DNA Structure

1
DNA Structure
2
Watson and Crick

• able to take all information from the work of
  scientists before them
• proposed a 3-D model of the DNA molecule capable
  of
• copying itself accurately
• being translated into a living organism

3
James Watson today-President of Cold Spring
Harbor Laboratory
4
Monomer

• building block of a larger molecule
• monomers are hooked together to make polymers

5
Polymers

• large molecule made of repeating subunits

6
DNA monomer

• nucleotide
• made of 3 parts
• pentose sugar (5 carbons)
• in DNA the sugar is deoxyribose

7
Deoxyribose
8
Phosphate group

• this is why DNA contains phosphorus
  (Hershey-Chase experiment)
• gives DNA a negative charge
• attaches to the fifth carbon on deoxyribose

9
Nitrogen bases

• are either purines or pyrimidines
• contain nitrogen
• purines have a double ring structure (adenine and
  guanine)
• pyrimidines have a single ring structure
  (cytosine and thymine)

10
Nucleotide structure

• the phosphate attaches to the 5 carbon of the
  sugar
• this end is known as the 5 end of the nucleotide
• the nitrogen base attaches at right angles to the
  1 carbon of the sugar

11
Phosphodiester bonds

• the next nucleotide must attach to the 3 end of
  the sugar
• the OH group is displaced and the phosphate group
  of the next nucleotide attaches to the 3 carbon

12
Chargaffs rules

• cytosine and guanine pair with 3 hydrogen bonds
• thymine and adenine pair with 2 hydrogen bonds
• AT and CG

13
(No Transcript)
14
Constant diameter of DNA

• in order for the DNA ladder to be even width all
  along the molecule
• a pyrimidine and a purine must pair together (2
  rings 1 ring3rings)
• this explains Chargaffs rules

15
Unnumbered Figure (page 292) Purine and pyridimine
16
Two chains are connected

• by hydrogen bonds
• each H bond is very weak
• many together make a strong bond
• but can be opened for
• replication

17
Anti-parallel orientation

• one strand is oriented 5---- 3
• the other is opposite-oriented 3 --- 5
• Think of two trains running on parallel tracks
• One going east, the other west
• Each has an engine and a caboose
• 5 end is engine, 3 end is caboose

18
Figure 16.5 The double helix
19
Rosiland Franklin

• took x-ray diffraction pictures of DNA
• Watson saw this and knew DNA was helical

20
Major Groove and minor groove

• is not an even helix like a spring
• is kind of drawn out
• Minor groove Major groove

21
number of bases per turn

• 10 bases per turn
• each base is 3.4 angstroms apart
• so from major groove to major groove is 34
  angstroms

22
(No Transcript)
23
http//campus.queens.edu/faculty/jannr/Genetics/im
ages/BX03_401a_c.WatsonCrickJPG
24
So what is DNA?

• DNA is like a hard drive that stores digital
  information
• Cant execute that information
• Needs an operating system
• Like a language-lets call it genetish
• If this is the book of life, what is reading
  it?
• How does the information in DNA get turned into
  action?