DNA Structure: What does DNA look like?

1. DNA Structure: What does DNA look like?

2. Watson and Crick • Watson and Crick studied the work of others to determine the structure of DNA • Figured that it is a “Double Helix”: • Twisted ladder

3. Chromosomes“DNA Packaging” • Chromatin: The substance inside a nucleus. • Chromosomes: Individual strands of DNA wound up in a tight package.

4. What are genes? • Passed from one generation to the next • Have to be exactly copied each time • Contain the information to: • Build cell parts • Determine what something looks like • Found on the chromosomes! (which are made of DNA)

6. DNA’s parts • DNA is made of NUCLEOTIDES • Each nucleotide has: • Phosphate • Sugar • Base containing nitrogen

7. 4 types of bases • There are 4 types of bases (see page 208 and 210) • Adenine • Thymine • Guanine • Cytosine • In the 1950s, Chargaff • discovered that A always • goes with T, and G with C

9. The Genetic Code

10. Were you paying attention? • What is the shape of the DNA molecule? __________________ • Who figured out the shape of this molecule? ______________ and ____________ 3. Sections of DNA that determine how something is built or what something looks like (a trait) are ___________

11. In the nucleus of a cell the DNA is wound up in tight packages called ____________ • What is each nucleotide made up of? ___________, ___________ and a _______________ • Which base goes with Guanine? ___________ with Thymine? ___________ • What do small 3 letter sections of the DNA code for? ________________

12. How does DNA replicate? • Replicate = copy • Watson and Crick also figured out how DNA replicates! • Steps to replicate: • “Double Helix” unwinds • Ladder unzips • New nucleotides come in to make two new strands

13. Steps to replicate:making a copy of the DNA 1. “Double Helix” unwinds and unzips • Enzyme (chemical) called helicase does this

14. Next, the exposed bases on each strand find new nucleotide partners

15. The end result!

16. Proteins: These are what the information in the DNA is for – to make the proteins that make the organism.

17. Protein SynthesisMaking Proteins DNA mRNA ribosome reads the codon (3 bases) tRNA adds proper amino acid

18. Transcription • Transcription is when a strand of mRNA (messenger RNA) is made from a gene (section of DNA code). • The DNA molecule is split down the middle by an enzyme only at that specific gene. • Then new bases come in and line up with the bases only on one side of the unzipped section of DNA.

19. Transcription Cont. • THE DIFFERENCES BETWEEN REPLICATION AND TRANSCRIPTION: • A single stranded mRNA molecule is created during transcription. • Uracil matches up with Adenine instead of Thymine during transcription. The RNA alphabet is AUCG instead of the ATCG of DNA • Instead of the sugar deoxyribose, RNA just has ribos (which is why it is RNA instead of DNA)

20. Protein Synthesis • After Transcription the mRNA strand can take the code outside of the nucleus. • The mRNA codon (piece of mRNA with a code for making proteins) goes to a ribosome. • At the ribosome pieces of tRNA (transfer RNA) bring amino acids to the ribosome and match them up with the code on the codon to make a protein. • Proteins are just a string of amino acids.

21. Quiz • What is ½ of each rung on the DNA ladder called? Nucleotide • What does Adenine pair with in DNA? Thymine • What type of RNA takes the code outside of the nucleus? mRNA • What are genes? Sections of Chromosomes or DNA

22. What does Adenine match up with in RNA? Uracil • What are the steps of protein synthesis? • mRNA is made. • The mRNA stand goes outside the nucleus to a ribosome. • tRNA brings amino acids to piece together to make a protein.

23. After DNA replication what are we left with? Two identical pieces of DNA • What part do enzymes play in DNA replication and transcription? They unzip the DNA (another kind of enzyme also zips it back up again).