DNA Structure and Function

DNA Structure and Function

KEY CONCEPTS

• Who helped discover DNA?

• What does DNA do for us?

• What is the structure of DNA?

• What is DNA made of?

VOCABULARY

• DNA• Adenine• Guanine• Cytosine• Thymine• Purines• Pyrimidines• Nucleotide

DNA

• DNA stands for deoxyribonucleic acid • Large molecule that contains all genetic

information• Functions of DNA:

– Directs the activities of cells– Contains the instructions cells use to make

proteins

• What kinds of things do living organisms use proteins for?

History

• Rosalind Franklin took the first x-ray pictures of DNA molecules

• The x-ray pictures helped scientists to determine the shape of DNA.

• What is the shape of a DNA molecule?

History

• James Watson and Francis Crick built the first DNA model

• They are given credit for first determining the double helix shape

Structure

• A strand of DNA is made of monomers called nucleotides

• Each nucleotide has three parts:

1. Sugar (deoxyribose)

2. Phosphate

3. Nitrogen base• The nitrogen base

always binds to the sugar of a nucleotide

Structure

There are four different DNA nitrogen bases: 1. Adenine

2. Guanine

3. Cytosine

4. Thymine

• Adenine and guanine are single-ringed purines

• Cytosine and thymine are double-ringed pyrimidines

Structure

• Label the following parts of the DNA nucleotides below: adenine, thymine, guanine, cytosine, purines, pyrimidines, phosphate, and sugar

Structure

• Nucleotides bond together to form a double stranded DNA molecule

• DNA’s structure looks like a twisted ladder– This structure is called the double helix

• The deoxyribose and phosphate form the “sidepieces,” of the ladder.

• Nitrogen bases bond together to form the “rungs,” of the ladder.

Structure

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Structure• Label the following parts of the DNA molecule below:

nucleotide, hydrogen bonds, sugar-phosphate backbone

Chargaff’s Base Pairing Rules

• Adenine always bonds to thymine

• Cytosine always bonds to guanine

• The nitrogen bases are bonded with weak hydrogen bonds

• Why do only certain nitrogen bases bind to each other?

Chargaff’s Base Pairing Rules

• Complete the other half of the DNA molecule below using Chargaff’s base pairing rules:

A T G A A C G T C A C C G T A C A T C G T

DNA and Chromosomes

• In eukaryotic cells, DNA molecules are tightly wound into chromosomes

• Where are chromosomes located in eukaryotic cells?

• Chromosomes contain all the DNA needed to carry out cellular functions

Histones

DNA and Chromosomes

• Label the following parts of the diagram below: double helix, chromosome, supercoils, coils, histones, proteins