DNA CHAPTER 12 Characteristics DNA Deoxyribonucleic Acid Found

DNA CHAPTER 12

Characteristics � DNA – Deoxyribonucleic Acid � Found in the nucleus of Eukaryotic Cells Ø mostly found loose in the form of chromatin Ø during mitosis condenses into chromosomes

Size of Genetic Material �Genome : All the chromosomes of an organisms (all your genetic material) �Chromosome �Gene –

DNA structure • • What type of macromolecule is DNA? A: nucleic acid What are nucleic acids made of? A: NUCLEOTIDES! phosphate, 5 carbon sugar, nitrogen base

DNA structure • What are the 4 types of nitrogen bases in DNA? RNA? • A: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)

Base Pairing • Adenine only pairs with Thymine • Guanine only pairs with Cytosine

• DNA is a double stranded chain of nucleotides with matching/complementary nitrogen bases making up the middle.

v. DNA looks like a ladder. v. Outside of the ladder is made up of repeating sugars & phosphates. v. The middle of the ladder is made up of the pairs of nitrogen bases. v. These bases are held together by hydrogen bonds. v. Bases are attached to the sides of the ladder by the sugar.

The two strands run in opposite directions! Phosphate - Sugar – Phosphate Antiparallel

DNA Replication • DNA must be able to do 3 things: 1. Code for the instructions that tell a cell how to work. 2. Must be easily copied. 3. Carry genetic information that can be passed down from one generation to the next. (parent offspring)

When would a cell copy or replicate it’s DNA? • During S phase…of course!

But…. HOW EXACTLY DOES THIS HAPPEN?

• We will make an identical copy of the double-stranded DNA by using the existing DNA as a template for the synthesis of 2 new DNA strands.

DNA Synthesis • Each strand of the DNA has all the information needed to make the other half! • For Example:

Question: • What would be the complementary DNA strand for the following DNA sequence? DNA CGTATG

Answer: DNA CGTATG GCATAC

3 Main Steps • Untwist Unzip Replicate! • Enzymes responsible for “unzipping” = Helicase – Unzipping = breaking of hydrogen bonds • Enzyme responsible for Replication = DNA polymerase

Untwist, Unzip, & Replicate! • Site of separation is called = replication fork

• DNA polymerase only works in one direction! • The original strand that is running in the same direction as replication is called the leading strand. • This strand is copies continuously in one long piece.

• The other strand can not be made continuously. • It must be made in pieces. • This strand is called the lagging strand.

Semi-Conservative Replication

Proofreading New DNA • DNA polymerase initially makes an error about once every 10, 000 letters it copies. • Enzymes such as DNA polymerase actually go back, proofread & correct these mistakes! • The new error rate for DNA that has been proofread is 1 in 1 billion! • But still some mistakes are made! • We call these mistakes mutations!