Components and Structure

1. To carry information from one generation to the next. 2. Put the information to work by determining heritable characteristics of organisms. 3. To be easily copied each time the cell reproduces.

DNA is a large molecule made up of monomers called nucleotides A nucleotide is made of 3 parts: Deoxyribose- a 5-carbon sugar Phosphate group Nitrogen base (of which there are 4) Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

The parts of the nucleotide are held together by covalent bonds. The shape of DNA is a double helix This means it looks like a ladder that has been twisted. The sugar and phosphate molecules alternate down the sides forming the backbone.

The nitrogen bases are in the middle, forming the rungs. Though there are only 4 different types of nucleotides (one for each nitrogen base), there are endless ways to arrange them, making each of us unique!

Source of DNAATCG Streptococcus Yeast Herring Human Percentages of Bases in 4 Organisms Look at the information about the nitrogen bases presented in the table above. What pattern(s) do you see? The percentages for A and T are similar and the percentages for C and G are similar.

Work with DNA led the discovery that the amount of A almost always equaled the amount of T and the amount of G almost always equaled the amount of C. Base Pairing Rule- A=T and C=G The bases in the pairs are said to be complimentary to each other. The bases in the pairs are held together by hydrogen bonds.

How many adenines are in a molecule of DNA that has 40 thymine? How many cytosine are in a molecule of DNA that has 76 guanine? If a DNA molecule has 200 bases and 30 of them are thymine, how many are cytosine?

Since DNA is basically the directions for everything that happens in the cell, it is necessary for every cell in an organism to have an exact copy of DNA. Replication occurs during the S phase of interphase in the cell cycle.

One side of the DNA strand serves as a template for the other side. This means that if you know the sequence of bases on one side, you automatically know the sequence of bases on the other side since the bases always pair up the same way. Ex. What is the compliment to the following strand? A T T C G A C C A G T A A G C T G G T C

Replication- the process by which a copy of DNA is made prior to cell reproduction Prokaryotes have a single loop of DNA (no nucleus); replication begins at a single point and proceeds in 2 directions. Eukaryotes have a long piece of DNA divided into chromosomes; replication occurs in many places at the same time.

The “players” in replication Helicase (enzyme)- unwinds and unzips DNA DNA polymerase (enzyme)- adds nucleotides to the template to make the new DNA strand The original strand of DNA Extra nucleotides used to build the new strand

How it happens?... Helicase unwinds and unzips the 2 strands of the double helix (the original strand) DNA polymerase adds new nucleotides, building the new strand, following the template of the original strand and using the base pairing rule. DNA polymerase also checks to make sure no mistakes have been made.

Using the sequences of DNA below, write the complements for each. 1. ATTATA 2. CATCAT 3. ACGTAC 4. AGGTCAATA TAATAT GTAGTA TGCATG TCCAGTTAT

On this diagram, indicate where helicase and DNA polymerase would be found. Helicase DNA Polymerase

1. What is the result of replication? Why is it needed? 2. What enzyme unzips the DNA? 3. “Unzipping” is easy because ________ bonds hold the bases together. 4. What enzymes adds nucleotides to the DNA template? 5. How does the enzyme in #4 “know” how to arrange the nucleotides being added? 6. Each new molecule of DNA has _______ strand(s) from the original molecule of DNA.