Lesson 2.1 - DNA & Inheritance

Question 1

Mendel’s work (1900)

Answer 1

Chromosomes observed (genotype), but unclear how it was connected to phenotype

Question 2

T.H. Morgan’s Group (1920s)

Answer 2

Showed that genes were carried on chromosomes; [20] proteins assumed to be genetic material; fruit flies

Question 3

Who initially performed the transforming principle?

Answer 3

Microbiologist Griffith

Question 4

Transforming Principle concluded that…

Answer 4

something from heat-killed S cells transformed live R cells; standard assumption was that proteins were responsible

Question 5

Transforming Principle Results (1928)

Answer 5

Smooth strains = virulent, rough strains = avirulent

Question 6

Indirect evidence supporting hypothesis that DNA is genetic material

Answer 6

• Using dyes that bind to DNA showed that
  
  • DNA doubles during “S” phase of cell cycle
  • Diploid (2n) and haploid (n) exists
    
    • After meiosis, gametes have 1/2 of DNA

Question 7

What are the results of the transforming principle (1944)?

Answer 7

R cells were transformed by DNA from heat-killed S cells; example of HGT

Question 8

Who performed transforming principle (1944)?

Answer 8

Avery, MacLeod, & McCarty

Question 9

Chargaff’s Rule

Answer 9

Purines = Pyrimidines (A = T, G = C)

No organism was 50/50 (e.g. Virus QX174 did not fit data bc single stranded)

Question 10

Rosalind Franklin (1951)

Answer 10

• Analyzed DNA helix with X-ray crystallography
  
  • Turn every 3.4 nm, Diameter of 2.0 nm

Question 11

How does X-ray crystallography work?

Answer 11

Create 2-D images by defracting rays onto plate

Question 12

How did the 3-D structure of DNA came to be?

Answer 12

• (1953) Models built using following data:
  
  • Alpha-helix by Franklin & Wilkins
  • Width & no. bases per turn by Franklin & Stokes
  • Purine = Pyrimidine by Chargaff

Question 13

Purine Bases

Answer 13

Adenine, Guanine

Question 14

Pyrmidine Bases

Answer 14

Cytosine, Thymine (DNA), Uracil (RNA)

Question 15

Who won the Nobel Prize in Physioology or Medicine (1962)?

Answer 15

Francis Crick, James Watson, & Maurice Wilkins

Question 16

Structure of DNA

Answer 16

• Nitrogenous base
  
  • Pyrimidine (1-ring)
  • Purines (2-ring)
• Pentose (5C) deoxyribose
• Phosphate (PO₄) group
• Major (2.2 nm) & Minor (1.2 nm) groove

Question 17

How is DNA synthesized?

Answer 17

• Connect sugar of one nucleotide, and phopshate of next
• Occurs via a phosphodiester link/bond, creating a backphone
  
  • 5’ of PO₄ of incoming nucleotide and 3’ OH

Question 18

What is the Hershey & Chase experiment (1952)?

Answer 18

• Bacteriophage T2 infects E. coli
  
  • Protein: ³⁵S
  • DNA: ³²P
• Demonstrated that DNA (not protein) transferred, & is genetic material = inheritance

Question 19

DNA sequences are always written…

Answer 19

5’ to 3’

Question 20

Deoxyribose sugar structure

Answer 20

Question 21

Ribose sugar structure

Answer 21

Question 22

3 Hypothesis Models for DNA Replication

Answer 22

Semiconservative, Conservative, and Dispersive

Question 23

What is the Meselson - Stahl experiment?

Answer 23

• Each round E.coli in ¹⁵N (red) medium was transfered to a ¹⁴N (orange) medium, DNA sediments halfway.
• Supports semiconservative model

Question 24

DNA polymerase can only add nucleotides to the _____ end of a growing DNA strand.

Answer 24

free 3’-OH

Question 25

DNA Replication Overview (terms: primase, primer, polymerase, leading and lagging strand, ligase)

Answer 25

* **Primase** binds to template strand, synthesizes RNA **primer** * Starts with RNA dNTPs, then DNA dNTPs * **DNA polymerase III** synthesizes DNA * **Leading strand** synthesized continously * **Lagging strand** (Okazaki fragments) ligated by **ligase**

Question 26

Why is the lagging strand looped during DNA synthesis?

Answer 26

It allows both strands to be synthesized concurrently by inverting the lagging strand

Question 27

Replisome

Answer 27

Proteins that unwind DNA and synthesize new strands

Question 28

Helicase

Answer 28

untwists and separates template DNA strands at replication fork

Question 29

Single-strand binding proteins

Answer 29

keep unpaired template strands apart during replication

Question 30

Gyrase

Answer 30

removes knots or create twists in duplex DNA; cuts ds DNA and passes one through the other

Question 31

Ligase

Answer 31

catalyze phophodiester bond formation between new DNA; links Okazaki fragments together

Question 32

Sliding ß-clamp

Answer 32

guides DNA polymerase and assists other proteins/enzymes

Question 33

Topoisomerase IV

Answer 33

passes one ds DNA through another; cuts ds DNA

Question 34

Bacteria & Archaea divide by...

Answer 34

* **Binary Fission** * Replication from single origin (ori) * Plasmids - 1 ori site * Replication around cirlce requires primer w/ available 3'-OH

Question 35

*E. coli uses \_\_\_\_\_\_\_\_\_* to cut one of the chromosomes to separated interlocked chromosomes.

Answer 35

Topoisomerase IV

Question 36

DNA Polymerase I (Characteristics, Function)

Answer 36

* 5' - 3' Polymerization: + * 3' - 5' Exonuclease: + * 5' - 3' Exonuclease: + * Function: Joins Okazaki fragments

Question 37

DNA Polymerase II (Characteristics, Function)

Answer 37

* 5' - 3' Polymerization: + * 3' - 5' Exonuclease: + * 5' - 3' Exonuclease: - * Function: Restarted stalled polymerase

Question 38

DNA Polymerase III (Characteristics, Function)

Answer 38

* 5' - 3' Polymerization: + * 3' - 5' Exonuclease: + * 5' - 3' Exonuclease: - * Function: Main replicase

Question 39

DNA Polymerase IV (Characteristics, Function)

Answer 39

* 5' - 3' Polymerization: + * 3' - 5' Exonuclease: - * 5' - 3' Exonuclease: - * Function: Repairs damaged DNA

Question 40

DNA Polymerase V (Characteristics, Function)

Answer 40

* 5' - 3' Polymerization: + * 3' - 5' Exonuclease: - * 5' - 3' Exonuclease: - * Function: Repairs damaged DNA, translesion, DNA synthesis

Question 41

3' - 5' Exonuclease function

Answer 41

* Makes cut at misplaced base; proofreading technique; can stop and go backwards * Bacterial DNA polymerase I, II, and III

Question 42

Nucleotide Excision Repair System (Cause of damage, solution)

Answer 42

* Damage caused by UV radiation & chemicals * e.g. Pyrimidine dimers (covalent bond b/t adjacent pyrimidines) * **Nuclease** cuts out damaged strand * Gap filled by DNA polymerase & ligase