translation翻譯過程.ppt

Translation,Once the DNA code has been Transcribed onto a mRNA molecule, mRNA leaves the nucleus and moves into the cytoplasm. In the cytoplasm the mRNA combines with the Ribosomes to make Enzymes/Proteins. The Process of reading the mRNA code and building a(n) Enzyme/Protein is called Translation, or Protein Synthesis.,In order for Translation/Protein Synthesis to occur a cell needs:,1. mRNA (carrying the DNA code) 2. Ribosomes 3. Amino Acids 4. tRNA (picks up amino acids in the cytosol and carries them to the ribosomes where they will be joined together to form a Protein),The mRNA is made in the Nucleus through the process of Transcription. mRNA is made up of RNA nucleotides. Each group of 3 nucleotides is called a Codon and codes for one amino acid of the newly forming Protein.,This Segment of a mRNA molecule is 7 codons long, 21 nucleotides, and will code for 7 amino acids,Ribosomes (the ribosomes are the actual site of Translation /protein synthesis),Made in the Nucleolus, made up of Ribosomal RNA, rRNA,Animals and Plants get their amino acids the same way they get their Nucleotides.,Transfer RNA (tRNA),tRNA is a small, folded RNA chain (74-93 nucleotides) that picks up and transfers specific amino acids to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for Amino Acid attachment and an Anticodon. The Anticodon is composed of complementary bases. Each tRNA molecule binds to only one type of amino acid. More than one tRNA exists for each amino acid.,Summary of Translation (or so you want to make a Protein),Lets begin in the nucleus The DNA has the code to instruct the Ribosomes as to which Proteins to make. Ok, 2 problems here: 1.) the DNA is in the Nucleus and the ribosomes are in the Cytoplasm, and 2.) the ribosomes cant read the DNA. Well theres an easy way to fix both problems its called Transcription. Through Transcription, the DNA code is placed onto a mRNA molecule which can 1.) leave the nucleus, travel into the cytoplasm and join with the ribosomes, and 2.) the ribosomes can Translate (read) the mRNA. So now we have the DNA code, by way of mRNA, in the cytoplasm that can instruct the Ribosomes as to which protein to make By the way, the difference between one protein and another protein is the order of the amino acids, the number of amino acids and its 3 dimensional shape.,Now lets say you are a ribosome you are just sitting around, in the cytoplasm, waiting for some amino acids to assemble into protein.you already have the instructions, remember the mRNA, but you cant get the amino acids yourself you need help. you need tRNA. The tRNA can pick up specified amino acids. and bring them to you in the correct orderbut how does I know which amino acid to pick up? The tRNA knows where to place its amino acid because the tRNA can read the mRNA codonthe mRNA codon is a transcribed version of the DNA codeit instructs the mRNA as to where it should place the amino acid. By the way.the first amino acid is always methionine, or sometimes referred to as “f-met”. So. Its this simple youre a tRNA molecule. You have an amino acid attached to you you simply move up or down the mRNA looking for the right place to drop off your amino acid. youll easily recognize where to place the amino acid its where your anticodon matches the mRNA codon. This process will continue until a “termination or stop” codon, located on the mRNA, instructs the ribosomes to break apartending translation.,Translation,1st letter Row 2nd Letter Column 3rd Letter - Sentence,Gene Regulation,Some genes can be “switched on” or “switched off”. When a gene is switched on.a protein is produced. when a gene is switched off a protein is no longer produced. How the organism is affected depends on the protein. An Operon is a gene switch. it is located on the DNA . What an operon really is is a series of genes that code for a particular protein. The first operon discovered is known as the “l(fā)ac-operon”.,The lac-Operon,The lac-Operon Four regions of DNA control the production of a protein such as the enzyme Beta-galactosidease (which is used to digest lactose) a structural gene that codes for the enzyme Beta-galactosidease. 2. an operator region right in front of the structural gene, where the repessor molecule attaches to prevent Transcription. 3. a promoter region where the RNA Polymerase binds to the DNA. 4. a regulator gene which codes for the Repressor. 5. A repressor is a molecule which binds to the operator and prevents transcription. The combined region of the operator and structural gene is called an operon.,regulator gene,DNA,Lac-operon,Editing DNA,About 65% of an organisms DNA is not used. its left over baggage from evolution. As a consequence, about 65% of the mRNA transcribed is also useless So the mRNA must be “edited” to remove the useless codes. This editing is accomplished by enzymes. The pieces of mRNA which are spliced out are called Introns. of course they cannot code for anything. The pieces of mRNA which are left in, after editing, are called Exons. of course they are the expressed codes.,Examples of Genes containing Exons and Introns,The Structure of a Chromosome,Chromosome Maps,A diagram that shows the location (locus, plural - loci) of a gene.,MUTATIONS,The replication of DNA is usually extremely accurate because DNA polymerase proofreads the DNA as it is produced. If necessary, DNA polymerase removes the incorrect nucleotide and replaces it. If the DNA is NOT repaired a Mutation will occur. A mutation is a change in the DNA This change will affect the protein which is produced and can eventually affect the organisms traits.,The 2 most common causes of mutations are:,Radiation (such as ultraviolet and x-ray) and, Various reactive chemicals called Carcinogens. If the Mutation occurs in a Somatic cell or body cell, it is not inheritable. If the Mutation occurs in a gamete, it is heritable.,Types of Mutations (Changes in the DNA affecting the resulting traits),The 2 most common mutations are: 1. Point Mutations 2. Frame-shift Mutations,Point Mutation,Changes in o