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Chromosomes and DNA Replication

12-2

Biology

Ms. Haut

Copyright Pearson Prentice Hall

DNA and Chromosomes

• DNA and Chromosomes• In prokaryotic cells, DNA is located in the

cytoplasm.• Most prokaryotes have a single DNA molecule

containing nearly all of the cell’s genetic information.


DNA and Chromosomes

• Many eukaryotes have 1000 times the amount of DNA as prokaryotes.

• Eukaryotic DNA is located in the cell nucleus inside chromosomes.

• The number of chromosomes varies widely from one species to the next.

http://www.humangenetik.uni-bremen.de/Karyotyp%20Hund.gif

Dog Karyotype

Pig Karyotype

http://www.animalgenome.org/edu/gene/pigkar.gif

Humans have:44 autosomes 2 sex chromosomes46 total

DNA and Chromosomes• Chromosome Structure

– Eukaryotic chromosomes contain DNA and protein, chromatin.

– DNA tightly coils around proteins called histones.

– DNA and histones form nucleosomes.

– Nucleosomes pack together, forming a thick fiber.



DNA Replication

• Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.

• What is the complementary strand for the following DNA sequence?

T A C G G A T T G A A GA T G C C T A A C T T C

DNA Replication

• In most prokaryotes, DNA replication begins at a single point and continues in two directions.


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DNA Replication

• In eukaryotic chromosomes, DNA replication occurs at hundreds of places (origins of replication).

• Replication proceeds in both directions until each chromosome is completely copied.

• Speeds up the time it takes to copy the DNA.


From Essential Biology with Physiology, 2 ed. By Campbell, Reece.


DNA Replication

• Duplicating DNA – Before a cell divides, it duplicates its DNA in a

process called replication. – Replication ensures that each resulting cell

will have a complete set of DNA.

DNA Replication

• DNA molecule separates into two strands

• Two new complementary strands following the rules of base pairing are made.

• Each strand of the double helix of DNA serves as a template for the new strand.

Copyright Pearson Prentice Hallhttp://images.suite101.com/230204_trans98.jpg

DNA Replication

•DNA replication depends on specific base pairing– DNA replication

• Starts with the separation of DNA strands– Then enzymes use each strand as a template

• To assemble new nucleotides into complementary

strands

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A

T

A T

C G

AC

T

A

Parental moleculeof DNA

Both parental strands serve as templates

Two identical daughtermolecules of DNA

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A

T

A T

C G

AC

T

A

Parental moleculeof DNA

Both parental strands serve as templates

Two identical daughtermolecules of DNA

Nucleotides

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

DNA Replication

• DNA replication is carried out by DNA helicase that “unzips” the molecule of DNA.

• Hydrogen bonds between base pairs are broken and the two strands of DNA unwind.


DNA helicase


DNA Replication

• DNA polymerase joins complementary nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand.


DNA Replication


In prokaryotic cells, DNA is found in the a) cytoplasm.

b) nucleus.

c) ribosome.

d) cell membrane.


The first step in DNA replication is a) producing two new strands.

b) separating the strands.

c) producing DNA polymerase.

d) correctly pairing bases.

What enzyme separates the 2 strands of DNA?DNA helicase

How does helicase separate the strands?by breaking the hydrogen bonds


A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand?

a) GCGAATTCG

b) CGCTTAAGC

c) TATCCGGAT

d) GATGGCCAG


In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to

a) unzip the DNA molecule.

b) regulate the time copying occurs in the cell cycle.

c) “proofread” the new copies to minimize the number of mistakes.

d) wrap the new strands onto histone proteins.


The structure that may play a role in regulating how genes are “read” to make a protein is the

a) coil.

b) histone.

c) nucleosome.

d) chromatin.