Chromosomes and DNA ReplicationChromosomes and DNA Replicationhttp://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.htmlanimation__dna_replication__quiz_1_.html

DNA and ChromosomesDNA and ChromosomesMany eukaryotes have 1000 Many eukaryotes have 1000 times the amount of DNA as times the amount of DNA as prokaryotes.prokaryotes.

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

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

DNA and Chromosomes

Eukaryotic Chromosome StructureEukaryotic Chromosome Structure

Chromosome

Supercoils

Nucleosome

DNA double helix

Histones

Coils

DNA and Chromosomes

DNA and ChromosomesDNA and Chromosomes

In prokaryotic cells, DNA is In prokaryotic cells, DNA is located in the cytoplasm.located in the cytoplasm.

Most prokaryotes have a single Most prokaryotes have a single DNA molecule containing DNA molecule containing nearly all of the cell’s genetic nearly all of the cell’s genetic information.information.

DNA and Chromosomes

Chromosome

E. Coli Bacterium

Bases on the Chromosomes

The Components and Structure of DNA

I The Components and Structure of DNAI The Components and Structure of DNA

DNA is made up of nucleotides. DNA is made up of nucleotides.

A nucleotide is a monomer of A nucleotide is a monomer of nucleic acids made up of:nucleic acids made up of:

• Deoxyribose – 5-carbon SugarDeoxyribose – 5-carbon Sugar

• Phosphate GroupPhosphate Group

• Nitrogenous BaseNitrogenous Base

The Components and Structure of DNA

There are four There are four kinds of bases kinds of bases in in DNA:in in DNA:

• adenineadenine• guanine guanine • cytosinecytosine• thyminethymine

The Components and Structure of DNA

Chargaff's RulesChargaff's Rules

Erwin Chargaff discovered that:Erwin Chargaff discovered that:–The percentages of guanine [G] and The percentages of guanine [G] and

cytosine [C] bases are almost equal in cytosine [C] bases are almost equal in any sample of DNA. any sample of DNA.

–The percentages of adenine [A] and The percentages of adenine [A] and thymine [T] bases are almost equal in thymine [T] bases are almost equal in any sample of DNA.any sample of DNA.

DNA and ChromosomesChromosome StructureChromosome Structure

Eukaryotic chromosomes Eukaryotic chromosomes contain DNA and protein, contain DNA and protein, tightly packed together to tightly packed together to form chromatin.form chromatin.

Chromatin consists of DNA Chromatin consists of DNA tightly coiled around tightly coiled around proteins called histones.proteins called histones.

DNA and histone molecules DNA and histone molecules form nucleosomes. form nucleosomes.

Nucleosomes pack together, Nucleosomes pack together, forming a thick fiber.forming a thick fiber.

The Components and Structure of DNA

DNA Double Helix

The Components and Structure of DNA

Watson and Crick discovered that Watson and Crick discovered that hydrogen bonds can form only between hydrogen bonds can form only between certain base pairs—adenine and thymine, certain base pairs—adenine and thymine, and guanine and cytosine. and guanine and cytosine.

This principle is called “the base pairing This principle is called “the base pairing rule”.rule”.

DNA ReplicationDNA ReplicationIIII

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

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

Copyright Pearson Prentice Hall

DNA ReplicationIn eukaryotic chromosomes, DNA In eukaryotic chromosomes, DNA replication occurs at hundreds of places. replication occurs at hundreds of places. Replication proceeds in both directions Replication proceeds in both directions until each chromosome is completely until each chromosome is completely copied.copied.

The sites where separation and The sites where separation and replication occur are called replication replication occur are called replication forks.forks.

Duplicating (replicating) DNA:Duplicating (replicating) DNA:

Before a cell divides, it duplicates its Before a cell divides, it duplicates its DNA in a process called replication. DNA in a process called replication.

Replication ensures that each Replication ensures that each resulting cell will have a complete resulting cell will have a complete set of DNA.set of DNA.

During DNA replication:During DNA replication: 1.1.The DNA molecule The DNA molecule

separates into two strands. separates into two strands. Each strand of the double Each strand of the double helix of DNA serves as a helix of DNA serves as a template for the new strand. template for the new strand. This is carried out by an This is carried out by an enzyme, DNA helicase, that enzyme, DNA helicase, that “unzips” a molecule of DNA at “unzips” a molecule of DNA at the the Hydrogen bonds Hydrogen bonds between between base pairs and the two base pairs and the two strands of DNA unwind.strands of DNA unwind.

DNA Replication

2. It produces two new 2. It produces two new complementary strands following complementary strands following the rules of base pairing as each the rules of base pairing as each nucleotide matches the exposed nucleotide matches the exposed base on each side of the ladder, base on each side of the ladder, DNA polymerase joins individual DNA polymerase joins individual nucleotides to produce a DNA nucleotides to produce a DNA molecule and then “proofreads” molecule and then “proofreads” each new DNA strand.each new DNA strand.

DNA Replication

Nitrogen Bases

Replication Fork

DNA Polymerase

Replication Fork

Original strandNew Strand

Growth

Growth

DNA Replication

END OF SECTIONhttp://www.youtube.com/watch?v=zdDkiRw1PdU

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