1. What are the three components of this DNA nucleotide?

2. What is the function of DNA in the cell?

• Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits.

• DNA achieves its control by holding the instructions on how to make all different kinds of proteins.

DNA

• All actions, such as eating, running, and even thinking, depend on proteins called enzymes.

So what? Why are proteins important????

DNA

• You are composed of proteins- your skin contains proteins….organs, muscles, bones…..

• Enzymes are proteins that control the chemical reactions needed for life.

Why is this important???

What do enzymes do?

• DNA is a polymer made of repeating subunits called nucleotides.

• Nucleotides have three parts:

a simple sugar,

a phosphate group,

and a nitrogenous base.

Phosphate group

Sugar

Nitrogenous base

What is DNA made of?

• The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.

• The simple sugar in DNA, called deoxyribose, gives DNA its name—deoxyribonucleic acid.

What is DNA made of?

Sugar

Phosphate group

• A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.

What is DNA made of?

Nitrogenous base

• In DNA, there are four possible nitrogenous bases:

Adenine (A) Guanine (G) Thymine (T)Cytosine (C)

What is DNA made of?

• Thus, in DNA there are four possible nucleotides, each containing one of these four bases.

What is DNA made of?

• The phosphate groups and sugar molecules form the backbone of the chain

DNA STURCTURE

• The nitrogenous bases stick out like the teeth of a zipper.

Nucleotide

• The phosphate groups and sugar molecules form the backbone

DNA STURCTURE

• The nitrogenous bases stick out like ladder rungs in the middle

Nucleotide

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

• In DNA, adenine always pairs with thymine,

A --- T

• and guanine always pairs with cytosine.

G --- C

DNA STRUCTURE

• These paired bases are called complementary base pairs.

• When something is twisted like a spring, the shape is called a “helix”.

• Because DNA is composed of two strands twisted together, its shape is called double helix.

DNA STRUCTURE

Chromosome

The sequence of nucleotides forms the unique genetic information of an organism.

The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

DNA STRUCTURE

• Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.

DNA STRUCTURE

• Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.

• The DNA in the chromosomes is copied in a process called DNA replication.

• Without DNA replication, new cells would have only half the DNA of their parents.

DNA REPLICATION

Replication of DNAReplication of DNA

ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

3’

5’

3’

5’

DNA Template

New DNA

Parental DNA

• DNA is copied during interphase prior to mitosis and meiosis.

• It is important that the new copies are exactly like the original molecules.

DNA REPLICATION

Proofreading New DNAProofreading New DNA

• EnzymesEnzymes proofread and correct these proofread and correct these mistakesmistakes

• The new error rate for DNA that has been The new error rate for DNA that has been proofread is proofread is 1 in 1 billion1 in 1 billion base pairing base pairing errorserrors

Talk to the people next to you about what a DNA nucleotide is and what it is made of.

2.What is a DNA nucleotide made of?

3.How many nucleotides are in the pic below?

Talk to the people next to you about when DNA replication takes place.

4. When does DNA replication occur?

Talk to the people next to you and make sure you understand complementary base pairs in DNA.

1.What is the complementary strand for:

ATCGGATCG

Talk to the people next to you about what DNA replication starts and ends with.

5. What is the end result of DNA replication?

Question 1

Which of the following is NOT a component of DNA?

D. proteins

C. nitrogenous bases

B. phosphate groups

A. simple sugars

The answer is D.

Question 2 Which of the following correctly comprises a

complimentary base pair?

D. cytosine – thymine

C. guanine – adenine

B. thymine – guanine

A. adenine – thymine

The answer is A.

Question 3Which DNA strand can base pair with the DNA strand shown here (Top of pic to bottom)?

D. T-C-C-A-G

C. T-G-C-A-G

B. T-G-C-A-T

A. T-A-C-G-T

To return to the chapter summary click escape or close this document.

The answer is B, T-G-C-A-T. In DNA, adenine pairs with thymine and cytosine pairs with guanine.

T

G

C

A

T