DNA Structure

Adapted from cmassengale 1

Learning Goals

Unit Learning Goal: You can analyze all of the structural relationships among DNA, genes, and chromosomes and cite substantial evidence for DNA replication, as part of the cell cycle, being essential to the molecular basis of heredity in viruses and living things. Presentation Learning Goal(s): 1. You can diagram and describe the structure of

Deoxyribonucleic acid including the labeling of all purines, pyrimidines, primes

2. You can describe why the structure of DNA can lead to mutations.

Unit Learning Goal Scale 4 - You can analyze all of the structural relationships among DNA, genes, and chromosomes and cite substantial evidence for DNA replication, as part of the cell cycle, being essential to the molecular basis of heredity in viruses and living things.

3 - You can analyze most of the structural relationships among DNA, genes, and chromosomes and cite some evidence for DNA replication, as part of the cell cycle, being essential to the molecular basis of heredity in viruses, and living things.

2 - You can explain some of the learning goal on your own but may need some help to complete the entire learning goal.

1 - You can answer questions about the learning goal but cannot give specifics using your own words.

DNA Overview • Stands for Deoxyribonucleic acid

• Made up of subunits called nucleotides

• Nucleotide made of: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base

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DNA Nucleotide

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O=P-O O

Phosphate Group

N Nitrogenous base (A, G, C, or T)

CH2

O

C1 C4

C3 C2

5

Sugar (deoxyribose)

O

DNA Structure • Two strands coiled together like

a ladder called a double helix. • “Sides” or “Backbone” made of a

pentose sugar, Deoxyribose, bonded to phosphate (PO4) groups by phosphodiester bonds.

• “Rungs” made of organic, nitrogen-containing bases bonded together by weak hydrogen bonds

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DNA Double Helix

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Nitrogenous Base (A,T,G or C)

“Rungs of ladder”

“Sides of ladder”

Phosphate & Sugar Backbone

Mutations @ Hot spots

• Most DNA has a right-hand twist with 10 base pairs in a complete turn

• Left twisted DNA is called Z-DNA or southpaw DNA

• Hot spots occur where right and left twisted DNA meet producing mutations

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A Closer View

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P

P

P

O

O

O

1

2 3

4

5

5

3

3

5

P

P

P O

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Nitrogenous Bases

• Double ring PURINES Adenine (A) Guanine (G) • Single ring PYRIMIDINES Thymine (T) Cytosine (C)

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T or C

A or G

Nitrogen Base-Pairing • Purines only pair with Pyrimidines

• Three hydrogen bonds required to bond Guanine & Cytosine

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C G

3 H-bonds

•Two hydrogen bonds are required to bond Adenine & Thymine

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T A

Antiparallel Strands

• One strand of DNA goes from 5’ to 3’ (sugars)

• The other strand is opposite in direction going 3’ to 5’ (sugars)

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Summary

Add to your DNA Model:

• Create a color coded key for 6 parts of DNA

• Label “sides” or “backbone” and “rungs”

• Identify purines, pyrimidines

• Draw in hydrogen bonds

• Label 3’ and 5’ ends to identify antiparallel nature of DNA (reference page 221 in textbook)

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