Chapter 4: Membranes and transport Flashcards
what are cell surface membranes made up of
- lipids (phospholipids and cholesterol)
- proteins
- carbohydrates
what is the structure of phospholipids made up of
- 1 polar hydrophillic phosphate head (faces water and forms H bonds)
- 2 non-polar hydrophobic fatty acid tails (faces away from water towards each other)
what do phospholipids form
the phospholipid bilayer
what forms the basic structure of membranes
phospholipids
what are the physical properties of the phospholipid bilayer
- fluid
- molecules free to move laterally by diffusion
- viscosity of olive oil
what affects the viscosity of the bilayer
- depends on hydrophobic interactions of fatty acid tails
- less hydrophobic interactions means it is more free to move and less viscous
- double bonds and fatty acid tail length affect membrane fluidity
what happens to the viscosity if there are 3 saturated fatty acid tails
- highly ordered packing
- less hydrophobic interactions so the membrane is more viscous
what happens to the viscosity if there is 1 unsaturated fatty acid tail between 2 saturated fatty acid tails
- double bond at kink disrupts close packing of 2 saturated fatty acid tails
- less hydrophobic interactions so the membrane is more fluid
what does a fluid membrane mean
phospholipid molecules are free to move laterally
what is meant by the fluid mosaic model of the membrane structure
protein molecules are scattered and float freely in the phospholipid bilayer
(like icebergs in the sea)
what is the function of cholesterol
- maintains membrane fluidity and therefore membrane stability
- prevents freezing at a low temperature
- acts as a plug (blocks the passage of polar molecules through the membrane
what is the permeability of the membrane
-membrane is partially and selectively permeable
what does movement across membrane depend on
- depends on molecular size and polarity
- small and uncharged molecules are permeable
- large polar molecules have restricted flow
- ions have restricted flow
how are large polar molecules and ions transported across membranes
using carrier and channel proteins
what are intrinsic proteins
proteins that are inside the bilayer
what are extrinsic proteins
proteins that are outside but close to the membrane
what is the arrangement and distribution pattern of protein molecules in the phospholipid bilayer
asymmetrical
what are the two types of intrinsic proteins
- partially transmembrane protein (found on one side of the phospholipid bilayer only)
- transmembrane protein (penetrates through the phospholipid bilayer with both ends hydrophillic and a hydrophobic center)
why do protein molecules remain inside the membrane
due to hydrophobic and hydrophillic interactions
what is the membrane structure maintained by
- hydrophillic interactions between hydrophillic phosphate heads and regions of proteins facing water
- hydrophobic interactions between hydrophobic fatty acid tails and other fatty acid tails, cholesterol and hydrophobic regions of protein
what is the function of carrier proteins
carry large polar molecules across the membrane by changing their shape
what is the function of channel proteins
for transportation of small charged ions and small polar molecules across the membrane
what is the function of cell surface receptor
- chemical signal (ligand) binds to the binding site of the cell surface receptor
- e.g. insulin on a liver cell or neurotransmitter from one nerve cell to another
what is ligand
a biological molecule which binds specifically to other molecules during cell signalling
what is the function of enzymes in the cell surface membrane
- thykaloid membrane of chloroplast for photosynthesis
- inner membrane of mitochondria for respiration
- microvilli of a gut epithelial cells for digestion
what is the electron transport chain
- a series of electron carriers
- found in thylakoid membrane (chloroplast) and inner membrane of mitochondria
what are antigens
- tell which are self or non self antigens
- identity of the cell
what are glycoproteins
carbohydrate chains that face the outside of the membrane
function of glycoproteins
- receptor site for chemical signal
- antigen of the cells for cell-cell recognition
when is cell-cell recognition needed
- growth and development (correct cells sticking together for forming tissues)
- immune response (only attacks nonself antigens)
what are nonself antigens
foreign cells
what are self antigens
cells from the same body
function of glycolipids
- stabilise membrane structure
- carbohydrate chains form hydrogen bonds with water
what are the uses of cell signaling
- homeostasis
- control and coordination of the body
what are the uses of cell signaling
- homeostasis
- control and coordination of the body
what does the cell signaling pathway involve
the stimulus response model (animals only)
what are the stages of the stimulus response model
- stimulus
- receptor
- coordinator/regulator/control center
- effector
- response
