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Chapter 12.1 – DNA Structure

Chapter 12.1 – DNA Structure I. DNA ( D eoxyribo n ucleic A cid) – a 2-chain polymer of nucleotides that we inherit A. Nucleotides have 3 parts: 1. Sugar – deoxyribose 2. Phosphate group – 1 P with 4 O’s 3. Nitrogen base (4 kinds). Nitrogenous base. Phosphate group.

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Chapter 12.1 – DNA Structure

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  1. Chapter 12.1 – DNA Structure I. DNA (Deoxyribonucleic Acid) – a 2-chain polymer of nucleotidesthat we inherit A. Nucleotides have 3 parts: 1. Sugar – deoxyribose 2. Phosphate group – 1 P with 4 O’s 3. Nitrogen base (4 kinds) Nitrogenous base Phosphate group Sugar (deoxyribose)

  2. Cytosine (C) Adenine (A) Guanine (G) Thymine (T) B. Nitrogen Bases: C. Arrangement of Nucleotides: 1. Phosphate groups and Deoxyribose sugar molecules form the backbone of the DNA “ladder,” by alternating 2. Nitrogenous bases face inward, like the rungs of a ladder

  3. II. The Structure of DNA A. Nitrogen bases hold the “rungs” of the DNA ladder together, forming the shape called a double helix 1. A & T pair, with 2 hydrogen bonds 2. G & C pair, using 3 hydrogen bonds  Thus, the 2 strands of DNA are complimentary B. Each strand has a 5’ and 3’ end, but they run in opposite directions (antiparallel)

  4. C. Nucleotide sequences are important! 1. All living organisms have deoxyribose sugars, phosphate groups, and nitrogen bases like A, G, C, and T in their DNA  It is the sequence of the bases that make us all different from each other 2. Sequences can be used to determine:  if 2 organisms that look alike from different continents are related  if 2 people are related  body identification at crime scenes DNA rap

  5. III. RNA (Ribonucleic Acid – 3 types) – a 1-chain polymer of nucleotides made from 2-chained DNA that helps to make proteins A. Nucleotides have 3 parts: 1. Sugar – ribose → 2. Phosphate group – 1 P with 4 O’s 3. Nitrogen base (4 kinds: A, C, G, U) Uracil Adenine

  6. Chapter 12.3 – DNA, RNA, & Protein I. The Central Dogma: DNA codes for RNA, RNA guides the synthesis of proteins A. Types of RNA 1. Messenger RNA (mRNA) – long strand of RNA nucleotides that are formed complimentary to one strand of DNA 2. Ribosomal RNA (rRNA) – associates with proteins to form ribosomes in the cytoplasm

  7. 3. Transfer RNA (tRNA) – smaller segments of RNA that transfer amino acids to the ribosome

  8. B. Transcription – synthesis of mRNA from DNA During this process, the DNA code is transferred to mRNA in the nucleus. The mRNA can then take the code into the cytoplasm for protein synthesis.

  9. 1. Double-stranded DNA is “unzipped” in the nucleus 2. An enzyme, RNA polymerase, binds to a specific section of DNA where mRNA will be made 3. RNA polymerase starts making mRNA from one strand of DNA, known as the template strand • DNA is read in the 3’ to 5’ direction • The mRNA strand is complimentary to the DNA template strand, and is made 5’ to 3’ • Uracil (U) is used instead of Thymine (T) 4. Eventually, mRNA is released. It will move from the nucleus, through nuclear pores, to the cytoplasm

  10. III. Translation – codons form a “3 base” code to translate mRNA into a protein A. mRNA arrives in the cytoplasm, at a ribosome

  11. B. tRNA molecules act as interpreters of the mRNA codon sequence • tRNA forms a cloverleaf shape and contains an anti-codon

  12. C. mRNA begins translation with an AUG “start” codon. tRNA brings the amino acid Methionine to begin the protein D. Translation continues by adding and linking amino acids in the sequence determined by the mRNA, until a “stop” codon is reached (UAA, UAG, or UGA)

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