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DNA Structure and Replication • Why is DNA important in your life? – DNA contains information that is critical to the structure and function of your body’s cells. – When new cells are made in your body, they must contain DNA and there needs to be a full set of DNA transferred accurately to these new cells – The instructions encoded in DNA play a major role in determining how your body operates – A child’s life depends on the accurate transmission of genetic information from his or her parents – DNA is the molecular basis of reproduction. – DNA is required for the building, maintenance, and regulation of all living organisms’ cells. • How are copies of genetic information made? – The process is called replication • In humans, as in all eukaryotes, the genetic material consists of long DNA molecules. – Packaged tightly in chromosomes (DNA molecule and many protein molecules) – One of the middle sized human chromosomes contains about 145 million nucleotides (nitrogen bases) – In each of your cells (except gametes and red blood cells), you have 23 pairs of chromosomes, for a total of 46 chromosomes. • Nucleotides are the building blocks (subunits of DNA) • Nucleic acid is a long chain (polymer), or strand made up of nucleotides • DNA Nucleotides – made up of a nitrogen base, a deoxyribose sugar, and a triphosphate group – will have one of four different nitrogen bases: Adenine (A), Cytosine ©, guanine (G), and thymine (T). • The DNA sequence is the order of the nitrogen bases along one strand of DNA. This sequence conveys information to certain parts of the cell How does this structure allow a DNA molecule to be copied to make another identical molecule? • 1. Pairing between nitrogen bases on opposite strands is always the same. – This bonding pattern is called complementary base pairing. – Adenine, a large base , bonds with thymine, a small base. – Guanine, a large base, bonds with Cytosine, a small base. • 2. Specific Enzymes are required for replication to take place – Begins with enzymes that separate the two DNA strands – Next, enzymes read the sequence of nucleotides on one strand, – Finally, enzymes create a new complementary strand by adding one nucleotide at a time to the new strand (DNA Polymerase). • Remember: A always bonds with T, and G always bonds with C. This means that the sequence of bases in the old strand determines the sequence of bases in the new strand. Each newly added base must complement the base in the old strand. Result: There are two molecules of DNA where previously there had been one. Each molecule contains one old strand and one new complementary strand. DNA molecule served as a pattern for a new copy of the genetic information that it encodes. Gene Mutations deletion, insertion, substitution pgs 582-583 • Mutations are changes in the DNA sequence that affect genetic information. • A. Gene Mutations result from changes in a single gene. 1. Point mutations affect one nucleotide in the DNA sequence. Some substitute one nucleotide for another which generally changes one amino in a protein. 2. Frame shift mutations occur when a point mutation involves the insertion or deletion of a nucleotide(nucleotides). Every amino acid in the protein is effected because the codons are now different. The protein is useless. 12-3 RNA and Protein Synthesis • Genes are coded DNA instructions that control the production of proteins within the cell. • The Structure of RNA – Consists of a long chain of nucleotides – RNA nucleotides contain the sugar ribose in place of deoxyribose and the nitrogen base uracil in place of thymine. • The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules. Types of RNA • In the majority of cells RNA molecules are involved in protein synthesis. • mRNA or messenger RNA serve as messengers from DNA to the rest of the cell. • rRNA or Ribosomal RNA molecules along with several dozen proteins form the ribosomes. • tRNA or Transfer RNA molecules transfer amino acids to the ribosomes as it is specified by coded messages in the mRNA • Transcription Model – Put together a DNA molecule – mRNA is transcribed similarly to the first steps of DNA replication. – How can a single strand of RNA be produced from DNA? – Is it necessary to use all the DNA? – Where does the mRNA go and what happens to the DNA? Transcription • An enzyme RNA polymerase attaches to the DNA at regions of the DNA known as promoters. – Promoters are specific nitrogen base sequences in DNA which signal the binding of RNA polymerase. – Similar DNA nitrogen base sequences serve as signals to stop RNA transcription. • RNA polymerase separates the DNA strands and uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA • Laser Disk on transcription. The Genetic Code • Proteins are made by joining amino acids into long chains called polypeptides or proteins. • The properties of proteins are determined by the order in which different amino acids are joined together to produce polypeptides • The language of mRNA instructions are in the form of codons, three nucleotides that specify a single amino acid that is to be added to the polypeptide chain. • There are 64 possible codons but some amino acids can be specified by more that one codon (Figure 12-17). • Note: AUG (methionine) the start codon and three stop codons. RNA Editing • Introns are intervening sequences of mRNA in the nucleus. • Exons or expressed sequences are spliced back together to form the final mRNA. • Some RNA molecules may be cut and spliced in different ways in different tissues making it possible for a single gene to produce several different forms of RNA. • Introns and exons may play a role in evolution • Using your DNA nucleotides put together a strand of DNA and then using the RNA nucleotides carry out transcription. Show intron splicing and write the nucleotide sequence of the mRNA on paper. Translation • During translation, the cell uses information from messenger RNA to produce proteins. • 1. mRNA must be transcribed from DNA in the nucleus and released into the cytoplasm. • 2. Translation begins when an mRNA molecules in the cytoplasm attaches to a ribosome – A start codon on the mRNA (AUG) attaches to the anticodon UAC on a tRNA which is carrying the amino acid methionine. – As the ribosome (rRNA) continues to move to the next codon of mRNA the anticodons of another tRNA carrying another amino acid bonds with the complimentary codons of mRNA. • 3. • 4. The ribosome forms a peptide (covalent) bond between the first and second amino acids. The ribosome also breaks the bond that had held the first tRNA to its amino acid and releases the tRNA molecule from the mRNA. The ribosome moves to the next codon. The ribosome eventually reaches a stop codon on the mRNA molecule. The polypeptide (protein) is released from the tRNA, the mRNA molecule is released from the ribosome and translation is complete. The roles of RNA and DNA • The DNA remains in the safety of the nucleus • RNA molecules go to the protein-building sites in the cytoplasm- the ribosome. Genes and Proteins • Many proteins are enzymes, which catalyze and regulate chemical reactions . • Genes for certain proteins can regulate the rate and pattern of growth throughout an organism, controlling its size and shape. • Proteins are the keys to almost everything that living cells do. • Quiz tomorrow over section 3 chapter 12