Pia VCTE
Page 2: Reflection and Refraction of Light
Reflection and Refraction:
Angle of refraction = angle of incidence on a smooth surface (reflected and incident rays in the same plane, opposite sides).
Refracted rays follow Snell's Law, where the refractive index indicates how fast light travels through a medium and how much light bends when entering a material.
Refractive index n of water = 1.33.
Speed of light in vacuum (c) is a referen
ce for calculating velocity of light in different mediums.
Page 3: Total Internal Reflection and Lenses
Total Internal Reflection:
Occurs when light moves from a medium with a higher refractive index to one with a lower refractive index at an angle over the critical limit.
This critical angle results in a refracted ray at 90° angle in air to glass.
Optical lenses:
Convex Lens: Focal point is formed behind the lens.
Concave Lens: Focal point is in front of the lens.
Page 4: Convex Lenses and Imaging
Convex Lens (Eye):
Beams focus at the focal point, producing images that are upside down and smaller, as seen in microscopes with magnifying glass, which forms enlarged virtual images.
Light microscope samples should be transparent with a thickness between 0.5mm and 0.2µm.
Page 5: Light Path in Microscopy
Components of Light Path:
Light source, collector lens, diaphragm (Leuchtfeldbleude), condenser objectives. ‘
Magnification in light microscopy (Moc = 250/foc, M = Mo * Mob):
Ocular lens magnification (Mo): 10 - 20x.
Objective lens magnification (Mos): 2 - 100X.
Diffraction:
Bending of light waves around obstacles: sin(θ) = X/d, where d = width of the slit.
Page 6: Diffraction and Microscopy
Diffraction in Microscopy:
A single point of light is never seen as a single point, appearing as an Airy disc, which limits resolution.
Size of the diffracted point is always larger than the point itself.
Resolving Power:
Refers to the minimal distance between objects affecting resolution.
Light-object interaction yields two readouts:
Amplitude: Decrease of amplitude indicates reduced brightness.
Phase: Object changes the light phase without amplitude change.
Page 7: Techniques in Light Microscopy
Brightfield Microscopy:
The specimen appears dark against a bright background, suitable for stained samples.
Darkfield Microscopy:
Signals from diffraction/reflection, with the specimen bathed in a halo of light. The borders appear bright against a dark background.
Phase Contrast Microscopy:
Interaction of light with phase objects results in a small phase shift, separating direct and diffracted light, creating a halo effect.
Page 8: Polarizing Microscopy
Polarizing Microscopy:
Optical effects depend on the angle between light and the optical axes of the specimen.
Requires two components in the light path:
Polarizer: Generates linearly polarized light before the specimen.
Analyzer: Conducts interference analysis; enhanced detection with a color camera.
Nomarski Differential Interference Contrast:
Similar to phase contrast, utilizes two prisms for vertical rays to generate enhanced contrast.
Page 9: Hoffman Modulation Contrast and Fluorescence Microscopy
Hoffman Modulation Contrast:
Uses grey filters to create sharp images of various focal planes.
Fluorescence Microscope:
Photon emission occurs after absorption, emitting at a lower energy.
Energy difference = Stokes Shift.
Defines rules of fluorescence with the Jablonski diagram depicting light absorption and emission transitions.
Page 10: Quantum Yield and Quenching Processes
Quantum Yield:
Ratio of emitted photons to absorbed photons before returning to the ground state.
Quenching Processes:
Mechanisms that decrease fluorescence intensity include collisional effects, static quenching, and various conditions highly dependent on pressure and temperature.
Page 11: Principle of Fluorescence Microscope
Advantages: Enables detection of weak fluorescence. Key components include:
Excitation filter, beam splitter, barrier filter, and light source (e.g., mercury, xenon).
Disadvantages: Susceptible to fading and costly.
Page 12: Absorbance and Transmission
Absorbance (Lambert-Beer Law):
OD = log(I0/I) = ε * c * d (where ε is molar extinction coefficient).
