Decoding DNA: Structure, Replication, and Protein Synthesis

1. DNA / Protein Synthesis

2. I. DNA Structure • Made up of 1000s of repeating units (nucleotides) • Each nucleotide has 3 parts: phosphate, sugar (deoxyribose) and a nitrogenous base

3. I. DNA Structure • DNA Nucleotides can have 4 different bases • Adenine • Cytosine • Guanine • Thymine

4. I. DNA Structure • Watson – Crick Model of DNA • 2 connected chains of nucleotides • Sides = phosphates and sugars held together by strong ionic bonds • Rungs = N. base pairs held together by weak hydrogen bonds • 2 chains are twisted in a spiral (double helix)

5. I. DNA Structure • The 4 bases only bind in a certain way • Adenine – Thymine (A – T) • Cytosine – Guanine (C – G) • The 2 strands are complimentary (A on one and T on the other)

6. I. DNA Structure

7. II. DNA Replication • DNA can copy itself with the help of enzymes • Happens during mitosis and meiosis in the nucleus of the cell • Process • DNA unwinds • 2 strands separate between the bases • Free nucleotides in cytoplasm enter nucleus and bind with complimentary bases on DNA strand • Makes 2 identical DNA molecules DNA replication

9. III. Gene Control of Cell Activities • Genes for a trait (phenotypes) are determined by the DNA nucleotide sequence • Genes control protein and enzyme synthesis and these control cell activities

10. III. Gene Control of Cell Activities • Example • Dominant gene for production of lactase (digests the milk sugar, lactose). • People who are recessive cannot make lactase, so they cannot digest lactose • The sequence of DNA nucleotides determines the sequence of amino acids in enzymes and other proteins • There is over 1 meter of DNA in EACH human cell

11. IV. RNA • Made of nucleotides but have 3 main differences • Sugar is ribose, not deoxyribose • Uracil (U) is substituted for Thymine (T) • Single stranded, not double stranded

12. IV. RNA • Messenger RNA (mRNA) • Made in nucleus and moves to ribosome • Formation (Transcription) • DNA unwinds and unzips • RNA nucleotides bind w/ complementary bases on DNA strand • DNA serves as a template (pattern) for the synthesis of RNA Transcription

13. IV. RNA • Sequence of nucleotides in mRNA contains the genetic code which determines the sequence of aa in proteins • EACH aa is represented by a SPECIFIC sequence of 3 nucleotides (codon)

14. IV. RNA • Transfer RNA (tRNA) • Found in cytoplasm • 20 different kinds of aa in cells, w/ at least one tRNA for each • Each tRNA has a 3 nucleotide sequence (anticodon) that is complimentary to the codon on the mRNA • tRNA carry the specific aa to ribosome and temporarily bind to mRNA during protein synthesis

15. V. Protein Synthesis • mRNA is made in nucleus from a section of DNA (gene for protein) (transcription) • mRNA moves to cytoplasm and binds to ribosome • aa are carried to mRNA/ribosome by tRNA • Anticodons on tRNA bind w/ codons on mRNA (bringing the aa with it) • aas bind together (forming PEPTIDE bonds)

16. V. Protein Synthesis • Once the aa binds, the tRNA breaks away to find a new aa • This continues (forming an aa chain that will eventually form a protein) until a STOP codon is reached. The STOP codon tells the ribosome to break away and release the protein Translation

17. Gene Mutations • ANY change in the sequence of nucleotides in DNA • MUST happen in sex cells in order to be passed on to offspring • Types • Addition (AAGCCA  AAGGCCA) • Deletion (AAGCCA  AGCCA) • Substitution (AAGCCA  AGGCCA) • Inversion (AAGCCA  ACGACA)

18. VII. Cloning • Make identical offspring from parent • Inject nucleus of body cell (2n) into an egg which had the nucleus removed • “Fertilized” egg is implanted into surrogate mother and new organism forms • Has been achieved in plants, frogs, mice, sheep, goats, cows and monkeys

20. VIII. Genetic Engineering • Transfer of genetic material from one organism to another • Process • Restriction enzyme is used to cut out a piece of DNA that has a desired gene from a donor organism’s DNA

21. VIII. Genetic Engineering • The piece of DNA is placed into a circular piece of bacterial DNA (plasmid) that was cut with the same restriction enzyme • The “recombined” DNA is placed into the new organism. The protein from the trait can now be made.

23. VIII. Genetic Engineering • Used to make human growth hormone and insulin • Genes were placed into bacteria. Now all of the offspring have the gene (mitosis) and they make the chemical • Get large amounts @ low cost • Plants can now contain genes to make chemicals that kill insects feeding on the plants

24. IX. Gel Electrophoresis • Used to compare DNA from different organism • Procedure • DNA is cut using restriction enzymes. This cuts at specific points making different sized fragments of DNA • Fragments are placed into wells on one side of gel

25. IX. Gel Electrophoresis • Electricity is run through the gel causing the (-) charged DNA to the (+) end (away from the wells) • Smaller fragments travel faster through gel, making them further away • Gel is then stained to show the “bar” pattern for the DNA sample Gel Electrophoresis

27. IX. Gel Electrophoresis • Used for: • Relating different DNA samples to each other • Determining the father of a child • Proving hospital mistakes (wrong child) • Proving guilt / innocence in a crime • Determining the genes responsible for some genetic diseases