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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 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 to each other one is oriented 5’ to 3’, the other 3’ to 5’ Basically, one side runs “right side up and one side runs upside down”. 7 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 to the replication forks 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!! Notice how it is different from DNA. 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. 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 Let’s see this in action: http://wwwclass.unl.edu/bioch em/gp2/m_biology/ animation/gene/ge ne_a2.html 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 the code in mRNA into a protein. To do this we use a special molecule called 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. tRNA anticodons match up with the mRNA codons. 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. This chart is based on mRNA codons!! Practice: 1. UCC Serine 2. AAG Lysine 3. UAA Mutations Mutations are changes in the DNA sequence that affect genetic information Types of gene mutations (changes in a single gene): Substitution ○ Original strand: TAC GCA TGG ○ Mutated strand: TAC GTA TGG Insertion ○ Original strand: TAC GCA TGG ○ Mutated strand: TAT CGC ATG Deletion ○ Original strand: TAC GCA TGG ○ Mutated strand: TCG CAT GG Insertions and deletions cause the biggest problems b/c Mutations Types of chromosomal Mutations (changes in whole chromosomes):