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 long b)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 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’some b)Continues in both directions until each c’some is completely copied 3. 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 bases b)Helicases unwinds and opens or “unzips” the double helix at the replication forks c)The double strand of DNA is now two single DNA strands d)At the replication forks DNA polymerase adds a complementary base to the now single strand of DNA e)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