what is stimulus
- changes from the set point/norm
- external/internal changes
what is the receptor
specialised group of cells to detect stimulus and converts it into signal to be transmitted
what is the coordinator/regulator/control center
transmission by:
- nervous system by electrical and chemical signals
- endocrine system by chemical signals
what is the effector
muscles, glands or organs that would produce the response
what is response
an action produced as the result of the stimulus to restore the set point
what is cell signalling
a mechanism by which (receptor) cells detect a stimulus and send message/signal to (coordinator and then effector) cells to carry out a response to the stimulus
what is cell signalling
a mechanism by which (receptor) cells detect a stimulus and send message/signal to (coordinator and then effector) cells to carry out a response to the stimulus
why are hormones a good signal molecule
because they are small molecules
how are animal hormones passed to the target cell
from endocrine gland cell to target cell through bloodstream
how are plant hormones passed to target cell
- from secretory cell to target cell
- short distance: from cell to cell by diffusion
- long distance: through phloem sap
what is the first step in cell signalling
secretion- endocrine gland cells secrete small quantities of hormones to tissue fluid and then hormone diffuses into the blood
what is the second step in cell signalling
transportation-hormones are carried by the blood stream throughout the body
what is the third step in cell signalling
reception-hormones (1st messenger/extra cellular messenger/signal molecule) bind to the receptors on cell surface membrane/cytoplasm/nucleus of target cells
what is the fourth step in cell signalling
transduction - in the target cell, 2nd messenger/intracellular messenger/signal molecule activates a series of cascading reactions to amplify the signal (increasing each reaction)
what is the fifth step in cell signalling
a specific response (e.g. gene expression (CHON/enzyme synthesis), secretion, movement, metabolic change
what are the main steps in cell signalling
- secretion
- transportation
- reception
- transduction
- response
what are intracellular receptors
- hydrophobic signal molecules can pass through the cell surface membrane and bind to the receptors in the cytoplasm or nucleus
- e.g. steroid hormones, oestrogen, progesterone, testosterone
what are the cell signaling types
- nicotine - accepting acetyleholine receptors
- glucagon receptor
- oestrogen receptor in the nucleus
what are subcellular membranes
- membranes of organelles with specialised function
- mitochondria for aerobic respiration
- chloroplast for photosynthesis
- lysosome for digestion within the organelle
- endoplasmic reticulum for protein transport
- golgi apparatus for collecting, modifying, transporting and distributing material
what is passive movement across membrane
- no cellular energy required
- movement comes from kinetic energy of particles
which movements across the membrane are passive
- simple diffusion
- facilitated diffusion (by channel and carrier proteins)
- osmosis
which movements across the cell membrane are active
- active transport
- endocytosis (phagocytosis and pinocytosis)
- exocytosis
what is active movement across the membrane (active transport)
needs cellular energy (ATP)
what is diffusion
the movement of molecules/ions from a region of higher concentration to a lower one down a concentration gradient until their concentration becomes even throughout the solution/equilibrium is reached
why isnt cellular energy needed for diffusion
because the molecules/ions move randomly due to their kinetic energy
what is the diffusion rate formula
(membrane surface area x concentration gradient across membrane)/membrane thickness or distance
what kind of molecules can diffuse through cell membranes
only small uncharged molecules can diffuse through cell membranes e.g. H2O, O2 CO2
what is facilitated diffusion
- diffusion of specific small ions/polar molecules through H2O filled polar channel in channel protein/pore protiens
- carrier proteins carrying large polar molecules through cell membrane by changing their shape
what is the characteristic about membrane that limits transport into and out of the membrane
the membrane is partially and selectively permeable
how is the membrane partially permeable
allows passage of substances of alpha polarity and size
how is the membrane selectively permeable
- channel proteins and carrier proteins only ‘select’ specific molecule to be transported across the membrane
- binding site shape of carrier protein is complementary to the molecular shape
what is osmosis
the net movement of water molecules from a region of high water potential to a region of lower water potential through a partially permeable membrane until the water potential becomes even on both sides of the membrane/equilibrium is reached
what is water potential
