DNA Ch 6.1 7th
Transcript of DNA Ch 6.1 7th
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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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