LECTURE 1: T see bilgy in an evlutinary cntext and review the three generalisatins f bilgy. T understand hw far back we have extended the fssil recrd since the days f Darwin. FIRST GENERALISATION OF BIOLOGY EVOLUTION THROUGH NATURAL SELECTION - Charles Darwin. - A great unifying thery in bilgy with this thery we can accunt fr diversity and similarities in plant and animal species. EVOLUTION - The Earth has a lng histry. 4.5-4.6 billin years. Life began abut 4 billin years ag. - All rganisms arse in the curse f this histry frm earlier, mre primitive frms. - As a cnsequence f this thery all rganisms are related r share a cmmn ancestr. A 2 step prcess: descent with mdificatin - Variability (via mutatins). - Ordering that variability by natural selectin. SECOND GENERALISATION OF BIOLOGY UNITY OF BIOLOGICAL PROCESSES - Because all rganisms share a cmmn ancestr, there is a unity f bilgical prcesses. - All rganisms have DNA. - All rganisms als have the machinery t carry ut the instructins frm the DNA prteins. - All rganisms share certain bichemical reactins. THIRD GENERALISATION OF BIOLOGY ALL ORGANISMS CONSIST OF CELLS - Cell = a bag, a clsed dmain where the chemical reactins required fr life are carried ut. - Cells have prbably succeeded because f the membrane separating the living prtplast and the harsh envirnment. Cell Thery - All living rganisms are cmpsed f cells. - All cells cme frm pre-existing cells. - The cell is the smallest rganizatinal unit. DARWIN S DILEMMA - Where did the first cells cme frm? - Hw did eukarytic cells evlve frm prkarytic cells? - Cambrian explsin the emergence f eukarytes greatly accelerated the pace f evlutinary change.
Nte: reprductin, changeable inheritance, metablic activity and cntainment (i.e. being surrunded by a membrane) define life. LECTURE 2: T understand the differences between prkarytic and eukarytic cells. T understand the structure, diversity and functin f archaea and bacteria and hw they differ. The imprtance f cyanbacteria. PROKARYOTIC VS EUKARYOTIC CELLS Prkarytes were the first cellular lifefrms t emerge. - Evlved in the ceans. - Earliest bacteria (predecessrs f cyanbacteria) were capable f anxygenic phtsynthesis. Evlving chlrphyll allwed prkarytes t capture inrganic CO 2 and turn it int rganic C, releasing O 2. THE GREAT OXYGENATION. Earth: inhspitable hspitable. Feature f Cells Prkaryte: Bacteria Prkaryte: Archaea Eukaryte Size Micrscpic 0.1-10µm Micrscpic (but can be macrscpic) Micrscpic 10-100 µm Chrmsme structure Circular Circular with histnes Linear with histnes Chrmsme number Single Single Multiple and variable Cell divisin Binary fissin Binary fissin Mitsis/meisis Internal cmpartmentalisatin Never Never Always, endmembrane system Flagella External, flagellin acts as a mtr External, flagellin acts as a mtr Internal, 9+2 arrangement f micrtubules Cytskeletn Rudimentary cytskeletn in sme Rudimentary cytskeletn in sme Micrfilaments (actin and intermediate), micrtubules Cell wall Peptidglycan N peptidglycan Smetimes cellulse, smetimes chitin, smetimes absent Uni r multicellular Unicellular Unicellular Smetimes multicellular Auttrphism Chemsynthetic = can xidise inrganic cmpunds and harvest energy Smetimes chemsynthetic, smetimes phtsynthetic Smetimes chemsynthetic (think extremphiles) Nitrgen fixing Smetimes Smetimes Never STRUCTURE OF PROKARYOTES - All prkarytes are surrunded by a semi-rigid cell wall. - Cell membrane phsphlipid, semi-permeable. - Cytsl liquid interir. - Ribsmes translate prtein. - Tgether the ribsmes and cytsl are the cytplasm. - DNA flws freely and is a single, circular strand. Smetimes phtsynthetic
- Outer capsule cmpsed f plysaccharides. Imprtant fr recgnitin f ther cells and disease resistance. - Pili allw prkarytes t lineup and transfer DNA back and frth between different cells. - Flagellum mvement. Cmpsed f a single prtein called flagella. Extra-cellular. - Rtary mtr turns the flagellum and prpels the cell. BINARY FISSION - Much simpler prcess than mitsis/meisis. - Allws prkarytes t divide every 20 mins. ARCHAEA VS BACTERIA - Mrphlgically similar can t tell them apart under a micrscpe. - Hwever vastly different DNA. - The tw central bilgical prcesses in archaea, genetic transcriptin and translatin, are mre similar t thse f eukarytes than bacteria. - Archaea lack a peptidglycan wall (a distinct feature f bacteria). - There are n knwn archaean pathgens. WHY STUDY PROKARYOTES? - Cause many diseases.
