Traffic - Week 2 (ch. 3) Flashcards
Plasma Membrane Structure - what it’s made of
phospholipid bilayer
Plasma membrane structure consists of…
hydrophilic (water loving) heads are polar,
face outward toward water
hydrophobic (water fearing) tails are nonpolar, face inward away from water
(in plasma membrane)
(1) barrier to diffusion - stops water soluble
molecules from passing through. water is small enough and it’s responsible for membrane fluidity
2. cholesterol
a. between phospholipids b. contributes to fluidity and stability
protein in membrane
a. some span the membrane - bridge spans the bay
(1) selective channels
(2) carrier proteins
proteins on one side of membrane
CRMFG
1) cell adhesion molecules (CAMs
2. receptors
(3) membrane bound enzymes
(4) filamentous meshwork
5. glycoproteins
Carbohydrates in plasma membrane
a. only on outer surface, bound to membrane proteins and lipids (glycoproteins, glycolipids)
b. important in recognition of cells of same type and tissue organization
c. involved in tissue growth (cells won’t overgrow) - won’t grow over side of petri dish
cell to cell adhesion
carbohydrates on membrane surface help arrange cells into groups, which are held together in various ways
types of cell to cell adhesion (FEECC)
FEECC
- CAMs (a protein and carbohydrate)
- extracellular matrix (only connective tissues)
a. cells not joined directly to other cells, but in matrix of carbohydrates and protein fibers
(1) collagen - resists tension (e.g., skin)
(2) elastin - stretch and recoil (e.g., skin, lungs)
(3) fibronectin - holds cells in position (all over body)
b. substances diffuse through, going between blood and tissues
c. important in normal cell functioning
Specialized junctions (TGD)
desmosomes, tight junctions and gap junctions
desmosomes (specialized junction)
cells join at particular spots, found all over body, particularly where stretch occurs (e.g., skin, muscle)
tight junctions
impermeable barrier, common in epithelial sheets where they prevent leakage. Looks sewn together
gap junctions
cells linked by protein tunnels, allows small molecules to pass between cells, important in some cells that transmit electrical activity (e.g., cardiac muscle)
Membrane transport - what determines it
two factors influencing transport - solubility of the substance in lipid, and size of substance
Passive transport
diffusion-molecules move down their concentration gradient (greater ➝ lesser concentration), charged particles move down electrochemical gradients. No ATP is used.
Types of Diffusion
FOS
a. simple diffusion -substance moves through lipid bilayer or protein channels (e.g., O2, CO2, some ions)
b. osmosis - water moves down its concentration gradient
c. facilitated diffusion uses a carrier protein that binds to the molecule to be transported and brings it to the other side of the membrane (e.g., glucose)
How different types of membrane transport work (small & big cars)
small, uncharged or nonpolar molecules move through lipid bilayer (e.g., O2 CO2, fatty acids)
ions and small polar molecules (like glucose) can move through channels or by carrier proteins if the right transporter exists
substances too big or without a special protein transporter need special mechanisms to get through the membrane
Filtration
Also passive transport - water and solutes forced through membrane by pressure (e.g., in kidneys)
Net diffusion
Diffusion from area A to area B minus diffusion from area B to area A
: Differences in arrow length, thickness, and direction represent the relative magnitude of molecular movement in a given direction.
Diffusion occurs if…
a substance can permeate the membrane
No diffusion occurs if…
If the membrane is impermeable to a substance
osmosis
H2O moves from side 1 to side 2 down its concentration gradient
Isotonic conditions
No net movement of water; no change in cell volume
Hypotonic conditions
Water diffuses into cells; cells swell
Hypertonic conditions
Water diffuses out of cells; cells shrink
Types of Active Transport (ATP used)
- carrier proteins transport substance against its concentration gradient (needs ATP to change conformation)
a. primary active transport
b. secondary active transport
primary active transport
energy from ATP used directly to transport a substance (e.g. Na+-K+ pump, in all cells)
secondary active transport (bus)
- driven by gradients set up by primary active transport
(1) in the digestive tract glucose and amino acids are “dragged along” with Na+ diffusing into cell (Na+ gradient set up by Na+-K+ pump) uses ATP as a 2nd step
Symport
When the transported molecule and cotransported ion move in the same direction
Antiport
When the transported molecule and cotransported ion move in opposite directions
Primary Active Transport in Sodium potassium pump
establishes Na+ concentration gradient from lumen to cell, which drives secondary active transport
Secondary Active Transport (about glucose)
creating glucose concentration gradient from cell to blood used for Facilitated Diffusion. Glucose hitches a ride with Na.
