Review ? - What are the four macromolecules? Lipids Carbohydrates Protein Nucleic Acids What is the monomer of nucleic acids and what do nucleic acids make up? Nucleotides; DNA and RNA

12-1 DNA

Scientists Involved in Discovery of DNA Watson and Crick 1953 article in “Nature” James Watson and Francis Crick built a model that explained how DNA carried information and could be copied. Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other. Watson Crick

http://youtu.be/zwibgNGe4aY Be ready to write down 3 things you remember from the video!

DNA Stands for… DNA: Deoxyribonucleic acid Very large biomolecule made up of nucleotides Called the “blueprints of life” because it contains genetic information for the construction of proteins. Proteins are essential for life.

Where is DNA located? Floats freely in the cytoplasm of__________ DNA is protected in the nucleus of__________.

Chromosomes and DNA A gene is a segment of DNA that is passed down from parents to children and confers a trait to the offspring. Genes are organized and packaged in units called “chromosomes.” Each gene encodes for a certain protein. {Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

DNA is made of nucleotides Nucleotide is a monomer of nucleic acids made up of 3 parts Deoxyribose sugar (5-carbon sugar) Phosphate group Nitrogenous base

Copyright Pearson Prentice Hall There are four kinds of Nitrogenous bases in in DNA: Adenine (A) guanine (G) Cytosine (C) Thymine (T) DNA is made up of nucleotides. Each nucleotide has three parts: a deoxyribose molecule, a phosphate group, and a nitrogenous base. There are four different bases in DNA: adenine, guanine, cytosine, and thymine. Copyright Pearson Prentice Hall

DNA Structure Made of 2 strands that wrap around each other to form a double helix (looks like a spiral staircase) The sides (a.k.a. the backbone) : Alternating Sugar, phosphate, sugar, phosphate The middle: Nitrogen bases paired together.

Base Pair Rule (Chargaff’s Rule): Adenine pairs with Thymine (straight letters) Guanine pairs with Cytosine (curved letters) DNA is a double helix in which two strands are wound around each other. Each strand is made up of a chain of nucleotides. The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine.

Copyright Pearson Prentice Hall Q: DNA is a long molecule made of monomers called a. nucleotides. b. purines. c. pyrimidines. d. sugars. a. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Q: In DNA, the following base pairs occur: a. A with C, and G with T. b. A with T, and C with G. c. A with G, and C with T. d. A with T, and C with T. b. Copyright Pearson Prentice Hall

12-2 Chromosomes and DNA Replication Photo credit: Jacob Halaska/Index Stock Imagery, Inc. Copyright Pearson Prentice Hall

Replication of DNA DNA molecules can build an exact copy of itself. This is called Replication. (ATP is the energy source) Replication is important for reproduction and must occur every time a cell divides. That way each cell has a complete set of instructions for making proteins. Replication ensures that each resulting cell will have a complete set of DNA.

Steps to DNA Replication In the nucleus, weak hydrogen bonds break between the nitrogen bases of DNA (A, T, G, C). This causes the DNA to unzip like a zipper. Enzymes in the nucleus called DNA Polymerase directs free floating nucleotides in the nucleus to attach to each strand following the rules of base pairing. Each strand serves as a template for the new strand. This results in two identical strands of DNA. This is called Semi- Conservative Replication, producing two copies of DNA that each contain one of the original strands Semi - Conservative Replication Video

Copyright Pearson Prentice Hall DNA Replication New Strand Original strand Nitrogen Bases Growth Growth During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand. Replication Fork Replication Fork DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand. DNA Polymerase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Q: The first step in DNA replication is a. producing two new strands. b. separating the strands. c. producing DNA polymerase. d. correctly pairing bases. b. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Q: A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? a. GCGAATTCG b. CGCTTAAGC c. TATCCGGAT d. GATGGCCAG a. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Q: In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to unzip the DNA molecule. regulate the time copying occurs in the cell cycle. “proofread” the new copies to minimize the number of mistakes. wrap the new strands onto histone proteins. c. Copyright Pearson Prentice Hall