Class Notes (808,754)
United States (313,251)
Biology (245)
BIOL 1020 (101)

BIOL 1020 16

7 Pages
Unlock Document

Auburn University
BIOL 1020
Anne- Marie Singh

BIOL 1020 – CHAPTER 16 LECTURE NOTES Chapter 16: DNA: The Molecular basis of inheritance I. Evidence that DNA is the genetic material a. What must genetic material do? i. the genetic material must be able to replicate itself ii. must be able to control living processes iii.must be able to explain mutation b. a model of genetic inheritance was in place in the early 1900s: i. Mendel’s “laws” of genetics – inherit one copy of each gene from each parent ii. chromosomes as locations/carriers of genes iii.distribution of chromosomes in making sex cells explains Mendel’s laws c. chromosomes are predominantly made of two things: protein and DNA d. from the late 1800s until the mid-1900s, most biologists believed that the genetic material was made of proteins, and that nucleic acids were inconsequential 1. proteins are very complex2. proteins have much variety e. DNA is required for genetic transformation of bacteria i. studies by Griffith in the 1920s of pneumococcus in mice 1. smooth (S) strain killed mice, rough (R) strain did not 2. heat-killed S strain did not kill mice, but heat- killed S + R strain killed mice 3. some “transforming principle” from the heat-killed S strain changed the R strain to make it deadly ii. studies by Avery and colleagues in the 1940s identified DNA as the “transforming principle” – but many were very skeptical of this result f. viruses inject DNA into bacteria and take them over: the Hershey-Chase experiments i. viruses that infect bacteria are called bacteriophages (shortened as phages) ii. viruses execute a “genetic takeover” of cells iii.using radioactive isotopes, phage were labeled with 35 32 either S to label proteins or P to label DNA iv. phage were incubated with bacteria to allow infection, and then shaken off the bacteria v. centrifugation then separated the bacteria into the pellet, with phage in the supernatant 35 32 vi. found that S stayed with the phage, while P was with the bacteria vii. Hershey and Chase concluded that phage injected DNA into bacteria to infect them viii. this convinced many more biologists that DNAis the genetic material, and the race to find the structure of DNAbegan ix. evidence gathered since the mid-1900s that DNAis the generic material has been overwhelming (much of the rest of this unit will cover that evidence) II. Structure of DNA a. recall the DNApolymer structure from deoxynucleotide monomers i. deoxynucleotide has 5-carbon deoxyribose sugar, phosphate, and nitrogenous base ii. nitrogen bases are the purines adenine (A) and guanine (G), and the pyrimidines thymine (T) and cytosine (C) iii. nucleotides are linked by a 3’, 5’ phosphodiester linkage iv. resulting chain has a 5’ end and a 3’ end v. the phosphates and sugars are collectively called the “backbone” of the strand vi. this structure had been fully worked out by the early 1950s b. Chargaff and colleagues had found that amounts of A = T and C = G c. x-ray diffraction studies by Rosalind Franklin and Maurice Wilkins indicated a helical molecule i. molecule has three repeating patterns that any model of its structure must account for ii. the data indicated a double helix iii. Franklin and Wilkins inferred that the bases are stacked like rungs of a ladder iv. DNAwas envisioned as a twisted ladder, with the sugar- phosphate backbone forming the sides and base pairs forming the rungs d. the accepted model for the structure of the DNAdouble helix was published by James Watson and Francis Crick in 1953 i. model explained all three repeating patterns seen in x-ray diffraction, as well Chargaff’s data on base ratios ii. double helix with antiparallel strands 1. each strand a nucleotide chain held together by phosphodiester linkages 2. strands held together by hydrogen bonds between the bases (basepairs) a. Apaired with T, with 2 hydrogen bonds predicted b. C paired with G, with 3 hydrogen bonds predicted 3. the strands were described as complementary: the sequence of one had to have an appropriate, complementary sequence on the other for the molecule to hold together 4. the double-helix model strongly suggested a way to store information in the sequence of bases, which indeed appears to be true iii.the determination of the DNAstructure by Watson and Crick is considered the major landmark of modern biology III. DNA replication is semiconservative a. DNAstructure suggests an obvious replication mechanism i. Watson and Crick noted that “specific [base]pairing...immediately suggests a possible copying mechanism for the genetic material” ii. the model suggested that each strand could serve as a template for making a complementary strand, so-called semiconservative replication 1. one strand old, one new iii.competing, less-elegant models were conservative replication (both strands either old or new) and dispersive replication (each strand a mix of old and new) b. experiments with E. coli supported the semiconservative repli
More Less

Related notes for BIOL 1020

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.