DNA & RNADNA & RNA The Nucleic AcidsThe Nucleic Acids

Remember: Each chromosome is a very long DNA molecule that contains many genes. The DNA controls the production of proteins within a cell.

Gene: A segment of DNA that is part of a chromosome that is responsible for inherited traits such as eye color, hair color, skin color, etc.

It directs the protein production that controls the cell.

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DNA: (Deoxyribonucleic Acid):•Is an organic molecule composed of nucleotides.•Is a molecule that is common to all living things, from bacteria to humans.•It is the blueprint of an organism; DNA is made of chains of nucleotides shaped much like that of a spiraling ladder, and they called it a double helix.

•A DNA molecule can NOT be viewed with a compound light microscope.•In 1953, Watson and Crick constructed the first model of DNA, and they called it a double helix.•Rosalind Franklin-used x-ray diffraction to determine that a chromosome has DNA in a spiraled shape.

Structure of DNA: (DNA is composed of nucleotides.)

Nucleotides of DNA have three Parts:1. Deoxyribose (a five carbon sugar)2. Phosphate group(these two bond together to make up the sides of the ladder)

3. 1 of 4 Nitrogen BasesAdenine (A) Guanine (G) *These hydrogen, weak, bonds together Cytosine (C) form the rungs of the ladder.

Thymine (T)

The 2 bases on the same rung of the DNA ladder are referred to as a base pair.In DNA

Cytosine always bonds with guanine, andThymine always bonds with adenine!

C=G G=CT=A A=T

•Base Pairing Rules. The strictness of base-pairing results in 2 strands that are complementary, which means the sequence of bases on one strand determines the sequence of bases on the other strand.

Example:1st strand of DNA has T C G A A T TThe other strand must have A G C T T A A

•All organisms contain chromosomes composed of DNA made up of nucleotides with adenine, thymine, guanine, and cytosine. •The reason organisms can be different from each other even though their genetic material is made of the same molecules is because the order of nucleotides in two different organisms are different. •It is the sequence of nucleotides that forms the genetic information of an organism.

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•How can organisms be different from each other if their genetic material is made of the same DNA: A, T, C, G?

•They are the different because the order of nucleotides in the 2 organisms is different.

Example: A squirrel differs from a rosebush because the order of nucleotides in its DNA is different.

Replication:During mitosis and meiosis the cells divide. Each time a cell divides it must make a copy of its DNA. ReplicationReplication is is the process by which DNA is duplicated, forming two the process by which DNA is duplicated, forming two identical copies from one originalidentical copies from one original.

These are the steps of replication:1. The enzyme helicase, in DNA breaks the hydrogen

bonds between the nitrogen bases that hold the two strands together, unzipping the DNA molecule.

2. As the DNA continues to unzip, free nucleotides from the surroundings in the nucleus bond to the single strands base pairing by DNA polymerase.

3. The enzyme ligase forms the sugar-to-phosphate bonds that connect nucleotides on each strand of DNA. It also adds hydrogen bonds between nitrogen-bases & “zips” the strand back up.

4. Since DNA polymerase adds the free nucleotides, it also acts as a spell-checker. Errors occur once for every billion nucleotides due to DNA Polymerase

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Replication of DNA doesn’t begin at one end of the molecule and proceed to the other. It occurs simultaneously at many points on the molecule, speeding up to process. Replication is completed when the entire molecule has been unzipped and replicated.

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Each new DNA molecule has one nucleotide strand from the original DNA molecule (template) and one nucleotide strand that has been newly synthesized (complementary strand)from free nucleotides in the cell.