Resurrecting the Extinct DNA Structure Resurrecting the Extinct

DNA is… Found in the nucleus of eukaryotic cells. Found in the cytoplasm of prokaryotic cells. Makes up chromosomes. A segment of DNA that results in a trait is called a gene. What is DNA?

DNA Structure DNA (deoxyribose nucleic acid) is arranged in a double helix or “twisted ladder.” Scientists Watson and Crick discovered this structure in 1953. They received the Nobel Prize for this. Twist

So…what is DNA? DNA is a long molecule made up of monomers called nucleotides (3 parts): phosphate five-carbon sugar called deoxyribose nitrogen base (there are 4 different nitrogen bases)

Sugar-Phosphate Backbone The sides of the DNA chain are made of alternating sugars and phosphates held together by strong covalent bonds. It is referred to as the sugar-phosphate backbone. Deoxyribose (sugar) phosphate

Nitrogen Bases Nitrogen bases fall into 2 categories… Pyrimidine - single ring Thymine (T) Cytosine (C) Purine - double ring Guanine (G) Adenine (A)

Base Pairing Rules The rungs of the “ladder” are made up of the nitrogen bases joined by weak hydrogen bonds. These bonds will only be formed between specific pairs of bases.

Base Pairing Rules A always bonds with T (2 H bonds) G always bonds with C (3 H bonds)

Can you build a DNA molecule? Drag & Drop DNA

Can you label the nucleotides?

DNA Replication

DNA Replication Before a cell divides, it duplicates its DNA. The DNA copying process is called replication. remember S phase: DNA replicates Replication ensures that each cell will have a complete set of DNA molecules. Replication starts many places on a chromosome at the same time and moves in both directions.

Steps of DNA Replication An enzyme called helicase comes in and breaks the hydrogen bonds between the nitrogen base pairs and “unzips” the DNA molecule into 2 separate strands. These strands serve as templates for the new strands.

Steps of DNA Replication 2. There are free nucleotides that are floating around in the nucleus. These form hydrogen bonds with each DNA strand according to the base pairing rules (A=T and C≡G).

Steps of DNA Replication 3. Another enzyme called DNA polymerase moves along each strand, attaching the corresponding nucleotides. 4. DNA polymerase remains attached until the entire strand has been copied. This process produces 2 DNA molecules, each with a new and an original strand. Replication Animation

Checking for Errors In DNA replication, there is a possibility for errors. DNA polymerase has a “proofreading” role. It can only add nucleotides if the previous one is correctly paired. If there is a mismatched nucleotide, the DNA polymerase backtracks and fixes the mistake. This helps ensure that each molecule is a perfect copy of the original.