Transcript D.N.A.
D.N.A. is a Nucleic Acid D.N.A is capable of…… • carrying genetic information to next generation • directing the cell to follow its orders • being easily copied DNA History Griffith 1928 Grew 2 distinct strains of bacteria (rough and smooth), injected mice and observed which died Transformation: one strain permanently changed into another More History… Avery 1944 Wanted to determine what was responsible for transformation Used enzymes to determine that DNA was the transforming factor. Hershey-Chase 1952 Studied viruses (bacteriophages) Determined that genetic information was not protein but DNA History of the Discovery of D.N.A 1952 – Rosalind Franklin studies the DNA molecule using a technique called X-ray diffraction. History of D.N.A. Cont’d. Watson and Crick They used Rosalind Franklin’s pictures of DNA to figure out the structure of D.N.A. established the structure as a double helix - like a ladder that is twisted. The two sides of the ladder are sugar phosphate backbone and are held together by hydrogen bonds. Basic Structure of D.N.A. The sides of D.N.A. alternate Sugar and Phosphate. (sides of the ladder) The bases make up the middle (rungs of the ladder) A–T C-G DNA: Deoxyribonucleic acid The building blocks of DNA are nucleotides, each composed of: a 5-carbon sugar called deoxyribose a phosphate group (PO4) a nitrogenous base (4 types) ○ Adenine (A), thymine (T), cytosine (C), guanine (G) Phosphate group Deoxyribose (sugar) Nucleotide! DNA Structure The two strands of nucleotides are antiparallel Basically, one side runs “right side up and one side runs upside down”. 9 The 4 Bases Bases come in two types: 1. Pyrimidines (cytosine and thymine) – Have one ring of carbon 2. Purines (guanine and adenine) – Have two rings of carbon Purines pair with Pyrimidines: Adenine with Thymine Guanine with Cytosine DNA Chromosome Structure Think back: When did we learn that DNA had to be replicated?? During the cell cycle in S phase DNA Replication Replication Steps: 1. DNA unzips 2. New nucleotides assemble 3. Two new strands of identical DNA are reproduced – each with one original stand. Replication Enzymes 2 Main enzymes involved 1. Helicase – unzips the DNA 2. DNA polymerase It has two main functions. ○ 1. Adds new bases ○ 2. “proofreads” The Big Picture When we want to make a protein we have to transfer the “code” from DNA on to a special molecule called RNA! This is called Transcription. So how do we get from the code from the bases to really make us a protein? RNA RNA stands for Ribonucleic Acid. It is a special molecule that carries the code from DNA out to the ribosomes so that we can make the right protein. It is our messenger!! RNA Similarities Phosphate Sugar Base Differences Sugar is ribose (DNA: deoxyribose) Single stranded (DNA: double helix) Has uracil as a base, not thymine It can travel outside of the nucleus. Proteins What is a protein? A protein is a large molecule made of smaller parts called amino acids. Every protein has a specific order of amino acids! ○ 20 amino acids exist in nature ○ The instructions for the order of amino acids comes from DNA Proteins are the building block for ALL living things! What do proteins do? Proteins have a variety of different functions that include: ○ Structure ○ Transport ○ Enzymes ○ Storage ○ Hormonal ○ Movement ○ Defense What proteins do… Proteins have several functions… Structure ○ Keratin: protein found in hair, fur and feathers Transport ○ Hemoglobin: transports oxygen in vertebrates Enzymes ○ Digestive enzymes: break down food Storage ○ Casein: found in milk, gives protein to young mammals Hormonal ○ Insulin: regulates blood sugar Movement ○ Actin and Myosin: responsible for muscle movement Defense ○ Antibodies: fight of infection and disease (immune system) Protein Production Where is DNA located in the cell? Nucleus! Where are proteins produced? Ribosomes in the cytoplasm! How do we get the instructions from the nucleus to the ribosomes? RNA! Transcription Transcription is the process of copying the code of DNA into RNA so it can go to the ribosome and make protein. Transcription takes places in the NUCLEUS A-U C-G T-A Transcription 3 STEPS 1. RNA polymerase (another enzyme) binds to the promoter region of DNA 2. RNA polymerase unzips the DNA and adds nucleotide bases A-U, C-G 3. RNA polymerase stops when it comes to a termination region of DNA Practice/Review So if one side of DNA has the following bases, what would the other side have? A C T G G T A C G A T A T G A C C A T G C T A T Using the original strand above, what would the RNA strand look like? U G A C C A U G C U A U Translation Now that we have our mRNA it is time to make a protein…..we do this at the ribosome. Translation – converting mRNA into a protein. To do this we use transfer RNA Transfer RNA Transfer RNA (tRNA) looks like a cross. It has three bases that attach at the bottom. We call these anti-codons. They attach to three bases on the mRNA which we call codons. At the top of the tRNA is an amino acid (the building block of proteins)!! Translation Steps – 8 easy steps!! 1. The newly made mRNA travels to the ribosome. 2. The ribosome reads the mRNA code in groups of three, called “codons.” Starts at AUG 3. Codons match up with anticodons 4. Another tRNA attaches to the next codon. Its amino acid is attached to the previous one. Translation 5. The first tRNA falls off 6. The ribosome moves along the mRNA, using tRNA to attach amino acids. 7. The process ends when a stop codon is reached (UGA, UAA, UAG). 8. The amino acid chain is released – it FOLDS into a 3-D structure called a protein. Amino Acid Chart So how do we know what amino acid is at the top of each transfer RNA? We use this cool chart. Start at the middle and work towards the outside. Remember amino acids go together to make proteins. This chart is based on mRNA codons!! Practice: 1. UCC Serine 2. AAG Lysine 3. UAA Stop Let’s Pull everything together! Practice Given the following DNA strand, give the corresponding mRNA strand that it would code for. DNA mRNA T A C A C C T C A A T T A U G U G G A GU U A A Now, use your chart and figure out the amino acid chain, that this mRNA would code for. Methionine – Tryptophan – Serine – STOP http://learn.genetics.utah.edu/content/begin/d na/transcribe/ Mutations Mutations are changes in the DNA sequence that affect genetic information 1. Point Mutation Substitution – base changed ○ Original strand: TAC GCA TGG ○ Mutated strand: TAC GTA TGG 2. Frameshift Mutation Insertion –base added ○ Original strand: TAC GCA TGG ○ Mutated strand: TAT CGC ATG G Deletion – base removed ○ Original strand: TAC GCA TGG ○ Mutated strand: TCG CAT GG Mutations Types of chromosomal Mutations (changes in whole chromosomes):