DNA Structure and Replication (Ch. 12-1, 12-2)

DNA DNA is one of the 4 types of macromolecules known as a nucleic acid. DNA is one of the 4 types of macromolecules known as a nucleic acid. DNA stands for deoxyribonucleic acid. DNA stands for deoxyribonucleic acid.

Components and Structure of DNA All living things use DNA to carry genetic information from one generation to the next (genes are made of DNA) All living things use DNA to carry genetic information from one generation to the next (genes are made of DNA) be easily and accurately copied before cell division. be easily and accurately copied before cell division.

Nucleotides The monomer, repeating subunits that make up nucleic acids, like DNA, are called nucleotides. The monomer, repeating subunits that make up nucleic acids, like DNA, are called nucleotides.

3 parts of a Nucleotide one 5-carbon sugar called deoxyribose one 5-carbon sugar called deoxyribose one phosphate group one phosphate group one nitrogenous (nitrogen- containing) base one nitrogenous (nitrogen- containing) base Open your notes and label the nucleotide!

2 types of Nucleotides 1) purines = (two rings) adenine (A) adenine (A) Draw Adenine in the first box ( upper Right) on your notes

Another Purine guanine (G) Draw guanine in the 2 nd purine box (middle Right) in your notes Draw guanine in the 2 nd purine box (middle Right) in your notes

2) pyrimidines (one ring) thymine (T)thymine (T) Draw thymine across from adenineDraw thymine across from adenine

2) pyrimidines (one ring) cytosine (C)cytosine (C)

Each strand of DNA has directionality. Each molecule will have a phosphate, or a 5’ end and a sugar molecule, or a 3’ end (3 prime). Each molecule will have a phosphate, or a 5’ end and a sugar molecule, or a 3’ end (3 prime).

DNA looks like a twisted ladder. The strands run in opposite directions; called antiparallel (like opposite flows of traffic)

One strand runs 5’ to 3’ while the other strand runs 3’ to 5’. 5’3’ 3’5’

Each base pair is made of 1 purine and 1 pyrimidine. Each base pair is made of 1 purine and 1 pyrimidine. 1. Adenine from one strand and thymine from the other always pair together with two hydrogen bonds,

2. guanine on one strand and cytosine on the other strand always bond together with three hydrogen bonds.

DNA and chromosomes DNA molecules are extremely long. In order to fit into cells, they must fold up as much as possible. DNA molecules are extremely long. In order to fit into cells, they must fold up as much as possible.

In humans, the amount of DNA in the nucleus is more than 1 meter long. In humans, the amount of DNA in the nucleus is more than 1 meter long. In Eukaryotic cells the DNA is bound to histone proteins forming chromatin in the nucleus. In Eukaryotic cells the DNA is bound to histone proteins forming chromatin in the nucleus. To fit the DNA into the nucleus, the DNA and histone proteins are packed tightly a process called supercoiling. To fit the DNA into the nucleus, the DNA and histone proteins are packed tightly a process called supercoiling.

Chromosome Histone Proteins DNA Label the picture inside your notes! Super Coiling!!! Nucleosomes

DNA Replication: How is DNA copied? The process of copying DNA is called DNA replication. The process of copying DNA is called DNA replication. Because DNA is double stranded, we can separate the 2 strands and create a new strand using 1 strand as a template. Because DNA is double stranded, we can separate the 2 strands and create a new strand using 1 strand as a template. Our end product is 2 identical double stranded DNA molecules. Our end product is 2 identical double stranded DNA molecules. Because of this, the two strands are called complementary (think about the angles in geometry). Because of this, the two strands are called complementary (think about the angles in geometry).

During DNA replication: the DNA is unwound and unzipped (the two strands of DNA separate) the DNA is unwound and unzipped (the two strands of DNA separate) each original DNA strand is used as a template (or model) to make a new DNA strand with base pairing each original DNA strand is used as a template (or model) to make a new DNA strand with base pairing New DNA strand

Remember: What do enzymes do? Enzymes are biological catalysts that help chemical reactions happen faster. Enzymes are biological catalysts that help chemical reactions happen faster. Forming and breaking chemical bonds takes energy. Forming and breaking chemical bonds takes energy. Enzymes lower the amount of energy needed to do make and break those bonds. Enzymes lower the amount of energy needed to do make and break those bonds.

Helicase unzips or separates the two DNA strands by breaking the hydrogen bonds between the nitrogenous bases Helicase unzips or separates the two DNA strands by breaking the hydrogen bonds between the nitrogenous bases The enzyme Primase lays down an RNA Primer a few base pairs long to which the new DNA can be added. The enzyme Primase lays down an RNA Primer a few base pairs long to which the new DNA can be added. Another enzyme, called DNA polymerase, adds new bases to the new DNA strand Another enzyme, called DNA polymerase, adds new bases to the new DNA strand DNA polymerase also “proofreads” the new DNA to check for errors DNA polymerase also “proofreads” the new DNA to check for errors The new DNA molecules are rewound by the enzyme Gyrase. The new DNA molecules are rewound by the enzyme Gyrase. ENZYMES USED IN DNA REPLICATION

When replication is complete, each DNA molecule is made of one old strand and one new strand. This is described as the semi-conservative model of replication. When replication is complete, each DNA molecule is made of one old strand and one new strand. This is described as the semi-conservative model of replication. Original DNA New DNA (one old strand, one new strand)

Chromosome Arrangement Prokarytoic cells (bacteria) Prokarytoic cells (bacteria) Prokaryotic cells have one circular chromosome that is free-floating in the cytoplasm. Remember, prokaryotic cells do not have a nucleus. Prokaryotic cells have one circular chromosome that is free-floating in the cytoplasm. Remember, prokaryotic cells do not have a nucleus. When prokaryotic cells copy their DNA, the process begins at one point in the chromosome and moves around the circle in both directions until complete. When prokaryotic cells copy their DNA, the process begins at one point in the chromosome and moves around the circle in both directions until complete. Write this and draw this picture in your notes under “Prokaryotic cells”

Eukaryotic cells Eukaryotic cells have more chromosomes than prokaryotic cells, and DNA replication begins at hundreds of places and continues in both directions until each chromosome is completely copied. Eukaryotic cells have more chromosomes than prokaryotic cells, and DNA replication begins at hundreds of places and continues in both directions until each chromosome is completely copied.

The point in the DNA where the two DNA strands are separating and replication is occurring is called the replication fork. The point in the DNA where the two DNA strands are separating and replication is occurring is called the replication fork. Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

DNA Polymerase only works in one direction (5’ to 3’). One strand is read and synthesized continuously while the other is synthesized in fragments. DNA Polymerase only works in one direction (5’ to 3’). One strand is read and synthesized continuously while the other is synthesized in fragments. New DNA strand Replication Fork Draw this picture in your notes under “Eukaryotic cells”