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Lecture 2

Lecture 2 Notes.docx

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Biology 1001A

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Biology 1100A Lecture 2 Notes (Cell Biology)  All organisms are composed of one or more cells. o All cells are contained within a lipid-bilayer of phospholipids. o Cells are divided into prokaryotic or eukaryotic:  Prokaryotic cells do not have membrane bound organelles.  DNA is coiled randomly within the cell and is dispersed throughout cytoplasm.  Eukaryotic cells contain membrane bound organelles such as mitochondria, Golgi complex, Endoplasmic reticulum, etc.  Endoplasmic reticulum is a network of channels and vesicles that transfer lipids and proteins within the cell. ER is divided into smooth and rough, denoting whether it has ribosomes attached to it o Rough ER aids in protein synthesis and transfer, whereas Smooth ER helps synthesize lipids for membranes.  Golgi complex receives proteins from the rough ER and further chemically changes them and also moves them; some are transferred outside the cell, some are imbedded in the plasma membrane, some are placed in lysosomes. o Released from cell is called exocytosis, absorption is called endocytosis.  Since organelles were not part of early cells, a theory of endosymbiosis came into effect, stating that organelles were engulfed by prokaryotic cells then due to mutual benefits, became part of the host cells. Evidence that supports this theory include: o Morphology: the shape of the cells and organelles. o Reproduction: the way that both prokaryotic cells and organelles divide (binary fission). o Genetic information: organelles contain DNA. o Transcription and translation: organelles contain a way to completely transcribe and translate for proteins. o e transport: organelles both use ATP in ETC.  Desaturase, an enzyme that adds double bonds in fatty acids, its activity goes up when the organism moves into colder temperature, due to the fact that it needs to keep the fluidity of the cell membrane.  Internal structure of a cell is enforced by a cytoskeleton composed of microtubules, intermediate filaments, and microfilaments. o Important in cell division; moving around chromatin.  A key trait in multicellular organisms is that there is a ‘division of labour’, where not all the cells are doing the same thing; cells co-operate and some cells are specialized to do specific tasks.  Membranes are fluid; the proteins within the membrane can move freely within the fluid membrane, the most common model is known as the fluid mosaic membrane model. o Membranes are asymmetrical to each ‘half’ (the inner and outer half of the lipid bilayer). o The dominant lipids found within a membrane are phospholipids, containing a polar head, a phosphate group and then a non-polar tail. o Fluidity is determined by the composition of the lipids within and the membrane and the temperature.  More unsaturated hydrocarbon tails, the more fluid the membrane will be.  The warmer it is, the more fluid the membrane will be, o Most membranes are made up of saturated and unsaturated fatty acids. o A group of compounds called sterols also affect fluidity, acting as buffers, o Membranes have four majors functions:  Transport: transport of proteins and substances through the membrane, both into and out of the cell  Enzymatic activity: a number of enzymes are membrane proteins.  Signal transduction: when specific substances bind to receptor proteins on the membrane surface, they alter something within the cell.  Attachment/Recognition: proteins within the cell membrane act as attachments for cytoskeleton parts, and acts as cell-to-cell recognition sites. o All proteins imbedded in the bilayer are called integral membrane proteins.  The two major groups of proteins are transmembrane proteins and peripheral membrane proteins:  Transmembrane proteins span the entire lipid bilayer, having regions that are exposed on both sides of the bilayer. o Transmembrane proteins contain stretches of amino acids that are mainly nonpolar, so that they can stay within the lipid bilayer.  Peripheral membrane proteins are just stationed on the surface of the bilayer. o Most are on the cytoplasmic side of the bilayer. o Some are parts of the cytoskeleton.  Some structures hold the peripheral membranes together. o Membranes acts as what can enter a cell and what cannot:  Hydrophilic and small, uncharged polar molecules (such as2H O, glycerol) can enter the cell via passive transport via diffusion. Larger molecules and Ions (Na , - + Cl, K ) cannot passive diffuse through the cell membrane.  There are two ways of passive transport:  Simple diffusion is where the compounds just simply diffuse across the membrane.  Facilitated diffusion is where proteins ‘aid’ the process, using the concentration gradient; when the gradient reaches zero, the process ends. o Facilitated transport is helped by transport proteins, a type of integral membrane protein. There are two types of proteins:  Channel proteins form a ‘channel’ for compounds to diffuse through; by creating a path so that hydrophilic molecules do not have to interact with the hydrophobic parts of the membrane.  Gated channels act as ion transporters. o The gates may be closed by voltage changes across the membrane, or via signal molecules. o E.g., ion channels are used for nerve conduction and controlling muscle contract
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