Cell Membranes (Ch.5)

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asymmetriscally distributed

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membrane proteins

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1 protein for every 25 phospholipid molecules - this ratio is variable

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membrane proteins

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inner mitochondrial membrane has __ protein(s) for every __ lipids

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1, 15

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myelin (coated nerve cells) have approx. ___ protein(s) for every ___ lipids

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1,70

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Many proteins have both ___ and ____ regions

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polar, nonpolar

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membrane proteins have both _____ and ______ R groups in their amino acid

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hydrophilic, hydrophobic

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for many protein molecules & lipid molecules, bonding is not_______

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covalent

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both protein molecules and lipid molecules are free to move around laterally

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fluid mosaic model

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2 kinds of membrane proteins

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Integral & peripheral

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have long hydrophobic amino acid areas

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Integral membrane proteins

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penetrate/ entirely cross the bilayer

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Integral membrane proteins

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form an alpha-helix region, interact w/ only the membrane core

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Integral membrane proteins

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hydrophilic R groups face the aqueous areas & interact w/ them

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Integral membrane proteins

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proteins that go completely through the membrane (hydrophobic)

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transmembrane proteins

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have a specific orientation - one side shaped such that it can act as a receptor for a signaling molecule

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transmembrane proteins

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the other side changes in response to the signal binding

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transmembrane proteins

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can't go entirely inside (do not penetrate the bilayer at all)

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peripheral membrane proteins

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some proteins can move around in the membrane while other membrane proteins are restricted in movement due to anchoring part of cytoskeleton. that causes ____

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an unequal distribution of these proteins

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some cells are speciallized to be anchored to the ___

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extracellular matrix

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exposed portion of the protein locks onto the ___, while internal region might tie to the _____

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extracellular polymers, cytoskeleton

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2 kinds of plasma membrane carbohydrates

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glycolipids and glycoproteins

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recognition signals for interacting w/ other cells - may change when cell becomes cancerous

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glycolipids

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recognition signals for other cells and proteins - use an "alphabet" of single sugars to create a diversity of messages

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glycoproteins

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cells can arrange themselves into groups by:

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cell recognition & cell adhesion

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one cell specifically binds to another cell of a certain type

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cell recognition

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the relationship between the two cells in "cemented"

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cell adhesion

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is essential in the formation and maintenence of tissues and multicellular organisms - occurs because of phospholipid bilayer recognition proteins

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tissue-specific & species-specific aggregation

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Only cells from the same species aggregate ex:)sponge

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if a sponge is disaggregated into cells, it can reaggregate into a sponge

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large glycoproteins (~80% sugar) is partly embedded in the phos. bilayer

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regonition proteins

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species-specific recognition portion faces ______ & is exposed to the ______

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outward, environment

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2 kinds of binding of cells in a tissue

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homotypic & heterotypic

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both cells have the same type of cell surface receptor & their interaction causes them to stick together - most cases ex:) sponge cells

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homotypic binding

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a plug and socket - mammalian sperm & egg cell binding

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heterotypic binding

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line body cavities & cover body surfaces

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epithelial tissues

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3 kinds of specialized cell junctions

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tight junctions,desmosomes, gap junctions

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hold cells together by acting like spot welds on adj. cells

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desmosomes

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one cell connects its fibrous networks of other cells

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desmosomes

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seals tissues & prevents leaks - prevents substances from moving through the intercellular space

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tight junctions

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restrict the migration of membrane proteins and phospholipids, therefore, can help polarize & stabilize the cell

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tight junctions

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facilitate communication between cells - dissolve materials, electric signals

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gap junctionc

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process of random movement toward the state of equilibrium- individual movement is random but net movement is directional until equilibrium - from region of highrer concentration to lower concentration

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diffusion

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in a solution, diffusion depends on:

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temp, physical size of the solute, electrical charge of the diffusing material, and the conc. gradient

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very fast over short distances, not adequate to distribute materials over length of the body, across layers of membranes/from 1 cell to another rapid enough to distribute small molecules & ions almost instantaneously

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diffusion

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permeability of membranes to diff. solutes can influence diffusion rates. Ex: a steroid will diffuse readily vs. a proetein of similar size. - although both will eventually achieve equilibrium

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diffusion across the bilayer

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hydrophobic interior of the membrane tends to exclude hydrophilic substances except water - water readiky passes through the lipid bilayer

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diffusion across the bilayer

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can move through ion channels - moves rapidly through protein-lined membrane channels

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water

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membrane-lined channels through which water can move

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aquaporins

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diffusion of water across membranes net movement - a completely passive process

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osmosis

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molecules move from a region of higher concent. to lower concent.

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osmosis

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water will diffuse from:

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region of its higher concentration (low conc. of solutes) to region of it's lower conc. (higher conc. of solutes)

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two solutions of equal solute conc.

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Isoionic solutions

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lower total solute conc. than the soln. to which it i being compared

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Hypotonic solution

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higher total solute conc. than the soln. to which it is being compared

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Hypertonic soln.

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Integrity of cells depends on:
Ex: RBCs in the plasma

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a constant solute conc.

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In pure water :
Plant cells ______
Animal cells_______

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-limit the amount of water intake (rigid cell wall),
-continue to take pure water in-eventually burst.

