Chapter 12

 DNA is a molecule often called the blueprint of life.  Its structure is a double helix (twisted ladder).  Every cell has DNA.  It is a nucleic acid.  Its monomer is a nucleotide. Play video

Each nucleotide is made up of three parts: 1. 5-carbon sugar 2. phosphate group 3. nitrogen base  The sugar and the phosphates make the backbone of the DNA molecule; the bases are the rungs of the DNA ladder.

Adenine Thymine Guanine Cytosine Chargaff’s Rule says adenine bonds to thymine and guanine bonds to cytosine. Purines have 2 rings in the structure and the pyrimidines have 1. In the DNA molecule, a purine bonds with a pyrimidine. They are held together by weak H bonds.

 Avery, Griffith, etc. determined that DNA stores and transmits genetic info from one generation to the next.  Linus Pauling- determined that proteins can take on a helix form.  Chargaff- determined A-T and C-G  Rosalind Franklin- develops crystallography  Watson & Crick- determines double helix shape

 Before a cell divides, it replicates (copies) its DNA; ensures new cells will get the same DNA.  During DNA replication, the DNA molecule separates into 2 strands then produces 2 new complementary strands following the rules of base pairing.  Each strand of the double helix of DNA serves as a template or model for the new strand.

Play video

 Carried out by a series of enzymes.  The enzymes “unzip” the molecule of DNA (breaks the H bonds between the base pairs).  The 2 strands of the DNA molecule unwind, each side serving as a template for the attachment of complementary bases.  The DNA polymerase enzyme zips up both of the new strands to their complementary sides.

 DNA is a molecule.  The DNA molecule contains a set of instructions for the synthesis (production) of proteins- genes.  The first step in decoding the genetic message is to copy part of the DNA nucleotide sequence from DNA to RNA.  These RNA molecules contain coded info for making proteins.

 RNA- long chain of nucleotides.  Made of 5-carbon sugar, phosphate group, and a nitrogen base.  3 main differences between DNA and RNA: 1. sugar is ribose not deoxyribose 2. it’s single-stranded 3. contains uracil, not thymine

 Three main types: 1. mRNA (messenger) 2. rRNA (ribosomal) 3. tRNA (transfer)

 DNA cannot leave the nucleus, but all of the materials to make new protein are located outside the nucleus.  Transcription occurs in the nucleus. 1. RNA polymerase enzyme unzips the DNA in a certain region where the instructions for making a protein are located (a gene). 2. One side of the DNA will be used as a template for mRNA to copy. 3. mRNA nucleotides will float in and match up with the DNA strand. Play Video

 Proteins are made by joining amino acids into long chains called polypeptides.  Each polypeptide contains a combination of any or all of the 20 different amino acids.  The properties of the proteins made are determined by the order in which the different amino acids are joined together.  The genetic code is read in three letters at a time = codon.  A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide.

4 bases = 64 different possible 3-base codons. Some amino acids can be specified by more than one codon. There are also STOP and START codons that tell the mRNA where to begin and where to end its reading of the DNA for each specific gene. Examples: GCU = Alanine AAA = Lysine CCU = Proline

 During translation, which happens outside the nucleus, the cell uses the info collected by mRNA from the DNA to produce proteins.  After leaving the nucleus, mRNA goes out into the cytoplasm and attaches to a ribosome.  As each codon of mRNA moves through the ribosome, the matching amino acid is brought into the ribosome with tRNA. Each tRNA carries only one kind of amino acid, which is in the form of the “anticodon,” or the opposite of the mRNA.  The ribosome joins the amino acids together and breaks the bond between the tRNA and the amino acid.  As the amino acids bond together, the polypeptide chain forms. The long chains bond together and make the protein. Play video

nucleus CELL DNA mRNA tRNA anticodon Amino acid ribosome rRNA in the ribosome joins mRNA and tRNA together; the goal is to bond the amino acids together to make the protein. TRANSCRIPTIONTRANSLATION & PROTEIN SYNTHESIS

 Mistakes in the genetic material are called mutations.  Although some mutations can cause genetic disorders, most mutations are not harmful.  Mutations are essential to the survival of a species as changes can contribute the organisms ability to adapt to the environment in different ways.  We need mutations!

 Gene Mutations: substitutions deletions insertions  Chromosomal Mutations deletions duplications inversions translocations

 Substitutions: the wrong nucleotide gets put in the sequence; usually affects no more than a single amino acid.  Insertions: an extra nucleotide get put into the sequence.  Deletions: a nucleotide gets left out of the sequence.  Insertions/deletions result in a “frameshift” mutation- the codon sequence that is read is changed from the point of the mutation to the end. This results in the wrong amino acids and therefore the wrong proteins getting produced.  The results of insertions and deletions are more dramatic in their effect. ATTCGGATCCC Play Video

 Deletions: loss of all or part of a chromosome.  Duplications: produces extra copies of parts of a chromosome.  Inversions: Reverse the direction of parts of a chromosome.  Translocations: occur when one part of a chromosome breaks off and attaches to another. Play Videos

 Agriculture has been altering the genetics of plants and animals for thousands of years through selective breeding.  Farmers will choose to mate animals/plants that have desirable traits that are the most profitable.  The result is hybridization (also called hybrid vigor/heterosis); offspring that is genetically superior to the parents.  Through the years we have developed breeds that are known for specific characteristics.  This has been achieved through inbreeding and line breeding.  Crossbreeding (breeding different breeds) often gives us the most heterosis, as this allows for more diversity in the gene pool.

 DNA is extracted from cells by opening the cells and removing organelles.  Restriction enzymes are added to DNA, and these enzymes will cut the DNA in specific areas.  DNA can be separated through gel electrophoresis. Play Video

 After the DNA is in a manageable form, the DNA sequence can be read and changed.

 The sequence can be read.  The DNA sequences can be cut and pasted (spliced) = Recombinant DNA  DNA can be copied -PCR (polymerase chain reaction) is a method used to copy the DNA -makes multiple copies of genes

 During transformation, a cell takes in DNA from an outside source. This external DNA becomes a component of the cell’s DNA.

 Plasmids are circular DNA bacteria  A piece is cut out and new is added  The plasmid is put back into the bacteria and since bacteria replicates fast, the DNA gets replicated as well.

In plant cells: 1.Recombinant DNA from the bacteria is exposed to plant cells. 2.The bacteria injects itself into plant cells. 3.Then that DNA gets into the chromosomes. 4.A new plant grows that has the new DNA as part of its genetic code. In animal cells: 1.DNA is directly injected into the nucleus of animal cell. 2.This adds the DNA to the chromosomes of the animal. 3.Genes are directly replaced in the animal cells.

 Genetic engineering makes it possible to transfer DNA sequences, including whole genes, from one organism to another.  Transgenic organisms- organisms that contain genes from another organism.  Genetic engineering has spurred the growth of biotechnology, which is a new industry that is changing the way we interact with the living world.

 Both transgenic animals and plants are used to improve the food supply, farming, and the health of people. Ex: Round-up Ready Corn Cloning: making copies of actual organisms; will benefit both agriculture and the medical industry.