7: Structural and Functional Unit of Life

Cells

Smallest living subunit of organism, most between 1-100 microns in diameter

Prokaryotic Cells

Don’t have true membrane-enclosed nucleus, no membrane bound organelles, nucleoid, small/circular DNA, unicellular

Nucleoid

Region where DNA is concentrated

Eukaryotic Cells

Membrane-bound organelles that compartmentalize their functions, nuclear envelope, large, linear DNA, unicellular/multicellular

Nuclear Envelope

Double membrane nucleus is bound in

Cellular Specialization

Degree of relaxed constraints on cell size + shape to allow cellular specialization within multicellular organisms

Genomic DNA

Regardless of specialization, genomic DNA contained within nucleus remains largely unchanged

Observable Differences

Arise from differential gene expression across specialized cell types, results in production of different proteins that leads to different structures + functions

Odd Prokaryote

Thiomargarita magnifica, unicellular organisms up to 2 cm length, membrane enclosed nucleoids, large water filled sac

Energy & Matter Transformations

System of internal membranes synthesize + modify proteins/lipids/carbs

Genetic Information Storage & Transmission

DNA in nucleus contains instructions to make proteins, ribosomes are sites of protein synthesis

Selective Permeability

Ability to differentiate between different types of molecules only allowing some molecules through, some properties stem from intrinsic diffusion rates for different molecules across membrane, activity of various protein-based membrane transporters affects relative rates of movement of various substances across biological membrane

Phospholipids

Make most of membranes of all cellular compartments, amphipathic molecules with hydrophobic tails + hydrophilic heads

Fluid Mosaic

Characterization of membranes of all compartments, dynamic structures composed of phospholipids, proteins, carbohydrates, + cholesterol

Catabolic Reactions

Break down large macromolecules into smaller molecules + releases energy

Anabolic Reactions

Use energy generated in catabolic reactions + raw materials gathered by cell to synthesize larger biomolecules

Endomembrane System

Separates cell into different compartments/organelles with unique conditions due to selective permeability of lipid bilayers (nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes)

Compartmentalization

Of nucleus structure achieved via nuclear envelope,

Nuclear Envelope

Double lipid bilayer separating nuclear contents from cytoplasm, both layers perforated by pore structures to regulate entry/exit of RNAs/proteins/macromolecules

Chromosomes

Discrete units genetic information/DNA is housed/organized into, # varies among organisms

Nucleolus

Most prominent features within undividing nucleus, where ribosomal RNA synthesizes + along with proteins imported from cytoplasm via nuclear pores assembled into ribosomal subunits, subunits exit nucleus + finally assemble into full ribosomes in cytoplasm

Ribosomes

Cellular machinery carrying out protein synthesis given certain set of genetic instructions,

Endoplasmic Reticulum (ER)

Accounts for more than ½ of total membrane in many eukaryotes, membrane continuous with nuclear envelop to allow RNA exported from nucleus to interact with ribosomes studded on outer surface of nuclear envelope + on rough surface of ER

Smooth ER

Lacks ribosomes, synthesizes lipids, detoxifies drugs + poisons, stores calcium ions

Rough ER

Surface studded with ribosomes, bound ribosomes that secrete glycoproteins covalently bonded to carbohydrates, distributes transport vesicles, secretory proteins surrounded by membranes, membrane factory

Golgi Apparatus

Flattened membranous sacs called cisternae, cis face region of organelle facing toward ER that receives material from ER, trans/shipping face posterior to cis face + points toward plasma membrane of cell

Steps of Transportation

Folded proteins + lipids from ER sent to cis face through transport vesicles, Golgi modifies/concentrates/tags products, tagged products sent into new vesicles (secretory vesicles) that bud off trans face of GA to transport to appropriate destination

Lysosomes

Sites of hydrolysis, membranous sacs of hydrolytic/digestive enzymes made in rough ER that are further refined in GA, work in relatively low pH (more acidic than cytosol) so must be contained within compartment formed by lysosome’s membrane, leakage all at once too much for cell survival, phagocytosis + autophagy

Lysosome Phagocytosis

Cell engulfed by another cell, forms food vacuole that’s lipid bilayer enclosed package of food brought in from outside of cell, hydrolytic enzymes digest macromolecular structures in whatever cell took in, 2 phospholipid bilayer compartments merge with one another

Lysosome Autophagy

Use enzymes to recyle cell’s own organelles + macromolecules

Vacuoles

Large vesicles derived from ER + GA with diverse functions, in plants serve as storage containers for proteins/important organic compounds (cells of seeds), small vacuoles may contain defensive chemistry that deters herbivory only after leaf experiences damage/pigments in flower petals attract pollinators

Central Vacuole

Most prominent feature in plant cell, cell main reservoir of inorganic ions (potassium/chloride), swollen with water that cytosol of plant cell appears pushed up against cell wall in thin layer

Transport Across Cell Membrane

Small molecules + water enter/leave cell through lipid bilayer/via transport proteins, larger molecules (polysaccharides, proteins) cross membrane in bulk

Vesicles

How large molecules (polysaccharides, proteins) cross membrane in bulk

Exocytosis

Transport vesicles migrate to membrane to fuse with it + release contents outside of cell, important for signaling + communication

Endocytosis

Molecules + large substances taken into cell via vesicles, membrane forms pocket that deepens + pinches off to form vesicle around material for transport

3 Endocytosis Types

Phagocytosis, pinocytosis, receptor-mediated endocytosis

Phagocytosis

Pinocytosis

Receptor-Mediated Endocytosis

Motor Proteins

Interaction required for cellular motility with elements of cytoskeleton, energy input as ATP

Mitochondria

Sit of cellular respiration

Chloroplasts

Sit of photosynthesis

Endosymbiotic Theory

Ancestor of modern eukaryotes engulfed ancestors of modern membrane-bound organelles, mutualism that’s not standard exploitation interaction

Evidence for Endosymbiotic Theory

Mitochondria + chloroplasts reproduce same way as prokaryotes, DNA + ribosomes similar to free-living prokaryotes, 2 membranes with inner one more like prokaryotes + outer like eukaryotes

Euglena

Genus of single-celled flagellate eukaryotes conditionally heterotrophic + autotrophic, chloroplasts have 3 membranes suggesting endosymbiotic event