Let’s Review!

• What is a macromolecule?

• What are the four kinds of organic molecules?

• What are nucleic acids made of?

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- A large organic molecule (made of carbon!)

- Carbohydrates, lipids, proteins and nucleic acids

- Phosphate group, 5-carbon sugar, nitrogenous base

What other molecule is made up of phosphates and 5-carbon sugar? (hint: it releases energy!)

• ATP!

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Adenine

Ribose 3 Phosphate groups

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• Nucleic Acids are the chemical link between generations dating back to the beginning of life on earth.

 

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• A nucleic acid is a complex macromolecule that stores information in cells in the form of a code.

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• Nucleic acids are made of long chains of nucleotides.

 • Nucleotides are made of three

components:

1. sugar

2. phosphate group

3. nitrogen base6

• Examples of nucleic acids are :

1. DNA

2. RNA

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DNA = deoxyribonucleic acid

 

its components are:

1. deoxyribose (sugar)

2. phosphate group

3. nitrogen base

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The Components and Structure of DNA

There are four kinds of bases in in DNA:

• adenine• guanine • cytosine• thymine

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• James Watson and Francis Crick proposed that DNA has a specific pairing between nitrogen bases:

Adenine (A) – Thymine (T)

Guanine (G) – Cytosine (C)

A and G are purines (AGgies eat Purina)

C and T are pyrimidines10

 • Watson and Crick

also said the paired nitrogen bases formed two long strands of nucleotides that compliment each other.

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• Nitrogen Bases are connected

between sugars and phosphates• They declared, “This structure is

a “double helix”.

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The Components and Structure of DNA

DNA Double Helix

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• DNA forms chromosomes, units of genetic information which pass from parent to offspring.

                        DNA is wound into structures called chromosomes during cell division (prophase)

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• If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

                

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• RNA has a different sugar than DNA

• RNA = ribonucleic acid

• It’s components are :

1. ribose (sugar)

2. phosphate group

3. nitrogen base16

• It also has different bases than DNA

adenine --- uracil

cytosine --- guanine

 

• RNA is also single stranded, not double stranded like DNA.

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DNA RNA

- Double stranded - Single stranded

- Sugar = deoxyribose

- Sugar = ribose

- Adenine pairs with Thymine

- Adenine pairs with Uracil

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I. Why Must DNA Replicate? • Every time a cell divides, it must

first make a copy of it’s chromosomes.

• Therefore, each cell can have a complete setof chromosomes.

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• Without replication, species could not survive and individuals could not successfully grow and reproduce.

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II. How DNA Replicates

• DNA is a molecule composed of TWO strands, each consisting of a sequence of nucleotides.

• The order of the nitrogen bases on one strand mandates the sequence of bases on the complementary strand.

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If you know the bases on one strand, you can predict which bases will occur on the complementary strand.

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

During Replication each strand serves as a template to create a new strand.

This is as easy as break dancing!

TCAGGGA

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III. Steps In Replication

1) Enzymes break down the hydrogen bonds between the two DNA strands, unzipping the molecule

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2) As the DNA unzips, free nucleotides (from surroundings in the nucleus) bond to the single strands by base pairing (A-T, G-C)

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3) Another Enzyme bonds the new nucleotides into a chain

** The result of this process is the formation of TWO DNA molecules, each identical to the original molecule.Replication! Rah,Rah, Rah!

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DNA Replication

Nitrogen Bases

Replication Fork

DNA Polymerase

Replication Fork

Original strandNew Strand

Growth

Growth

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1. What are the two types of nucleic acids?2. What are the three components of a

nucleotide?3. What are the similarities between DNA and

RNA? What are the differences?4. Describe the process of DNA replication.5. Why does a DNA molecule undergo

replication?

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