The Structure of DNA

Bell Ringer: What does DNA have to do with cell division (mitosis & meiosis)?

Before cell division (like mitosis above) can occur, a cell must first make an identical copy of its DNA during interphase.

Which monomer makes up nucleic acids, such as DNA?

1. Amino acids
2. Nucleotides
3. Glucose
4. Fatty acids

Recall from yesterday...

A nucleotide is the monomer for nucleic acids.

They are made up of 3 main parts: 

1) Nitrogenous base

2) Sugar

3) Phosphate group

Sugar & Phosphate

The sugar and the phosphate make up the backbone of DNA.

The sugar found in DNA's backbone is deoxyribose (which is where DNA gets its name: deoxyribonucleic acid)

Nitrogenous Bases

There are four different nitrogenous bases that make up the nucleotides of DNA.

1) Adenine     2) Thymine

3)Cytosine     4) Guanine

Adenine always pairs with thymine.  Cytosine always pairs with guanine. 

The base pairs are held together by hydrogen bonds.

Base Pairing Rules

If A always pairs with T and C always pairs with G, you can use one side of the DNA strand to figure out what the opposing side would look like.  That's why they say DNA has complementary strands.

What would be the complementary strand to ACTGATTG?

Double Helix

DNA's shape is known as a double helix.  A double helix looks like a ladder with its two sides twisted around each other.

The center is held together by weak hydrogen bonds between the nitrogenous bases.

Draw and label a DNA molecule in your notes. Be sure to include the sugar phosphate backbone & bases. Upload your picture here.