The Structure of DNA

2. The Structure of DNA

3. DNA • DNAis often called the blueprint of life. • In simple terms, DNA contains the instructions for making proteins within the cell.

4. The Shape of the Molecule • DNA is very long. • The basic shape is like a twisted ladder or zipper. • This is called a double helix.

5. The Double Helix Molecule • The DNA double helix has two strands twisted together.

6. O -P O O O C C D = deoxyribo N = Nucleic A = Acid Nucleotide (One section of DNA) One deoxyribose (sugar) together with its phosphate (acid) and base make a nucleotide. O Phosphate C Nitrogen base C C Deoxyribose O

7. One Strand of DNA nucleotide • One strand of DNA is a chain of nucleotides. • One strand of DNA has many millions of nucleotides.

8. Four nitrogenous bases DNA has four different bases: Cytosine C Thymine T Adenine A Guanine G

9. Base Pairs

10. Chromosome DNA double helix Coils Supercoils • DNA is coiled VERY tightly to fit inside of a cell • -nucleus of human cell contains more than • 3 feet of DNA

11. DNA RNA Copying the Code • Occurs in the nucleus before protein synthesis. • 1. DNA is unzipped by enzymes. • 2. mRNA copy of the DNA is made by bases pairing. • 3. After completion, mRNA breaks off—DNA strands • rejoin after a copy is made. • 4. mRNA leaves nucleus and travels to ribosome • for protein synthesis.

12. Two Stranded DNA • Remember, DNA has two strands that fit together something like a zipper. • The rungs are the nitrogenous bases

13. Important: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

14. The earth is 150 billion m or 93 million miles from the sun. DNA by the numbers • Each cell has about 2 m of DNA. • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun more than 400 times. • DNA has a diameter of only 0.000000002 m.

15. Copying the Genetic Code - Protein Synthesis

16. A U G G G C U U A A A G C A G U G C A C G U U • This is a molecule of messenger RNA. • It was made in the nucleus by transcription from a DNA molecule. codon mRNA molecule

17. ribosome A U G G G C U U A A A G C A G U G C A C G U U A ribosome on the rough endoplasmic reticulum attaches to the mRNA molecule.

18. Amino acid tRNA molecule anticodon U A C A U G G G C U U A A A G C A G U G C A C G U U • A transfer RNA molecule arrives. • It brings an amino acid to the first three bases (codon) on the mRNA. • The three unpaired bases (anticodon) on the tRNA link up with the codon.

19. U A C C C G A U G G G C U U A A A G C A G U G C A C G U U • Another tRNA molecule comes into place, bringing a second amino acid. • Its anticodon links up with the second codon on the mRNA.

20. chemical bond C C G U A C A U G G G C U U A A A G C A G U G C A C G U U • A chemical bond forms between the two amino acids.

21. C C G U A C A U G G G C U U A A A G C A G U G C A C G U U • The first tRNA molecule releases its amino acid and moves off into the cytoplasm.

22. C C G A U G G G C U U A A A G C A G U G C A C G U U • The ribosome moves along the mRNA to the next codon.

23. C C G A A U A U G G G C U U A A A G C A G U G C A C G U U • Another tRNA molecule brings the next amino acid into place.

24. C C G C C G A U G G G C U U A A A G C A G U G C A C G U U • A chemical bond joins the second and third amino acids to form a chain of amino acids.

25. G U C A C G A U G G G C U U A A A G C A G U G C A C G U U The process continues. The amino acid chain gets longer. This continues until a termination (stop) codon is reached. The protein is then complete.

26. Nucleus Messenger RNA Messenger RNA is formed in the nucleus. Lysine Phenylalanine tRNA Methionine Ribosome Start codon mRNA Each tRNA anticodon must pair with the proper mRNA codon for protein synthesis to occur.

27. Growing amino acid chain Ribosome tRNA Lysine tRNA mRNA mRNA direction Ribosome • Once pairing occurs, amino acids are attached by • chemical bonds to form a amino acid chain (protein) • that is ready to be used by the cell