Unit 2: Cell Structure & Function

Prokaryotic vs. Eukaryotic Cells

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes possess them.

Pinocytosis

extracellular fluid

Transport proteins

specialized transmembrane proteins that move ions, small molecules, and nutrients across biological cell membrane

Ribsomes in cytsol

Only function in the cytosol (enzymes) and are known as free ribosomes

What types of molecules require protein?

Ions and large polar molecules require transport proteins; very large materials use vesicular transport.

Glycoproteins

Carbohydrate-tagged proteins used in cell recognition, signaling, and identification

Secretory Pathway

Ribosome on RER → transport vesicle → Golgi → secretory vesicle → plasma membrane → exocytosis.

Rough Endoplasmic Reticulum (RER)

Synthesizes and begins the modification and folding of proteins for secretion or membranes.

Smooth Endoplasmic Reticulum (SER)

Performs lipid synthesis, alcohol/drug detoxification, and metabolism.

Golgi Apparatus

Modifies, sorts, and packages proteins and lipids into vesicles.

Lysosome

Contains hydrolytic enzymes to digest macromolecules, pathogens, and cellular waste.

Mitochondrion

Produces ATP via cellular respiration; inner folds increase surface area for reactions.

Chloroplast

Performs photosynthesis; internal thylakoid membranes increase surface area.

Plant vs. Animal Cells

Plants have cell walls, chloroplasts, and central vacuoles; animals commonly have lysosomes and centrosomes.

Compartmentalization

Membranes create specialized environments and increase usable surface area, improving reaction efficiency and

material exchange

Endosymbiotic Theory Evidence

Mitochondria and chloroplasts have circular DNA, prokaryotic ribosomes, double membranes, and binary fission.

How does an altered shape affect transport proteins like aquaporins or CFTR

It reduces or completely prevents transport.

Can water cross the lipid bilayer without aquaporins?

Yes, but it moves slowly since aquaproins speed up water movement

Do ions require membrane proteins to cross the bilayer?

• Yes, ions cannot cross without membrane proteins.

In enzymes, what can a changed active site do?

reduce catalysis and cause the substrate or a toxic intermediate to accumulate.

What hydroxyl functional group does alcohol contain?

-OH

Effect of Gene Mutation

Alters mRNA codons, amino acid sequence, primary structure, protein folding, 3D shape, and function.

Phospholipid Bilayer Structure

Amphipathic molecules with hydrophilic phosphate heads facing water and hydrophobic tails facing inward.

Membrane Cholesterol

Fits among phospholipid tails to help stabilize membrane fluidity.

Direct Membrane Passage

Small nonpolar molecules like O₂ and CO₂ cross the lipid bilayer most readily.

Active Transport

Moves substances against a concentration gradient using energy, typically ATP, and a carrier protein.

Simple diffusion

own a concentration gradient; no ATP; small nonpolar molecules and some small uncharged polar molecules.

osmosis

Diffusion of water, water moves from an area of low solute concentration to an area of high solute concentration through a semipermeable membrane.

Facilitated diffusion

Down a gradient through a channel or carrier; no ATP; used by ions and polar solutes

Exocytosis

Vesicle fuses with plasma membrane to release products such as proteins or glycoprotein-containing mucus

Endocytosis

Membrane brings material into cell

Sodium-Potassium Pump

Transports 3 Na⁺ out and 2 K⁺ into the cell per ATP hydrolyzed.

Animal Cell in Hypotonic Solution

Swells and may lyse due to net inward water movement.

Animal cell in a hypertonic solution

Shrivels, net water out of cell

Plant Cell in Hypertonic Solution and their net water movement

Plasmolyzes, resulting in reduced turgor pressure and wilting, net water out of cell

Plant cell in hypotonic solution

Turgid; increased turgor pressure

Plant and animal cell in isotonic solution

Flaccid, Normal; no net movement

Water Potential Equation

Ψ = ΨP + ΨS (Water potential equals pressure potential plus solute potential).

IONIZATION CONSTANT

SODIUM=2 SUCROSE=1

Water Movement Direction

Water moves from higher water potential (less negative) to lower water potential (more negative).

Surface Area-to-Volume Ratio (SA:V)

Smaller cells have a larger SA:V ratio, allowing for more efficient material exchange.