Chapter 4 – Evolutionary Origin of Cells and Their General Features

Protobiont

Aggregate of prebiotically produced molecules within a boundary; possible precursors of living cells.

Liposomes

Vesicles surrounded by a lipid bilayer, may have been a form of protobiont. Can be catalyzed by clay.

RNA world

Hypothetical period when RNA contained both information and catalytic activity.

Prokaryotic cells

Cells lacking a nucleus and other membrane-bound organelles; relatively simple (bacteria and archaea)

Eukaryotic cells

Cells containing a nucleus and other membrane-bound organelles; exhibit extensive compartmentalization (protists, fungi, plants, and animals)

Cytosol

The region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane.

Cytoskeleton

Network of protein filaments (microtubules, intermediate filaments, and actin filaments) within the cytosol.

Microtubules

Long, hollow cylinders composed of tubulin subunits; important for cell shape, organization, and chromosome sorting.

Intermediate filaments

Rope-like structures made of various proteins; function as tension-bearing fibers.

Actin filaments (microfilaments)

Composed of actin subunits; dynamic and provide shape and strength.

Motor Proteins

Use ATP to promote movement (cargo, filaments, or bending).

Cilia and Flagella

Cell appendages containing microtubules and dynein that bend to produce movement.

Nuclear Envelope

Double-membrane enclosing the nucleus with nuclear pores for transport.

Chromatin

Complex of DNA and proteins forming chromosomes.

Nucleolus

Region of ribosome assembly within the nucleus.

Endomembrane System

Network of membranes including the nuclear envelope, ER, Golgi, lysosomes, vacuoles, peroxisomes, and plasma membrane.

Endoplasmic Reticulum (ER)

network of membranes connected to the nuclear membrane

• rough ER: ribosome for protein processing

• smooth ER: lacks ribosomes, involved in metabolism & lipid synthesis

Golgi Apparatus

Stack of flattened membranous sacs (cisternae) for protein sorting, processing, and secretion.

Lysosomes

Small organelles containing acid hydrolases for breaking down macromolecules, functions best at acidic pH.

Vacuoles

Compartments for storage, water balance, or degradation; prominent in plants and fungi.

Peroxisomes

Small organelles that catalyze diverse reactions, including breakdown of nutrients and toxins; produce hydrogen peroxide.

Semiautonomous Organelles

Mitochondria and chloroplasts that grow and divide and contain distinct genetic material but rely on other parts of the cell for some functions.

Mitochondria

Converts chemical energy into ATP.

Chloroplasts

Performs photosynthesis, capturing light energy to synthesize organic molecules.

Endosymbiosis Theory

Theory that mitochondria and chloroplasts originated from bacteria living inside a primordial eukaryotic cell.

Extracellular Matrix (ECM)

Meshwork of secreted materials outside the cell's membrane in animal cells.

Cell Wall

Strong and rigid structure outside the cell's membrane in plant cells; made of cellulose and other polysaccharides.