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Chapter 6 Section 1

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` List 3 important events that led to understanding

the structure of DNA

` Describe the basic structure of a DNA molecule

` Explain how DNA molecules can be copied

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` Inherited characteristics are determined by

genes

` Genes are passed from generation to

generation` Genes are parts ofchromosomes

` Chromosomes are made of proteins & DNA

` DNA stands fordeoxyribonucleic acid

` DNA is the genetic material that determinesinherited characteristics

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` Material that makes up genes can do 2 things Give instructions for building & maintaining cells

Must be able to be copied each time a celldivides

each cell will contain identical genes

` This could be done with complex molecules

(proteins)

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` Nucleotides: consist of a sugar, a phosphate, & a

base

` Nucleotides are identical except for the base

` The 4 bases are: ADENINE

THYMINE

GUANINE

CYTOSINE

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` Each base has a different shape

` Bases are referred to using their first letter

` A adenine

` T thymine

` G guanine

` C - cytosine

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http://www.freewebs.com/genetics37/4Nucleotides.JPG

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` Erwin Chargaff (1950s biochemist)

` Discovered that the amount ofadenine always =

the amount ofthymine

` The amount ofguanine always = the amount of

cytosine

` These rules helped scientists to better understand

the structure of DNA

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` Rosalind Franklin (Britain) made images of DNA

molecules

` Using X-ray diffraction to make the images

` X-rays are aimed at the DNA molecule, the pattern

made by rays bouncing off is captured on film

` Showed the spiral shape

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http://www.uic.edu/classes/bios/bios100/lectures/x-ray-diffraction.gif

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` Proposed that DNA structure was like a long

twisted ladder

` Their model perfectly fit Chargaff and Franklinsfindings

` The model helped to explain how DNA is copied

and functions in a cell

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http://www.nature.com /scitable/nated/content/24263/sadava_11_8_large_2.jpg

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` The double ladder design is known as the double

helix

` 2 sides of the ladder are made of alternating sugar& phosphate parts

` The rungs are made of a pair of bases

` A pairs with T;G pairs with C

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` Pairing of bases allows the cell to replicate (make

copies of) DNA

` Each base always bonds with only one other base(complementary bases)

` Example: the sequence CGAC bonds to the

sequence GCTG

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` During replication, a DNA molecule is split down

the middle where the bases meet

` Each side is used as a pattern for a new strand

` Complementary nucleotides are added to each

side of the ladder

` 2 DNA molecules are formed

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http://library.thinkquest.org/C006188/basics/pictures/dna_replication.gif

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` DNA is copied every time a cell divides

` Each new cell gets a complete copy of all the DNA

` The job of unwinding, copying, and re-winding the

DNA is done by the proteins within the cell

` Other proteins help to carry out instructions in the

code of the DNA

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