DNA and RNA Ch 12 DNA Deoxyribonucleic Acid

DNA and RNA Ch 12

DNA • Deoxyribonucleic Acid • Macromolecule responsible for the transmission of genetic material between generations • What is the molecular structure? ? ?

DNA Structure Must Have 3 Characteristics 1. Composed of Genes 2. Genes have to carry information from generation to generation 3. DNA must be able to copy itself easily

Finding the Structure of DNA • 1928 = Griffith – Studied disease causing bacteria – Found that bacteria pass on the ability to cause disease to their offspring (inheritance) • 1944 = Avery – repeated Griffith’s experiment – discovered that DNA is what stores and transmits genetic information

Finding the Structure of DNA • 1952 = Rosalind Franklin – used X-Rays to discover that DNA is a double helix w/ nitrogen bases in the center • 1952 = Chargaff – discovered that the nucleotides that make up DNA are in equal proportions – A = T and G = C

Finding the Structure of DNA • 1953 = Watson and Crick – credited with discovering the structure of DNA – used Franklin’s and Chargaff’s findings to build a model on their own – Published their results 1 st = Nobel Prize

The Structure of DNA 1. Made up of Nucleotides 2. Shaped like a double helix (twisted ladder) 3. Hydrogen bonds hold it together 4. The rungs of the ladder are paired nitrogen bases

Nucleotides • Bonded together to form DNA • 3 Parts of a Nucleotide – 1. 5 -Carbon Deoxyribose Sugar – 2. Phosphate Group – 3. Nitrogen Bases (adenine, guanine, thymine, cytosine)

Nitrogen Bases • Purines = 2 carbon rings (adenine and guanine) • Pyrimidines = 1 carbon ring (cytosine and thymine) • Adenine always bonds to Thymine (A - T) • Guanine always binds to Cytosine (G - C)

Prokaryotic vs. Eukaryotic DNA • Prokaryotic DNA – plasmid shaped (circular chromosome) – located in the cytoplasm • Eukaryotic DNA – long strands of DNA and proteins compacted together – 1000 x’s longer than prokaryotic DNA – located in the nucleus

DNA Replication • Nitrogen base pairing allows the DNA to make a copy of itself • Strands can both be used to make identical copies of DNA = complimentary strands

DNA Replication Process 1. An enzyme unzips the DNA (breaks the hydrogen bonds between base pairs) 2. Another enzyme attaches new base pairs to each strand (matches A to T and G to C) 3. Another enzyme proofreads the DNA and checks for any mistakes in base pairing 4. The last enzyme seals all the new hydrogen bonds between the new base pairs Result = 2 Complimentary Strands

Replication Animation • http: //www. youtube. co m/watch? v=zd. Dki. Rw 1 P d. U

Sample Replication Problems • Original Strand = A T C G A T C • Complimentary = T A G C T A G • Org. Strand = TCGACTA • Comp. Strand = A G C T G A T

RNA and Protein Synthesis Chapter 12 -3

Central Dogma • DNA carries the genetic code and transcribes an RNA copy of the code • The RNA copy is translated by ribosomes to make protein 1 DNA 2 RNA Transcription Protein Translation

Genes • Coded DNA instructions for making a protein (recipe) • A specific sequence of DNA • DNA to RNA to Protein

Why do we need RNA if DNA holds all the genetics? • DNA must be protected… • If DNA is damaged – then the coding sequence is changed – then a mutation occurs – Then…

What is RNA? • Ribonucleic Acid – Sugar = Ribose not deoxyribose – Single stranded instead of double stranded – Uracil (U) instead of Thymine (T) – Made from a strand of DNA

3 Types of RNA 1. Messenger RNA (m. RNA) = carry the instructions for making amino acids into proteins 2. Ribosomal RNA (r. RNA) = make up ribosomes 3. Transfer RNA (t. RNA) = transfers the amino acids to the ribosomes to be made into proteins

Making a Protein • Step #1 = Make a RNA strand from a sequence of DNA (transcription) • Step #2 = Use the RNA strand to make a specific protein (translation)

Transcription • The process by which a piece of DNA is copied to make a complimentary RNA strand • Requires several enzymes • Occurs within the nucleus

Transcription Process 1. An enzyme unzips a portion of the DNA 2. An enzyme joins base pairs to one of the strands (U instead of T) to make m. RNA 3. The new strand of m. RNA is detached 4. An enzyme joins the DNA back together 5. Junk m. RNA (introns) are deleted and the m. RNA that will be expressed (exons) stays link

Protein Synthesis/Translation • The m. RNA is used to assemble amino acids into proteins • 20 possible amino acid = make billions of different combinations • Occurs on the ribosome

Translation Process 1. m. RNA attaches to the ribosome 2. Every 3 letters in a m. RNA is a codon and specifies a specific amino acid 3. The t. RNA’s carry the amino acids to the m. RNA 4. Each t. RNA has an anticodon that bonds to a specific codon sequence on the m. RNA 5. The amino acids are bonded together to form a polypeptide (protein) link/m_biology/animation/gene_a 3. html

Genes and Proteins • Genes = instructions for making proteins • Proteins = make up enzymes = control all processes in the cell/body *** Take Home Message **** PROTEINS ARE IMPORTANT!!!!! link. AP 1302

How to do the homework problems: Given = DNA Strand 1. Make a complimentary m. RNA strand from the DNA strand. U instead of T 2. Divide the m. RNA into codons (3’s) 3. Find the corresponding amino acid using Fig. 12 -17 on pg. 303. (First Letter Middle) 4. Always start at AUG and end at UGA, UAA, or UAG

Example Problem: DNA = T A C T T T A CGACT m. RNA = A U G A A A U GCUGA Codons = AUG – AAA – UGC – UGA Amino Acids = Start – Lysine – Cysteine – Stop