12-2 CHROMOSOMES & DNA REPLICATION

I. DNA & CHROMOSOMES

1. Prokaryotic cells do not have nuclei

a) DNA is located in the cytoplasm

b) Have singular circular DNA

IN YOUR TEXTBOOK: ANALYZING DATA PG. 296

•Read “Synthesis of New DNA Molecules” •Answer questions 1-3

PROKARYOTIC C’SOME STRUCTURE

Circular DNA in the cytoplasm

2. Eukaryotic cells have 1000 times more DNA than prokaryotes

3. DNA is located inside the nucleus in the form of c’somes

4. The number c’somes is different for each speices

5. DNA Length a) A chromosome of prokaryotes have

DNA that is about 1.6mm longb) A chromosome of a eukaryotes have

DNA molecule is about 2 inches long

6. DNA Structure-• Made of both DNA and

protein

7. Chromatin- DNA tightly coiled around proteins, located in the nucleus

8. Histones- protein molecule around which DNA is tightly coiled in chromatin

EUKARYOTIC CHROMOSOME STRUCTURE

DNA is located inside the nucleus

DISCUSS W/ PARTNER:

•Fig. 12-10 pg. 297•What are chromosomes made of?•What is a nucleosome? •Why would it be advantageous to the cell to have its DNA molecules tightly condensed into nucleosomes during mitosis?

ANSWERS:

•What are chromosomes made of? Proteins called histones and DNA•What is a nucleosome? A beadlike structure composed DNA wrapped around a histone molecule•Why would it be advantageous to the cell to have its DNA molecules tightly condensed into nucleosomes during mitosis? To prevent the chromatin from tangling and to make separation and division of the chromatin more efficient during mitosis.

2. DNA REPLICATION

1. DNA replication in prokaryotes:a) DNA replication starts at a single point

in the c’some, then moves in 2 directions.

b) This happens until the whole c’some is replicated

2. DNA Replication in Eukaryotes:a) Replication happens at hundreds of

places on the c’someb) Continues in both directions until each

c’some is completely copied3. Replication Forks- the sites where

separation & replication take place

4. DNA Polymerase- an enzyme that joins individual nucleotides to make a new DNA molecule

5. Helicases- enzyme that unwinds the DNA molecule

6. How DNA Replication Occurs:a) The hydrogen bonds are broken b/w the basesb) Helicases unwinds and opens or “unzips” the double

helix at the replication forksc) The double strand of DNA is now two single DNA

strandsd) At the replication forks DNA polymerase adds a

complementary base to the now single strand of DNAe) Replication takes place in both directions until each

chromosome is completely copied.f) After the new strand is added DNA Polymerase

“proofreads” the new strand to make sure each strand is a perfect copy of the old stand

7. Each stand is a template for the new strand:• Old strand A, the

new strand will have a T

• Old strand C, the new strand will

have a G

Replication Fork

8.In prokaryotes DNA replication starts at one site

9.In eukaryotes which are larger DNA replication takes place at hundreds of places on the DNA strand.

DNA REPLICATION VIDEO