DNA & RNA

Objectives 3. Describe the structure of nucleic acids. 3.1 Describe the similarities and differences in the structure of DNA and RNA. 3.2 Describe the processes of replication and transcription.

What is DNA? DNA – Deoxyribonucleic Acid DNA is the molecule that stores and transmits genetic information from parent to offspring. Every cell in every organism on the planet. Every cell has the same DNA which is mostly found in the nucleus of a cell Human DNA consists of 3 billion base pairs in a molecule of human DNA The discovery of DNA and its properties is credited to many scientists. Fredrich Miescher studied the compound found in the nucleus of cells which was discovered to pass on genetic information by Joachim Hammerling Phoebus Levene discovered the three main components of DNA Rosalind Franklin used x-ray crystallography to reveal the helical structure of DNA James Watson and Francis Crick used Franklin’s information to build a model of DNA

DNA’s structure Structure – Double strand molecule that looks like a twisted ladder. There are three parts to each strand: 1. Phosphoric Acid 2. Deoxyribose Sugar Alternate and make up the sides of the ladder 3. Nitrogen Base – makes up the rungs Two categories with 2 types of nitrogen bases each Purines: Adenine and guanine Pyrimidines: Thymine and cytosine Can only pair adenine with thymine and guanine with cytosine. These are called base pairs. The three together make a nucleotide Three nucleotides make a codon

DNA Replication An enzyme called DNA gyrase makes a nick in the double helix and each side separates An enzyme called helicase unwinds a portion of the double stranded DNA, in an area called the replication fork Several small proteins called single strand binding proteins (SSB) temporarily bind to each side and keep them separated An enzyme called DNA polymerase “walks” down the DNA strands and adds new nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing strand A sub unit of the DNA polymerase proofreads the new DNA An enzyme called DNA ligase seal up the fragments into one long continuous strand The new copies automatically wind up again.

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DNA KEY CHAINS

Part 1: Get Your Materials 1. Choose your large beads for the sugar and phosphate molecules that make up the backbone. You will need 26 beads of 2 different colors for a total of 52 beads. Color the key on your DNA Guide. 2. Choose your small beads for the nitrogen bases. You will need 6 beads of 4 different colors for a total of 24 beads. Color the key on your DNA Guide. 3. Get a piece of thick wire from your teacher and bend it in half. 4. Cut a piece of thin wire – 20 inches in length - and bend it in half. 5. Add two SUGAR beads – one on each side – to the THICK wire. 6. Next add two PHOSPHATE beads– one on each side of the wire.

Part 2: Build Your DNA Molecule 7. Place one A bead and one T bead in the middle of the THIN wire. and hold it in place at the top of the phosphate beads. Line up the THICK and THIN wires on each side and hold at the top. 8. Slide one SUGAR bead down one end of the thin wire and thread the thick wire through as you push it towards the bottom of the keychain - both wires are need to be threaded "inside" the large bead. Add another SUGAR bead on the other side in the same way. 9. Slide one PHOSPHATE bead down one end of the thin wire and thread the thick wire through as you push it towards the bottom of the keychain - both wires are need to be threaded "inside" the large bead. Add another PHOSPHATE bead on the other side in the same way. 10. Pull the large beads down towards the bottom of the keychain and pull on the ends of the thin wire to make the small beads fit tightly in place.

11. Hold one of the thin wires near the end and add a G bead and a C bead. Thread the end of the other thin wire back through the G and C beads in the opposite direction make the wires form an X shape. Pull the ends as if you were “tying” a knot. Thread the other end of the wire through the little beads in the opposite direction. Pull on both ends of the thin wire to “tie” it together 12. Add more big beads (SUGARS & PHOSPHATES) to the backbone – TWO on each side. Thread the THIN wire through the large beads as you add the big beads to the THICK wire. 13.Continue building the DNA molecule following the same process. Remember the process… Thread two wires through two big beads on the sides, Cross two wires through two small beads in the middle & tie. Remember … Make sure you keep the bases paired correctly – A with T and G with C. Make sure to keep your wires pulled tight as you add all of the bases. Go slow and try not to get kinks in the THIN wire!

CAUTION: Untwisting and twisting your keychain too many times will make it break! Part 3: Finishing the Double Helix 14. Once you have added all the base pairs, twist the ends of the thin wire together tightly and add a key ring to the other end of the keychain. 15. Twist the ends of the thick wire and the thin wires together all at once! 16. Use the wire cutters (pliers) to cut off the ends leaving it ½ inch long. Use the pliers to “tuck” the ends in between the large beads so it won’t poke you. 17. Twist your DNA strand around a pencil or finger and gently pull on the ends to create the double helix shape.

What is RNA? RNA stands for ribonucleic acid, a nucleic acid present in all living cells. The principle role of RNA is to act as a messenger carrying instructions from DNA for controlling synthesis of proteins Some viruses RNA carries its genetic information rather then the DNA

RNA’s structure Structure: mRNA is a single stranded molecule that looks like half a ladder cut down the middle of the rungs. tRNA is a folded strand with an anticodon along one side. There are three parts to each strand. 1. Phosphoric Acid 2. Ribose Sugar Alternate and make up the side of the ladder 3. Nitrogen Base – makes up the rungs Two categories with 2 types of nitrogen bases each Purines: Adenine and guanine Pyrimidines: Uracil and cytosine Can only pair adenine with uracil and guanine with cytosine. These are called base pairs. The three together make a nucleotide Three nucleotides make a codon/anticodon

Building Proteins Building proteins is much like building a house: The master blueprint is DNA which contains all of the information to build a new protein (house) The working copy of the master blueprint is called messenger RNA (mRNA), which is copied from DNA The construction site is either the cytoplasm in prokaryotic cells (bacteria) or the endoplasmic reticulum (ER) in eukaryotic cells (plants and animals) The building materials are amino acids The construction workers are ribosomes and transfer RNA molecules This is done in two steps – RNA transcription and translation

RNA Transcription This is the copying of the master blueprint (DNA) to the working blueprint (mRNA) The transcription is preformed by an enzyme called RNA polymerase goes through the following process: First the RNA polymerase binds to the DNA strand at a specific sequence of the gene called a promoter Unwinds and unlinks the two strands of DNA Uses one of the DNA strands as a guide or template Matches new nucleotides with their complements on the DNA strand ( G with C, and A with U) Binds these new RNA nucleotides together to form a complementary copy of the DNA strands (mRNA) Stops when it encounters a termination sequence of bases (stop codon)

Translation Translation is where the construction workers take the working blueprint (mRNA) and use its instructions to build the house (protein) mRNA strand moves out of the nucleus into the cytoplasm and attaches to a ribosome tRNA anticodons (series of 3 nucleotides) match or pair with the first codon on the mRNA Another tRNA anticodon matches or pairs with the second codon on the mRNA The amino acids on the other side of the tRNA bond First tRNA leaves to go pick up another amino acid Process continues down the length of the mRNA strand

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