vesicular transport (bulk transport) - active transport
large molecules or multimolecular substances enclosed in pieces of membrane. endocytosis and exocytosis
what is Intercellular communication and signal transduction
cells must communicate so they can coordinate their activities (maintain homeostasis, control growth and development)
3 types of intercellular communication
gap junctions, signal molecules, chemical messengers
gap junctions
a. small molecules and ions directly exchanged between cells
b. important in spread of electrical signals (cardiac
and smooth muscle, very rarely neurons)
signal molecules
on cell surface allow direct interaction
a. WBC - phagocytes (body defense cells) recognize and
kill invading cells
4 types of chemical messengers
PHNN
paracrines, neurotransmitters, hormones, neurohormones
paracrines
act locally (e.g., histamine in inflammatory response)
neurotransmitters
act locally; nerve cells release them to other nerve cells, muscles, or glands
hormones
acts over long distances, released into blood by endocrine glands
neurohormones
act over long distances, released into blood by special nerve cells (neurosecretory neurons)
Pathways of chemical messengers
- specialized protein receptors on plasma membrane bind with a particular messenger
- channel regulation
- tyrosine kinase pathway
- second messenger systems (most common pathway). triggers events and many possible responses
3 general ways of eliciting a response - chemical messengers
(1) opening (most commonly) or closing
chemically- gated receptor channels in the membrane (regulates movement of ions in/out of cell)
(2) activating receptor-enzymes
(3) transferring signal to second messenger (most common) (an intracellular chemical messenger) which initiates a series of events inside cell
channel regulation (this is a pathway for chemical messengers)
a. channel proteins open/close (act like gates)
b. receptor binding site is part of the channel, messenger binds ➝ channel opens
c. eg., neurotransmitters trigger movement of Na+,K+, or both across the membrane, which changes the electrical activity of cell (muscle and nerve cells)
tyrosine kinase pathway
a. messenger binds and activates a receptor-enzyme (usually a protein kinase that phosphorylates another protein)
b. creates a chain reaction that activates a particular protein that brings about the response
c. eg., insulin and growth factors
all second messenger systems (most common pathway - chemical messengers)
(1) messenger binds to receptor (G-protein- coupled receptor)
(2) enzyme on inside of membrane activated by G-protein
(3) intracellular second messengers are activated, and diffuse through the cell to trigger appropriate response
(4) typically a cascade is initiated and response accomplished by altering structure/function of particular proteins
cAMP pathway (2nd messenger system)
(1) messenger binds to receptor
(2) activates G protein which activates adenylyl cyclase (on cytoplasm side)
(3) ATP ➝ cAMP, which diffuses through cell
(4) cAMP-dependent protein kinase activated, then phosphorylates a particular intracellular protein (this changes the protein’s shape/function, bringing about the appropriate response)
(5) can switch cellular processes on or off, eg., heart rate changes, formation of sex hormones in typical female, breakdown of stored glucose in liver, water conservation in kidneys
Ca2+ pathway (2nd messenger system)
(1) messenger binds to receptor
(2) activates G protein which activates phospholipase C (on cytoplasmic side of membrane)
(3) PIP2 ➝ DAG + IP3 (phosphatidylinositol bisphosphate,
diacylglycerol, inositoltriphosphate)
(4) IP3 increases Ca2+ in cytosol (from stores in ER), Ca2+ diffuses through cell and binds to the protein calmodulin, which in turn activates another protein, bringing about the appropriate response
(5) pathway important in cell movement such as smooth muscle contraction
very low concentrations of first messengers…(chemical messengers)
trigger large responses - one messenger molecule can result in millions of product molecules
receptors can be
regulated (number, affinity for messenger)
the two major second messenger systems can
interact, and there are others
Apoptosis
an interesting example of a signal transduction (just transmitting signals)
pathway
2. programmed cell death
reason for programmed cell death
development
b. tissue turnover
c. immune system (infected cells and worn- out phagocytes)
d. old, damaged or mutated cells
how apoptosis works
cell detaches from neighboring cells and shrinks, killed from the inside by caspases (little scissor), which take apart DNA, cytoskeleton, etc.
a. cells normally receive signals for survival,which block the pathway causing apoptosis
(1) absence of growth factors or detachment from
extracellular matrix act as triggers
b. can receive “death signals” that override life pathway.
