-Membranes allow ADAPTATION because their composition can change.
Importance in LIMIT
-Limits cell's energy by accumulating certain molecules(proteins, DNA/RNA, glycogen and others) while excluding others (sodium, calcium,silicone
-it sets boundries
-acts as barrier to diffusion to larger and or/ polar molecules. This decreases ENERGY DEMAND (enhancing survival chance) of the cell (by trapping some molc. in and others out.
Importance of COMPARTMENTATION
-like the cell membrane; internal membranes can subdivide processes within and improve EFFICIENCY
ex. electron transport componetns are highly organized within INNER MITOCHONDRIAL MEMBR., and this makes passage of e- highly efficient.
pathways for glucose handling are localized to the CYTOSOL, while the enzymes of the Krebs cycle are found in the MITOCHONDRIAL MATRIX
enzymes of f.acid synthesis (cytosol) are seperated by enzymes of f. acid catabolizm (beta oxidation) by the inner mitochondrial membrane
-Nuclear Envelope seperates DNA and processes like REPLICATION and TRANSCRIPTION from other proceses in the cell
SIGNAL TRANSDUCTION of hydrophilic signals is localized to proteins on cell membrane.
TRANSPORT across internal memrbanes helps to maintain unique intrancellular compartments for the processes of each compartment.
Importance of ADAPTATION
membranes allow adaption because their composition can change. the content of membranes can change over time in response to alterations in the extracellular environment
What PROPERTIES of membranes enhance the chance of SURVIVAL?
Why are flexible
-flexibile cause membrane components are NOT covelantly bound to each other. FLUID MOSAIC MODEL
gives abiltiy to shift position, while Van Der Waals bonds will promote adherence to neighboring lipids. (lipid bilayer)
What does flexibility of membranes allows for?
-MOVEMENT of the cell: membranes get distorted, but cells can change position or shape white their membranes maintain their compartmentation functions
-GROWTH of the cell- FLuidity of membranes allows for additional membrane to be added or taken away (Endo and Exocytosis)
cell growth, synaptic vesicle recyclin, neurotran horm release, nerve regent. and insulin regualrtion of glucose transport anre all processes which are depended on the ability of a cell to add or remove membrane.
Self-Sealing membrane property
tendency of a mebane to recombine to form and intact barrier after small or minor "tears"
what does this Self-Sealling property allow for the membrane to do?
-allows for cell division
-allows for endo and exocytosis, phagocytosis
process by which hydrophilic signals (polypetpide hormones and neurotransmitters) can be stored in a cell and released when appropriate stimulus signasl the cell to release the hydrophilic signal
-Exocytosis allows for expansion of cell membrane
-mecanism to incorporate new protein molc into membranes
-allong with endocytosis it leads to the ability to regularte transport and signal sensitivity in target cells (membrane remodeling)
how does exocytosis works?
signal (ligand binds to cell surface receptero or transcient depolorization)
signals triggers cascade which then - increases intracellular Ca+, interactions of SNARE and SNAP proteins, and hydrolysis of ATP
vessicle drawn close to cell membrane where outer leaflter with vessicle will fuse with inner leaflet of teh cell membrane
then inner vessicle leaflet fusses with outter membrane leaflet
this results in the interior of the vesicle now being contious withthe exracellular fluid-what was inside the vesible is now a part of the extracellular fluid
movement of materials into the cell by way of membrane bound vesicles.
pinocytosis-intravscular content is simply extracellular fluid
phagocytosis-where endocytosis actually brings in particulate matter suchs as small pieces of collaged by process of osteoclast.
endocytosis is involved in a number of disease precesses, including hepatitis, poliomyelities, AIDS, iron toxicity
How does Endocytosis work?
-pinocytosis isn't regulated; cell membrne invaginates and the stem pinches off to form new vesicle
-inner leaflet of an endocytotic vesible is comprised of the outer leaflet of the cell membrane
Receptor Mediated Endocytosis
in this form of endocytosis there is an an assembly of clathrin protein molecules at the location where the membrane invagination occurs.
-coated pit-initial invagination which includes the occupied receptors.
