Biology

Unit 6 Notes: DNA

(1) What is DNA?• Type of Nucleic Acid.

• Stored in the nucleus of eukaryotic cells.

• Stores genetic information/code, to make all proteins for the cell (or organism).

(2) DNA Structure• The molecule is made of 2 spiraling strands of nucleotides

(“double helix”).

• The strands face in opposite directions (“anti-parallel”).

• Made of monomers called “nucleotides”.

• Nucleotide is made of:

• Deoxyribose Sugar

• Phosphate

• Nitrogenous Base

• Types of DNA Nitrogenous Bases:

• Adenine (A)

• Thymine (T)

• Guanine (G)

• Cytosine (C)

(3)Base Pairing • “Chargaff’s Rule”: Explains how the nitrogenous bases pair within

a DNA molecule.

• A’s pair with T’s.G’s pair with C’s.

• So if on one strand you have:A-T-G-C-G-A

On its other strand it would be:T-A-C-G-C-T

(4) The “Code”• The unique genetic instructions (or the “code”) is stored in the

NITROGENOUS BASES within DNA.

• Every 3 nitrogenous bases makes up what is called a CODON.

• The unique sequence of codons tells the cells how to sequence amino acids, to make specific proteins.

(5) DNA Replication• REMEMBER:

• Replicate = Copy

• Cells replicate their DNA during the S-Phase of the Cell Cycle.

• Cells need to replicate their DNA so that each new cell they make (during mitosis/meiosis), has its own copy of DNA.

• Since the code is stored in the nitrogenous bases:

• The cell cuts apart the nitrogenous bases between the two strands.

• Enzymes match up nucleotides to each strand, based on their n-bases.

• Everything gets reconnected.

• You end up with 2 DNA molecules (each “semiconservative”).

(6) Semi-Conservative?• Semi = ½

Conserve = To save

• Semi-Conservative:When DNA is replicated, each new molecule has 1-original strand saved, and makes 1-new strand.

• This helps increase the accuracy and efficiency of replication.