Cell Theory 1 All known living things are composed of one or more cells 2 All new cells are created by pre existing cells dividing in two and reproducing 3 The cell is the most basic unit of structure and function in all living organisms Prokaryoes vs Eukaryotes P small simple single celled organisms bacteria E larger and multicelular and 15 times wider V 1 000 times greater P first cells to appear on planet and E appeared 1 5 billion years later Most Ps have cell walls made of peptidoglycan and external appendages flagellum COMMON STRUCTURES OF ALL CELLS cell membrane provides barrier btw interior and exterior of cell and regulated flow of subtances coming in or out all cells have cytoplasm fluid that occupies space inside cell and where chemical reactions that enable life take place All cells contain DNA for instructions on synthesizing proteins contain ribosomes molecular machines that use the instructions contained in DNA to build all proteins needed by the cell DIFFERENCES P does not contain nucleus or organelles Chloroplasts only exist in E prions infectious proteins causing diseases like mad cow disease not cells nuclear envelope double layer membrane surrounding nucleus mitochondria take fuel in the form of glucose and convert is to usable energy ATP chloroplasts only in plants energy transfer provide sugar by capturing energy from the sun and using that energy to build sugar molecules endoplasmic reticulum ER series of sacs and tubes that put together proteins and other cellular components Golgi apparatus proteins that were build by ER are delivered to difference part of cell vesicles and vacuoles membrane bound save that function in storage and transport and can fuse with plasma membrane Lysosomes specialized vesicles found only in animal cells recycle cellular parts or destroy external invaders photosynthesis chloroplasts harvesting solar energy to make sugars from CO2 antibiotics substances produced by one type of organism and used to kill or suppress other organisms overuse of antibiotics lead to evolution of superbugs Cytoskeleton formed by a series of protein filaments cell structure and framework for cell activities actin cell movement maintaining shape connection to other cells intracellular transport centriole spatial organization of cell and cell division microtubules form appendages such as flagellum of the sperm cell and cilia of the cells of respiratory system Plasma Membrane cell boundary determines what enters and exists cell and how it reacts with environment constant motion like flowing river describe as fluid mosaic phospholipid bilayer main fabric of membrane semipermeable allows cytoplasm chemistry different from external environment hydrophobic core blocks diffusion of hydrophilic ions and polar molecules while some molecules need proteins to transport them fluidity allows cell to change shape permitting growth and movement regulated by types of phospholipids and presence of cholesterol ability of molecule to pass through membrane depends on polarity and to some extent size many nonpolar molecules flow through easily charged ions seldom go through Maintaining Proper Fluidity of Membrane phospholipids with differing fatty acid tails have different levels of mobility in the membrane needs good ratio of saturated to unsaturated fatty acids in animal cell membranes mostly made of saturated fats so relatively stable not too fluid at high temps cholesterol molecules interfere with movement and reduce fluidity low temps cholesterol keeps saturated fat tails from packing and maintains fluidity sterols used by some cells to maintain proper membrane fluidity integral proteins proteins that need to be embedded in membrane to carry out their functions peripheral proteins proteins that are attached to inner or outer surface of membrane Archaeans living in extreme environments hydrocarbon tails linked to glycerol ban bone composed of S layers and lack peptidoglycan How molecules Enter and Exit Cells 1 molecules can pass across membrane diffusion and active transport 2 molecules can be transported into cell without passing across membrane endocytosis 3 molecules can send signals for actions within the cell without actually passing across the membrane themselves signal transduction molecular substances enter and exit the cell so that nutrients and waste can be exchanged cell can perform its function the cell can send appropriate signals to other cells ex adding ink to beaker of water simple diffusion both small and large molecules spontaneously move form areas of high concentration to areas of low concentration following random movements Brownian motion Molecules can be divided into 4 categories with regard to ability to cross membrane these hydrophobic molecules can easily cross because of interaction with nonpolar lipids small size allows them to pass through small temporary holes in membrane 1 nonpolar molecules 2 small polar molecule 3 large polar molecules 4 ionic compounds difficulty crossing because of size and poor lipid interaction charge interacts badly with lipids making it difficult to cross size polarity and charge affect ability to cross facilitated diffusion process of moving permeable molecules across a membrane using channels or pores moving down a concentration gradient process driven by simple diffusion so does not require input of additional energy from the cell steep pH gradient across lysosome s membrane which contrasts with equilibrium state where concentration of hydrogen ions would be the same inside out to decrease pH inside lysosome concentration of protons will need to be greater inside the lysosome than in the cytoplasm protons will need to move form a low concentration to high concentration requires cell to do work to move ion against concentration gradient active transport cell expending energy and actively moving to pump the ions against concentration gradient energy sours is the hydrolysis of ATP facilitated diffusion and active transport both require transport proteins that act as channels or ports in the membrane Endocytosis and Exocytosis materials can be taken up or ejected in bulk without passing through the cell s plasma membrane endocytosis material is engulfed within an infolding of the plasma membrane then brought into cell within cytoplasmic vesicle to begin particle encounters cell cur face and produces dimple or pit in the membrane pit deepens and finally pinches off to form vesicle phagocytosis uptake of large solid