-coated pits continue to invaginate and pinch off forming a coated vesicle
-coated vesicles fuses with 1' lysosomes to form 2' lysosomes
-lysomes digest the contents of coated vesicle and release a.a, sugand and nucleuotides for cell use
what three things do endocytosis and (exocytosis?) require?
1. energy (ATP hydrolysis)
2. presence of calcium on the extracellular fluid (outside)
3. contractile elements of the microfibrils in the cell
Cell membranes are selectively PERMEABLE
They regulate what may enter and exit the cell.
the shell of water molecules surrounding a dissolved molecule, ion, or other compound and stabilizes it
hydrophilic compound will shed this as they diffuse into the bilayer, making it hydrophobic and able to be attracted to the hydrophobic core environe.
What diffuses through the lipid bilayer?
nonpolar molecules, O2, CO2, fatty acids
membrne sturcture helps to keep undesired compounds out of the cell while "trapping" desired compounds insided the cell while providing avenues for appropriate movement of comopunds across the membrane
Selective permeability of membrane structure
Hydrophilic glucose cannot diffuse via lipid bilayer
so an integral glucose trasnport protein will transport it with its hydrophibc exterior and hydrophilic interior (GLUT 1-GLUT12).
Why is glucose phosphorylated by HEXOKINASE?
- phosphate makes the glucose-6-phosphate even more hydrophilc than glucose and
-because glucose-6-P cannot pass through GLUT-4 is then stuck in the cell, committed to further
What is COMPOSITION of membranes?
provide barrier to diffusion and hydrophobic inner core that can be used to anchor proteins to the membrane
provide ACTIVE FUNCTIONS associate with membranes; act as receptors, transporters(active and facilated), effectors(producing 2nd messengeds) sites for energy production, physical linking sites bw the cell and the extracellurar
serve roles in RECOGNITION (recognize chemical signals
Sugars are presented in membranes as GLYCOPROTES AND GLYCOLIPIDS
membrane composition changes over time
Via Endo and Exocytosis (composition of leaflets differ from each other
FLIP-FLOP in cell membrane
lipids and to much less extent, proteins can move from inner to outer leaflet (or vise versa)
what requires membrane transports and what doesn't
Active transport, facillitated diffusion, endocytosis and exocytosis
what do active transport and facillated diffusion exhibit during transport
Saturable kinetics (Tmax) bc there are a finite number of transport molecules
-Cell surface receptors are present in target cells of hydrophilic signals(neurotransmiters, autocines and panracrines, and polypetptide hormones)
-binding of the signald to the cell surface recepter is just teh beginning of a cascade of events that oftern involce GTP-binding proteins, effectors and eventual generation of one ore more second messengers.
Primary Active: ATP is directly hydrolyzed to provide energy
Secondary Active: energy source is the electrochemical gradient of and ion (commonly sodium (Na+/K+ pump); ATP will be hydrolyzed subsequent to the transport to maintain the energy of the driving gradient
secondary active transport
Difference in Channels vs Transporters
Both are proteins that allow movement of chemicals across memerbnes, but
-channels are proteins which allow FLOW of IONS down their electrochemical gradient.
-Channels allow much higher rates of FLUX(faster)
-Channels do NOT exhibit saturable kinetics
Examples of Facilitated Transporters
HCO3-/Cl (exchanger in red bloods cell)
GLUT1 glucose transport found in red blood cells and many other cells
GLUT4 (muscle, fat, heart) is insulin dependent
Examples of ACTIVE TRANSPORTERS
Na/K ATPase (electrochemical antiporter)
SERCA Pumps (ATPase electrochemical uniporter)
ATP Synthase (inner mitochondrial membrane)
Intestinal and Renal Glucose Pumps (Sodium-Dependent)
ABC Transporter (ATP Binding Cascade- pumps for a.a, peptideds, lipids, bile salts etc)
Intestinal and Renal Amino Acid Pumps (Sodium-Dependent)
Calcium Pumps in many cells (Sodium Dependent)
What type of Active Transport are the Sodium-dependent pump and what kids are the ATPases?
-Sodium-dependent: Secondary Active Transport
-ATPase are Primary Active Transport
Examples of CHANNELS
Voltage gagted Sodium Potasium channerls (provide actions potentials in excitable cells liker neruons and muscle