Cell Membranes, Transport, and signaling Flashcards
Composition of cell membrane (general)
Fluid mosaic model composed of a lipid bilayer and some cholesterol
The phospholipids of the cell membrane
3 carbon glycerol backbone, 2 fatty acid tails into the membrane, P and Alcohol
inner leaflet borders what
the cytoplasm
outer leaflet borders what
ECF
the head group of the fatty acids are ____ and made of what
charged/polar-composed of phosphate and alcohol into ECF (aqueous)
Fatty acid tails are ____
nonpolar- for the inner membrane/cytoplasm
Amphipathic
Polar headgroup borders aqueous environment, fatty acids for nonpolar tails (it has one end with a charge and one without)
Cholesterol (describe structure and function)
6 ringed strucuture to regualte and stabalize fluidity and can regulate bound peripheral proteins
Integral proteins
crosses one or more sides of the membrane (i.e. transport protein/channel/hormone receptor)
Peripheral proteins
loosely associated with the membrane, does not permeate into the bilayer
location of carbs on/in cell wall
outside-can connect to ECM
Carbohydrates
types-2, and functions-3
glycolipids and glycoproteins-
- regulate prt function
- attach protein to ECM
- marks cell as self
marks cell as self
carbs
Simple diffusion
From high to low [c], random thermal motion, rate depends on concentration and stops at equilibrium
Factors that determine if something will diffuse and which cross easier through cell membranes?
Size (smaller go faster/easier)
Polarity (nonpolar cross easier)
Osmosis
define, stops when?
simple diffusion of water, water moves from high concentration to low concentration and stops moving when the hydrostatic P exactly opposes osmotic pressure
Facilitated diffusion will move via
Carrier proteins (transporters or exchnagers)
Can cholesterol cross membrane via simple diffusion? (it is large)
YES, because it is very nonpolar
Passive facilitated diffusion
down a concentration gradient from high to low
Substrate Size moved via facilitated diffusion
larger molecules
The transport maximum velocity is known as what? Define it
Vmax: when all carrier molecules (protein transporters) are saturated, therefore transport cannot happen any faster
150 mm NaCl is how many mosm
150x2=300
150mm glucose is how many mOsm
150x1=150
Tonicity
considers whether or not a molecule can cross the membrane- only considers osmolarity of inactive molecules
Osmolarity Calculation
(molar concentration) x (# of osmotically active particles)
Does urea matter for tonicity?
No-it crosses readily
Tonicity and Osmolarity of 150mM NaCl, 300mM urea
300ton, double NaCl and ignore urea
Osmolarity=600
**I will use urea in the example
ignore for ton
use for osmolarity
isotonic ton
normal (300)
hypertonic ton?
high (>300)
Hypotonic ton
low (<300)
Do Na+ and K- cross the membrane? Urea? Why does it matter?
Na and K Do not! so consider these for tonicity
Urea does
though! So DO NOT count for ton
Cell in hypotonic solution
Swells, H20 goes in
How to calculate tonicity
molar concentration x number of osmotically active particles, IMPERMEANT particles
(DO NOT COUNT UREA)
Cell in hypertonic solution does what
shrinks-cell volume will go down (lose H20)
Hypernatremia/water intoxication
low plasma sodium, increases water concentration inside and there is too much in the blood and moves into the tissue!
kidney and liver disease clinical relevance
lose protein via urine, can get edema b/c maybe not making enough protein
Specificity of carrier proteins
chemical binding to just one amino acid or molecule-competition is also to be considered
Does facilitated diffusion require energy
It is passive-uses concentration gradients (from high to low)
3 main types of ion channels (acvtivated by..)
NT, voltage, or stretch
Ion channels move substances how
down concentration gradients
specificity of ion channels
Very specific/selective
Rate of ion channels
VERY HIGH RATES of flow-moves millions of ions/s
Size of ions moving through ion channels
SMALL
Rate of ion channel vs transporter
Ion channel much faster-does not need to change conformation in order to transport–just like an open door!
