DNA: Genetic Material

Review:  All living things must have genetic material Species must be able to pass on that genetic material to future generations.

DNA: Deoxyribonucleic acid  It is located in the nucleus of cells in eukaryotes.  It is found in the cytoplasma of prokaryotes  It is the blueprint that makes you who you are.  It is described as a double helix.

DNA: Deoxyribonucleic acid DNA is a type of organic compound.  It is used for storing and transmitting genetic info  It is found in in all living organisms  Eukaryotes – in nucleus only.  Prokaryotes - free floating.

The Structure of DNA

Building Blocks of DNA Nucleotides: subunits that make up the extraordinarily long thin molecule of DNA. Each nucleotide consists of three parts:  A phosphate group  A five-carbon sugar molecule  A nitrogen base

Building Blocks of DNA  The five-carbon sugar molecule is called deoxyribose.  The phosphate group is attached to the sugar and is the same for all molecules of DNA.  These two molecules form the backbone of a DNA strand.

Building Blocks of DNA The nitrogen base found in each nucleotide of the DNA molecule is one of four different bases:  Adenine (A)  Guanine (G)  Thymine (T)  Cytosine (C)

9 Chargaff’s Rule Adenine Thymine Adenine must pair with Thymine Guanine Cytosine Guanine must pair with Cytosine The bases form weak hydrogen bonds G C TA copyright cmassengale

Building Blocks of DNA Purines: a class of organic molecules that have a double ring of carbon and nitrogen atoms  Adenine  Guanine

Building Blocks of DNA Pyrimidines: a class of organic molecules that have a single ring of carbon and nitrogen –Thymine –Cytosine

Chargarff’s Rules Base pairing rules: for the DNA in each Organism –The amount of guanine always equals the amount of cytosine (number of G = number of C) –The amount of adenine always equals the amount of thymine (number of A = number of T)

Why are the bases so picky?

DNA is a Double Helix 1953: Watson and Crick  Using the base pairing rule and X-ray photos from 1950 made a 3-D model using tin and wire.  The result was the double helix, a “spiral staircase” configuration

DNA is a Double Helix The Double Helix Model:  It has a sugar and phosphate backbone  Adenine pairs with Thymine Guanine pairs with Cytosine Guanine pairs with Cytosine  The nitrogen bases are held together by hydrogen bonds.  Due to the base pairing the two strands are complementary to each other

DNA is a Double Helix Write the complementary strand for the following sequence AGTCCTGAAATCGG TCAGGACTTTAGCC

DNA Replication Before a cell can divide:  the DNA in the nucleus of the cell must be copied.  this process is called Replication  Replication ensures that each new cell receives an exact copy of the cells genetic information.

DNA Replication  During Replication the DNA molecule “untwists” into two strands or replication forks.  The separation occurs at the hydrogen bonds between the nitrogenous bases.

DNA Replication  The separation of the replication fork is accomplished by an enzyme called Helicase.  The helicase breaks the DNA molecule into two strands

DNA Replication The original individual strands serve as a template for the building of two new complimentary strands of DNA

DNA Replication Polymerase an enzyme, joins new nucleotides to each existing strand according to the base pairing rule: Adenine >Thymine and Guanine > Cytosine Adenine >Thymine and Guanine > Cytosine

DNA Replication  The two new molecules “re-twist”  Each new DNA molecule consists of one original strand and 1 new strand  As a result DNA Replication is said to be semi- conservative

DNA Replication Practice Using the base pairing rule what complimentary strand would produced from the following DNA base sequence(s) A C T G G C A CG __ ________________ AGGTATACC __ ________________

DNA Replication Practice A DNA molecule is 60 nucleotide bases long. 40 of the nucleotide bases are identified as adenine. How many thymine nucleotides must there be in this DNA molecule? How many Cytosine? Guanine? A DNA molecule is 60 nucleotide bases long. 40 of the nucleotide bases are identified as adenine. How many thymine nucleotides must there be in this DNA molecule? How many Cytosine? Guanine? Adenine __ Thymine __ Cytosine __ Guanine __ Adenine __ Thymine __ Cytosine __ Guanine __ A DNA molecule is 100 nucleotide bases long. 20 of the nucleotide bases are identified as Guanine. How many Cytosine nucleotides must there be in this DNA molecule? How many Adenine? Thymine? A DNA molecule is 100 nucleotide bases long. 20 of the nucleotide bases are identified as Guanine. How many Cytosine nucleotides must there be in this DNA molecule? How many Adenine? Thymine? Adenine __ Thymine __ Cytosine __ Guanine __