The Structure of DNA

DNA is a nucleic acid. There are two types of nucleic acids: __________ or deoxyribonucleic acid __________ or ribonucleic acid RNA DNA

The four major classes of macromolecules are: Carbohydrates Proteins Lipids Nucleic acids

DNA is composed of nucleotides. nucleotide DNA

A nucleotide is made of three parts: A Phosphate group A Sugar A Base A NUCLEOTIDE P Base Sugar

A NUCLEOTIDE

P Adenine Sugar Four different nucleotides P Thymine Sugar P Cytosine Sugar P Guanine Sugar They differ in their base!!!

The four different bases in DNA are: Adenine --- A Thymine --- T Cytosine --- C Guanine --- G The language of DNA consists of only four letters! Imagine that!!!

DNA is shaped like a double helix --- two complementary strands of nucleotides twist around each other like a twisted ladder.

The phosphate groups and sugars make up the sides of the ladder, and the bases make up the steps. The steps consist of two bases bonded together by hydrogen bonds.

The bases pair up as follows: adenine bonds with thymine, A --- T cytosine bonds with guanine: C --- G

What molecule is this? ________________ A nucleotide phosphate sugar base ? ? ?

Label the phosphate, sugar and base. P S ? B ? ?

phosphate sugar base nucleotide hydrogen bonds What is this a molecule of? __________DNA

DNA

DNA Replication

The duplicating or copying of DNA. One DNA Two DNA 1 21 What is DNA replication.

When is DNA replicated? During interphase, before a cell divides by mitosis or meiosis.

If DNA is not replicated: The new cells have half the chromosomes (DNA). cell divides 2 2 4

DNA must be replicated So the new cells have the same amount of DNA as the original cell. cell divides 4 4 DNA is duplicated 4 8

If you know the base sequence of one strand of DNA, Recall that A T and C G

1. An enzyme unzips the double helix, separating the two strands. 2. An enzyme (DNA polymerase) attaches free-floating nucleotides, one by one, to the exposed bases on each strand. 3. The result is two identical DNA molecules. The steps in DNA replication:

An enzyme unzips the double helix, separating the two strands.

Nucleotides attach to the exposed bases on each strand.

The result is two identical DNA molecules.