Transmission:
Filters made of dyed glass to block/pass specific wavelengths, critical parameters include:
Center wavelength, bandwidth, transmission percentage.
Types of filters: Bandpass, longpass, shortpass.
Page 13: FRET (Fluorescence Resonance Energy Transfer)
FRET Basics:
Involves fluorophore (donor) and acceptor with overlapping emission and absorption spectra.
FRET efficiency strongly depends on the distance (2-9nm).
Applications:
Protein confirmation, enzyme kinetics, protein phosphorylation analysis using FRET.
Page 14: Molecular Beacons and Hybridization Proximity Beacons
Molecular Beacons:
Comprise a fluorophore (donor), quencher (acceptor), loop region for target DNA binding, and stem region ensuring high on-off contrast.
Hybridization Proximity Beacons:
FRET occurs between donor of one and acceptor of another beacon for increased specificity.
Page 15: Properties of Fluorophores
Fluorophores:
Re-emit light post-excitation, contain multiple aromatic groups.
Intrinsic fluorophores function without additional modification, while extrinsic involve protein labeling agents.
Autofluorescence is common in certain proteins due to inherent properties.
Page 16: Fluorescence and Protein Labeling Reagents
Extrinsic Fluorophores: Used for enhancing visibility in biological samples, including:
Covalent probes, fluorescent dyes (e.g., Fluorescein, Rhodamines) that may self-quench.
High photostability and suitability for DNA probes or fluorophores enriching active cells.
Page 17: Detection of Nucleic Acids and Fluorescent Proteins
Ethidium Bromide: A mutagen detecting DNA; newer alternatives include less toxic SYBR Green and GelGreen.
Fluorescent Proteins: Isolated from bioluminescent organisms, used as versatile genetic markers.
Essential processes include FRAP for analyzing molecular mobility in vivo.
Page 18: Principle of FRAP (Fluorescence Recovery After Photobleaching)
FRAP Technique:
Measures fluorescence recovery post-bleaching; quantifies molecular dynamics through fluorescence recovery over time.
Page 19: SEM (Scanning Electron Microscopy)
SEM Principles:
Uses electron beams for high-resolution imaging, components include an electron gun, condenser system, and detectors within a vacuum to avoid interference.
Primary and secondary electron interactions provide information about sample structure and composition.
Page 20: Scanning in SEM
Scanning Process:
Electron beam focused to a fine point, scanned line by line to collect signals for imaging; resolution defined by interaction depth and electron beam diameter.
Page 21: Electron Emission and Sample Preparation in SEM
Electron Emission:
Secondary electrons provide higher resolution data, while backscattered electrons are used for contrast in electron samples. Coating samples with a thin layer minimizes charging effects.
Page 22: Contrast in SEM
Types of Contrast:
Topographical contrast highlights surface details.
Orientation contrast emphasizes structural orientation.
Sample preparation steps critical for effective imaging, including fixation, dehydration, and coating.
Page 23: Resolving Power and Resolution in Microscopy
Resolving Power:
Limited by wavelength of illumination; ideal resolution is about half the wavelength used; multiple factors affect imaging quality.
Page 24: TEM vs. SEM
TEM (Transmission Electron Microscope) requires thin samples while SEM can handle bulkier specimens; differing illumination techniques highlight variations in imaging.
Page 25: Components of TEM
TEM Main Components:
Electron source, high-voltage acceleration, and magnetic lenses for focusing; standard EM-grid used for sample support.
Page 26: Electron Sources in TEM
Types of Electron Sources:
Field Emitting Gun (FEG) and thermal electron emitters for producing high-resolution images; focus is achievable through magnetic field adjustments.
Page 27: Lens Defects in Electron Microscopy
Lens Defects:
Astigmatism due to contamination of the aperture; compensated through a means called stigmatizing to realign electron beams.
