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Protein Production Protein Production Overview Structure of Proteins Importance of Proteins Instructions for Protein Production Transcription Translation Polysome Regulation of Protein Production Fate of Proteins Protein Production Protein Structure ● Basic building blocks are amino acids (peptides) – 20 known amino acids – All amino acids contain a single carbon backbone with an amino group at one end and a carboxyl group at the other – Differ from each other by their unique 'R' group (functional group) Protein Production Protein Structure ● Have 4 important levels of structure – Primary ● – Secondary ● ● – ● 3D structure achieved when bonds form between segments of the growing secondary structure which fold on itself Can be denatured Quaternary ● ● ● Result of bonding between segments of the growing primary structure as it folds on itself Alpha helix or beta pleated sheet forms Tertiary ● – Simple sequence of amino acids Bonding between several proteins in their tertiary structure to form a large macromolecule Hemoglobin The sequence by which amino acids are put together helps determine the level of structure of a protein which then determines how the protein can be used by the cell Protein Production Importance of Proteins ● Proteins are important organic compounds to all cells – Enzymes – Structure & Repair – Reproduction (Cell Division) Protein Production Importance of Proteins ● Proteins are important organic compounds to all cells – Enzymes ● Control the rate of chemical reactions in the cell Protein Production Importance of Proteins ● Proteins are important organic compounds to all cells – Structural elements for growth and repair of the cell Protein Production Importance of Proteins ● Proteins are important organic compounds to all cells – Reproduction ● For example, the spindle fiber which separate sister chromatids in karyokinesis Protein Production Instructions for Protein Production ● ● ● Specific proteins are produced from instructions contained in genes Genes = specific regions along one strand of the double-stranded DNA molecules Each gene can only produce one specific protein Protein Production Protein Production is a twofold process – Transcription ● ● – Information on the gene of DNA is copied to a molecule of messenger RNA (mRNA) Preserves the integrity of the DNA Translation ● ● Copied information on mRNA is translated into molecules containing a specific sequence of amino acids (proteins) Occurs in the ribosomes Protein Production Protein Production – Transcription ● 3 Steps – Initiation – Elongation – Termination Protein Production Protein Production – Transcription ● Initiation – RNA polymerase binds to the promoter site ● Promoter site = part of the DNA that signals where to begin transcription ● RNA polymerase = the enzyme that builds mRNA – Helicase unwinds the DNA to expose the gene Protein Production Protein Production – Transcription ● Elongation – RNA polymerase moves along the exposed gene building mRNA – mRNA will contain a base sequence that compliments the base sequence on the gene Protein Production Protein Production – Transcription ● Termination – RNA polymerase reaches the terminator site-a portion of the DNA at the end of the gene that signal the stop of transcription – The completed mRNA dissociates from the RNA polymerase and DNA molecules and is ready for translation Protein Production -TranslationProtein Production ● Translation – mRNA leaves the nucleus for the cytoplasm where it finds ribosomes – mRNA threads itself through the ribosome – Ribosome has 2 sites on it for reading the bases on the mRNA which are passing through Protein Production -TranslationProtein Production ● Translation – Ribosomes expose 3 sequential mRNA bases (triplet) at a time at each of these sites – Each triplet is a codon which specifies an amino acid – Ribosomes translate codons into an amino acid sequence that becomes a polypeptide chain (protein) Protein Production -TranslationProtein Production ● Translation – Translation of codons is achieved by tRNA & enzymes – tRNA contains an anticodon which is complementary to a specific mRNA codon – tRNA carries the amino acid specified by its anticodon Protein Production -TranslationProtein Production ● Translation – In the ribosome tRNA anticodons bind to mRNA codons – Amino acids on adjacent tRNAs are brought together, peptide bonds are created and a polypeptide forms – At the end of the mRNA a stop codon is read, and the protein, now complete, detaches Protein Production Translation & Polysomes ● ● In cytoplasm mRNA attaches to MANY ribosomes forming a polysome Translation of a single mRNA occurs on the polysome forming MANY identical proteins from a SINGLE mRNA Protein Production Regulation of Protein Production – Prokaryotic Cells ● – Gene expression is regulated primarily during transcriptional level Eukaryotic Cells ● Gene expression is regulated at the epigenetic, transcription, and posttranscription levels ● ● ● ● Epigenetic level = when the DNA is uncoiled and loosened from nucleosomes Transcriptional level = during active transcription of DNA to mRNA Translational level = during active RNA translation to a protein Post-Translational level = after the protein has been made Protein Production How does Protein Production differ between eukaryotic and prokayotic cells? ● ● Prokayotic Cells – Transcription occurs in nucleoid area – Translation occurs in the ribosome – First amino acid in the protein is always methionine – Transcription & translation occur almost simultaneously Eukaryotic Cells – Transcription occurs in nucleus – Translation occurs at the ribosome – First amino acid in the protein is always formylmethionine – Translation occurs only after the initial mRNA molecule (pre-mRNA) is modified to the final mRNA Fate of the Proteins ● ● ● Proteins formed on free ribosomes are generally used by the cell Proteins formed on ribosomes attached to the ER (rough ER) are generally exported out of the cell How does this occur? Fate of the Proteins ● ● Proteins to be secreted are made in ribosomes of rough ER As they are synthesized new protein enter the interior of the ER Fate of the Proteins ● ● ● Proteins are packaged into vesicles & leave ER for the Golgi bodies In the Golgi body the proteins are sorted, modified and stored Eventually these proteins are repackaged into new vesicles, leave the Golgi body for the cell membrane and are released by exocytosis Protein Production in Action