https://homeostasis.scs.carleton.ca/wiki/index.php?action=history&feed=atom&title=EvoSec_2025W_Lecture_7 2026-04-22T08:59:55Z Revision history for this page on the wiki MediaWiki 1.42.1 https://homeostasis.scs.carleton.ca/wiki/index.php?title=EvoSec_2025W_Lecture_7&diff=24983&oldid=prev 2025-01-28T22:15:32Z

<p>Created page with &quot;&lt;pre&gt; Lecture 7 --------- SYMBIOSIS Biology questions - what seemed particularly confusing? - swallowing but not digesting? - eukaryotic vs prokaryotic cells - endosymbiosis - microtubules, basal body - how did prokaryotic cells cooperate? cells are encapsulated by membranes - polar/non-polar structures **--------- ^^^ a fat molecule in a membrane (phospolipid) the ** is the polar head, the ---- is the nonpolar body polar = has a bit of a charge nonpol...&quot;</p> <p><b>New page</b></p><div>&lt;pre&gt;<br /> Lecture 7<br /> ---------<br /> <br /> SYMBIOSIS<br /> <br /> Biology questions - what seemed particularly confusing?<br /> - swallowing but not digesting?<br /> - eukaryotic vs prokaryotic cells<br /> - endosymbiosis<br /> - microtubules, basal body<br /> - how did prokaryotic cells cooperate?<br /> <br /> cells are encapsulated by membranes<br /> - polar/non-polar structures<br /> <br /> <br /> **---------<br /> <br /> ^^^ a fat molecule in a membrane (phospolipid)<br /> the ** is the polar head, the ---- is the nonpolar body<br /> <br /> polar = has a bit of a charge<br /> nonpolar = neutral (no charge)<br /> <br /> Water has a &quot;dipole moment&quot;, i.e., has a partial charge<br /> <br /> O ---<br /> / \<br /> H H +++<br /> <br /> H has one electron in its outer shell<br /> O has 6<br /> but O wants 8 electrons<br /> - and oxygen is very attractive to electrons<br /> <br /> So in a collection of H2O molecules, they will &quot;stick&quot; to each other,<br /> forming structures<br /> <br /> Oil &amp; water don&#039;t mix because oil is made up of hydrophobic molecules, so they want to be away from water (because they are neutral)<br /> <br /> *---- ----* &lt;---- this is a membrane<br /> H2O *---- ----* H2O<br /> *---- ----*<br /> *---- ----*<br /> *---- ----*<br /> *---- ----*<br /> *---- ----*<br /> <br /> <br /> What happens when one membrane touches another?<br /> - they merge!<br /> <br /> phagocytosis<br /> - one cell enveloping another (to eat it)<br /> <br /> how is this possible? remember the cytoskeleton<br /> <br /> <br /> prokaryotes vs eukaryotes<br /> - prokaryotes were the first cells<br /> - basically, bacteria<br /> - very small, no organelles, no nucleus<br /> - DNA is in rings, not chromosomes<br /> - only one membrane, dividing inside and outside<br /> <br /> eukaryotic cells are thousands of times larger<br /> - many internal membranes<br /> - many internal structures, &quot;organelles&quot;<br /> - DNA in chromosomes<br /> - VERY complex structures, mix of DNA &amp; proteins<br /> <br /> Lynn Margulis says eukaryotic cells are symbiotic combinations of prokaryotic cells<br /> <br /> Large software systems are evolved, not designed<br /> Evidence<br /> - large software projects (mostly) fail<br /> - especially when they are to replace existing systems<br /> <br /> - how can you say code is designed when nobody understands so much code?<br /> <br /> Large code bases don&#039;t have requirements<br /> - they just exist, and they either work or they don&#039;t<br /> <br /> If you add code to your program, why do you trust it to work as it should?<br /> - documentation<br /> - author&#039;s reputation<br /> - community validation (is it widely used by others)<br /> - your experience<br /> - one you start using it<br /> <br /> How much of the above comes from the code itself?<br /> <br /> So how do living systems incorporate code?<br /> <br /> Now, we do run untrustworthy code all the time<br /> - on the web<br /> - how is this okay?<br /> - we sandbox the code!<br /> <br /> <br /> But sandboxing is more of a goal rather than a mechanism<br /> - but we have lots of ways of isolating code<br /> - idea is the limit the effects of the downloaded code<br /> <br /> What&#039;s a membrane except the cell&#039;s sandbox?<br /> - well, a mechanism for sandboxing<br /> <br /> But what about if we want to do things that aren&#039;t permitted inside the sandbox?<br /> - we give permission and pray it works<br /> <br /> &lt;/pre&gt;</div>

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