Page 28: Electron Scattering in Biological Samples
Electron Scattering Types:
Elastic scattering involves minimal energy transfer, while inelastic scattering transfers energy to the sample, affecting imaging contrast significantly.
Page 29: Negative Staining Techniques
Negative Staining:
Enhances contrast while minimally damaging samples; common substances include phosphotungstic acid and uranium acetate for biological specimen preparation.
Page 30: Sample Preparation in Electron Microscopy
Preparation Techniques:
Involves embedding samples in resins and creating ultra-thin sections for electron beam interaction; includes numerous steps for achieving suitable thickness and protection.
Page 31: Microtome Utilization
Microtome Usage:
Device cuts thin sections from embedded samples, followed by staining and transferring sections onto grids for imaging analysis.
Page 32: Cryo Techniques in Sample Preservation
Cryo Techniques:
Multiple methods for freezing samples, including slow, fast, and extremely fast freezing, affect preservation quality significantly.
Page 33: Freezing Aqueous Solutions and Antifreeze Agents
Freezing Mechanisms:
Pure water exhibits unique freezing patterns affected by crystallization; antifreeze agents enhance freezing efficiency.
Page 34: Plunge Freezing Techniques
Plunge Freezing:
Method for preparing vitrified samples swiftly in ethane; involves specific handling techniques to maintain sample integrity.
Page 35: Freeze Drying and Etching Techniques
Freeze Drying:
Process involves sublimation to preserve samples, critical in enhancing structural analysis under microscopy; shadowing techniques can enhance imaging details.
Page 36: Cryo-EM and Structure Determination
Cryo-EM:
Focuses on protein structure analysis at low temperatures, maintaining molecular integrity during imaging processes.
Page 37: Tomography in Electron Microscopy
Tomography Techniques:
Single Particle Averaging in cryo-EM; employs focused ion beam systems to structure samples for high-resolution imaging based on tilting series.
Page 38: Data Processing and Model Generation in Tomography
Data Processing:
Emphasizes on transforming tilt series into 3D models using various algorithms for resolution improvement.
Page 39: Single Particle Analysis Techniques
Single Particle Averaging:
Molecules are deposited and imaged, with identification challenges concerning adhesion and orientation.
Page 40: Sample Preservation Techniques in Histology
Sample Preservation:
Essential steps include perfusion, fixation, and dehydration methods to stabilize specimens for microscopic analysis.
Page 41: Tissue Processing Techniques
Processing Steps:
Involve replacing water in tissue with wax for embedding; specific techniques for paraffin infiltration and sectioning are critical for further analysis.
Page 42: Staining Techniques in Histological Analysis
Staining Techniques:
Used to enhance visibility of cellular structures, addressing parameters like background signal for optimal results.
Page 43: Antigen Retrieval and Blocking Techniques
Antigen Retrieval:
Necessary step to enhance access for antibodies, utilizes methods like heat-induced epitope retrieval for improved immunodetection.
Page 44: Antibody Blocking Techniques
Blocking Techniques:
Essential to minimize nonspecific binding by employing enzyme, biotin, and protein blocking approaches in immunohistochemistry.
Page 45: Antibody Binding and Signal Amplification
Antibody Interaction:
Direct and indirect methods have respective pros and cons regarding sensitivity and specificity for detecting target antigens.
Page 46: Sealing Techniques in Immunohistochemistry
Sealing Importance:
Critical for long-term preservation of staining results and protection from external environmental effects.
Page 47: Signal Amplification Methods in Immunohistochemistry
Amplification Procedures:
Involves avidin-biotin complex methods and polymer-based technologies for enhancing detection sensitivity in tissue samples.
Page 48: Controls in Immunohistochemical Analysis
Control Importance:
Positive and negative controls are vital in ensuring reliable results during staining procedures based on binding specificity.
