AP Biology- Unit 2

Cell Structure & Function

Why Are Cells Small?

Greater surface area to have more efficient exhange of resources

All Cells Contain…

-Plasma membrane

-Cytosol (liquid part of cytoplasm)

-Ribosomes

-DNA

Types of Cells

Prokaryotes- lack membrane-bound structures, circular chromosomes

Eukaryotes- membrane-bound structures (organelles), linear chromosomes

Endosymbiotic Theory

Organelles in eukaryotes developed from prokaryotes due to internal symbiotic relationship

Plasma Membrane

Separates cell from external environment

-Selective permeability: chooses what materials enter/exit

Phospolipids

Head region- hydrophilic, polar

Tail region- hydrophobic, nonpolar

Not bonded, attracted due to polarity

Nucleus

Contains genetic instructions

-nuclear envelope, nuclear pores, nucleolus, chromatin

Ribosomes

-Not a membrane bound structure

-Protein synthesis

-Either free in cytoplasm or attached to the ER

Endoplasmic Reticulum

Smooth ER- no ribosomes, for lipid synthesis, carb storage, detox of poison

Rough ER- with ribosomes, makes secretory proteins (hormones, enzymes)

Golgi Apparatus

Processing- folds/chemically modifies proteins from ER

Distribution- packages proteins via vesicles

Lysosome

Breakdowns cell materials, contains hydrolytic enzymes, can trigger apoptosis

Mitochondria

Cell respiration- release of ATP

-matrix, site of the Krebs Cycle

Chloroplast

Carry out photosynthesis

-Stroma surrounds internal membranes, location of the Calvin Cycle

-Inside stroma is thylakoid, contains pigments

Vacuoles

Membrane bound

-Central: osmoregulation in plants

Cell Wall

Surrounds cells, similar to exoskeleton

-only in prokaryotes+plants

Tight Junctions

Tight fusion of membranes from adjacent cells

-seals off areas

Gap Junctions

Open channels between cells

-allows communication between cells

Desmosomes

Anchor junctions between cells

-ex. tin cans + string

-found in muscle tissue

Passive Transport

-Moves materials DOWN concentration gradient

-doesn’t require energy

-will eventually reach equilibrium

Diffusion

-type of passive transport

-net movement of molecules

Osmosis

-type of passive transport

-uses aquaporin to pass through phospholipid bilayer

Tonicity

Concentration of water relative to plasma membrane

-isotonic: equal solute concentration

-hypotonic: low solute concentration

-hypertonic: high solute concentration

Facilitated Diffusion

-type of passive transport

-carries large and charged ions through plasma membrane

Active Transport

-Diffusion that requires ATP

-Moves materials UP concentration gradient

Bulk Transport

-Moves large items into/out of cell

-Requires ATP

Exocytosis

-type of bulk transport

-movement of materials out of cells using vesicles

Endocytosis

-type of bulk transport

-movement of materials into cells using vesicles

Fluid Mosaic Model

Lots of chemicals are embedded in the phospholipid bilayer

-cholesterol

-proteins