weber uiuc edu 24 August 2007 MCB150 Lecture 02 Lecture 02 24 August 2007 Announcements Homework Fridays post lecture questions are now due by noon on Monday not noon on Saturday as listed in the downloadable notes o There are no pre lecture questions for today due to the lack of a textbook o Pre lecture questions will always be due before the lecture o At 2PM the post lecture questions will be opened up They can be answered from the lecture material o Monday s post lecture questions are due by Tuesday noon Similarly for Wednesday s o The submissions do not have any feedback We can answer them as many times as we like but the last set of answers submitted at the time of the deadline are those that will be considered our final answers Our grades will be based off of these All course section changes must be completed by 5pm on the 5th of September o Be careful on the switch you cannot do an add and a drop simultaneously Therefore it is possible for you to lose you spot in a section This can happen if you try to drop then the section you want to add fills up locking you out Bring the last day s handouts to class if we want to follow along o He may continue the lectures by starting from the previous lecture s notes o There will not be another chance to get printed notes except when they are handed out on the same day as the lecture The notes are available for download Carl Woese Kindoms vs Domains He was interested in determining evolutionary relationships based upon ribosomal RNA sequences Why ribosomal RNA o It is evolutionarily ancient o It is found in all living organisms except viruses though for the purposes of this course viruses are not counted as living even though they can replicate o It serves the same function in every organism o It is slow to change it is highly conserved Therefore changes must be significant Conclusions drawn by Woese company o Prokaryotes are two different life forms Bacteria formerly called eubacteria E g E coli Archaea the ancient prokaryotes These are frequently found in extreme environments such as extreme temperatures high pressures acidic environments high salt content odd gasses or anaerobic conditions etc In other words conditions that are thought to have been typical of earth shortly after life began Page 1 of 3 weber uiuc edu 24 August 2007 MCB150 Lecture 02 o These conclusions were based upon observations of the sequences and it was discovered that the archaea are actually more closely related to the eukaryotes The new tree of life now is considered to consist of three domains the bacteria the archaea and the eukaryotes o The branching of these occurred many millions to billions of years ago In 2003 Woese won the Crawford prize for this research Physical Characteristics Note the physical characteristics of the various cell types and how they are similar to one another and how they differ The relationship between the genomes is not always reflected in the observed physical characteristics Today there are 634 complete genomes that have been sequenced with over 1365 prokaryotes and 731 eukaryotes partially sequenced Other genes have been used for comparisons and these can result in different webs of relationships Why o Handoff of material from one species to another acquiring traits not having evolved independently is considered horizontal transfer o Vertical descent is the concept that one organism was the direct ancestor of another Species Cells Why to species differ All life is composed of cells Why o Life needs an exclusionary environment it needs to be protected from damaging influences found in the environment The tenets of cell theory o The cell is the fundamental unit of life o All organisms are composed of cells o All cells come from pre existing cells Why are cells so small o Need to move raw materials and products in and out Size Surface area to volume ratio is crucial o Larger volumes permit more reactions but have a small surface area in comparisons o Larger surface area to volume ratios is found in smaller cells Larger cells cannot support of the reactions necessary for life How small is small o Cells are 1 100um typically Resolution the ability to identify the separation of two objects that are close to each other o The resolving power of light microscopes is 0 2 um o Subcellular structures require higher resolution Consequently TEM is frequently used Dark dense The darker the objects are those that absorb the electrons more than the others Page 2 of 3 weber uiuc edu 24 August 2007 MCB150 Lecture 02 Cell Structures Some cells most cells actually have a cell wall and are relatively rigid o Animal cells do not have a cell wall Within the wall is the cell membrane o Why is there a membrane Separation regulation Membranes are selectively permeable The membranes are used to interact with or stick to their neighbors Microscopic Views of Prokaryotes Light microscope views vs EM views of prokaryotes The following items are structures visible under LM and EM Some bacteria have a polysaccharide capsule The capsule is used to protect the wall if there and membranes The capsule is also used as a mechanism to stick to surfaces Cell wall if present The plasma membrane The nucleoid region Not that this is NOT a nucleus The nuclear material is found in the cytosol Dark specs in EM images are ribosomes Ribosomes are the protein synthesizing units of cells Microscopic View of Eukaryotes Plasma membrane in EM the plasma membrane looks like an oreo dark light dark regions A nucleus a membrane bound organelle o In the nucleolus Maintenance and replication of the genome Transcription of the genome Production and assembly of ribosomes Mitochondria the energy producing units Nuclear envelope outer and inner envelopes o The outer membrane is continuous with the endoplasmic reticulum The endoplasmic reticulum o There are two types of ER smooth and rough o The rough ER contains ribosomes embedded in it o The ER is used for the processing and secretion of chemicals Ribosomes o Ribosomes are often found in chains which permits multiple copies of proteins to be produced from one strand of mRNA The Golgi Apparatus o Like the post office of the cell More details on this later Page 3 of 3