BIO 201 Cell Biology with Todd Hennessey Week Nine Notes
BIO 201 Cell Biology with Todd Hennessey Week Nine Notes BIO 201
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This 6 page Class Notes was uploaded by ChiWai Fan on Friday April 1, 2016. The Class Notes belongs to BIO 201 at University at Buffalo taught by TODD HENNESSEY in Spring2015. Since its upload, it has received 113 views. For similar materials see CELL BIOLOGY in Biology at University at Buffalo.
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Date Created: 04/01/16
Cell Biology on April 1, 2016 (All images taken from Professor Hennessey’s slide—edited by ChiWai Fan) Chapter 11: The cell cycle and cell division (nuclear division/DNA division) Prokaryotic Cell Division (Bacterial Cell Division)—Got one piece of closed circular DNA Make sure DNA is identical! One piece of closed circular double-stranded bacterial DNA Daughter cells (one to two) What would happen if you added radioactive thymidine ( H-T) during DNA replication? Would both daughter cells be radioactive? YES. How is DNA replicated? Meselson-Stahl Experiments 1. Grow bacteria on “heavy” nitrogen ( N) to metabolically label all DNA (N-15 isradioactive nitrogen) creating all heavy nitrogen 2. Then switch to regular “light” nitrogen ( N). All newly replicated DNA will be “light” but the old, parental DNA will be “heavy” This way you can tell which DNA is new and which is old. You want to know how they replicate from parental cell to daughter cells. (Unnatural to natural) How could you separate heavy DNA from light DNA? 3. Use density gradient centrifugation to separate heavy (higher density) and light DNA. They actually used cesium density gradients instead of sucrose. Separation of Bacterial DNA by density centrifugation Hybrid=one strand heavy with one strand light. Add mix of light, heavy, and hybrid DNA to a Cesium density gradient 15 What would you see if you added “normal” bacterial DNA that is not N? You will only see N-14. First generation: one becomes two Second generation: two becomes four Three Possible Models for DNA Replication—hypothesis Blue is old. Red is new Dispersive replication (hybrid): produces two molecules with old and new DNA interspersed along each strand Conservative replication (light and heavy): preserves the original molecule and generate an entirely new molecule. (Copy machine) Semiconservative replication (hybrid): produces molecules with both old and new DNA, but each molecule would contain one complete old strand and one new one. Can’t tell if it is dispersive or semiconservative. But you can tell it is or is not conservative. Semi-conservative replication—how DNA replicates First generation: can only tell if it is conservative Second generation: tells if it is dispersive or semiconservative If you started the other way around with N-14 then switched to N-15. You will have heavy and hybrid instead of light and hybrid. DNA Replication in Eukaryotes-we have lots of pieces of linear DNA Use metabolically labeled DNA and look at mitotic chromosomes 1. Must use mitotic cells to see compacted chromatids 2. Use BrdU (bromodeoxyuridine) to substitute for thymidine in DNA A:T A:BrdU (Use BrdU for T) newly made DNA will have BrdU instead of T 3. Thymidine stains dark. BrdU doesn’t. Thymidine DARK. BrdU DON’T. (newly made DNA will not stain dark because they have BrdU) 4. All T is dark, all BrdU is light, hybrid is dark If both sides of X is light, then it is all BrdU. Note: BrdU will not go into RNA, we’re looking at mitotic chromosomes. BrdU will go in newly made DNA (NOT RNA!) Structure-function--BrdU is a structural analog of thymidine In Eukaryotes Note: All T is dark, all BrdU is light, hybrid is dark WENT FROM HYBRID TO ALL OF SAME KIND (RED STRANDS) parental DNA actually opens up and gets doubled In Second generation IF IT IS LIGHT, YOU KNOW IT’S ALL BRDU. Both strands are new Thymidine=dark MITOTIC CHROMOSOME IS MADE OF TWO CHROMATIDS (LIGHT ONE IS ONE CHROMATID (double stranded) AND DARK ONE IS ANOTHER ONE CHROMATID (double stranded)) ALL DNA RPLICATION IS SEMI-CONSERVATIVE You can’t tell if it is semi conservative in first generation. But you can tell during second generation. How does DNA replicate? DNA replicates to make DNA. DNA transcripts to make RNA How can you tell it is replication and not transcription? A is paired with T What if it was transcription? A would be paired with U <-not transcription because there’s A-T The Cell Cycle—Not about cell division. It is about nuclear division (dividing DNA) Not all cells divide: RBC Different cells spend different amount of time in M-phase and Interphase. Not all cells spend the same amount of time in each phases Mitosis is not cell division. It is nuclear division. You have to divide DNA before the cells can pinch off and come apart for cell division Mother cells divide and want daughter cells to have identical gene information. M-phase: Mitosis & Cytokinesis Interphase: G1 & S-phase: when they replicate DNA (DNA synthesis) & G2
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