Topic 1 - Intro to cell biology (lec 2)

The size of the nucleus how large is a mitochondria

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Unformatted text preview: n avergae prokaryote and eukaryote cell. The size of the nucleus, how large is a mitochondria is and so on > Ribosome diameter - 0.007um = 7nm >Nucleus diameter- 0.006nm= 6um >Mitochondria length - 3 x10^(-6) = 3um > Giraffe axon length - 1x10^(6) um= 1m > Microfiliment diameter - 0.007um = 7nm BIO 1140 – SLIDE 5 Time to 95% equilibration of O2 by diffusion Why are cells small? SA:V ratios Rates of diffusion Adequate concentrations or synthetic capacity L L L X time 0.1 mm 0.067s 1 mm 6.7 s 1 cm 10.9 min 1m 78 d Length = L Surface area = 6· L· L = 6L2 Volume = L· L· L = L3 SA:V = Length = 2L Surface area = 6· 2L· 2L = 24L2 Volume = 2L· 2L· 2L = 8L3 SA:V = (see Fig. 2.5) BIO 1140 – SLIDE 6 Fig. 4-1 Becker et al. 2009 > Three major arguments to why cells are small 1) Surface Area: volume ratios. The volume of a cell tells u how much it needs interms of nutrients moving in and waste products moving out. The surface area (SA) of the cell is the area over which exchange can take place. If the surace area and the volume are not well matched, the cell is either starved of nutrients or builds up waste products and it can't survive. You need to have enough SA for exchange to occur to match the cell volume. The problem with the increase of the cell size is that the ratio of the SA:V falls. Ex: SA = 24L^2 V=8 L^3 SA/V = 24L^2/8 L^3 =3:1 >The SA:V ratio is falling as the cell become larger. As the volume increases and the SA does not keep up with it than u cant get enough nutrients and can't get enough waste product out. 2) Rates of Diffusion. Things move around in the cell by difussion. The basic mechinism in the cell for movement is diffusion.Diffusion is fine aslong as the distances are small. For example for a molecule of (O) that has to travel 0.1mm takes 0.67s, which is fine. For small distances diffusion travels at a resonable time, but for large distances it does not, its too slow. Cells can not afford to get large b/c the rate of diffusion can't keep up. This provides major constrate on the cell size. 3) Adequate concentartion or Synthetic capacity. As cell size increases the # of molecules that have to be synthesized in order for reaction to occur gets larger.You have to have some basic concentration of substrate for a reaction to occur. For the basic reaction to occur the cell has to synthesis/bring in the substrate. The larger the cell, the more molecules that need to be synthesized, and the cell is unable to provide that many molecules to acheive the concentration. Prokaryotic and eukaryotic cells differ in their solutions to the problem of size Prokaryotes For review, see http://salinella.bio.uottawa.ca/BIO1130/Lectures/PDF/BIO1130_lct03_STDNTVERX3.pdf Solution stay small, typically 1-5 µm Simple structure: cell wall, plasma membrane, cytoplasm that lacks organelles (cyanobacteria possess photosynthetic membranes), ribosomes, nucleoid, flagellum prokaryotes Ribosomes Cytoplasm Nucleoid Plasma membrane Cell wall Bacteri...
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This note was uploaded on 02/19/2014 for the course BIO 1140 taught by Professor Fenwick during the Winter '07 term at University of Ottawa.

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