-
fluid mosaic model
- structural model of the plasma membrane
- the molecular arrangement of the plasma membrane resembles an ever-moving sea of fluids and a mosaic of many different proteins
- some proteins float freely, some are anchored
-
plasma membrane
- made of
- 1. phospholipids (75%) - amphipathic
- 2. cholesterol - (20%) - slightly amphipathic - stay in the nonpolar tail region
- 3. glycolipids - (5%) - carbohydrate/lipids - ONLY in membrane layer that faces the EXTRACELLULAR liquid - make the two layers asymetric (different)
-
integral proteins
peripheral proteins
- parts of plasma membrane that are fully embedded in it - removing them will destroy the membrane
- integral proteins are amphipathic
- peripheral proteins are not firmly embedded - attached to one side or the other - can be removed without hurting the membrane
-
Transmembrane protein
- span the entire lipid bilayer and protrude into the cytosol and extracellular fluid
- many integral proteins are transmembrane proteins
-
glycoproteins
glycocalyx
- proteins with carb groups attached to the end that protrude into the extracellular fluid
- glycocalyx is a glycoprotein "signature" that allows cells to recognize one another - hydrophillic and attracts a thin layer of fluid to the surface of many cells - red blood cells slippery
-
Functions of Membrane Proteins
- Ion channels
- Transporter
- Receptor
- Cell Identity marker
- Linker
- Enzyme
-
Ion channels
- integral protein
- water filled pores that move specific ions through the plasma membrane
- selective - diff levels of specifity - cation channel - moves all cations through - sodium channel - moves only sodium
- most plasma membranes have specific channels for several common ions
- most numerous ion channels - K+ or Cl - - fewer for Na+ and Ca2+
-
Transporter
- integral protein
- moves ions and polar substances across the membrane by changing shape
-
Receptor
ligand
- integral protein - not necessarily transmembrane
- each receptor recognizes and binds a specific ligand that alters cells function in some way
- ligand - a specific molecule that binds to a receptor
-
Cell identity markers
- glycoprotein & glycolipids - distinguished your cells from anyone else's
- enable cell to recognize other cells of the same type during tissue formation
-
Linker
- Integral or peripheral
- anchor proteins in the plasma membrane of neighboring proteins to one another - anchors filaments inside and outside the plasma membrane providing structural stability and shape for the cell
-
Enzymes
- integral or peripheral
- catalyze specific chemical reactions at the inside or outside surface of the cell (depends on which direction active site faces)
- substrate in - product out
-
membrane fluidity
- FLUID AND DYNAMIC
- phospholipids and membrane proteins are not rigidly fastened - move around - spaces open and close so water and materials can move through
- proteins are not constant - numbers change - increased or decreased upon needs of the cell
-
Membrane Permiability
- selective permiable
- 1. non-polar, uncharged particles can cross membrane anywhere (O2, CO2, steroids)
- 2. slightly permiable to water and urea(waste product from breakdown of amino acids) travel through small gaps that open and close
- 3. other molecules need help to cross
-
concentration gradient
- difference in concentration of a chemical from one place to another
- Extracellular fluid - higher concentration of O2 and Na+ (sodium ions)
- Intracellular fluid - higher concentrations of CO2 and K+ (potassium ions)
-
membrane potential
electrical gradient
- difference in electrical charges inside and outside the plasma membrane
- at rest:
- + postive = extracellular
- - negative = intracellular
- electrical gradient is the difference in electrical charges of two regions - membrane potential is difference across a membrane
-
electrochemical gradient
combines influence of concentration and electrical charge gradient on the movement of an ion
-
passive transport
diffusion across a membrane - substance moves down its concentration gradient using only kinetic energy - no input of energy from the cell
-
active tansport
ATP used to drive substances up the concentration gradient
-
Diffusion across a plasma membrane is influenced by:
- 1. Steepness of the concentration gradient (steep moves faster)
- 2. Temperature
- 3. Mass of the diffusing substance (large particles move slow)
- 4. Surface area
- 5. diffusion distance (greater distance takes longer)
-
Osmosis
Tonicity
- movement of water across a membrane - move from high to low to reach equalibrium
- Tonicity - measure of the solutions ability to change the volume of a cell by altering their water content
- Isotonic - concentration same on both sides - no flow of water
- Hypotonic solututuin - less solute in solution so water moves into cell
- Hypertonic - more solute in solution so water moves into cell
-
Hemolysis
Crenation
- RBC in a hypertonic solution - water enters cell and causes it to burst
- Crenation - cells in a hypertonic solution - water leaves cell and cell shrivles
-
aquaporins
plasma membrane proteins that allow water to move through quickly
-
hydrostatic pressure
osmotic pressure
- pressure exerted by the weight of water - U tube - weight will cause water to move back across membrane - equilibrium is reached when the hydrostatic pressure and the osmosis move at the same rate
- osmotic pressure - the amount of pressure needed to stop osmosis - U tube - amount of pressure needed to force both tubes to have equal water
-
Edema
excess interstitial fluid in the brain - given a hypertonic solution so water leaves interstitial fluid and enters blood where is can be extracted by the kidneys
-
Diffusion through the lipid bylayer
