A & P Chapter 3: Cellular Form and Function

Cell shape and size

• 200 types of cells

• most cells are 10-15 um in diameter

• an overly large cell cannot support itself; may rupture

Membrane proteins - Receptor

Binds to chemical messengers such as hormones sent by other cells

Membrane proteins - Enzyme

An enzyme that breaks down a chemical messenger and terminates its effects

Membrane proteins - Channel

Constantly open and allows solutes to pass into and out of the cell

Membrane proteins - Gated channel

A gate that opens and closes to allow solutes through only at certain times

Membrane proteins - Cell-Identity Marker

A glycoprotein acting as a cell-identity marker distinguishing the body’s own cells from foreign cells

Membrane proteins - Cell-adhesion molecule

Molecule that binds one cell to another

Microvilli

extensions (1-2 um) that increase surface area; developed in cells specialized in absorption

Cilia

hair-like processes (7-10 um long); single, nonmotile found on most cells; serves as “antenna” for monitoring nearby conditions

Flagellum

whiplike structure; tail of sperm is only functional flagellum in humans, much longer than cilia

Pseudopods

continually changing extensions of the cell that vary in shape and size; aid in cellular locomotion and capturing foreign particles

Plasma membranes are selectively permeable. (follow their concentration gradient) What does this mean?

allows some substances to move across and inhibits other molecules; Small, non-polar molecules (CO2, O2) freely cross the membrane by passing through the phospholipid bilayer, Large or polar molecules cannot freely cross

Passive mechanisms

require no ATP (ex. filtration, diffusion, osmosis)

Active mechanisms

consume ATP (ex. active transport and vesicular transport)

Carrier-mediated mechanisms

use a membrane protein to transport substances across membrane

Filtration

Particles are driven through membrane by physical pressure

Simple diffusion

Net movement of particles from place of high concentration to place of lower
concentration- down concentration gradient

Osmosis

• Net flow of water through a selectively permeable membrane
• Water moves from an area of higher water (lower solute) concentration to an area of lower water (higher solute)
concentration

Aquaporins

channel proteins in membrane specialized for water passage

Osmolarity

osmotic concentration; quantity of nonpermeating solutes
per liter of solution
- Body fluids contain a mix of many chemicals, and osmolarity is the total
osmotic concentration of all solutes

Tonicity

ability of a surrounding solution to affect fluid volume and pressure in a cell
- Depends on concentration of nonpermeating solutes

Tonicity- Isotonic solution

causes no change in cell volume

Tonicity- Hypotonic solution

causes cell to absorb water, swell, and possibly burst (lyse)
• lower concentration of nonpermeating solutes than intracellular fluid (ICF)
• Distilled water is an extreme example

Tonicity- Hypertonic solution

causes cell to lose water and shrivel (crenate)
• higher concentration of nonpermeating solutes than intracellular
fluid (ICF)
• Ocean water is an example

Facilitated diffusion

• Carrier proteins move solute down its concentration gradient (high to low concentration)

• Doesn’t consume energy

Primary Active Transport

• Moves things UP its concentration gradient (low to high concentration)

• Uses energy

• Sodium-potassium pump

Secondary Active Transport

• Carrier proteins move solute through membrane

• Uses energy indirectly

• Sodium-glucose transporter

  moves glucose into cell, up its concentration gradient, while simultaneously carrying sodium down its gradient

Vesicular Transport

• Used to move large molecules

  Endocytosis - brings substances into the cell

  Exocytosis - expels substances from the cell

• Uses energy

Cell Organelles

• Allows for compartmentalization

• Perform specific functions

• Isolate potentially harmful reactions

Organelles without nucleus:

ribosomes, centrosomes, centrioles, basal bodies

Cytoskeleton

• Structural support

• Cell shape

• Directs movement of materials (microfilaments, intermediate fibers, microtubules)

Nucleus

• Largest organelle

• Contains DNA

  Nuclear Envelope - double membrane around nucleus

• Material within nucleus is called Nucleoplasm

  Includes threadlike chromatin (DNA and proteins)

Rough Endoplasmic Reticulum

• Parallel, flattened sacs covered with ribosomes

• Produces phospholipids and proteins

Smooth Endoplasmic Reticulum

• Lacking ribosomes

• Synthesizes steroids and other lipids

• Calcium storage

• Detoxification

Ribosomes

• Small granules of protein and RNA

  Free - floating in cytoplasm; synthesize proteins for immediate use in cell

  Bound - attached to outer surface of endoplasmic reticulum

Golgi complex

• Synthesizes carbohydrates and modifies newly synthesized proteins from rough endoplasmic reticulum

• Packages products into membrane-bound Golgi vesicles

  Secretory vesicles

  Lysosomes

  Some vesicles fuse with plasma membrane for export

Lysosomes

• Membrane-bound vesicles

• Contains digestive enzymes and are highly acidic

• Digest large molecules

• Recycle cellular resources

• Produced by Golgi apparatus

Peroxisomes

• Similar to lysosomes

• Specializes in lipid detoxification

• Produces hydrogen peroxide when digesting lipids

• Hydrogen peroxide is toxic… Catalase is a substance that converts this

Vacuoles

• Membranous sacs that are larger than vesicles

• Stores materials that occur in excess

Mitochondria

• Synthesizing energy (ATP)

• Surrounded by double membrane

  Cristae - Inner membrane folds

  Matrix - Spaces between cristae

• “Powerhouse” of cell

Centrioles

• Short cylindrical assembly of microtubules

• Cell division

• Two centrioles lie perpendicular to each other within the centrosome