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The DNA Connection

The DNA Connection. Key Concepts: What forms the genetic code? How does a cell produce proteins? How can mutations affect an organism? Key Terms: Messenger RNA Transfer RNA. The Genetic Code. Main function of genes is to control the production of proteins Genes and DNA: Chromosomes

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The DNA Connection

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  1. The DNA Connection Key Concepts: What forms the genetic code? How does a cell produce proteins? How can mutations affect an organism? Key Terms: Messenger RNA Transfer RNA

  2. The Genetic Code • Main function of genes is to control the production of proteins Genes and DNA: Chromosomes are made of DNA. Genes are sections of a DNA molecule that codes for one specific protein. May contain several hundred to a million or more base pairs (Ex. AGGTCACGAATTTTCCGG)

  3. Order of Bases • The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced. • Proteins are made of amino acids – A group of 3 base pairs codes for a specific amino acid • Ex. CGT = alanine (an amino acid) • The order of the 3 base code units determines the order of the amino acids and makes the different proteins

  4. How Cells Make Proteins(Protein Synthesis) The Role of RNA • Protein synthesis takes place on ribosome in cytoplasm • RNA acts as a messenger to take the DNA’s information in the chromosomes to the ribosomes in the cytoplasm • RNA similar to DNA, yet different in some key ways: • single strand • ribose sugar • Bases – same - adenine, guanine and cytosine • different – uracil instead of thymine

  5. Types of RNA • Messenger RNA – copies code from DNA in the nucleus and carries message to ribosomes in the cytoplasm • Transfer RNA – carries amino acids to ribosome and adds them to the growing protein molecule

  6. Translating the Code First Step: 1. DNA molecule unzips between base pairs 2. DNA directs the production of a strand of messenger RNA 3. To form the RNA strand – RNA bases pair with DNA bases. Guanine with Cytosine, but uracil pairs with adenine instead of Thymine

  7. Translating the Code Second step: 1. Messenger RNA leaves nucleus and attaches to a ribosome in the cytoplasm 2. Messenger RNA provides the code to make the protein molecule 3. The ribosome moves along the messenger RNA strand

  8. Translating the Code Third Step 1. Molecules of transfer RNA attach to messenger RNA 2. Bases of transfer RNA read the message by pairing up 3-letter codes to bases of messenger RNA 3. Molecules of transfer RNA carry specific amino acids that link in a chain 4. Order of amino acids is determined by order of 3-letter code on messenger RNA

  9. Translating the Code Fourth Step 1. Protein molecule grows longer as each transfer RNA adds an amino acid 2. When done the transfer RNA is released into the cytoplasm and can pick up another amino acid 3. Each transfer amino acid picks up the same type of amino acid

  10. Mutations • A mutation is any change in a gene or chromosome • Mutations can cause a cell to produce an incorrect protein during protein synthesis. • As a result of a mutation, the organism’s trait or phenotype, may be different from what it normally would have been • If a mutation is in a body cell, it will not be passed on to the offspring. If it is a sex cell, it can be passed on and can affect the offspring’s phenotype

  11. Substitution Insertion Deletion

  12. Types of Mutations Some mutations happen during DNA Replication: • A single base may be substituted for another • One or more bases may be removed from a section of DNA or new bases inserted Some mutations happen during Meiosis: • Chromosomes don’t separate correctly • Cell can end up with too many or too few chromosomes • Cell could end up with fragments of chromosomes

  13. Effects of Mutations • Mutations introduce change in an organism and so are a source of genetic variety • Some mutations are harmful, some are helpful, and some don’t affect the organism • Whether a mutation is harmful or not depends partly on the environment • A mutation causing an albino animal in the wild would be harmful, but if the animal lived in the zoo, it would not matter

  14. Effects of Mutations • Helpful mutations improve an organism’s chances for survival and reproduction • Ex. Bacteria that have mutations that have given them resistance to antibiotics are more likely to survive and reproduce

  15. Credits • http://www.sciencewithmrmilstid.com/media/chromosomalDNA.png • http://www.medceu.com/images/molecularmachine.jpg • http://www.accessexcellence.org/RC/VL/GG/images/protein_synthesis.gif • http://faculty.irsc.edu/FACULTY/TFischer/bio%201%20files/protein%20synthesis%20overview.jpg • http://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/6632005/EssGen_BaseSubstitutionFig1_MID_0.jpg

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