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may be aided by proteins - polar substances e.g. a.a. & sugars & charged substances e.g. ions

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diffusion

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involves proteins embedded in the plasma membrane - channel proteins and carrier proteins

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facilitated diffusion

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lined w/ polar a.a. - nonpolar a.a face the outside of the channel towards the fatty acid tails of the lipid mol. - e.g. ion channels

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channel proteins

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gated: various mechanisms for controlling the opening & closing. Once open, millions of ions/second can rush through.

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Ion channels

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speed and direction of ions depends on_______

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conc. gradient

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Ion cahnnels are ______ for one type of ion

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specific

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involves not just opening a channel but actual binding to the transported substance e.g. sugars & a.a.

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carrier proteins

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allow diffusion in both directions

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carrier proteins

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conc. gradient can be kept by metabolizing the transported substance e.g. as soonas glucose enters the cell, it is metabolized, therefore the cell's glucose conc. remains low and the movement of glucose continues

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carrier proteins

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rate of movement through these is dependent on conc. ONLY to a point.

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carrier proteins

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if the limited # of carrier protein mol. are loaded w/ solute mol. they are _________

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saturated

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______ can limit the # of molecules that can move into the cell/unit of time

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saturation

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ions or molecules move across the membrane from regions of lower conc. to rgions of higher conc. (against the conc gradient)

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active transport

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In active trasport, ATP is used ______

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directly or indirectly

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3 kinds of protein driven active transport

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uniport transporters, symport transporters, and antiport transporters

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move a single type of solute ex: Ca2+, in one direction

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uniport transporters

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move 2 solutes in the same direction e.g. a.a. transport may be coupled to Na+ transport

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symport transporters

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Na+ moves from higher conc _____ the cell down the conc gradient to the _______ of the cell. As this occurs, a _______ is moved up the conc gradient & into the cell as well.

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outside, inside, amino acid

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moves two solutes in opposite directions e.g. Na+ K+ pump

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antiport transporters

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for each molecule of ATP used __ Na+ ions are pumped ___ and ___ K+ ions are pumped ___

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3, out, 2, in

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uses ATP directly for the pumping of the system

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primary active transport

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uses ATP indirectly to establish the ion gradient.

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secondary active transport

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gradient is used to move a substance e.g. in symport and antiport systems

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secondary active transport

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only cations e.g. Na+ K+ pump

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primary active transport

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in intestinal cells, glucose is move up its conc gradient, while moving Na+ down its conc gradient

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secondary active transport

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both Na+ & glucose enter the cell Na must be pumped out again, but the energy harvested from the glucose more than pays for this energy expense

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secondary active transports

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bring macromolecules, large particles, small molecules, & even other cells inside a cell e.g. proteins, polysaccarides, nucleic acids, & triglycerides - too large and charged to enter through the membrane

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Endocytosis

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3 kinds of Endocytosis

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phagocytosis, pinocytosis, and receptor-mediated endocytosis

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involves the largest vesicles (can be entire cells) transported inside the cell

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phagocytosis

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cellular feeding process of unicellular protists

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phagocytosis

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white blood cells defend the body against invading foreign cells by means of ______

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phagocytosis

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very small vesicles - dissolved substances and fluids are brought into the cell - nonspecific

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pinocytosis

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the layer of cells separating blood capillaries from surrounding tissue aquire fluids from the blood by means of ______

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pinocytosis

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similar to endocytosis, but highly specific

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receptor-mediated endocytosis

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In receptor-mediated endocytosis, receptor proteins are exposed on the outside of the cell in ________

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coated pits

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The cytoplasmic surface of a coated pit is coated by proteins, such as _____

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clathrin

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________ is the method by which cholesterol is taken up by most mamalian cells

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receptor-mediated endocytosis

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cholesterol is transported throughout the body with _________

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Low-density lipoproteins (LDL)

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genetic disorder in which LDL receptors are deficient and there are extremely high levels of cholesterol in blood

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Hypercholesterolemia

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moves materials out of the cell - vesicle membrane fuses with plasma membrane and is transported outside. ex:) waste, enzymes, hormones, neurotransmitters

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exocytosis

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involved in info. processing to initiate, modify or turn off a cell function

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membranes (are more than just simple barriers)

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important in energy transformation ex:) inner mitochondrial membrane: energy of feul molecules to ATP

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membranes (are more than just simple barriers)

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An example of membrane involved in energy transformation in thalakoid membranes of chloroplasts

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light energy to chemical bond energy

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involved in organizing chemical reactions into "assembly line" reactions that proceed more rapidly & efficiently

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membranes (are more than just simple barriers)

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actively participate in many cellular processes; continually form, move and fuse; are similar and can interconverge; major chemical dif. depend on their locations and functions.

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Membranes (are dynamic)

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In membrane synthesis in Euk. cells,the ___ synthesizes and distributes the phosphlipids

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smooth endoplasmic reticulum (SER)

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In membrane synthesis in Euk. cells, _______ form proteins that are inserted into the RER

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ribosomes

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In membrane synthesis in Euk. cells, each _____ changes its membranes to carry out specific functions

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organelle

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sum total of all the chem. conversions in a cell

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metabolism

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link simple molecules to make complex ones - energy-stroing reactions

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anabolic reactions