Diseases associated with apoptosis
problems in pathways likely involved in Alzheimer’s, Parkinson’s and AIDS
d. not enough apoptosis may play role in cancer. mitochondria play a role (release cytochrome c which activates caspases)
4. does not trigger an inflammatory response
Membrane Potential
separation of charges across a plasma membrane
membrane potential (just separation of charges)
- separated charges have the potential to do work - electrical force of attraction can be harnessed
- measured in millivolts (mV) –
more charges separated ➝ greater potential - all plasma membranes have potential
- due to unequal distribution of a few key ions
Ions involved in membrane potential
- Na+
- K+
- A- (large anionic intracellular proteins)
Na+-K+ pump
- responsible both directly and indirectly for establishing membrane potential
Na+-K+ pump Directly
- directly generates about 20% of membrane potential
a. actively transports 3 Na+ out for every 2 K+ in
(1) leaves cell slightly negative inside
(2) establishes concentration gradients (Na+ high outside, K+ high inside)
(3) passively, Na+ ➝ in, K+ ➝ out
how Na+-K+ pump indirectly creates membrane potential
a. membrane is more permeable to K+than to Na+ (more K+ channels open)
b. K+ will passively flow out,increasing membrane potential
(1) K+ flows out until concentration gradient is
balance by electrical gradient (negative charges inside attract K+)
c. very little Na+ leaks back in (closed channels) leads to resting membrane potential of -70mV in a typical nerve cell (sign means more negative inside)
Other effects of membrane potential
- A- cannot leave the cell (too large)
a. contributes to negative charges that balance leakage
of K+ out of cell - Cl- distribution influenced by membrane potential a. high outside
b. negative charge inside cell drives Cl-out (cells
permeable to Cl-, but most do not actively transport it)
membrane potential does what to muscles?
nerve impulses muscle contraction and secretory cells
b. significance in other cells not understood
selective protein channel
to transport substances across membrane (e.g., ions), opening filled with water, channel is specific
carrier protein
also transport specific molecules across membrane
receptors
- bind with molecules on outer surface and initiate changes in cell (chemicals in blood only influence cells with the right receptors)
(protein on one side) membrane-bound enzymes
chemical reactions at inner or outer membrane surface
filament meshwork
on inner side bind with cytoskeleton to maintain cell shape and for movement
CAMS
stick out from outer surface and secure cell to other cells (cadherins “zip” cells together in tissues/organs), also cell communication (growth, defense responses), integrins span the membrane and link cytoskeleton to external environment and relay regulatory signals.
more solutes =
less water
Phosphorelate
ATP is used
Chloride likes to hang out with
sodium, so it will be outside the cell
endocytosis (pino/phagocytosis) - bulk transport
(1) fuse with lysosomes which break down
substance and release products to cell (e.g.,
bacteria)
(2) vesicle travels to opposite side of cell and
releases contents (cells lining capillaries)
exocytosis - bulk transport
(1) secretion of large polar molecules like
hormones and enzymes
(2) adding components to membrane
Phospholipid heads
polar, want to face water
phospholipid tails
non-polar, away from water
fluid mosaic model
The fluid mosaic model describes the cell membrane as a tapestry of several types of molecules (phospholipids, cholesterols, and proteins) that are constantly moving.
pump
active transport is used
not enough apotosis
cancer
ending in “ase”
means enzyme
80% of membrane potential comes from
passive flow of ions
cellular respiration is how…
we get energy from food, glucose.
ATP is just
stored energy
cellular respiration is…
glycolysis, citric acid cycle and electron transport
in diffusion, charged particles move down…
electrochemical gradients
some proteins on one side of membrane…
Usually glycoproteins - some allow cells to recognize “self” and interact with one another.
Dynamic equilibrium
Diffusion from area A to area B
Diffusion from area B to area A
No net diffusion