non-polar, hydrophobic molecules can move through without use of ATP
-
Diffusion through membrane channels
- Ion-specific channels - may be gated or permanently open
-
Facilitated Diffusion
Transport Maximum
- substances bind to carrier proteins embedded in plasma membrane
- carrier proteins change shape and release them on the other side
- REQUIRES NO ATP
- Transport occurs DOWN a concentration gradient
- TRANSPORT MAXIMUM - the number of transporters in the plasma membrane places an upper limit on the rate that facilitated diffusion can occur - at that point it cant go faster even if solute concentration is increased - the process becomes saturated
-
Active Transport
Primary Active Transport
Secondary Active Transport
- ATP USED
- primary - pumps ions AGAINST concentration gradient
- sodium/potassium pump - Na+/ K+/ ATPase
- cells expend 40 % of ATP on sodium/ potassium pumps - pumps Na+ out and K+ in against concentration gradient
- Secondary - indirectly uses energy from primary transport - high concentration of Na+ outside so some diffuses back into cell - carries with it other substances against their concentration gradient
-
Symporters
Antiporters
- In secondary active transport - if transporters move two substances in the same direction they are symporters
- Antiporters move two substances in opposide directions against their concentration gradient
-
Endocytosis
Receptor - mediated endocytosis
Phagocytosis
Pinocytosis
- Process that brings bulky substances into the cell - uses vessicles
- Receptor-mediated endocytosis - receptors in plasma membrane catch ligands - for vessicle
- Phagocytosis - eating - engulfs particle to break it down - non-specific
- Pinocytosis - drinking - takes droplets of extracellular fluid into cell
-
Vessicle
Exocytosis
- vessicle - small, spherical sac made of plasma membrane
- Exocytosis - process that takes bulky substances out of the cell - secretory cells, nerve cells (neurotransmitters)
-
phagocyte
- specific cells that are able to carry out phagocytosis
- macrophages - located in body tissues
- neutrophils - type of white blood cell
-
pseudopod
false feet - projections of the cells plasma membrane and cytoplasm
-
Transcytosis
vessicle move substance into, across, and out of the cell
-
intracellular fluid
- cytosol - cytoplasm that surrounds organelles 55% of cell volume
- cytoplasm refers to cytosol and all organelles except nucleus
- mostly water 75 - 90% with ions, nutrients, ATP, and wastes
-
cytoskeleton
- network of protein filaments that extent throughout the cytosol
- give support, shapes, and movement to the cell
-
Three parts of cytoskeleton
- 1. Microfilaments - small - around edge of cell - give shape and support
- 2. Intermediate Filaments - thicker than micro - strong - attached to cell membrane and project into cells - help attach cells to one another
- 3. Microtubules - tubes - grow out form centrosome - give cell shape - involved in movement (flagella & celia) - mitotic spindle
-
Microvilli
fingerlike projections of the plasma membrane - increase surface area of membrane - increases places for transport across the membrane - abundant on cells involved in absorption
-
centrosome
- critical for cell divisioncomposed of two centrioles (tubes 9 triplets) at right angles
- microtubule processing plant
-
Celia
- hair-like projections on cell surface - microtubules
- function to propell fluid over surface of the cell
-
flagella
- microtubules
- single whip-like extenstion
- moves entire cell - only human cell is sperm
-
Ribosome
- site of protein synthesis
- made of protein and RNA
- can be free or attached
-
RER
- attached ribosomes - makes plasma membrane for cell
- makes phospholipids and secretes proteins make by attached ribosomes
-
SER
- 1. synthesizes steroids, fatty acids
- 2. detoxifies drugs in liver cells
- 3. stores calcium in muscle cells
-
Golgi Complex
- flattened membrane sacs
- processes & ships proteins make by RER
- cis - in - faces RER
- trans - out - faces plasma membrane
-
Lysosome
- vesicle forms by golgi complex
- contains digestive enzymes - digest food, worn out organelles, entire cells
- autophagy - lysosome digest a worn out organelle and releases the components into the cytosol to be resued
- autolysis - lysosome destroys entire cell - tissue deterioration just after death
-
mitochondron
- double membrane
- can self replicate
- more mitochondira in tissue that expends more energy (muscles)
- cristae inner membrane - lots of folds- site of ATP production
- matrix - large inner fluid filled cavity
-
nucleus
parts of the nucleus
- most cells have one - some blood cells have none and skeletal muscle cells can have more than one
- Nuclear Envelope - double membrane
- nuclear pores - openings in the nuclear envelope - control movement of substances between the cytoplasm and nucleus
- nucleoli - produce ribosomes - made of protein, DNA, RNA
- chromatin - mass of DNA, protein, and RNA - when cell is in interphase chromatin is a granular mass - during - when getting ready to divide the chromatin coils up into the double helix of DNA
-
genes
chromosomes
chromatin
genome
- genes - cell's hereditary units
- chromosomes - genes are arranged along chromosomes (human somatic cells have 46 chromosomes)
- chromatin - inside the nucleus - complex of DNA, proteins, and RNA
- genome - total genetic information carried in a cell
-
chromatids
replicated DNA that is still attached at the centromere
-
nucleosome
histones
linker DNA
chromatin fiber
- nucleosome - double- stranded DNA (double helix) wrapped twice around a core of histones
- histones - a core of 8 proteins that DNA wraps around
- Linker DNA - holds adjacent nucleosomes together
- chromatin fiber - in cells that arent dividing, histone promotes coiling of nucleosomes into larger fiber
|
|