Cell membrane transduction 1
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Cell MembraneCell Membrane
Transport systemsTransport systems
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OverviewOverview Cell membrane Cell membrane separatesseparates living cell from nonliving living cell from nonliving
surroundingssurroundings– thin barrier = 8nm thickthin barrier = 8nm thick
Controls traffic in & out of the cellControls traffic in & out of the cell– selectively permeableselectively permeable– allows some substances to cross more easily than allows some substances to cross more easily than
othersothers Made of Made of phospholipidsphospholipids, , proteinsproteins & other & other
macromoleculesmacromolecules Provide:Provide:
1. Fluidity1. Fluidity
2. Asymmetry2. Asymmetry
3. Formed closed compartments3. Formed closed compartments
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Chemical compositionChemical composition
Lipids – about 60%Lipids – about 60% Proteins – about 40%Proteins – about 40% Carbohydrates – about 1-3%Carbohydrates – about 1-3% Water and minerals – very small Water and minerals – very small
amountamount
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Membrane fat Membrane fat composition variescomposition varies Fat composition affects flexibilityFat composition affects flexibility
– membrane must be fluid & flexiblemembrane must be fluid & flexible about as fluid as thick salad oilabout as fluid as thick salad oil
– % unsaturated fatty acids in phospholipids% unsaturated fatty acids in phospholipids keep membrane less viscouskeep membrane less viscous cold-adapted organisms, like winter wheat cold-adapted organisms, like winter wheat
– increase % in autumnincrease % in autumn
– cholesterol in membranecholesterol in membrane
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Membrane ProteinsMembrane Proteins Proteins determine membrane’s specific Proteins determine membrane’s specific
functionsfunctions– cell membrane & organelle membranes each have cell membrane & organelle membranes each have
unique collections of proteinsunique collections of proteins Membrane proteins:Membrane proteins:
– peripheral proteinsperipheral proteins loosely bound to surface of membraneloosely bound to surface of membrane cell surface identity marker (cell surface identity marker (antigensantigens))
– integral proteinsintegral proteins penetrate lipid bilayer, usually across whole membrane penetrate lipid bilayer, usually across whole membrane transmembranetransmembrane protein protein transport proteinstransport proteins
– channels, permeases (pumps)channels, permeases (pumps)
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Membrane ProteinsMembrane Proteins
Membrane phospholipids act as a Membrane phospholipids act as a solvent for membrane proteinssolvent for membrane proteins
Integral (intrinsic)Integral (intrinsic)– Most membrane proteins are Most membrane proteins are
integral components of the integral components of the membrane (70%)membrane (70%)
– Penetrate the matrix from the outer Penetrate the matrix from the outer surface to the inner surface surface to the inner surface
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AP Biology
Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembraneproteins
Filaments ofcytoskeleton
Peripheralprotein
Glycoprotein
Phospholipids
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Functions of membrane Functions of membrane proteinsproteins TransportTransport StructureStructure ReceptorsReceptors EnzymesEnzymes AntigensAntigens
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Many Functions of Membrane ProteinsMany Functions of Membrane Proteins
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
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Membrane Membrane carbohydrates carbohydrates Play a key role in Play a key role in cell-cell cell-cell recognitionrecognition– ability of a cell to distinguish one cell ability of a cell to distinguish one cell
from anotherfrom another antigensantigens
– important in organ & important in organ & tissue developmenttissue development
– basis for rejection of basis for rejection of foreign cells by foreign cells by immune systemimmune system
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Transport Across Transport Across MembranesMembranes 11. Macrotransport. Macrotransport
2. Microtransport2. Microtransport
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AP Biology
Macrotransport Moving large molecules into & out of cell
through vesicles & vacuoles endocytosis
phagocytosis = “cellular eating” pinocytosis = “cellular drinking”
exocytosis
exocytosis
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AP Biology
Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered bymolecular signal
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MicrotransportMicrotransport
1. Passive1. Passive 2. Active2. Active
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Passive transportPassive transport 1. Simple diffusion1. Simple diffusion
2. Facilitated diffusion2. Facilitated diffusion
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Simple diffusionSimple diffusion Movement of molecules in response to a Movement of molecules in response to a
concentration gradient.concentration gradient. It doesn’t need energyIt doesn’t need energy
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AP Biology
Facilitated Diffusion Diffusion through protein channels (permeases)
channels move specific molecules across cell membrane
no energy needed Movable Immovable
“The Bouncer”“The Bouncer”
open channel = fast transport
facilitated = with help
high
low
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Mechanism of the Facilitated Mechanism of the Facilitated diffusiondiffusion
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Active transportActive transport
Occurs against a Occurs against a concentration gradient and so concentration gradient and so it requires energy.it requires energy.