Primary Active Transport and give ex
Uses ATP energy to move molecules against a gradient and directly uses ATP (ex Na/K ATPase)
-cell loses ATP
Secondary Active Transport and ex
what are the two types?
Use energy, but not directly using ATP.
-Uses energy from a gradient that was previously built up/existed.
i.e. Moves Na down its gradient and harnesses that energy by coupling with molecule transport
2 types= symport and antiport
Symport Secondary Active Transport
The two molecules are moved in the same direction
Antiport
The two molecules are moving in opposite directions
Vesicular transport (define)
pinching off of the cell membrane into or out of the cell
endocytosis-vesicular transport
What are the 3 types?
large molecules-slow (pino, phago, and RM endocytosis)
3 types;
pino, phago, and receptor mediated endocytosis
Exocytosis
vesicle inside the cell fuses with the PM and releases its contents into the ECM
Second Messenger systems
why use them? What do they cause?
They get the signals across the cell membrane and to the target cell
They cause intracellular amplification via cascade pathways allowing one signal molecule to create 1000s of signaling molecules
Adenyly cyclase/cAMP
explain the process
Can be stimulatory (Rs) or inhibitory (Ri):
the receptor for stimulatory hormone cAMP couples to G protein –> modifies Gs protein –> this binds to adenlyl cyclase –> converts ATP to cAMP
increase in cAMP causes what
increased cAMP dep PKA which phosphorylates proteins (not sure we need to know this)
Phospolipase C/inositol triphosphate (IP3)
Explain the pathway… (long)
The first messenger binds to magic 7 receptor
–> receptor changes
conformation
–> One G protein subunit (Gq) dissociates and bonds to phospholipase C
(PLC, signaling lipid)
–> PLC cleaves PIP2 into IP3 and DAG
–> IP3 is hydrophilic and goes into the endoplasmic reticulum
–> IP3 mobilizes Ca++ from intracellular stores (releases Ca++)
–> Ca++ affects smooth muscle/release vesicles
Tyrosine Kinase
Function and explain pathway
attach a phosphate group to tyrosine residues in proteins
i. receptor is an integral protein, needs an agonist, has an enzyme that will phosphorylate tyrosine on proteins
ii. this phosphorylated tyrosine kinase protein can then be an enzyme and phosphorylate other proteins – ex: insulin, growth factors
ion channels (indirect action):
hormone may directly bind to ion channels or might have a 2nd messenger that modulates these channels
Hormone Regulation of gene expression
What? How do they? Function?
This applies to hormones that act on cytosolic and nuclear receptors (steroid hormones) thus need no secondary messenger-
They can get to the nucleus via carrier or membrane proteins and turn on the gene increasing translation of protein and leads to a biological effect
Cell osmolarity is ~?
300mosm
Isosmotic
Solution has same osmolarity as cell (=300mOsm)
Hyposmotic
Solution has less solutes than cell (<300mOsm)
Hyperosmotic
Solution has more solutes than cell (>300mOsm)
Size of molecules moved via carrier proteins
Relatively large molecules (sugars, drugs, AAs)
Transport Maximum Velocity (Vmax) and facilitated diffusion
when all carrier proteins are saturated with molecules the process cannot go any faster
Compare the rate of ion channels vs carrier channels
Ion channels are much faster!! They are just like an open door
PDE: Phosphpodiesterse
degrades cAMP to AMP
Hormone pathway that requires a secondary messenger (pathway)
The hormone binds the receptor –> G protein –> effector protein –> secondary messenger is released –> goes through ion channel
IP3 mobilizes Calcium.. this will result in what
Ca++ released from the ER/SR increase intracellular [Ca++] and act on calmodulin
Calmodulin will then bind to other proteins and increase their activity
Hormone Regulation of gene expression
Rate? Longevity?
Slow-but long lasting
Hormone Regulation of gene expression
location of receptors
cytosolic and nuclear receptors IN the cell
the hormone enters through a carrier protein or channel
