Eukaryotic Cell Structure Quiz

Eukaryotic Cellular Structure

• Eukaryotic cells have various components, including nuclei, microtubules, Golgi apparatus, actin fibers, and mitochondria. These parts perform different functions essential for cellular activities.

Substructures of Animal & Plant Cells

• Diagrams show animal and plant cells with labeled organelles, including numbered items: plasma membrane, mitochondria, lysosomes, nuclear envelope, nucleolus, nucleus, smooth ER, rough ER, Golgi complex, secretory vesicles, peroxisomes, cytoskeletal fibers, microvilli, cell wall, vacuole, and chloroplast.

Major Components of Eukaryotic Cells

• Plasma membrane: 700 μm².
• Internal membranes & organelles: 7,000 μm².
• Cytoskeleton: 94,000 μm².

Organelles

• Single-Membrane Bound: Smooth Endoplasmic Reticulum, Rough Endoplasmic Reticulum, Lysosome, Golgi Apparatus, Peroxisome, Vacuoles & Vesicles.
• Double-Membrane Bound: Nucleus, Mitochondrion, Chloroplast.
• Non-Membrane Bound: Ribosomes, Proteasomes, Cytoskeleton elements, Cilia & Flagella, Centrosomes, Basal Bodies.

Nucleus

• Typically the largest organelle in animal cells.
• Considered the "control center" of the cell.
• Contains most of the cell's DNA.
• Has a double-membrane structure: outer nuclear membrane, inter-membrane space, inner nuclear membrane.
• Contains nucleoplasm, where the nucleolus synthesizes rRNA.
• Also includes a nuclear lamina composed of lamin proteins lining the inner nuclear membrane surface.
• Contains nuclear pore complexes (NPCs).

Endoplasmic Reticulum (ER)

• A single-membrane bound organelle, extensive network of closed, flattened membrane-bound sacs.
• The ER membrane is continuous with the outer nuclear membrane, and its lumen is continuous with the intermembrane space of the nucleus.
• Divided into two components: rough ER (RER) and smooth ER (SER).

Rough ER

• Immediately adjacent to the nucleus.
• Studded with ribosomes on its cytosolic surface, which synthesize proteins.
• Site of initial protein processing, for proteins exported from the cell, embedded in the plasma membrane, or destined for the Golgi apparatus and lysosomes.
• Nascent polypeptides associate with Rough ER membrane.
• Chaperones assist protein folding; enzyme modifications occur.

Ribosomes

• Sites of protein synthesis (translation), consist of rRNA and proteins.
• Ribosomes may be free (in cytosol) or bound to the rough ER.
• A functional ribosome consists of two subunits (large and small), designated by S values.

Fates of Proteins Synthesized on Bound or Free Ribosomes

• Proteins synthesized on bound ribosomes are destined for: export from the cell, plasma membrane embedding, or the ER, Golgi, or lysosomes.
• Proteins synthesized on free ribosomes are for use in cytosol, nucleus, mitochondria, chloroplasts, peroxisomes.

Golgi Apparatus

• Series of flattened membrane-bound sacs (cisternae).
• Acts as the cell's "post office," receiving, modifying, sorting, and packaging proteins and lipids.
• A polarity exists, with cis, medial, and trans Golgi faces.
• Contains different luminal enzymes for protein modifications. Proteins arrive from rough ER in transport vesicles.

Secretory Pathway

• Movement of proteins from bound ribosomes through rough ER, transport vesicles, cis-Golgi, medial-Golgi, trans-Golgi, transport vesicles, plasma membrane, or lysosomes.

Lysosome

• Animal cell's "digestive system" and "garbage disposal system."
• Contains hydrolytic enzymes (acid hydrolases).
• Breaks down polymers into smaller subunits within the low pH (around 4.8) lysosomal lumen.
• V-class proton pumps bring in H+ and Cl- channels bring in Cl-.
• Digest materials taken up by the cell, digest damaged or aged organelles (autophagy), and are involved in apoptosis.
• Several human diseases are caused by defects in specific lysosomal enzymes, like Tay-Sachs disease, affecting the breakdown of glycolipids and leading to their accumulation.

