Introduction to DNA Structure

Vocabulary DNA (Deoxyribonucleic Acid) – A nucleic acid that contains a deoxyribose sugar. Is a long molecule that is made up of units called nucleotides Nucleotides – Monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base. The THREE basic units of DNA

DNA DNA contains the genetic code of an organism, with traits expressed through proteins made by cells DNA can be found in the nucleus and mitochondria.

2 rings 1 ring

Double Helix DNA resembles a twisted ladder, with sugars and phosphates on sides, and nitrogen bases as rungs

5’ has a free Phosphate 3’ end has a free Sugar

Nitrogen Bases The nitrogen bases of DNA from complementary base pairs with adenine pairing with thymine, and cytosine pairing with guanine The nitrogen bases spell out a coded message.

Quiz: DNA 4. What does a double helix look like? 5. What does DNA stand for? Degraded Nucleic Acid Deoxyribose Nitrogenous Acid Deoxyribonucleic acid 6. What was Rosaline Franklin known for? Finding out the structure of DNA Taking pictures of DNA with a x-ray Discovering the existence of DNA 7. What are Watson and Crick known for? Name the three parts of a nucleotide. Find the complimentary strand for the following DNA strand: ATTTCGTGCAGA ?????????????? 3. Do purines of pyrimidines have two rings?

Introductions to DNA Replication

Replication DNA replication happens in the Synthesis phase of the cell cycle Happens BEFORE mitosis Replication

DNA Replication When DNA is replicated or copied, it results in two IDENTICAL strands. Replication happens in three simple steps: The two original strands of DNA are separated by helicase DNA Polymerase adds complimentary nucleotides to each strand. Two DNA molecules form that are identical to the original.

Step 1: DNA Separates The DNA helix unwinds with the help of enzymes called DNA helicases. Nucleotide bases separate at an area called the replication fork.

Step 2: DNA Polymerase adds nucleotides New Strands forming At the replication fork, DNA Polymerase move along each DNA strand and add complimentary nucleotides. Adenine with thymine Cytosine with Guanine Two new strands begin to form.

Step 3: Two DNA Molecules form DNA polymerase continues adding nucleotides until all the DNA has been copied. DNA polymerase detaches and two new identical DNA molecules are left.

DNA Polymerases other role… Because errors can occur in DNA replication, DNA polymerase also has a role in fixing the new DNA strands. DNA polymerase fix mismatched nucleotides

DNA Replication in Eukaryotes Eukaryotes have one long DNA strand for each chromosome semi conservative model (new double helix has 1 parent strand + 1 new daughter strand) replication fork Parent strand Daughter strand

DNA REPLICATION in Prokaryotes Prokaryotes have one circular DNA replication fork

PASTA DNA LAB Follow Procedure I to make a model of DNA. Follow the directions EXACTLY the same EXCEPT instead of tying the noodles on string, GLUE THEM on to notebook paper. In Procedure two, make a model of DNA “unzipping” or separating on another piece of paper. The show 2 identical DNA strands that were made. They should look EXACTLY like the first DNA strand.

Pasta DNA Wheels- Sugar Noodle-Phosphate Paper clip- Bases

From DNA to Protein Transcription

Transcription & Translation Making Proteins… …involves a series of steps. Transcription & Translation mRNA is made in transcription. Protein is made in translation.

RNA RNA differs from DNA in three ways: Single stranded Has uracil instead of thymine nitrogen bases Contains ribose sugar instead of deoxyribose in its backbone.

Transcription in 3 easy steps Step 1 Transcription starts when RNA polymerase binds to a specific DNA sequence that tells cell to START transcription. Remember, A,T,C, and G “spell” out messages. START

Next, the RNA polymerase unwinds and separates the DNA. Step 2 Next, the RNA polymerase unwinds and separates the DNA.

Step 3 Last, RNA polymerase adds complimentary RNA nucleotides to the DNA strand. The polymerase adds: cytosine to guanine and guanine to cytosine adenine to thymine BUT uracil to adenine.

Why make Messenger RNA? Messenger RNA When a cell needs a protein, mRNA is created. mRNA carries instructions for building a protein and delivers it out side of the nucleus. Messenger RNA

ACTIVITY! ^_^ Your objective is to take the following DNA strands and transcribe them into RNA. Materials: Pipe cleaners and colored beads. Green: Adenine; Yellow: Guanine; Red: Thymine; Blue: Cytosine; White: Uracil. Procedure: Transcribe the SECOND STRAND of each of the following DNA sequences. Make your DNA and RNA using the pipe cleaner given and the colored beads. Show me your RNA strand. If it is correct then turn into me your RNA sequences written down on paper. Return the beads and pipe cleaners DNA sequence one Strand one: ATGCTGAAG Strand two: TACGACTTC DNA sequence three Strand one: TATCGTAGT Strand two: ATAGCATCA DNA sequence two Strand one: CGCTTAAAC Strand two: GCGAATTTG DNA sequence four Strand one: ATGCAATAG Strand two: TACGTTATC

From DNA to Protein Translation

Vocabulary Amino acids: make PROTEINS Ribosomal RNA are part of the structure of ribosomes. They hold the mRNA and two tRNAs in place during translation tRNA molecules are single strands of RNA that carry a specific amino acid with them. Amino acids: make PROTEINS

Vocabulary Codons: instructions written as three nucleotide sequences. Each codon corresponds to an amino acid or start or stop signal. Ex: GUA  Valine UUC Phenylalanine

To build a protein… …we must move on to our next step that moves our RNA out of the nucleus and into the cytoplasm.

Translation mRNA moves into the cytoplasm where it binds with a rRNA, and a tRNA carrying an amino acid. The codon is ready to receive the next tRNA and its amino acid

Peptide bond Once mRNA is holding two tRNAs, each carrying specific amino acids, enzymes form peptide bonds between the two amino acids. The tRNA in the first site prepares to detach, leaving behind the amino acid.

Another tRNA fills in the empty site. This process repeats until a STOP codon is reached (UAG, UAA, or UGA). The amino acid chain is release, forming into a new protein.

Amino acids form protein. Transcription Amino acids form protein.