Watson and Crick Watson and Crick studied the
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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
Chromosomes “DNA Packaging” • Chromatin: The substance inside a nucleus. • Chromosomes: Individual strands of DNA wound up in a tight package.
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)
DNA’s parts • DNA is made of NUCLEOTIDES • Each nucleotide has: – Phosphate – Sugar – Base containing nitrogen
4 types of bases • There are 4 types of bases (see page 208 and 210) – – Adenine Thymine Guanine Cytosine • In the 1950 s, Chargaff • discovered that A always • goes with T, and G with C
The Genetic Code
Were you paying attention? 1. What is the shape of the DNA molecule? _________ 2. 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 ______
4. In the nucleus of a cell the DNA is wound up in tight packages called ______ 5. What is each nucleotide made up of? ______, ______ and a ________ 6. Which base goes with Guanine? ______ with Thymine? ______ 7. What do small 3 letter sections of the DNA code for? ________
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
Steps to replicate: making a copy of the DNA 1. “Double Helix” unwinds and unzips – Enzyme (chemical) called helicase does this
• Next, the exposed bases on each strand find new nucleotide partners
The end result!
Proteins: These are what the information in the DNA is for – to make the proteins that make the organism.
Protein Synthesis Making Proteins • DNA m. RNA ribosome reads the codon (3 bases) t. RNA adds proper amino acid
Transcription • Transcription is when a strand of m. RNA (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.
Transcription Cont. • THE DIFFERENCES BETWEEN REPLICATION AND TRANSCRIPTION: – A single stranded m. RNA 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)
Protein Synthesis • After Transcription the m. RNA strand can take the code outside of the nucleus. • The m. RNA codon (piece of m. RNA with a code for making proteins) goes to a ribosome. • At the ribosome pieces of t. RNA (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.
Quiz 1. What is ½ of each rung on the DNA ladder called? Nucleotide 2. What does Adenine pair with in DNA? Thymine 3. What type of RNA takes the code outside of the nucleus? m. RNA 3. What are genes? Sections of Chromosomes or DNA
4. What does Adenine match up with in RNA? Uracil 5. What are the steps of protein synthesis? 1. m. RNA is made. 2. The m. RNA stand goes outside the nucleus to a ribosome. 3. t. RNA brings amino acids to piece together to make a protein.
6. After DNA replication what are we left with? Two identical pieces of DNA 7. What part do enzymes play in DNA replication and transcription? They unzip the DNA (another kind of enzyme also zips it back up again).
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