Page 49: Direct vs. Indirect Antibody Detection
Detection Methods:
Comparison between direct and indirect antibody detection methods outlines pros and cons, particularly dealing with sensitivity and specificity challenges.
Page 50: Tissue Cytometry Analysis Techniques
Tissue Cytometry:
Imaging and analysis of properties of cell structures within stained biological samples using advanced scanning techniques.
Page 51: Scanning Modes in Tissue Analysis
Scanning Techniques:
Varied modes for imaging, including brightfield and fluorescence imaging, tailored for specific applications in histological analysis.
Page 52: Segmentation Techniques in Tissue Analysis
Analysis Techniques:
Nuclear and cell compartment segmentation using detected nuclei for phenotyping and total stained area measurements in biostatistics.
Page 53: Troubleshooting Background Signal Issues
Background Signal Troubleshooting:
Identifying various causes of signal degradation, including vibrations, photobleaching, and unspecific binding issues.
Page 54: Molecular Cloning and Its Applications
Molecular Cloning:
Techniques for isolating DNA sequences and their importance in biotechnology for generating copies of genes and protein function analysis.
Page 55: Gene Regulation and Analysis Techniques
Gene Analysis:
Comparison of gDNA and cDNA, examining mutation effects and regulatory regions, instrumental for genetic research.
Page 56: Phage Display Techniques
Phage Display:
Utilizes phages that infect bacteria to present fusion proteins for isolating specific binding partners in drug discovery applications.
Page 57: Applications of Recombinant DNA Technologies
Recombinant DNA:
Emphasizes the importance of host organisms in gene expression studies, focusing on bacteria, yeast, and animal cells for transgenic research.
Page 58: Vectors for Genetic Engineering
Vectors in Genetics:
Role of backbones for gene isolation and expression in target cells; focusing on expression vectors and reporter genes for identification.
Page 59: Cell Motility Mechanisms
Cell Motility:
r Involves actin microfilaments for structural support and transport within cells, significant in various biological processes.
Page 60: Regulating Cell Motion
Regulatory Mechanisms:
Importance of signaling molecules in maintaining cellular polarity and actin dynamics for effective cell migration.
Page 61: Adhesion and Retraction Mechanics in Cells
Cell Adhesion:
Processes like focal adhesions involve integrins linking the extracellular matrix (ECM) to the actin network, critical for stability.
Page 62: Mechanosensitivity in Cell Response
Cellular Mechanosensitivity:
The response of cells to mechanical stress and changes in adhesion strength, impacting cellular structures.
Page 63: Chemotherapy Effects on Cell Behavior
Chemo-induced Changes:
Impact of chemotherapy on cell stiffness and tissue elasticity, affecting cellular responses and differentiation.
Page 64: Biomimicry in Tissue Engineering
Biomimicry:
Designing microenvironments that mimic natural ECM properties to enhance cell functionality in tissue engineering.
Page 65: Overview of Bioreactor Applications
Bioreactors:
Systems for controlling conditions to aid in tissue engineering and cell behavior studies; impacts include nutrient delivery and mechanical stress applications.
Page 66: Bioreactor Functionality and Goals
Bioreactor Goals:
Focus on supporting tissue development and studying cell functions under physiologically relevant conditions.
Page 67: Types of Bioreactor Systems
Bioreactor Types:
Includes stirred vessel, hollow fiber bioreactors, and perfusion systems, each with unique advantages for culturing cells.
Page 68: Specialized Bioreactor Designs
Specialized Bioreactors:
Innovations including dual-chamber systems and strain mimicking to replicate physiological conditions in tissue constructs.
Page 69: Wave Bioreactor Systems
Wave Bioreactor System:
Using rocking motion to enhance cell culture conditions, ensuring even nutrient distribution in a single-use manner.
Page 70: Advanced Bioreactor Technologies
Advanced Systems:
Incorporating magnetic or manipulative forces to apply stress directly to cells, promoting enhanced performance and understanding of cell mechanics.