Chapter 8 Notes/ DNA and RNA I. DNA (deoxyribonucleic acid); Strands that contain the genetic information that is found in our chromosomes. The shape is a double helix.

A. Composition; Nucleotides that are bonded. together A. Composition; Nucleotides that are bonded together. A nucleotide is made of a phosphate group that is bonded to a deoxyribose sugar and a nitrogenous base.

1. Nitrogenous bases; Purines will bond to. pyrimidines 1. Nitrogenous bases; Purines will bond to pyrimidines. They are held together with hydrogen bonds. a. Purines; adenine and guanine b. Pyrimidines; thymine and cytosine

*thymine and adenine always bond together, *cytosine and guanine always bond together.

B. DNA replication;. Replication is. directional,. meaning it has B. DNA replication; Replication is directional, meaning it has to occur in a very specific direction.

1. An enzyme, DNA helicase splits the DNA strand at 1. An enzyme, DNA helicase splits the DNA strand at the hydrogen bonds, separating the base pairs, and unzipping the molecule.

2. Nucleotides that are floating free, are attached to the their base pair by hydrogen bonding. 3. Another enzyme (DNA polymerase) bonds these nucleotides into a chain.

4. When replication is complete, there are 2 identical 4. When replication is complete, there are 2 identical molecules of DNA. Each new molecule is made of a parent strand and a complementary daughter strand.

II. RNA (ribonucleic acid); Single stranded A. Composition; like DNA, RNA is composed of nucleotides. There are three major differences in DNA and RNA. 1. ribose sugar instead of deoxyribose 2. uracil instead of thymine 3. DNA is double stranded; RNA is single stranded.

B. Types; 1. r-RNA; Ribosomal RNA and protein make up the beadlike structures known as ribosomes. 2. m-RNA; Messenger RNA takes instructions from DNA in the nucleus to the ribosomes in the cytoplasm. Instructions are in the form of three nitrogenous bases called a codon. * Codon determines which amino acid will be attached at the ribosome.

3. t-RNA; Transfer RNA carries amino acids 3. t-RNA; Transfer RNA carries amino acids to the ribosome so that they can form a chain. III. Protein Synthesis; Making proteins A. Transcription; Occurs in the nucleus. DNA is split, as if replication is about to occur. A complementary strand of m- RNA codons is formed using the DNA strand as a template.

B. Translation; 1. m-RNA leaves the nucleus and attaches to a ribosome. 2. The start codon (AUG) attracts a complementary anticodon of t-RNA that carries the amino acid methionine. This starts the protein synthesis.

3. A new t-RNA molecule carrying an amino acid 3. A new t-RNA molecule carrying an amino acid attaches to the ribosome and m-RNA strand next to the previous molecule. 4. The amino acids on the t-RNA molecules join by peptide bonds, and the t-RNA molecule is released.

5. A chain of amino acids is formed until a stop 5. A chain of amino acids is formed until a stop codon is reached on the m-RNA strand.

6. The ribosome will release the strand of 6. The ribosome will release the strand of amino acids, at which time they will fold or coil into a very specific shape. The folded/ coiled amino acid has now become a protein.

IV. Mutations; May be caused by errors in replication, IV. Mutations; May be caused by errors in replication, transcription, cell division, or by external factors. Mutations may have negative effects, or beneficial effects. A. Cell types 1. Body cells; mutations that occur in body cells might cause problems for the individual that has the mutation. 2. Reproductive cells; if mutations that occur in reproductive cells the altered gene may become part of the genetic makeup of the offspring.

B. Mutation types; 1. Changes in single base pairs a. Frame shift: A single base is added or deleted from the DNA sequence. When the m-RNA is transcribed the entire strand will be out of position by one base. Example- Crohn’s disease is a frame shift caused by an addition of Cytosine. This changes the position of the stop codon, and keeps a protein from being produced that would normally control intestinal bacteria.

b. Point mutation; A change in a single base pair in DNA. Cystic fibrosis is the result of a base change that prevents a gene from forming properly. Normally this gene would control the movement of water into and out of the cells. Tay-Sachs disease is caused by a change in a single base. This prevents an enzyme (protein) known as hexosaminidase from being produced. Hexosaminidase is used in a chemical reaction breaks down excess lipids in the brain.

2. Chromosomal mutation; Alterations in the structure of chromosomes a. Deletion; part of a chromosome is left out. b. Insertion; part of a chromatid breaks off and attaches to its sister chromatid. This causes a duplication of genes on the same chromosome.

c. Inversion; Part of a chromosome breaks off and reattaches backwards. d. Translocation; Part of one chromosome breaks off and is added to a different chromosome.

Some examples of Chromosomal mutations- Deletions - Duchenne’s muscular dystrophy Insertion- Huntington’s disease Inversion- Angelman’s syndrome- Infants are often born with a small head. Early development is often delayed. Children 2 to 3 years old start to experience seizures. translocation- many types of lymphoma and leukemia, both of which are cancers that may have other causes as well.

V. Causes of mutations; A. Mutagens; Any agent that can cause a change in DNA. 1. Radiation; x-rays, cosmic rays, ultraviolet light, and nuclear radiation 2. Chemical; some causes are dioxins, benzene, asbestos, and formaldehyde. 3. High temperatures B. Spontaneous mutations; random mistakes in base pairing, mitosis, or meiosis.