🧫 Chapter 6: A Tour of the Cell

Endomembrane System

The collection of membranes inside and surrounding a eukaryotic cell that characterizes structural continuity and transfer via vesicles.

Extracellular Matrix (ECM) of ANIMAL cells

A meshwork surrounding animal cells consisting of:

• glycoproteins (collagen, fibronectin)

• prroteoglycans

• integrin cell-surface receptors

Smooth Endoplasmic Reticulum

Region of the ER that lacks ribosomes; functions in lipid synthesis, carbohydrate metabolism, drug/poison detoxification, and calcium ion storage (Ca²+).

Rough Endoplasmic Reticulum

Region of the ER studded with ribosomes; functions in the synthesis of (produces) secretory proteins (glycoproteins) packaged in transport vesicles and manufactures membranes.

Plasma Membrane Function

a selective barrier that encloses cell contents and regulates the passage of oxygen, nutrients, and wastes

Nucleolus Function

A specialized structure in the nucleus consisting of chromosomal regions where ribosomal RNA (rRNA) is synthesized and assembled.

Nuclear Envelope and Pore Complex

a double membrane enclosing the nucleus

Pore complexes regulate the entry and exit of proteins, RNA, and macromolecules

Golgi Apparatus

An organelle consisting of stacks of flat membranous sacs (cisternae) that modifies, stores, and routes/transports products of the endoplasmic reticulum. (Lipids, proteins, and other macromolecules)

• receiving cis face

• shipping trans face

Ribosome

Complexes of rRNA and protein that perform protein synthesis

Exist free in the cytosol or bound to rough ER/nuclear envelope

Lysosome

A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells used to digest (hydrolyze) macromolecules, damaged organelles, or engulfed material.

Peroxisome Function

A metabolic compartment containing enzymes that remove hydrogen atoms from the substrate, producing hydrogen peroxide (H2O2) converted to water. (plant cell)

Microtubules Structure and Function

Hollow rods made of tubulin dimers

• maintain cell shape

• guide organelle movement

• form spindle fibers

• power cilia/flagella

Centrosome and Centrioles

Centrosome: the microtubule-organizing center near the nucleus

• Contains a pair of CENTRIOLES, each composed of 9 sets of triplet microtubules

Mitochondrion

Enclosed by two membranes

• Inner membrane: folded into cristae, creating 2 compartments: the intermembrane space and mitochondrial matrix

The site of cellular respiration; it uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels.

Cilia and Flagella Motility Structure

Microtubule-containing extensions projecting from cells

• “9 + 2” arrangement of outer doublets and central microtubules

Cillia: back and forth beating motion

Flagella: propeller-like beating motion

Chloroplast Structure

contains flattened sacs called “thylakoids” (stacked into grana) suspended in fluid called stroma (site of photosynthesis) PLANT CELL

Plasmodemata

Open channels through plant cell walls that connect the cytoplasm of adjacent cells, allowing passage of water, small solutes, and RNA.

Vacuole Types

• Food vacuoles: formed by PHAGOCYTOSIS in animals

• Contractile vacuoles: pumps OUT excess water in parameciums

• Central vacuoles: water/nutrient storage in plants

Animal Intercellular Junctions

• Tight junctions: impermeable junctions that prevent molecules from passing through the intercellular space (fluid leakage)

• Desmosomes: anchoring junctions that bind to adjacent cells like Velcro. Form internal tension-reducing networks of fibers; plaques on the surface of the membrane attach to protein filaments (fasten cells into strong sheets)

• Gap junctions: cytoplasmic channels that allow intercellular communication. Also allow ions and small molecules to pass through channels formed by connexon protein cylinders.

Microfilament Function (Actin Filament)

2 intertwined strands of actin

• support cell shape

• drive muscle contraction

• cytoplasmic streaming

• cell motility

Intermediate Filament Function

Fibrous proteins coiled into cables (keratin)

Reinforce cell shape and permanently anchor organelles like the nucleus.

Phagocytosis

engulfing cellular food particles

Autophagy

recycling the cell’s own damaged organelles and organic material

Endosymbiont Theory

The theory that mitochondria and chloroplasts originated as prokaryotic cells engulfed by an ancestral eukaryotic cell, evolving into a single organism.

Cell Fractionation

A technique that breaks up cells and uses CENTRIFUGATION to separate cell components based on size and density.

Light Microscopy

LIGHT MICROSCOPES use visible light and lenses (live specimen viewing)

Electron Microscopy

ELECTRON MICROSCOPES (transmission-electron and scanning-electron) use electron beams for much higher resolution.

Surface Area-to-Volume Ratio

As a cell grows, volume increases faster than surface area

Small size ensures sufficient area to exchange materials across the plasma membrane