Functions of the Cell

plasma membrane

outer boundary that allows cell interaction with its external environment

nucleus

directs cell activities

cytoplasm

located between plasma membrane and nucleus; contains organelles that perform functions

functions of the cell

cell metabolism and energy use, synthesis of molecules that are specific for the type of cell, communication, reproduction and inheritance

plasma membrane functions

separates cytoplasmic substances from extracellular environment of the cell, encloses and supports the cell contents, attaches to the extracellular environment or to other cells, ability to recognize and communicate with other cells, determines what moves into or out of cell

plasma membrane composition

lipids and proteins with a very small amount of carbohydrates

glycolcalyx

combination of carbs and lipids (glycolipids) and proteins (glycoproteins) on outer surface

phospholipid

bilayer, polar heads facing water in the interior and exterior of cell (hydrophilic), non-polar tails facing each other on the interior of membrane (hydrophobic)

cholesterol

interspersed among phospholipids, amount determines fluid nature of the membrane, providing stability to the membrane

integral membrane proteins

extend deeply into membrane, often extending from one surface to another; can form channels through the membrane

peripheral membrane proteins

attached to integral proteins at either the inner or outer surfaces of the lipid bilayer or to polar heads of phospholipids

glycoproteins or glycolipids

allow cells to identify one another or other molecules, distinguish between self-cells and foreign cells, recognition of oocyte by sperm cell, intercellular communication

cadherins

integral protein, attach cells to other cells

integrins

integral protein, function in pairs to attach to extracellular molecules

transport proteins

involve carrier proteins or channels in the cell membrane

specificity

for a single type of molecule based on shape, transport protein characteristic

competition

among molecules of similar shape, transport protein characterisitc

saturation

rate of transport limited to number of available carrier proteins, transport protein characteristic

channel proteins

integral membrane proteins that form tiny channels through membrane; determines size, shape, and charge of what can move through

leak ion channels

nongated, always open; responsible for the permeability of the plasma membrane to ions when the plasma membrane is at rest

gated ion channels

open or closed by certain stimuli

voltage-gated ion channel

open when there is a change in charge across the plasma membrane

cystic fibrosis

genetic disorder that affects chloride ion channels and causes cells to produce thick, viscous secretions

carrier proteins

also called transporters; integral proteins move ions from one side of membrane to the other

uniporter

moves one ion/molecule, carrier protein form

symporter

moves two ions/molecules in the same direction as the same time (cotransport), carrier protein form

antiporter

moves two ions/molecules in opposite directions at the same time (countertransport), carrier protein form

receptor proteins

proteins or glycoproteins in membranes with an exposed receptor site on the outer cell surface, can attach to specific chemical signal molecules and act as an intracellular communication system, ligand can attach only to cells with the specific receptor

G protein complex

consists of proteins alpha, gamma, and beta

enzyme

some act to catalyze reactions at outer/inner surface of plasma membrane