1. Primary1. Primary
2. Secondary2. Secondary
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Primary active transportPrimary active transport
This is transportation of the This is transportation of the ions by the help of special ions by the help of special enzymatic transport systems enzymatic transport systems (ATP-ases)(ATP-ases)
Na K – ATP-aseNa K – ATP-ase
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Secondary active Secondary active transporttransport This is transportation of the molecules This is transportation of the molecules
by the help of electro- chemical by the help of electro- chemical potential of some ions (Na, H).potential of some ions (Na, H).
1. Symport systems move 2 molecules 1. Symport systems move 2 molecules in the same directionin the same direction
2. Antiport systems move 2 molecules 2. Antiport systems move 2 molecules in the opposite directionin the opposite direction
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Highest level – nervous system
Intermediate -hormonal regulation
Intracellular(enzymes)
Levels of the homeostasis regulation
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SYNTHESIS OF SIGNALLING MOLECULES
RELEASE OF SIGNALLING MOLECULES
TRANSPORT OF SIGNAL TO TARGET CELLS
DETECTION & BINDING OF SIGNAL BY SPECIFIC RECEPTOR
CHANGES DUE TO RECEPTOR-SIGNAL COMPLEX
SIGNAL REMOVAL & RESPNOSE TERMINATION
STEPS IN CELL SIGNALINGSTEPS IN CELL SIGNALING
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CLASSIFICATION OF INTERCELLULAR COMMUNICATION
Intercellular signaling is subdivided into the following classifications:
Autocrine signals target the cell itself. Sometimes autocrine cells can target cells close by if they are the same type of cell as the emitting cell. An example of this are immune cells.
Paracrine signals target cells in the vicinity of the emitting cell. neurotransmitters represent an example.
Endocrine signals target distant cells. Endocrine cells produce hormones that travel through the blood to reach all parts of the body.
Juxtacrine signals target adjacent (touching) cells. These signals are transmitted along cell membranes via protein or lipid components integral to the membrane and are capable of affecting either the emitting cell or cells immediately adjacent.
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JUXTACRINE SIGNALINGJUXTACRINE SIGNALING
MEMBRANE-ANCHORED LIGANDSMEMBRANE-ANCHORED LIGANDS
NEIGHBOURING CELLS
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e.g.*Notch signalling.
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Hormones – organic biologically active compounds of different chemical nature that are produced by the endocrine glands, enter directly into blood and accomplish humoral regulation of the metabolism of compounds and functions on the organism level.
Hormonoids (tissue hormones) – compounds that are produced not in glands but in different tissues and regulate metabolic processes on the local level, but some of them (serotonin, acetylcholine) enters blood and regulate processes on the organism level.
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Specific stimulus for hormones secretion is:
-nervous impulse
-concentration of the certain compound in blood passing through the endocrine gland
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Membrane receptors
To receive and pass on chemical or physical signals, cells are equipped with receptor proteins.
Membrane-located receptors can be divided into three parts, which have different tasks.
1. The receptor domain reacts specifically to a given signal
2. The effector domain of the receptor is usually separated by a membrane, a mechanism for signal transfer between the domains is needed.
3. By binding or interconversion, many receptors activate special mediator proteins, which then trigger a signal cascadeOther receptors function as ion channels. This is particularly widespread in receptors for neurotransmitters
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Metabotropic receptor’s
action
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Ion channels
Ion channels facilitate the diffusion of ionsthrough biological membranes. Some ionchannels open and close depending on themembrane potential (voltage-gated channels, A) in response to specific ligands (ligandgated channels, B).
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