Chapter 7 Flashcards
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What is the historical significance of microscopes in cell biology?
Microscopes were invented in 1590 and refined during the 1600s. Key discoveries include Robert Hooke observing cell walls in 1665 and Antoni van Leeuwenhoek observing living cells later.
What is the principle of light microscopy (LM)?
Light microscopy involves passing visible light through a specimen and focusing it using glass lenses. It can magnify objects up to ~1,000× their actual size and resolve details up to 0.2 micrometers (200 nm).
What are the different types of light microscopy?
Brightfield Microscopy: Light passes directly through the specimen, often requiring staining.
Phase-Contrast Microscopy: Amplifies density variations for examining living cells without staining.
Differential Interference Contrast (DIC): Highlights density differences for a 3D appearance.
Fluorescence Microscopy: Uses fluorescent dyes or antibodies to visualize specific molecules.
Confocal Microscopy: Uses a laser to focus on a single plane, eliminating out-of-focus light for sharp, 3D images.
Deconvolution Microscopy: Computationally processes blurry images from multiple planes into a clearer 3D reconstruction.
Super-Resolution Microscopy: Combines fluorescent signals to resolve structures as small as 10–20 nm.
What is electron microscopy (EM) and its types?
Electron microscopy uses electron beams instead of light for imaging, offering ~100× higher resolution than light microscopy. Types include:
Scanning Electron Microscopy (SEM): Examines surface structures with 3D imaging.
Transmission Electron Microscopy (TEM): Examines internal structures by passing electrons through a thinly sliced, heavy-metal-stained specimen.
Cryo-Electron Microscopy (Cryo-EM): Freezes specimens at < -160°C, preserving natural structures without preservatives.
What are the applications of microscopy in cell biology?
Microscopy reveals the structure and function of organelles such as the nucleus, mitochondria, and ribosomes. It combines with cytology (cell structure) and biochemistry (chemical processes) for a deeper understanding of cellular metabolism.
What are the key technical advancements in microscopy?
Fluorescent Markers: Label specific structures for high-detail visualization.
Confocal and Deconvolution Microscopy: Sharpen images of living tissues and cells.
Super-Resolution Microscopy: Uncovers subcellular structures previously unseen.
Cryo-EM: Enables 3D imaging of complex protein structures and other macromolecules in their native states.
What are the concepts of magnification, resolution, and contrast in microscopy?
Magnification: Enlarges objects, allowing study of microscopic structures.
Resolution: The ability to distinguish fine details; inversely related to wavelength. LM limit: 200 nm; EM can resolve to ~2 nm or smaller.
Contrast: Enhances visibility using dyes, staining, or fluorescence.
How do light microscopy (LM) and electron microscopy (EM) compare?
Medium: LM uses visible light; EM uses electron beams.
Resolution Limit: LM ~200 nm; EM ~2 nm.
Living Cells: LM can image living cells; EM requires sample preparation that kills cells.
3D Imaging: Confocal microscopy (limited) in LM; SEM (high detail) in EM.
Applications: LM for basic cell structure and live-cell imaging; EM for organelle and protein structure.
What is cell fractionation and its purpose?
Cell fractionation is a process to separate and analyze cell components based on size and density, used to study specific organelles and their functions (e.g., isolating mitochondria for cellular respiration studies).
Describe the process of cell fractionation.
Homogenization: Tissue cells are broken down using a blender to create a homogenate.
Centrifugation: Homogenate is spun in a centrifuge, separating components by size and density.
Differential Centrifugation: Sequential centrifugation steps separate organelles of decreasing size.
What are the common features of prokaryotic and eukaryotic cells?
Both have a plasma membrane, cytosol, chromosomes (carry DNA), and ribosomes (synthesize proteins).
What are the key differences between prokaryotic and eukaryotic cells?
Prokaryotic Cells: No nucleus, DNA in a nucleoid region, lack membrane-bound organelles, typically 1–5 µm in diameter.
Eukaryotic Cells: True nucleus with DNA enclosed in a double membrane, contain membrane-bound organelles, typically 10–100 µm in diameter.
What factors influence cell size?
Size Limits: Smallest known cells (e.g., mycoplasmas) are 0.1–1 µm in diameter; typical bacteria are 1–5 µm; eukaryotes are 10–100 µm.
Surface Area-to-Volume Ratio: Larger surface-to-volume ratios in smaller cells are critical for efficient transport of oxygen, nutrients, and waste.
What is the significance of the surface area-to-volume ratio in cells?
As cell size increases, the surface area grows slower than volume, affecting the efficiency of nutrient and waste transport. Specialized cells (e.g., intestinal cells) increase surface area using microvilli.
What is the structure and function of the nucleus in eukaryotic cells?
The nucleus contains most of the cell’s genetic material, enclosed by the nuclear envelope with pores for molecular transport. It organizes DNA into chromosomes and synthesizes ribosomal RNA (rRNA) in the nucleolus.