Phagocytosis

• Process where a cell engulfs a pathogen or other large particle. Phases involve formation of a phagosome, merging with a lysosome, and digestion of contents.

Cellular Structures Delivering Materials to Lysosomes

• Endocytosis, phagocytosis, and autophagy are processes where material is brought into a cell and delivered to lysosomes for breakdown and recycling.

Peroxisomes

• Degrade fatty acids and toxic compounds.
• Contain oxidases which leverage oxygen (O2) to oxidize organic substances and produce hydrogen peroxide (H₂O₂).
• Also contains catalase, which breaks down H₂O₂ into water (H₂O) and oxygen (O₂).
• Self-assembling organelles, "life span" of a day.
• Involved in peroxisomal biogenesis

Endomembrane System

• A group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.
• Includes the nuclear envelope, endoplasmic reticulum membranes, the Golgi apparatus, vesicles, and lysosomes.

Mitochondrion

• Double-membrane bound organelle.
• Basic structure: outer membrane, intermembrane space, inner membrane with infoldings called cristae, and a lumen termed the matrix.
• Contains circular mtDNA, granules, and mitoribosomes.
• Site of aerobic cellular respiration, referred to as the "powerhouse of the cell".

Vesicles & Vacuoles

• General term for a variety of single-membrane bound sacs.
• Vacuoles (plant cells): storage site for ions and nutrients; uptake of water by osmosis creates pressure to push membrane against cell wall.

Cytoskeleton Elements

• Responsible for maintaining and changing cell shape, internal transport, anchoring internal and external components, cell movement, and chromosome movement during cell division.
• Includes microtubules (polymers of a and ẞ tubulin), microfilaments (polymers of actin), and intermediate filaments (various proteins).

Functions of Microtubules

• Move chromosomes during cell division.
• Form centrioles, basal bodies, and centrosomes.
• Serve as tracks for vesicle and vacuole movement.
• Provide internal scaffolding for eukaryotic cilia and flagella.

Cilia & Flagella

• Locomotor structures (cytoplasmic extensions) that differ in length.
• Cilia are shorter, moving in an oar-like motion.
• Flagella are longer, moving in a whip-like manner.
• They share a 9+2 microtubule arrangement.

Functions of Microfilaments

• Involved in cell contraction (like cleavage furrow formation during cytokinesis).
• Anchor for extracellular elements.
• Play a role in cytoplasmic streaming.

Functions of Intermediate Filaments

• Form a scaffold for the cell.
• Part of the internal lining of the inner nuclear membrane.

Size Range of Cells

• A size chart showing the relative sizes of viruses, bacterial cells, typical human cells, and various cellular components such as mitochondria, lysosomes, ribosomes, plasma membranes, and even a hydrogen atom, ranging from thousands of micrometers down to less than 0.0001 micrometers.

Different Types of Microscopes

• Techniques like bright-field microscopy, phase contrast microscopy, differential interference contrast microscopy, fluorescence microscopy, confocal microscopy, offer different ways to view biological samples and structures.

Preparing Tissues for Microscopy

• Tissues are fixed, embedded into blocks, and are cut into sections using techniques like microtomes to view sections of tissue with a microscope.

Deconvolution Fluorescence Microscopy

• Deconvolution microscopy sharpens fluorescent images by reducing blurring effects due to light and depth-of-field.

Differential Centrifugation

• A method to isolate different cellular components by separating them based on their density and size through centrifugation at different speeds and times. Components like nuclei, mitochondria, plasma membranes, ribosomes, and soluble cytoplasm are separated.

Cell Fractionation and Differential Centrifugation

• Technique for separating components through centrifugal forces.

Equilibrium Density-Gradient Centrifugation

• Method to further separate organelles by density differences within a sucrose gradient medium. Examples of isolated organelles include lysosomes, mitochondria, and peroxisomes, separated by density.