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RNA and Protein Synthesis Chapter 8 Sections 4 - 7 3 main differences between RNA and DNA: 1. Sugar in RNA is ribose; Sugar in DNA is deoxyribose 2. RNA is single stranded; DNA is double stranded 3. RNA contains uracil in place of thymine 3 Types of RNA 1. Messenger RNA (mRNA)- disposable copy of DNA to carry instructions to assemble proteins at the ribosome 2. Ribosomal RNA (rRNA)- RNA inside the ribosome to make the ribosome exist 3. Transfer RNA (tRNA)- transfers amino acids in the cytoplasm to the growing polypeptide chain in the ribosomes to construct proteins Protein Synthesis is the process of converting mRNA into a protein. It is the process of how proteins are made. Protein Synthesis has 2 steps: 1. Transcription -takes place in nucleus 2. Translation -takes place in ribosome Transcription converts a DNA gene into a single-stranded mRNA molecule. In other words, Transcription is a process that copies DNA to make a strand of mRNA. Takes place in Nucleus. Transcription begins at specific locations on DNA called promoters. Enzyme called RNA Polymerase separates DNA strand by breaking H bonds between nucleotide pairs. Separated strands of DNA are used as templates to assemble strand of mRNA. RNA Polymerase start site nucleotides DNA Templates Nucleotides pair with one template strand of DNA. RNA polymerase bonds the nucleotides back together. The DNA helix winds again as the gene is transcribed mRNA DNA RNA Polymerase Nucleotides RNA polymerase moves along the DNA The mRNA strand detaches from the DNA once the gene is transcribed. It will leave the nucleus to find a ribosome floating in the cytoplasm or find a ribosome on the Rough ER. This event marks the end of Transcription and the beginning of Translation. mRNA Transcription Overview The transcription process is similar to replication. • Transcription and replication both involve complex enzymes and complementary base pairing. • The two processes have different end results. – – Replication copies all the DNA; transcription copies a gene. Replication makes one copy; transcription can make many copies. one gene growing RNA strands DNA Translation converts mRNA into a protein. This process involves translating the language of nucleic acids (base sequences) into a language of proteins (amino acids). A gene carries a code to make one protein. A gene can be anywhere from 300 to 3000 base pairs long. Code written in language with only 4 “letters”: A, C, G, U Code read 3 letters at a time (each 3 letter “word” known as a codon) to make an amino acid. codon for methionine (Met) ***Amino acids are the building blocks of proteins. codon for leucine (Leu) Steps to Translation: 1. mRNA leaves nucleus and attaches to ribosome. 2. Translation begins with tRNA in ribosome binding to AUG, the start codon, which signals the ribosome to assemble amino acids in a polypeptide chain to create a protein. 3. Each tRNA has an anticodon whose bases are complementary to the codon on mRNA. tRNA brings amino acids to ribosomes and build a polypeptide chain, which creates a protein. anticodon codon 4. Ribosome moves along mRNA, and bind new tRNA molecules to mRNA codons and link amino acids together to create a polypeptide chain. 5. The now empty tRNA molecule exits the ribosome. 6. A complementary tRNA molecule binds to the next exposed codon. 7. The polypeptide chain grows until tRNA reaches 1 of the 3 stop codons (UGA, UAA, UAG). At the end of translation, the protein is released, folded into a 3D structure, transported in a vesicle to the Golgi Apparatus to be modified and “shipped” to its final destination within the cell or outside of the cell. Protein molecule stop codon The Genetic Code is the language of mRNA. tRNA translates this 4 letter language into amino acids, so a protein can be created. You read 3 letters at time. Example: AUG CCC GGG AUU UGA translates into the following amino acid polypeptide chain: Methionine-Proline-Glycine-Isoleucine-STOP STOP is not an amino acid. It simply tells the tRNA to terminate the translation process and to not add anymore amino acids to the polypeptide chain. • The central dogma includes three processes: 1. Replication 2. Transcription 3. Translation replication transcription • RNA is a link between DNA and proteins. translation Mutation- a change in an organism’s DNA that affects genetic information and may or may not affect phenotype (physical appearance). Gene Mutations result from changes in a single gene. Many kinds of mutations can occur, especially