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What does DNA look like?

What does DNA look like?. Unit 5: Seventh Grade. For many years, the structure of a DNA molecule was a puzzle to scientists. In the 1950’s, two scientists deduced the structure while experimenting with chemical models. They later won the Nobel Prize for helping to solve this puzzle.

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What does DNA look like?

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  1. What does DNA look like? Unit 5: Seventh Grade

  2. For many years, the structure of a DNA molecule was a puzzle to scientists • In the 1950’s, two scientists deduced the structure while experimenting with chemical models. • They later won the Nobel Prize for helping to solve this puzzle.

  3. What is DNA? Breaking it down • As you know, inherited characteristics are determined by genes. • Genes are passed from one generation to the next. • Genes are parts of chromosomes. • Chromosomes are structures in the nucleus of most cells. • Chromosomes are made of protein and DNA • So, DNA is the material that makes up your chromosomes that determine your inherited characteristics

  4. What Does DNA stand for? • DNA stands for: • Dexoyribo • Nucleic • Acid • But is written out as deoxyribonucleic acid

  5. The pieces of the puzzle • Scientists knew that the material that makes up our genes must do two things: • Give instructions for building and maintaining cells • Must be able to be copied each time a cell divides so that each cell could contain identical genes • Scientists eventually discovered that DNA is made of subunits called nucleotides

  6. Nucleotides: Subunits of DNA • DNA is made of subunits called nucleotides. • A “subunit” is a subdivision of a larger unit. • For example: a subdivision you live in is a smaller unit of a city or town. • It takes many subunits working together to make up a whole, functioning unit. • Nucleotides are the subunits that make up DNA

  7. Nucleotides: The subunits of DNA • Although it may look complicated, the DNA in a cell is really just a pattern made up of different parts called nucleotides. • Nucleotides are molecules that, when joined together, make up DNA

  8. Nucleotides: The Subunits of DNA • Nucleotides are made up of a sugar, a phosphate, and a base. • All nucleotides are the same except for the base. • There are four different kinds of bases: • Adenine • Thymine • Guanine • Cytosine

  9. The Four Nucleotides • Each of the four bases has a different shape. • Scientists often refer to a nucleotide’s base by the first letter of it’s base • A = Adenine • T = Thymine • G= Guanine • C = Cytosine • Annie Takes Good Care

  10. Nucleotides and DNA • Imagine a set of blocks that has only four shapes, or an alphabet that has only four letters. • DNA is a long string of these blocks or letters.

  11. Chargaff’s rules • Edwin Chargaff, a biochemist, discovered that the amount of adenine (A) always equaled the amount of thymine (T). • A = T • He also found out that the amount of guanine (G) equals the amount of cytosine (C) • G= C • Annie Takes Good Care

  12. Chargaff’s rules • These findings are known as Chargaff’s Rules • At the time, these findings were thought to be relatively unimportant, but later on, Chargaff’s rules helped scientists understand the structure of DNA

  13. Watson and Crick • After looking at x-ray images of DNA showing that DNA has a spiral shape, scientists James Watson and Francis Crick concluded that DNA must look like a long, twisted ladder. • This discovery eventually helped explain how DNA is copied and how it functions in a cell.

  14. DNA’s double structure • DNA looks like a twisted ladder. • This shape is known as a double helix. • The sides of the ladder are made of alternating sugar and phosphate parts. • The rungs are made of a pair of bases.

  15. Rungs of the ladder • The rungs of the ladder are made of the bases adenine, thymine, guanine, and cytosine. • Adenine on one side of the rung always pairs with thymine (A, T) • Annie Takes • Guanine always pairs with cytosine on a rung (G,C) • Good Care

  16. Making Copies of DNA • These pairings of the bases allows the cell to replicate, or make copies of, DNA. • Each base only bonds with only one other base. • Furthermore, pairs of bases are complementary to each other. • For example GCAC will bond with CGTG • Ex: TGCA will bond with:

  17. How copies are made • During replication, a DNA molecule is split down the middle, where the bases meet. • As the bases are exposed, complementary nucleotides are added to each side of the split ladder. • Two new DNA molecules are formed. • Half of each molecule is the old DNA • Half of each molecule is the new DNA

  18. When copies are made • DNA is copied every time the cell divides • Each new cell gets a complete copy of all the DNA.

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