The Structure of the DNA Molecule

Middle School

ScienceDr. Romano

DNA stands for:D: DeoxyriboseN: NucleicA: Acid

DNA is too small to see, but under a microscope it looks like a twisted up ladder!

Every living thing has

DNA

That means that you have

something in common with a zebra, a tree, a

mushroom and a beetle!!

DNA is made up of steps and rails of a ladder.

This is a rail

This is a step

Green can only go with Red

Purple can only go with Yellow

Deciphering DNA's structure.

1. DNA is made up of subunits which scientists called nucleotides

2. Each nucleotide is made up of-a sugar- a phosphate- a Nitrogen base

DNA Subunits

• Are called nucleotides:

DNA Subunits

There are 4 different bases in a DNA molecule:

a. adenine (a purine) b. cytosine (a pyrimidine) c. guanine (a purine) d. thymine (a pyrimidine)

DNA Molecule

• The DNA molecule is one of the greatest scientific discoveries of all time

• It was described by James Watson and Francis Crick in 1953

• Watson and Crick used the photo of DNA from Rosalind Franklin

• DNA is what makes up our genes which decides each organism's physical characteristics.

Watson and Crick

Rosalind Franklin and Photo 51

DNA is like a fingerprint because everyone’s is a little

different!

How would the police look at DNA to figure out who committed a crime?

You can tell people apart by their fingerprints………

and their DNA!

Within cells, DNA is organized into structures called chromosomes.

DNA Molecule

These chromosomes are duplicated before cells divide, in a process called DNA replication.

Summary of DNA Structure

• DNA is a double helix• DNA has a base-pair rule: A –T, C—G• The N bases are on the inside of the ladder• The sugar and phosphate groups are on the

outside rungs of the ladder

Suspect #1 DNA sample

Our DNA has different sizes of pieces so it makes a different pattern when it’s all

cut up.Suspect #2 DNA sample

In DNA profiling, the lengths of sections of DNA are compared between people. This is a technique used for identifying a criminal

                         

                         

This is what it really looks like!!!

Suspect #1 Suspect #2

Genetic fingerprinting is used in forensic science, to match suspects to samples of blood, hair, saliva or semen.

DNA Replication

Steps of DNA Replication

• The two strands of the DNA molecule “unzip”

• Each strand becomes a “template” or model to make a new matching strand

• A always bonds with T and C always bonds with G

• Two new identical DNA strands form!