a measurement of the tendency of water molecules to move and is proportionate to the number of free water molecules
what is the water potential of pure water
0 kPa at atmospheric pressure (P atm)
what is the water potential of a solution
less than 0 kPa at Patm
what is the formula for water potential
water potential = solute potential + pressure potential
what is solute potential
the extent by which the solute lowers the water potential
why does adding solutes to water lower the water potential
the solute dissolves, attracting water molecules around it to form hydration shells, lowering the number of free water molecules
what is the correlation between water potential and solute potential
- water potential is proportional to solute potential
- when the water potential drops the solute potential drops
- when the solute increases, the solute potential decreases
what is pressure potential
a measure of the hydrostatic pressure that tends to move water from one place to another
-it is the contribution of pressure to H2O potential
what is the pressure potential at atmospheric pressure
pressure potential = 0 kPa at Patm
what happens to pressure potential when the pressure is more or less than atmospheric pressure
- when P> Patm,, pressure potential >0kPa (+)
- when P< Patm,, pressure potential <0kPa (-)
what is the correlation between water potential and pressure potential
- water potential is proportional to pressure potential
- positive pressure creates a pushing force that increases water potential
- negative pressure creates a suction force that decreases water potential
what is the path of net water movement out of the cell
vacuole -> tonoplast -> cytoplasm -> partially permeable cell surface membrane -> external environment
all through osmosis
what is the path of net water movement out of the cell
vacuole -> tonoplast -> cytoplasm -> partially permeable cell surface membrane -> external environment
all through osmosis
what is incipient plasmolysis
- when the water potential keeps dropping until 0kPa (when the cell surface membrane stops not pushing against the cell wall in plant cells)
- the starting part of plasmolysis
what is incipient plasmolysis
- when the water potential keeps dropping until 0kPa (when the cell surface membrane stops not pushing against the cell wall in plant cells)
- the starting part of plasmolysis
what is plasmolysis
- cell surface membrane shrinks away from the cell wall
- becomes flaccid
what is the Na+ - K+ pump
transport of specific molecules/ions by specific carrier proteins against their concentration gradient/uphill using ATP through a partially permeable membrane where a potential difference (charge difference) is built up across the membrane
what is the importance of the Na+-k+ pump
- nerve impulse transmission
- kidney function for selective reabsorption of glucose, amino acids, vitamins and hormones
- osmo regulation
- raw material for CHON synthesis, glycolysis, protein synthesis etc.
properties of carrier proteins
-globular protein
-specificity for particles transported
opening on one side of the membrane only
-not gated
-thousands/millions particles transported per time
-can be a pump
-transports in same and different direction (symporter/cotransporter and antiporter)
properties of channel protein
- globular protein
- specificity for particles transported
- opening on both sides of membrane
- gated by pores
- one to a few particles transported at a time
- cannot be a pump
- cannot be a symporter/cotransporter or antiporter
what is endocytosis
bulk transport of materials into the cell with the expenditive of ATP (due to change in shape of cell surface membrane
what are the two types of endocytosis
- phagocytosis
- pinocytosis
what is phagocytosis
- ‘cell eating’ process
- takes in solid particles by engulfing and forms phagocytic vacuole/phagosome
- e.g. white blood cell engulfing bacteria or amoeba engulfing food
what is phagocytosis
- ‘cell eating’ process
- takes in solid particles by engulfing and forms phagocytic vacuole/phagosome
- e.g. white blood cell engulfing bacteria or amoeba engulfing food
what is pinocytosis
- ‘cell drinking’ process
- takes in fluid
which is bigger vacuole or vesicle
vacuole
first step of exocytosis
vesicle carrying useful material to be secreted or waste to be excreted out of the cell
second step of exocytosis
membrane of vesicle fuses with cell surface membrane
third step of exocytosis
materials are released out of the cell
fourth step of exocytosis
membrane of vesicle becomes part of the cell surface membrane
when is active transport used
- specific ions/molecule
- across membrane by carrier proteins
which transport processes need a membrane
- facilitated diffusion
- osmosis
- active transport
problems caused by large sized organisms (related to surface area) and how r they solved
- the bigger the size (mass), the smaller the surface area:volume ratio -solved by increasing surface area e.g. alveoli
- distance increases from site of exchange- solved by transport system
