copied" (using complementary base pairing) as a "messenger" nucleotide sequence of RNA (mRNA) gene 3 gene 1 DNA gene 2 (nucleus) (a) TRANSCRIPTION messenger RNA (cytoplasm) Transcription of gene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands. protein (b) TRANSLATION Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA. Protein Synthesis 1. Transcription… b. RNA polymerase catalyzes synthesis of mRNA; similar to DNA replication and DNA polymerase • • Promoter sequence binds RNA polymerase Termination signal is a sequence of nucleotides at end of genes that tell RNA polymerase to stop transcription gene 3 gene 1 DNA gene 2 (nucleus) (a) TRANSCRIPTION messenger RNA (cytoplasm) Transcription of gene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands. protein (b) TRANSLATION Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA. Protein Synthesis 1. Transcription… c. The entire DNA molecule in a chromosome is not transcribed, only a specific gene or family of genes is transcribed chromosome DNA gene 1 gene 2 (a) initiation template strand RNA polymerase gene 3 (b) elongation RNA direction of transcription beginning of gene DNA RNA polymerase growing RNA molecules (a) RNA polymerase termination signal (b) RNA Initiation, Elongation and Termination gene 3 gene 1 DNA gene 2 (nucleus) (a) TRANSCRIPTION messenger RNA (cytoplasm) Transcription of gene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands. protein (b) TRANSLATION Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA. Protein Synthesis 2. Translation—nucleotide sequence of mRNA used to synthesize a sequence of amino acids (polypeptide or protein) a. Occurs on the endoplasmic reticulum using ribosomes rough endoplasmic reticulum ribosomes 0.5 micrometers smooth endoplasmic reticulum 0.5 micrometers vesicles Protein Synthesis 2. Translation… b. mRNA codons are used to specify amino acids c. Ribosomes "read" mRNA codons to synthesize a specific amino acid sequence (a) messenger RNA A Codon = three nucleotide bases (b) ribosome (contains ribosomal RNA) catalytic site large subunit tRNA/amino acid binding sites small subunit Protein Synthesis 2. Translation… d. Each of the 20 amino acids has a specific "carrier" transfer RNA (tRNA) that brings the amino acid to the ribosome e. Complementary base pairing between the mRNA and tRNAs determines the amino acid sequence (c) transfer RNA attached amino acid anticodon (a) messenger RNA (b) ribosome (contains ribosomal RNA) catalytic site large subunit tRNA/amino acid binding sites small subunit (c) transfer RNA attached amino acid anticodon Protein Synthesis 2. Translation… f. Ribosomes need to recognize the beginning and end of the mRNA message • 1) Initiation (start) codon: AUG (methionine) • 2) Stop codons: UAA, UAG, UGA amino acid initiation complex methionine tRNA small ribosomal subunit (a) A tRNA with an attached methionine amino acid binds to small ribosomal subunit, forming an initiation complex. tRNA mRNA (b) The initiation complex binds to the end of an mRNA and travels along the mRNA until it encounters an AUG codon. The anticodon of the tRNA pairs with the AUG codon. second binding site catalytic site first binding site (c) The large ribosomal subunit binds to the small subunit, with the mRNA between the two subunits. The methionine tRNA is in the first binding site on the large subunit. large ribosomal subunit catalyic site (d) A second tRNA enters the second binding site. Its anticodon pairs with the codon in the mRNA. The tRNA carries an attached amino acid. peptide bond (e) The catalytic site catalyzes the formation of a peptide bond that links the two amino acids. Both amino acids are now attached to the tRNA in the second binding position. catalytic site tRNA detaches ribosome moves one codon to right (f) The “empty” tRNA is released and the ribosome moves one codon to the right. The tRNA with the two amino acids is now in the first tRNA binding site. The second tRNA binding site is empty. catalytic site (g) Another tRNA, with an anticodon complementary to the next mRNA codon, enters the second binding site. This tRNA carries the next amino acid to be added to the chain. (h) The catalytic site forms a peptide bond that attaches the new amino acid at the end of the chain. The chain of three amino acids is now attached to the tRNA in the second binding site. The empty tRNA in the first site will be released and the ribosome will move one codon to the right. completed peptide stop codon (i) Binding of tRNAs and formation of peptide bonds between amino acids continues until the ribosomes reaches a stop codon. No tRNA binds to stop codons. Instead, protein “release factors” signal the ribosome to release the newly made protein. The mRNA is also released, and the subunits separate. second binding site initiation complex amino acid methionine tRNA (a) small ribosomal subunit tRNA mRNA catalytic site first binding site (b) (c) catalytic site tRNA detaches catalytic site large ribosomal subunit peptide bond ribosome moves one codon to the right (d) (f) (e) catalytic site completed peptide (g) (h) (i) stop condon gene (a) gene in DNA (template strand) codon (b) mRNA (codons) anticodon (c) tRNA (anticodons) amino acids (d) protein (amino acids) Review Protein Synthesis Two Major Steps of Protein Synthesis Transcription & Translation Initiation, Elongation and Termination