In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from...
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Transcript of In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from...
![Page 1: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/1.jpg)
![Page 2: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/2.jpg)
In 1953, Watson and Crick recognize that DNA is a double-helix.
X-ray crystallography image from Franklin that provides clue to DNA structure
![Page 3: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/3.jpg)
The Components and Structure of DNA
• DNA is in the shape of a twisted ladder, called a double helix.
– The sides of the DNA are made up of
1. Deoxyribose (sugar)2. Phosphate group (links the
deoxyribose together)
– The “rungs” of DNA are made up of bases
1. Adenine 2. Cytosine3. Guanine4. Thymine
![Page 4: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/4.jpg)
Nucleotides always pair together.
“Base Pairs”Purines Pyrimidines
Adenine Thymine
Guanine CytosineIn 1949, Chargaff determined that their were equal parts A and T, and equal parts of G and C
![Page 5: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/5.jpg)
Base Pairing
![Page 6: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/6.jpg)
DNA Replication• Helicase “Hacks” the
two strands open at the hydrogen bonds.
• The DNA molecule separates into two strands
• DNA Polymerase “pastes” matching nucleotides on each half of the “unzipped” DNA.
![Page 7: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/7.jpg)
1. Helicase “Hacks” the DNA strands apart by breaking the hydrogen bonds between the nitrogen bases.
2. DNA Polymerase “reads” the nucleotide base sequence and “pastes” the correct nucleotide to the growing strand.
Old StrandOld Strand
New Strands
DNA replication is “Semi-Conservative.” DNA has one old strand and one new strand after replication is complete.
![Page 8: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/8.jpg)
• Amount of DNA varies per organism– Bacteria have ~600,000 base pairs their
genomes. (A genome is an organism’s complete set of DNA.)
– Humans have ~3,000,000,000 base pairs in our genome.
– http://en.wikipedia.org/wiki/Genome
• Each human chromosome contains 50-250 million base pairs.
This single-celled organism, Amoeba dubia, has a larger genome than you do.
![Page 9: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/9.jpg)
Chromosome Structure• DNA is long.
– E. coli bacterium is about 2 μm in length, yet it contains about 1.6 m of DNA.
– A single human cell contains ~1.8m of DNA!
(There is enough DNA in your body to stretch from here to the moon and back 70 times!!)
• Chromosomes are supercoils of DNA– Double-stranded DNA coils around histone
proteins, called chromatin– Chromatin forms coils, and then those coils
form coils again - supercoils
![Page 10: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/10.jpg)
![Page 11: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/11.jpg)
![Page 12: In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure.](https://reader036.fdocuments.us/reader036/viewer/2022062308/56649ef55503460f94c085fa/html5/thumbnails/12.jpg)
Genes• Genes are the regions of DNA that are
instructions for making proteins (a few make RNA).
• Humans have 20,000-25,000 genes.
• Only about 2% of our DNA is genes– The noncoding regions function to provide
chromosomal structural integrity and to regulate where, when, and in what quantity proteins are made.
• Compare genes: http://en.wikipedia.org/wiki/Gene