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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

• 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. sugar2. phosphate group3. nitrogen base

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• Examples of nucleic acids are :1. DNA2. RNA

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DNA = deoxyribonucleic acid its components are:

1. deoxyribose (sugar)2. phosphate group3. 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 pyrimidines

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Watson & CrickDiscovered the structure of DNA

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 • 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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What are chromosomes???

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Nucleotides make up DNA DNA winds into ChromatinChromatin condenses into ChromosomesChromosomes contain GenesGenes are sections of DNADNA is made of nucleotides

Chromosomes contain Instructions for making YOU!!!

• 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 base

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• It also has different bases than DNA

adenine --- uracilcytosine --- 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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What are chromosomes???

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Nucleotides make up DNA DNA winds into ChromatinChromatin condenses into ChromosomesChromosomes contain GenesGenes are sections of DNADNA is made of nucleotides

Chromosomes contain Instructions for making YOU!!!

• 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. 24

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.

TCAGGGA

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III. Steps In Replication

1) Enzymes break down the hydrogen bonds between the two DNA strands, unzipping the molecule 26

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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