DNA Structure and Function

Question 1

Nucleic Acids

Answer 1

(DNA & RNA) are used to store and transfer information

Question 2

Johann Miescher

Answer 2

• Investigated the chemical composition of the nucleus
• Isolated an organic acid that was high in phosphorus
• He called it nuclein
• We call it DNA

Question 3

Griffith Discovers Transformation

Answer 3

1928, Attempting to develop a vaccine

• Isolated two strains of Streptococcus pneumoniae
  
  • Rough strain was harmless
  • Smooth strain was pathogenic-causes disease

Question 4

Transformation

Answer 4

• Harmless R cells had been transformed by material from the dead S cells
• Descendants of the transformed cells were also pathogenic

Question 5

Mystery of the Hereditary material

Answer 5

-Originally believed to be an unknown class of proteins
-Thinking was:
-heritable traits are diverse
-molecules encoding traits must be diverse
proteins are made of 20 amino acids and are structurally diverse

Question 6

What is transforming material? Oswald and Avery

Answer 6

• Cell extracts treated with protein-digesting enzymes could still transform bacteria
• Cell extracts treated with DNA-digesting enzymes lost their transforming ability
• Concluded that DNA, not protein, transforms bacteria

Question 7

Bacteriophages

Answer 7

• Viruses that infect bacteria
• Consist of protein and DNA
• Inject their hereditary material into bacteria

Question 8

Hershey and Chase’s Experiments

Answer 8

• Created labeled bacteriophages
  
  • some with radioactive sulfur
  • some with radioactive phosphorus
• Allowed bacteria labeled viruses to infect bacteria
• Asked: where are the radioactive labels after infection?

Question 9

Structure of the Hereditary Material: Hershey and Chase

Answer 9

• Experiment showed that DNA is the hereditary material
• Scientists raced to determine the structure of DNA
• 1952-Watson and Crick proposed that DNA is a double helix

Question 10

Structure of Nucleotides in DNA

Answer 10

• Each nucleotide consists of:
  
  • Deoxyribose (5-carbon sugar)
  • Phosphate group
  • A nitrogen-containing base
• Four bases/nucleotides:
  
  • Adenine, Guanine, Thymine, Cytosine

Question 11

Composition of DNA: Chargaff

Answer 11

• Amount of adenine relative to guanine differs among species
• Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosine
• A=T and G=C

Question 12

Rosalind Franklin’s Work

Answer 12

• Was an expert in x-ray crystallography
• Used this technique to examine DNA fibers
• Concluded that DNA was some sort of helix

Question 13

Watson-Crick Model

Answer 13

• DNA consists of two nucleotide strands
• Strands run in opposite directions
• Strands are held together by hydrogen bonds between bases
• A binds with T and C with G
• Molecules is a double helix

Question 14

Patters of Base Pairing

Answer 14

• A’s are across from T’s

- C’s are across from G’s

Question 15

DNA Structure Helps Explain How it Duplicates

Answer 15

• DNA is two nucleotide strands held together by hydrogen bonds
• Hydrogen bonds between two strands are easily broken
• Each single strand then serves as template for new strand

Question 16

DNA Replication

Answer 16

• Each parent strand remains intact

- Every DNA molecule is half “old” and half “new”

Question 17

Enzymes in Replication

Answer 17

• Enzymes unwind the two strands
• DNA polymerase attaches complementary nucleotides
• DNA ligase fills in gaps (ligate:to stick together)
• Enzymes wind two stands together

Question 18

DNA Repair

Answer 18

• Mistakes can occur during replication
• DNA polymerase can read correct sequence from complementary strand and, together with DNA ligase, can repair mistakes in incorrect strands
• Info is stored in DNA, transferred/transcripted to sequences of RNA, and then translated to proteins

Question 19

RNA

Answer 19

• not T, there is U-uracil.

- A bonds with U