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Chapter 16: The Molecular Basis of Inheritance. Important Point:. If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!. Chromosomes consist of both DNA and Protein

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Presentation Transcript
important point
Important Point:

If you are having trouble

understanding lecture material:

Try reading your text

before attending lectures.

And take the time to read it well!

the hereditary material

Chromosomes consist of both DNA and Protein

  • DNA was discovered before its role in heredity was understood
  • People had a sense that chromosomes embodied inheritance before they understood that DNA was the hereditary material
  • People did not want to believe that DNA was the hereditary material since it is not complex enough
  • Instead, people believed that proteins must be the hereditary material—they were wrong
  • Transformation (I.e., Griffith’s experiment, which is mediated by DNA) was discovered before it was understood that it was mediated by DNA
The Hereditary Material
transformation
Transformation

Griffith, 1928

transforming principle sensitivity to dnase
Transforming Principle Sensitivity to DNase

Hi, I’m Oswald Avery. I figured out that the transforming principle is DNA!

I did this by treating transforming principle with different enzymes, proteases, RNases, DNases… only DNase destroyed its activity

Avery, MacLeod, McCarty (1944)

avery macleod mccarty 1944
Avery, MacLeod, McCarty (1944)

Hi, I’m Theodosius Dobzhanky. I wrote: “Genetics and the Origin of Species” (1937)

Hi, I’m Colin M. MacLeod

Hi, I’m Maclyn McCarty

Colin M. MacLeod, Maclyn McCarty, Detlev Wulf Bronk, Theodosius Dobzhansky, and Wendell M. Stanley

Hi, I’m Detley Wulf Bronk. I asked, “Are aliens living among us” (really)

Hi, I’m Wendell M. Stanley. I crystalized (and then X-rayed) tobacco mosaic virus!

erwin chargaff
Erwin Chargaff

I made an important observation on the chemistry of DNA

maurice wilkins 1950

I took the first quality X-ray diffraction images of DNA, and am credited with sparking the interests of both Watson and Crick in the question of DNA’s structure

Maurice Wilkins (1950)

Rosalind Franklin worked under me

the double helix
The Double Helix

Strand complementarity

Strand polarity

Antiparallel strands

nucleotide incorporation

3’ OH

Nucleotide Incorporation

Pyrophosphate hydrolysis powers nucleotide addition

lagging leading strands
Lagging & Leading Strands

Both daughter strands are laid down in the 5’ to 3’ direction

~100-2000 bases long, depending on species

replication fork components
Replication Fork Components

Yes, difficult to read, but it is in your text!

replication fork
Replication Fork

Topoisomerase acts here

proofreading
Proofreading

“During DNA replication, DNA polymerases proofread each nucleotide against its template as soon as it is added to the growing strand. Upon finding an incorrectly paired nucleotide, the polyerase removes the nucleotide and then resumes synthesis. (This action is similar to fixing a typing error by using the ‘delete’ key and then entering the correct letter.)” p. 305, Campbell & Reece (2005)

the problem of ends
The Problem of Ends

Erosion of ends

a solution telomeres
A Solution: Telomeres

Telomere are sequences found on the ends of Eukaryotic DNA that are added on by an enzyme called telomerase

Telomeres erode so that genes don’t have to!