Cell Structure Study Guide 1 Four tenets of cell theory 1 The cell is the basic unit of life 2 All organisms are composed of one or more cells 3 New cells arise only from division of pre existing cells 4 Cells evolved from more primitive common progenitor cells along three branches of an evolutionary tree Principles of modern microscopy methods o The optical path of a conventional light microscope The light emitted from the lamp hits the mirror which directs the light upwards through the condenser then the specimen stage through the objective projection lens and finally through the detector into the eye Light passes through the specimen and forms the image directly o How to determine the resolution of an objective lens Resolution is the resolving power of the microscope Determined using the formula half the angular width of the cone of rays collected by the objective lens Since maximum is 180 sin n the refractive index of the medium separating specimen from objective and condenser lens has a max of 1 the wavelength of light used For white light 53 um is used Also the nsin is called the numerical aperture o Fluorescence and principles of fluorescence microscopy Fluorescence The phenomenon in which a chemical absorbs light at one wavelength and emits it at a specific and longer wavelength 3 Major steps 1 Excitation 2 Excited State Lifetime 3 Fluorescence Emission Works differently than the conventional microscope o Hits the dichroic mirror which reflects it down through the objective and to the specimen It then reflects off the specimen back upwards through the projection lens and detector into the eye o o o There are many different fluorescent probes with ranging wavelengths o Immunofluorescence Labeling of antibodies antigens with fluorescent probes Two steps 1 Localization 2 Quantification Confocal Fluorescence Microscopy o Differs from conventional microscopy in that the point is in focus and is able to reach the detector In conventional fluorescent microscopy the emitted light is from an out of focus point and is largely excluded from the detector B is confocal C is conventional o Two applications of fluorescence microscopy o Shows that lipids and membrane proteins are laterally mobile 1 FRAP Fluorescence Recover After Photobleaching o This picture shows how FRAP proves that lipids and membrane proteins are laterally mobile This is shown after step 3 where one would assume if they were NOT laterally mobile that the recovery would look just like the picture before However instead the bleached reagents are scattered laterally along the cell o Proves protein protein interactions 2 FRET Fluorescence Resonance Energy Transfer o o Transmission Electron Microscopy Path is similar to the conventional light microscope However the beam is a laser beam which cannot be seen by the naked eye The resolution is higher due to a shorter wavelength laser v air Also the sample must be stained and in a fixed position within a vacuum Protein Structure and Function o Amino Acids There are 20 amino acids Each differs from the other only in the properties of their R groups Amino acids arrange linearly using peptide bonds to form a polypeptide There are 3 classes of hydrophilic water loving amino acids 1 Basic Charge 2 Acidic Charge 3 Polar 0 Charge 1 Class of hydrophobic water hating amino acids 1 class of Special amino acids o Order of amino acids dictates structure 4 different levels of organization 1 Primary Structure Each type of protein specific order of AA 2 Secondary Structure Strings of amino acids form specific 3D secondary structures o Cylinder Helix o Block arrow Sheet Interaction of pleated planar backbones stabilized by H bonds between C O of aa in one strand and NH of aa in the other strand R groups alternately stick up and down from sheet Are stabilized by hydrogen bonds between C O of aa n and NH of aan 4 The chemical nature of the R groups determines the nature of helix surface or region of surface 3 Tertiary Structure Overall conformation of polypeptide chain Stabilized by hydrophobic interactions between aa side chains In extracellular proteins may be stabilized by Cys disulfide bonds In some proteins the tertiary structure is the highest level of organization The organization of several polypeptide chains to make a single multimeric protein complex Polypeptide subunits are held together by hydrogen bonds and or disulfide bonds 4 Quaternary Structure Here s a picture that encapsulates all 4 different levels of organization o Proteins and Peptides Protein Linear polymers of amino acids Amino Acids arrange linearly using peptide bonds to form a peptide There are two ends to the peptide the N terminus amino end and the C terminus carboxyl end o From structure to function Sickle Cell Anemia A Glu Val mutation Biological Membrane o Chemical composition of biological membrane Plasma Membrane Surrounds eukaryotic cells Phospholipid bilayer o Made up of hydrophilic phospholipid head groups with hydrophobic fatty acyl side chains Biological membrane Barrier that defines aqueous compartments in which the internal environment has properties which are different from the external environment Major structural components are lipids specifically phospholipids o Lipids are membrane structural components o The most prevalent membrane lipids have a glycerol backbone and fatty acid tails o There are three types of lipids Phosphoglycerides Sphingolipids Steroids o Lipids are synthesized in the Endoplasmic Reticulum Phospholipids Have a glycerol backbone They have two hydrophobic fatty acid tails The head group is polar charged and is known as the hydrophilic head It is attached by a phosphate group Amphipathic o One end hydrophilic differs in solubility from the other end hydrophobic 4 Components for phospholipids i Phosphate Group ii Amino Acid iii Glycerol iv Fatty acid tail Hydrophilic head groups maximize contact with water while the hydrophobic tails minimize contact with water and attract to one another Phospholipids are fusible and self healing no covalent bonds hold phospholipids to each other Phospholipid bilayer spontaneously closes to form the a aqueous and external internal liposome compartments The presence of two tails and the lengths of those tails prevent the formation of a micelle Fatty Acids o Fatty acid tails form hydrophobic core o The degree of C C bonds determines the fluidity of the core o Unsaturated fatty acid tails Form an inflexible kink in the tail Kinked tails pack more