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DNA: The Molecule of Heredity

Explore the structure, function, and replication of DNA, the molecule that contains our genetic information and serves as the blueprint of life. Discover the key components of DNA, the base pairing rules, and how RNA is involved in protein synthesis. Learn how DNA sequencing can be used to compare and analyze genetic information.

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DNA: The Molecule of Heredity

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  1. DNA The Molecule of Heredity Chapter 11.1

  2. DNA - Deoxyribonucleic Acid • Strands of repeating molecules that make up our chromatin and chromosomes • Contains genetic information (genes)

  3. DNA is called the “Blueprint of Life” Why? • DNA tells cells which proteins to make • The proteins then cause our individual characteristics

  4. The Structure of DNA - DNA is in a Double-helix shape • It is double-stranded and wound up like a twisted ladder • 2 strands attached to each other Discovery credited to James Watson and Francis Crick. Watson and Crick with DNA Model, 1953.

  5. DNA Structure continued • It is a very long molecule made up of repeating subunits called nucleotides

  6. 3 Parts of a Nucleotide 1) Phosphate group 2) Simple sugar -DNA has a Deoxyribose sugar -RNA has a Ribose sugar 3) Nitrogenous base -A, T, C, or G

  7. 4 Nitrogenous Bases in DNA • Adenine • Thymine • Guanine • Cytosine Pyrimidines Purines

  8. Special BasePairing Rules *Adenine pairs with Thymine: A-T T-A *Cytosine pairs with Guanine: C-G G-C

  9. The DNA Strand * Bases held together by hydrogen bonds. * Sugar and phosphate are considered backbone

  10. What are the proper pairings for the base strands shown: 1. A T C G T T T A C G C G T 2. T G C T A T A C C G T A A 3. C T A G C G A T G T C G T

  11. Answers • A T C G T T T A C G C G T T A G C A A A T G C G C A 2. T G C T A T A C C G T A A A C G A T A T G G C A T T 3. C T A G C G A T G T C G T G A T C G C T A C A G C A New Strand = Complementary strand Old Strand = Template Strand

  12. RNA - ribonucleic acid • Molecules that “read” the DNA and make proteins using the information in DNA • RNA are the worker molecules.

  13. 1.RNA is single stranded 2. RNA has the sugar ribose (not deoxyribose) 3. RNA has the nitrogen base uracil instead of thymine. 3 ways RNA is different from DNA

  14. RNA nitrogenous bases • RNA bases • Adenine • Uracil (in DNA this is thymine) • Cytosine • Guanine • Rules: • Same pairing as DNA except a U goes where a T was in DNA • A pairs with U (A-U) and C pairs with G (C-G)

  15. IF the DNA strand is A T C G G C A T Then the RNA complement strand is U A G C C G U A IF the DNA is A T A C G T A C G Then the RNA complement strand is U A U G C A U G C RNA base pairing examples

  16. Practice Time!

  17. Three types of RNA • mRNA = Messenger RNA • Carries information from nucleus to cytoplasm (ribosomes in cytoplasm) • rRNA = Ribosomal RNA • Make ribosomes which are where amino acids are assembled into proteins • tRNA = Transfer RNA • Carries amino acids to the ribosome to be assembled into proteins

  18. DNA Replication - 2 from 1 1. Why do cells need to replicate their DNA before dividing? 2. During what phase of the cell cycle does replication occur?

  19. 4 Steps to DNA Replication Step 1: Enzyme (helicase) initiates (starts) replication by unzipping the DNA

  20. Step 2: Another enzyme (DNA polymerase) attaches new nucleotides following base pairing rules

  21. Mistake causes a bulge DNA poly. finds & piece is cut out DNA poly. repairs with correct base DNA poly. continues down strand Step 3: Error Checking As it moves down the strand, the enzyme DNA polymerase: • Checks for errors 2. Then fixes them This process is called proofreading

  22. Step 4: Original DNA Original DNA New DNA 2 Identical copies -1 old strand (template) -1 new strand (complementary) Enzymes twist the new strands (creating the double helix)

  23. Steps of DNA Replication • Enzyme (helicase) unzips the DNA • Enzyme (DNA polymerase) attaches new nucleotides according to base pairing rules • DNA polymerase checks for errors and fixes them. • End up with two identical daughter DNA strands that enzymes retwist.

  24. STOPPING POINT

  25. DNA Sequencing Each organisms has a unique sequence of DNA The closer two individuals are related, the more alike their sequences are. What are some ways that we use this knowledge?

  26. The Central Dogma

  27. DNA Structure and Base Pairs (Adenine) A = T (Thymine) ( Cystosine) C = G (Guanine)

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