- Decmpsers and recyclers critical in remving dead rganic matter, recycling carbn, nitrgen, sulfur, degrading txic chemicals etc. - Agents in industrial and agricultural prcesses. E.g. bacteria fermenting fd. - Nitrgen fixatin i.e. can bring nitrgen int rganic material. - GM bacteria prduce pharmaceuticals human insulin, human grwth hrmne etc. CYANOBACTERIA - Majr primary prducers. - Cntain chlrphyll A and generate mlecular xygen during phtsynthesis (similar t plants and algae nt ther bacteria). - Respnsible fr the earth s atmsphere becming xygen-rich. - Strmatlites which frmed frm the activities f cyanbacteria are the ldest fssil evidence f life n earth. LECTURE 3: T understand the cmplex structure and differentiatin f eukarytic cells and the pssible rigin f mitchndria and chlrplasts thrugh the prcesses f endsymbisis. FEATURES OF THE EUKARYOTIC NUCLEUS - Duble membrane nuclear envelpe. Inner and uter which are jined at nuclear pres (annular pres). Outer membrane is cntinuus with ER. Nuclear pres regulate the passage f prteins and RNA int and ut f the nucleus.
- Nuclelus sub-regin cntaining ribsme genes. Nucleus can cntain ne r several. Darkly staining regins. Cntain high cncentratins f RNA, prtein and DNA. Site f synthesis f ribsmal RNA (rrna) and assembly f ribsmal subunits fr exprt t the cytplasm fr prtein synthesis. - DNA. Lng DNA mlecules wind arund clusters f histne mlecules (simple prteins) t frm nuclesmes (=1 histne grup with DNA wrapped arund). This arrangement allws DNA t twist int a helix, frming a chrmatin strand. (DNA has a negative charge because f phsphate backbne and histnes have a psitive charge allws assciatin between them). Eukarytes have multiple chrmsmes (vs prkarytes which have a single, circular mlecule). - Mitchndria pwerhuse f the cell. Cells may cntain ne r several. AEROBIC RESPIRATION generate ATP. Duble membrane. Outer membrane smth, permeable. Inner membrane arranged int flds (cristae) t increase SA, highly impermeable. Matrix space (inside inner membrane) cntains mitchndrial ribsmes and cpies f mitchndrial DNA. Enzyme cmplexes are respnsible fr ATP synthesis. - Chlrplasts energy catchers f plants. Cells may cntain ne r many. PHOTOSYNTHESIS cntain chlrphyll, a light-absrbing pigment. Duble membrane. Outer. Inner frms flattened disc-like sacs, thylakids, which lie n tp f each ther frming stacks, grana. Large SA f internal membranes increases ability t capture light (chlrphyll is assembled n thylakid membranes).
ORIGINS OF COMPLEX ORGANELLES Mitchndria believed t be derived frm purple bacteria. Chlrplasts believed t be derived frm cyanbacteria. PRIMARY ENDOSYMBIOSIS - Endsymbisis = an rganism living inside anther (fr the benefit f them bth). - Mitchndrial evlutin is thught t have preceded the evlutin f chlrplasts. - A eukarytic hst engulfed a purple bacterium (prkaryte) in a fd vacule = phagcytsis. - The purple bacteria didn t get digested (perhaps because f a mutatin in the cell wall). - The purple bacterium lst its autnmy and became an rganelle. - Evlutin f the chlrplast invlved primary endsymbisis. - Chlrplast evlved frm cyanbacteria. SECONDARY ENDOSYMBIOSIS - When eukarytes stle their chlrplast frm anther eukaryte rather than engulf a prkaryte. - Prtistan pirates. - The number f membranes arund the chlrplast indicates whether primary r secndary endsymbisis. 2 membranes = primary. 3 r 4 membranes = secndary.
EVIDENCE FOR THE ENDOSYMBIOTIC THEORY Mitchndria and chlrplasts: - Are mrphlgically similar t bacteria. I.e. they lk like prkarytes. - Are surrunded by an uter membrane similar t a cell membrane. - Are semi-autnmus. They retain their wn genme (DNA, RNA). - Als retain their wn ribsmes. - Similar metablism t existing prkarytes. - Sme chlrplasts still have the bacterial peptidglycan wall between the inner and uter membranes.