Chapter 12-2 DNA Replication and Chromosomes

I. Prokaryotic DNA Replication A. ONE circular strand of DNA in cytoplasm of cell. Called a nucleoid or plasmid. B. DNA strand stretched out is approx 1.6mm in length. C. Replication begins at ONE point and goes in TWO directions until entire plasmid is replicated. Plasmid

II. Eukaryotic DNA Replication A. DNA is contained in nucleus of cell. Each species has a different number of DNA strands/chromosomes B. Approximately 1-2 meters of DNA in every human cell nucleus! C. Begins at 100’s of points and goes in TWO directions until chromosome is replicated.

Five Steps of DNA Replication

Step 1:UNCOILS Ladder unwinds

Lets zoom in and look at the Inside of a replication bubble.

a. Replication Bubbles

Step 2: (UNZIPS) a.Starts at each end of the bubble. b. the point where separation and replicaiton begin is called a replication fork. c. The enzyme Helicase breaks the Hydrogen bonds between the base pairs inside the replication bubbles. Replication forks Replication bubble

Step 3: BRING IN FREE NUCLEOTIDES. Now the enzyme DNA polymerase can direct base pairing from the 5’ end toward the 3’ end of each parent strand building a Complementary strand (new) according to the parent strand(template) a 5’ a. DNA polymerase Brings free nucleotides according to parent strand. a 3’ 5’ 3’

Label the replication bubble. Label the replication fork.

b. How many phosphates Does the new nucleotide have? Do not show c. I am just typing stuff to cover up This box I don’t want seen.

Step 4: REZIP This energy is used to Re-establish the c. Energy is released When this bond is broken. Step 4: REZIP This energy is used to Re-establish the Hydrogen bonds between the Nitrogen bases

a.

They continue until they join together b. Remember:There are multiple replication bubbles along the DNA molecule Replication bubble They continue until they join together

They continue to grow until they join together c. They continue to grow until they join together. They continue to grow until they join together

They continue to grow until the join. d. Now there are two molecules of DNA. e. Each made of two strands composed of: -one Original (parent) strand and -one New (complementary) strand. They continue to grow together and live happily. They continue to grow until the join.

f. This is called semi-conservative replication

Step 5: (RECOIL) Now the 2 strands can wind back up.

a. Now the cell is ready for mitosis (cell division.)

b.

III. Chromosome/DNA Composition A. DNA and protein form the chromatin B. Wound up chromatin forms a chromosome. C. How is DNA able to fit into a cell? Histones are round proteins that cluster together to form a structure called a nucleosome. Nucleosome’s job is to wind chromatin strand into compact structure to fit in the nucleus. http://www.youtube.com/watch?v=gbSIBhFwQ4s&NR=1&feature=endscreen

DNA Double helix