Lecture 10a Flashcards
What properties should the molecule of inheritance have?
- Information content: must instruct cell how to make everything
- Replication
- Regulation: control expression to adapt to environment
- Variation: changes lead to different function, basis for evolution
What is the difference between S and R strain cells?
S: virulent type enclosed in capsule, smooth appearance
R: Nonvirulent type, no capsule, rough appearance
What happens when mice are injected with live S cells?
Live R cells? Heat killed S cells? Heat killed S cells with live R cells?
Live S cells: mouse dies
Live R cells: mouse lives
Heat killed S cells: mouse lives
Heat killed S cells with live R cells: mouse dies and live S cells recovered (transformation occurs, live R cells converted to live S cells)
Describe the mouse experiment that provided support that DNA is the transforming principle.
Different components of the heat killed S strain extract were destroyed (Polysaccharides, protein, lipid, RNA, DNA) then mixed with live R cells and injected into mice. Live S cells were recovered from all experiments except when DNA was destroyed. People were still skeptical after this experiment because they thought DNA might just be activating a protein.
Describe the phage experiment that determined DNA is the transforming principle.
The experiment uses two sets of T2 bacteriophage. In one set, the protein coat is labeled with radioactive sulfur (35S), not found in DNA. In the other set, the DNA is labeled with radioactive phosphorus (32P), not found in amino acids. Only the 32P is recovered from the E. coli, indicating that DNA is the agent necessary for the
production of new phages. Radioactive sulfur was mostly recovered in phage ghosts. Radioactive phosphorous was mostly recovered in bacteria.
What are the three main building blocks of DNA?
4 nitrogenous bases, deoxyribose sugar, phosphate
Which bases are purines (2 rings)?
A and G
Which bases are pyrimidines (1 ring)?
T and C
How many hydrogen bonds between A and T?
2
How many hydrogen bonds between G and C?
3
What are defining characteristics of DNA?
Double helix, strands are antiparallel, purine-pyrimidine pairing, hydrogen bonds between bases, sugar-phosphate backbone on outside, bases point inward
Describe chromosome structure in prokaryotes.
One chromosome, circular, devoid of proteins associating with DNA. DNA is readily accessible to RNA polymerase.
What are nucleotides composed of?
Phosphate group, deoxyribose sugar, and one of the four nitrogenous bases
What did the X ray diffraction image show?
DNA is long, skinny, has two parts parallel to each other, and helical.
Describe chromosome structure in eukaryotes.
Chromosomes packaged into chromatin. Multiple linear chromosome are wound around histone spools. 8 histone proteins assemble to make a make a spool. The extent of coiling changes with cell cycle. Most of the time uncoiled and not able to see in nucleus.
