Lecture 5: Nucleic Acids and the Encoding of Biological Information - Learning Objectives: Chapter 3.1-3.2

Question 1

Describe Frederick Griffith’s groundbreaking experiment

Answer 1

• 1st experiment suggesting bacteria are capable of transferring genetic information and molecular information between organisms.
• virulent strain: caused pneumonia and death in mice
  • nonvirulent strain: healthy mouse

Question 2

Describe the Avery, MacLeod, McCarty experiment and explain

how it proved that DNA is the genetic material

Answer 2

• DNA extracted from heat-killed virulent cells and RNA and protein.
• Untreated extract can transform nonvirulent cells into virulent cells.
• Only extracts treated with the enzyme that destroys DNA were unable to transform nonvirulent bacteria.

Question 3

Relate the regulation of transcription and translation to the formation of different cell types in the body (at a very basic level)

Answer 3

• Transcription and translation are tightly regulated: can be turned on or off according to the needs of a cell.

• The diversity of cell types in the body arises from differences in transcription and translation

Question 4

Know and compare where transcription and translation takes place in eukaryotes and prokaryotes.

Answer 4

Prokaryotic cells: transcription and translation both occur in the cytoplasm

Eukaryotic cells: transcription occurs in the nucleus and translation occurs in the cytoplasm

Question 5

Know the components of a nucleotide and relate the negative charge of DNA to the presence of phosphate groups

Answer 5

• deoxyribose sugar
• nitrogenous base
• one or more phosphate groups

At cellular pH, the phosphate group has two negative charges on its oxygen atoms: gives DNA its negative charge

Question 6

Describe the polarity of DNA with respect to its 5’ and 3’ ends

Answer 6

DNA has polarity: one end differs from the other; free 5’ phosphate group and a free 3’ hydroxyl group.

Question 7

Know the properties of the double helix

Answer 7

Properties
• two strands of DNA wrap around each other to form a helix that coils to the right
• sugar-phosphate backbones wind around the outside of the molecule and the bases point inward
• outside contours form the major and minor grooves; sites of protein contact
• the two strands are antiparallel: they run in opposite directions.

Question 8

Chargaffs rule?

Answer 8

%A=%T

%G=%C

Question 9

Describe hydrogen bonding and base stacking

Answer 9

• Hydrogen bonds are weak but contribute to the stability of the DNA double helix
• Base stacking: nonpolar surfaces of the bases stack tightly and repel water; contributes to the stability of DNA

Question 10

Know the basic structure of chromatin and the function of histone proteins

Answer 10

Chromatin In eukaryotes: DNA in the nucleus
exists as linear chromosomes

Packaging problem:
chromosomes are 1000s of times longer than the diameter of the cell

Solution: Packaged with proteins called histones

Histone proteins: rich in positively charged amino acids; form ionic bonds with the negatively charged sugar-phosphate backbone of the DNA