11 03 2014 Signal Transduction Signaling happened way before multicellularity o Needed to respond to things in the physical environment such as external signals Unicellular organisms respond to abiotic factors such as glucose levels and also signals from cells around them o They can tell how many other organisms are around them Three basic components i Reception by the receptor ii Transduction by relay molecules in a pathway iii Response by activation of a cellular action Can consist of a single protein that will bind to the signal and do something new such as go into the nucleus and bind to DNA Membrane impermeable the receptor must be inside the plasma membrane phospholipid bilayer o Something will bind to the protein on the side that is in the extracellular matrix o This causes the shape of the protein to change on the side that is in the cytoplasm o This change of shape relays a message Membrane permeable receptor can be in the cytoplasm o Same steps but occurs inside of the cell Changes in ion concentration can cause a signal transduction pathway o Gated ion channels o Change metabolism Examples of cellular response to a signaling pathway o Gene regulation o Cytoskeleton conformational changes To turn on pathway there is an input of information from previous steps and to turn off that pathway you have to output that information to the next step it is usually always on Kinases o Uses ATP to attach a phosphate to turn the pathway on o A kinase is a type of enzyme that attaches phosphate o To turn off the pathway the phosphate is removed o This process is always on o Bacterial two component system In prokaryotes 2 different proteins receptor protein in plasma membrane response protein in the cytoplasm both can be in either the on or off state which is determined by the concentration of the signal input domain is where the signal bonds transmitter domain is where the phosphate could bond and where the transformation will happen phosphate goes from the transmitter domain of one protein to the receptor domain of another protein o second messenger cyclic AMP when pathway is on cyclase is on and makes cAMP when the cAMP gets too high a protein breaks it down negative feedback Cellular Motion Microfilaments each monomer has 3 interactions o Made of actin Microtubules each monomer has 4 interactions o This causes them to have different properties o Alpha and beta tubulents Both microtubules and microfilaments change their location by depolymerizes and repolymerizeing o Microtubules With GTP microtubules form With GDP microtubules depolymerize and disassemble o Microfilaments When ATP binds to the actin it polymerizes When ADP binds to the actin it depolymerizes Cytoskeleton and cell shape o Microtubules cannot stretch o They do not dictate the shape but they do dictate the way that the cellulose forms o Animal cells do not have a cell wall or a rigid structure so under the plasma membrane there is a network of microfilaments that hold the shape of the cell They are like ropes in that they will not break when stretched or pushed they will only curl Dictate how the cell s shape changes during development They help hold the shape of the cell Amoeboid motion Motor proteins o Only possible when cells are attached to some surface including other cells o Microfilaments are involved in motion Everything in the amoeba is moving in the same direction as its motion Microfilaments push the cell forward and others are being pulled from the end of the cell to shorten it from the back o In order to get movement you must either pull microfilaments or push microtubules past each other we need motor proteins o There is ADP in the feet region when they come in contact with the microtubule the ADP pops off and ATP attaches causing a conformational change which bring the foot closer which propels the other leg forward and that leg gets rid of its ADP and brings in ATP repeating the process o Cytokinesis in plant and animal cells Animal cell ring of microfilaments attach to the membrane and shorten along cleavage furrow and pinch cell in half Plant cell forms a whole new cell wall between the original cell made of microtubules microtubles realign along plane of cell division Cilia and flagella o Extracellular o Once they are made they stay for a lifetime o Flagella are long cilia are short o Structure 9 pairs of 2 microtubles in a circle with 2 microtubles in the center there are connecting proteins that connect microfilaments and microtubules that prevent the microtubules from sliding past each other they cause the microtubules to bend which causes motion muscle cells o to shorten a muscle cell structurally all that is needed is to move motor proteins along a piece of cytoskeleton o muscles are made up of huge cells that go from attachment point to attachment point actin Multicellularity The evolutionary timeline o Origin of the earth 4 6B o First cells prokaryotes 3 2B Diversification of metabolism Photosynthesis not oxygen producing but still using light energy 3 2B Oxygenic photosynthesis as reduced compounds in environment were becoming more and more rare huge change into using water for 3 0B photosynthesis atmosphere becomes full of oxygen Aerobic respiration 2 5 B o First eukaryotes 1 8B o Plant animal divergence 1 6B o First multicellular organism Fossil data 6B Molecular data 1 2B Developed independently of plant cells and animal cells o Ability of cells to generate a lot more energy allows the cells to do a lot of different things The evolution of eukaryotes o Prokaryotes with no internal organelles or membranes however they are organize Nucleoid membrane o The prokaryotes have invaginations foldings of the plasma Has different functions in different parts of the Thylakoid membrane evolved because of these membrane invaginations Endosymbiosis theory heterotrophic eukaryote engulfed either the chloroplast or mitochondria Undigested Since they were both mutually beneficial to each other it stayed around Three layers to chloroplast in eukaryotic host cell Thylakoid membrane Inner membrane from the prokaryotic cell Outer membrane from the eukaryotic cell Driving forces for evolution of multicellularity o The only other way they can get stuff besides diffusion is phagocytosis To limit its being eaten the pray can grow in size to increase their chances of passing their genes to offspring However as the cell gets larger the volume increases and there is more metabolic demand which limits the maximum