during replication. •Some gene mutations change phenotype. –A mutation may cause a premature stop codon. –A mutation may change protein shape or the active site. –A mutation may change gene regulation. Chromosomal Mutations- involves changes in the number and structure of chromosomes. Chromosomal mutations usually occur during crossing over and may affect many genes. Chromosomal mutations tend to have a big effect. There are 7 main types of mutations: 1. Point Mutation (aka Substitution) 2. Frameshift Mutation 3. Deletion 4. Duplication 5. Insertion 6. Inversion 7. Translocation 1. Point mutations (aka Substitutions)- occur at a single point in DNA sequence and generally change one amino acid in the polypeptide chain. Example: Sickle Cell Anemia Sickle cell anemia is a disease in which red blood cells form an abnormal crescent shape. (Red blood cells are normally shaped like a disc.) Sickle-shaped cells deliver less oxygen to the body's tissues. They also can clog more easily in small blood vessels, and break into pieces that disrupt blood flow. People with sickle-cell anemia have a survival advantage. Sickleshaped red blood cells are resistant to the infectious parasite that causes malaria, and people with this trait were more likely to survive malaria epidemics. Point Mutation/Substition A point mutation is a simple change in one base of the gene sequence. This is equivalent to changing one letter in a sentence, such as this example, where we change the 'c' in cat to an 'h': Original: The fat cat ate the red rat. Point Mutation: The fat hat ate the red rat. 2. Frameshift mutation- insertion or deletion of nucleotide. It causes big changes because it can alter protein shape by making it unable to perform normal functions. Example: Tay-Sachs Disease Children with Tay-Sachs, a progressive neurodegenerative disease that attacks nerve cells, usually die before age 5. Frame-shift mutation In a frame shift mutation, one or more bases are inserted or deleted, the equivalent of adding or removing letters in a sentence. But because our cells read DNA in three letter "words", adding or removing one letter changes each subsequent word. This type of mutation can make the DNA meaningless and often results in a shortened protein. An example of a frame-shift mutation using our sample sentence is when the 't' from cat is removed, but we keep the original letter spacing: Original: The fat cat ate the red rat. Frame Shift: The fat caa tet her edr at. 3. Deletion Mutations that result in missing DNA are called deletions. These can be small, such as the removal of just one "word," or longer deletions that affect a large number of genes on the chromosome. Deletions can also cause frameshift mutations. In this example, the deletion eliminated the word cat. Original: The fat cat ate the red rat. Deletion: The fat ate the red rat. Example: Cystic Fibrosis 4. Duplication Mutations that result in the addition of an extra copy of DNA are called duplications. Duplications can also cause frameshift mutations, and general result in a nonfunctional protein. Original: The fat cat ate the red rat. Insertion: The fat cat cat ate the red rat. 5. Insertion Mutations that result in the addition of extra DNA are called insertions. Insertions can also cause frameshift mutations, and general result in a nonfunctional protein. Original: The fat cat ate the red rat. Insertion: The fat cat dog ate the red rat. 6. Inversion In an inversion mutation, an entire section of DNA is reversed. A small inversion may involve only a few bases within a gene, while longer inversions involve large regions of a chromosome containing several genes. Original: The fat cat ate the red rat. Insertion: The fat tar der eht eta tac. 7. Translocation Translocation results from the exchange of DNA segments between nonhomologous chromosomes. More example diagrams of mutations • Some gene mutations do not affect phenotype. – A mutation may be silent. – A mutation may occur in a noncoding region. – A mutation may not affect protein folding or the active site. • • • • Mutations in body cells do not affect offspring. Mutations in sex cells can be harmful or beneficial to offspring. Natural selection often removes mutant alleles from a population when they are less adaptive. Mutations may have led to drastic and quick evolutionary changes Mutations can be caused by several factors. • Replication errors can cause mutations. • Mutagens, such as UV ray and chemicals, can cause mutations. • Some cancer drugs use mutagenic properties to kill cancer cells.