1. Pyrimidine, hydrogen bond, DNA polymerase, base pair, helicase. DNA Replication Warm-up Questions: Scientists have discovered that certain cells with a defect in a gene called p53 can cause a serious disease. Gene p53 normally prevents the cell cycle from continuing until proper chromosome replication has occurred. Defective p53 genes can cause cells to undergo uncontrolled growth. Which type of disease is most likely to be caused by a defect in p53? a.cancer b.chicken pox c.strep throat d.pneumonia “Thymine—guanine—thymine—cytosine” describes — (6A) a.nucleotides within an RNA strand b.a sequence of bases within a DNA section c.points of DNA separation during protein synthesis d.tRNA codons for specific amino acids

2. DNA Structure Cont. DNA is composed of purine and pryrimidine bases. Adenine and guanine are purines. Purines are the larger of the two types of bases found in DNA. Cytosine and thymine are pyrimidines. The bases in DNA are connected by hydrogen bonds. The sequence of base pairs carries the genetic information. The backbone of DNA is made up of alternating sugar (deoxyribose) and phosphate groups.

3. DNA Replication DNA replication is the process of producing two identical replicas from one original DNA molecule. The first step in DNA replication is the separation of the two DNA strands that make up the helix. An enzyme, DNA helicase unwinds and unzips the DNA strand. The unzipped DNA forms a Y- shape called the replication fork.

4. DNA Replication Cont. Each separate DNA strand now has its sequence of bases exposed and unpaired. DNA polymerase enzymes match up each one of these exposed bases, in turn, with free nucleotide triphosphates; A with T, and G with C. DNA polymerase then uses energy and joins the new sections together with new hydrogen bonds.

5. DNA Replication Cont. Each end of the genetic sequence in each side of the split DNA strand has a 3’ and a 5’ end. DNA polymerase works in the 5’ to 3’ direction. In the genetic code, a stop codon is a nucleotide triplet within mRNA that signals a termination of translation.

6. DNA Replication Video We will watch the following video. You will be responsible for taking notes on the video in your journal. DNA Replication Video.

7. Replication and Mitosis Memes