The Secret Code

Genes• Genes, which are sections of DNA, are

known to:– Carry information from one generation to

the next.– Put that information to work by determining

the heritable characteristics of organisms.– Be easily copied, because all of a cell’s

genetic information is replicated (copied) every time a cell divides.

How do we know that all of our genetic information

comes from DNA?

Thanks to many scientists and many experiments over the last ≈ 80 years.

• Griffith• Hershey and Chase• Franklin• Watson and Crick

DNA• Nucleic Acid:

Deoxyribonucleic Acid (polymer)

• Made up of units (monomers) called nucleotides.– Three components:

•5-carbon sugar: Deoxyribose

•A phosphate group•A nitrogenous base

NucleotideNucleotide

DNA Structure• Called a double

helix– Twisted Ladder– Backbone (sides) :

5-carbon sugar and phosphate groups

– Rungs: nitrogenous bases

Nitrogenous bases• Our alphabet has 26 letters

– Can create many different words many different sentences billions of different books of information.

• DNA’s alphabet has 4 letters– A, T, C, and G– Create 3 letter words Amino acids

proteins billions of different organisms

Nitrogenous bases• Purines:

– Adenine

– Guanine

• Pyrimidines:– Thymine

– Cytosine

DNA Replication

Replication: The process of making a copy of DNAReplication: The process of making a copy of DNAThe “parent” molecule has two complementary The “parent” molecule has two complementary strands of DNA.strands of DNA.Each is base paired by hydrogen bonding with its Each is base paired by hydrogen bonding with its specific partner:specific partner:

A with T and G with CA with T and G with C

DNA Unzips

The first step in replication is the separation of the The first step in replication is the separation of the two strands. two strands.

An enzyme called DNA helicase unzips DNAAn enzyme called DNA helicase unzips DNA

New nucleotides added

Each parental strand now serves as a template Each parental strand now serves as a template that determines the order of the bases along a new that determines the order of the bases along a new complementary strand.complementary strand.

an enzyme called DNA polymerase adds the an enzyme called DNA polymerase adds the basesbases

Gaps are closed (zipped closed)

The nucleotides are connected to form the sugar-The nucleotides are connected to form the sugar-phosphate backbones of the new strands. DNA phosphate backbones of the new strands. DNA ligaseligaseEach “daughter” DNA molecule consists of one Each “daughter” DNA molecule consists of one parental strand and one new strand….semi-parental strand and one new strand….semi-conservativeconservative

• Reviewing DNA Replication• Replication #2• Replication #3 and more

Here are some interesting Facts!

• A single strand of DNA (one chromosome) is about 2 inches long when uncoiled.

• Each human cell contains 46 chromosomes (6 to 9 feet of DNA)

• Your body contains 75-100 trillion of cells.• All of your DNA (when uncoiled and tied

together) could make about 6000 trips from the Earth to the Moon.

A few more cool things about DNA

• It takes about 8 hours for one of your cells to copy all of its DNA.

• Our entire DNA sequence is called a Genome…and there is an estimated 3,000,000,000 DNA bases

• This would take up about 3GB of storage• If you could type 60 wpm, 8 hours/day…it would

take you 50 years to type this.• 99.9% of our DNA is the same…it is the 0.01% that

makes you who you are!