Protein Synthesis PDF

By Dr/ Eman Elsaid Khalifa Lecturer of cellular and molecular biology Nile Valley university  Protein Synthesis The Protein-making Process https://www.youtube.com/watch?v=gG7uCskUOrA  Protein Synthesis (Gene Expression) Proteins make up all living materials  P...

By Dr/ Eman Elsaid Khalifa Lecturer of cellular and molecular biology Nile Valley university  Protein Synthesis The Protein-making Process https://www.youtube.com/watch?v=gG7uCskUOrA  Protein Synthesis (Gene Expression) Proteins make up all living materials  Proteins are composed of amino acids – there are 20 different amino acids Different proteins are made by combining these 20 amino acids in different combinations These amino acids come from the food we eat. Proteins we eat are broken down into individual amino acids and then simply rearranged into new proteins according to the needs and directions of our DNA.  Proteins are manufactured (made) by the ribosomes The Central Dogma Information passes from the genes (DNA) to an RNA copy of the gene, and the RNA copy directs the sequential assembly of a chain of amino acids  Steps to Make a Protein 1. Transcription DNA → RNA 2. Translation RNA → Protein (Chain of amino acids)  Step 1: Transcription A. Transcription: a complementary single strand of mRNA is copied from part of the DNA in the nucleus A. RNA Polymerase, an enzyme, unwinds DNA strand B. RNA polymerase “reads” one strand of DNA bases and makes the RNA strand c. mRNA leaves and DNA strands will coil back up RNA Polymerase I rRNA If DNA is TACCAGTTT RNA Polymerase II mRNA RNA Polymerase III tRNA mRNA will be AUGGUCAAA  mRNA editing 1. mRNA editing: cutting and splicing mRNA before it leaves the nucleus a. Introns- (intruders) “junk DNA” that doesn’t code for proteins are cut out b. Exons- “good DNA” that code for proteins stay and are expressed 2. Introns are removed and exons are spliced together. 3. Edited mRNA is sent out of nucleus to ribosome 4. The exons can be spliced together in different sequences to produce different mRNA’s = different proteins Transcription: DNA → RNA Step 2: Translation 1.How the code is read: a.Every 3 bases on mRNA represents a code for an amino acid = codon. b.Amino acids are abbreviated most times by using the first 3 letters of the amino acid’s name. Met = methonine Leu = leucine  Reading the Codon Chart Examples: AUG = Methionine CAU = Histidine UAG = Stop First Third Position Position Try these: Answers: GCU: Alanine UAC: Tyrosine CUG: Leucine UUA: Leucine This chart only works for mRNA codons. https://www.youtube.com/watch?v=LsEYgwuP6ko  Step 2: Translation Translation - Translating of a mRNA codons into a protein (amino acid chain) – Takes place on ribosomes in cytoplasm  Step 2: Translation 1. Edited mRNA attaches to a ribosome 2. As each codon of the mRNA molecule moves through the ribosome, the tRNA brings the proper amino acid to the ribosome. – Notice the anticodon on tRNA – it is complementary to the mRNA codon – The amino acids are joined together by chemical bonds called peptide bonds to build an amino acid chain called a “polypeptide”  A series of three adjacent bases in an mRNA molecule codes for a specific amino acid—called a codon. Each tRNA has 3 nucleotides Amino acid that are complementary to the codon in mRNA. Each tRNA codes for a different amino acid. Anticodon Regulation of Protein Synthesis Start codons: found at the beginning of a protein – Only one – AUG (methionine) Stop codons: found at the end of a protein (end of a polypeptide chain) Three stop codons that do not code for any amino acid therefore making the process stop: UAA, UAG,UGA  Translation Nucleus mRNA  Lysine Phenylalanine t RNA Methionine  Anticodon Ribosome mRNA Start codon  Translation Growing polypeptide chain The Polypeptide “Assembly Line” Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide mRNA Translation direction Ribosome  Roles of RNA and DNA The cell uses the vital DNA “master plan” to prepare RNA “blueprints.” The DNA molecule remains within the safety of the nucleus, while RNA molecules go to the protein- building sites in the cytoplasm—the ribosomes. Protein Synthesis