Anatomy Chapter 3 - The Cellular Level of Organizing

passive processes

movement of substances down a concentration gradient until equilibrium is reached; do not require cellular energy in the form of ATP

diffusion

movement of molecules or ions down a concentration gradient due to their kinetic energy until they reach equilibrium

simple diffusion

passive movement of a substance down its concentration gradient through the lipid bilayer of the plasma membrane without the help of membrane transport proteins

substance transported during simple diffusion

nonpolar, hydrophobic solutes (oxygen, CO2, nitrogen gases, fatty acids, steroids, fat-soluble vitamines.) polar molecules (water, urea, small alcohols)

facilitated diffusion

passive movement of a substance down its concentration gradient through the lipid bilyaer by transmembrane proteins that function as channels or carriers

substances transported in facilitated diffusion

polar or chagred solutes, glucose, fructose, galactose, vitamines, ions (K, Cl, Na, Ca)

Osmosis

passive movement of water molecules across a selectively permeable membrane from an area of higher to lower water concentration until equilibrium is reached

substances transported in osmosis

solvent —> water in living systems

active processes

movement of substances against a concentration gradient; requires cellular energy in the form of ATP

active transport

Active process in which a cell expends energy to move a substance across the membrane against its concentration gradient by transmembrane proteins that function as carriers.

substances transported in active transport

Polar or charged solutes

Primary active transport

Active process in which a substance moves across the membrane against its concentration gradient by pumps (carriers) that use energy supplied by hydrolysis of ATP.

substances transported in primary active transport

Na⁺, K⁺, Ca²⁺, H⁺, I⁻, Cl⁻, and other ions.

Secondary active transport

Coupled active transport of two substances across the membrane using energy supplied by a Na⁺ or H⁺ concentration gradient maintained by primary active transport pumps. Antiporters move Na+ (or H⁺) and another substance in opposite directions across the membrane; symporters move Na⁺ (or H⁺) and another substance in the same direction across the membrane.

substances transported in secondary active transport

Antiport: Ca²⁺, H⁺ out of cells.

Symport: glucose, amino acids into cells.

Transport in Vesicles

Active process in which substances move into or out of cells in vesicles that bud from plasma membrane; requires energy supplied by ATP

Endocytosis

Movement of substances into a cell in vesicles

Receptor-mediated endocytosis

Ligand–receptor complexes trigger infolding of a clathrin-coated pit that forms a vesicle containing ligands.

substances transported in Receptor-mediated endocytosis

Ligands: transferrin, low-density lipoproteins (LDLs), some vitamins, certain hormones, and antibodies.

Phagocytosis

“Cell eating”; movement of a solid particle into a cell after pseudopods engulf it to form a phagosome.

substances transported in Phagocytosis

Bacteria, viruses, and aged or dead cells

Bulk-phase endocytosis

“Cell drinking”; movement of extracellular fluid into a cell by infolding of plasma membrane to form a vesicle

substances transported in Bulk-phase endocytosis

Solutes in extracellular fluid.

exocytosis

Movement of substances out of a cell in secretory vesicles that fuse with the plasma membrane and release their contents into the extracellular fluid

substances transported in exocytosis

Neurotransmitters, hormones, and digestive enzymes

transcytosis

Movement of a substance through a cell as a result of endocytosis on one side and exocytosis on the opposite side

substances transported in transcytosis

Substances, such as antibodies, across endothelial cells. This is a common route for substances to pass between blood plasma and interstitial fluid

plasma membrane

• structure: Fluid mosaic lipid bilayer (phospholipids, cholesterol, and glycolipids) studded with proteins; surrounds cytoplasm

• functions: Protects cellular contents; makes contact with other cells; contains channels, transporters, receptors, enzymes, cell-identity markers, and linker proteins; mediates entry and exit of substances

cytoplasm

• structure: Cellular contents between plasma membrane and nucleus—cytosol and organelles.

• function: Site of all intracellular activities except those occurring in the nucleus

cytosol

• structure:  Composed of water, solutes, suspended particles, lipid droplets, and glycogen granules. The cytoskeleton is a network in the cytoplasm composed of three protein filaments: microfilaments, intermediate filaments, and microtubule

• function: Fluid in which many of cell’s metabolic reactions occur. The cytoskeleton maintains shape and general organization of cellular contents; responsible for cell movements.

organelles

• structure: Specialized structures with characteristic shapes

• function: Each organelle has specific functions

centrosome

• structure: Pair of centrioles plus pericentriolar matrix

• function: The pericentriolar matrix contains tubulins, which are used for growth of the mitotic spindle and microtubule formation

cilia and flagella

• structure: Motile cell surface projections that contain 20 microtubules and a basal body

• function: Cilia: move fluids over cell’s surface; flagella: move entire cell

ribosome

• structure: Composed of two subunits containing ribosomal RNA and proteins; may be free in cytosol or attached to rough ER

• function: protein synthesis

endoplasmic reticulum

• structure: Membranous network of flattened sacs or tubules. Rough ER is covered by ribosomes and is attached to the nuclear envelope; smooth ER lacks ribosomes

• function: Rough ER: synthesizes glycoproteins and phospholipids that are transferred to cellular organelles, inserted into plasma membrane, or secreted during exocytosis; smooth ER: synthesizes fatty acids and steroids, inactivates or detoxifies drugs, removes phosphate group from glucose-6-phosphate, and stores and releases calcium ions in muscle cells

lysosome

• structure: Vesicle formed from Golgi complex; contains digestive enzymes

• function: Fuses with and digests contents of endosomes, phagosomes, and vesicles formed during bulk-phase endocytosis and transports final products of digestion into cytosol; digests worn-out organelles (autophagy), entire cells (autolysis), and extracellular materials

peroxisome

• structure: Vesicle containing oxidases (oxidative enzymes) and catalase (decomposes hydrogen peroxide); new peroxisomes bud from preexisting ones

• function: Oxidizes amino acids and fatty acids; detoxifies harmful substances, such as hydrogen peroxide and associated free radicals

proteasome

• structure: Tiny barrel-shaped structure that contains proteases (proteolytic enzymes)

• function: Degrades unneeded, damaged, or faulty proteins by cutting them into small peptides

mitochondrion

• structure: Consists of an external and an internal mitochondrial membrane, mitochondrial cristae, and mitochondrial matrix; new mitochondria form from preexisting ones

• function: Site of aerobic cellular respiration reactions that produce most of a cell’s ATP. Plays an important early role in apoptosis

nucleus

• structure: Consists of a nuclear envelope with pores, nucleoli, and chromosomes, which exist as a tangled mass of chromatin in interphase cells

• function: Nuclear pores control the movement of substances between the nucleus and cytoplasm, nucleoli produce ribosomes, and chromosomes consist of genes that control cellular structure and direct cellular functions

golgi complex

• structure: Consists of 3–20 flattened membranous sacs called saccules; structurally and functionally divided into entry (cis) face, medial saccules, and exit (trans) face.

  
  

• function: Entry (cis) face accepts proteins from rough ER; medial saccules form glycoproteins, glycolipids, and lipoproteins; exit (trans) face modifies molecules further, then sorts and packages them for transport to their destinations

interphase

Period between cell divisions; chromosomes not visible under light microscope

G₁ phase

Metabolically active cell duplicates most of its organelles and cytosolic components; replication of chromosomes begins. (Cells that remain in the G1 phase for a very long time, and possibly never divide again, are said to be in the G0 phase)

S phase

Replication of DNA and centrosomes

G₂ phase

Cell growth, enzyme and protein synthesis continue; replication of centrosomes complete