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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