4 cell membranes & transport Flashcards

Question

3. glycolipids

Answer 1

-lipids with carbohydrate chains attached -carbohydrate chains project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)

Answer 2

-proteins with carbohydrate chains attached -carbohydrate chains also project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)

Answer 3

📌 INTRINSIC/integral: proteins embedded within the membrane; located in the inner or outer phospholipid monolayer 📌 common => span the entire membrane – these are known as transmembrane proteins eg transport proteins (cross whole membrane) 📌 can also be found on the inner or outer surface of the membrane, these are known as extrinsic proteins (or peripheral proteins)

Answer 4

📌Form the basic structure of the membrane (phospholipid bilayer) 📌 tails form a hydrophobic core comprising the innermost part of both the outer and inner layer of the membrane 📌Act as a barrier to most water-soluble substances (the non-polar fatty acid tails PREVENT POLAR molecules or ions from PASSING across the membrane) ;; ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell and unwanted water-soluble molecules cannot get in 📌phospholipids can be chemically modified to act as signalling molecules by: -Moving within the bilayer to activate other molecules (eg. enzymes) -Being hydrolysed which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm

Answer 5

📌 cholesterol regulates the fluidity of the membrane 📌 Cholesterol molecules sit in between the phospholipids, PREVENTING them from packing TOO CLOSELY together when LOW TEMP; PREVENTS membranes from FREEZING & fracturing. 📌INTERACTION between cholesterol and phospholipid tails also STABILISES the cell membrane at HIGHER temperatures by STOPPING the membrane from becoming TOO FLUID [Cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together] 📌Cholesterol also contributes to the IMPERMEABILITY of the membrane to ions and increases mechanical strength and stability of membranes 📌w/o cholest. => membranes break down so cells burst

Answer 6

📌 RECEPTOR MOLECULES: contain carbohydrate chains that exist on the surface (the periphery / extrinsically) 📌allows glycolipids and glycoproteins to bind with certain substances at the cell’s surface 📌3 main types: 1) SIGNALLING receptors for hormones + neurotransmitters, 2) receptors involved in ENDOCYTOSIS, 3) receptors involved in CELL ADHESION & STABILISATION [as the carbohydrate part can form hydrogen bonds with water molecules surrounding the cell] 📌SOME = cell markers/ANTIGENS, for CELL-TO-CELL RECOGNITION (eg ABO blood group antigens are glycolipids & glycoproteins that differ slightly in their carb chains) 📌

Answer 7

📌TRANSPORT proteins create HYDROPHILIC CHANNELS allowing ions + polar molecules to TRAVEL THRU membrane *AND* transp. prot. allow the cell to control which substances enter or leave -each transport protein SPECIFIC TO A PARTICULAR ION OR MOELCULE 📌number of transport proteins in a section of membrane helps to control the rate of transport as required by that cell

Answer 8

increased proportion of saturated fatty acid chains as the chains pack together tightly so there is a high number of intermolecular forces between the chains INCREASED SAT. FATTY ACID CHAINS => PACK TGT TIGHT => HIGH NUMBER OF IMF BETWEEN CHAINS A lower temperature as the molecules have less energy and therefore are not moving as freely which causes the structure to be more closely packed LOW TEMP => MOLECULES LESS ENERGY, NOT MOVING AS FREELY => MORE CLOSELY PACKED =>highimf

Answer 9

- INCREASED proportion of UNSATURATED fatty acid chains => chains are bent so chains less tightly packed => LESS IMF -HIGHER temp => molecules more energy so move more freely, increasing membrane fluidity

Answer 10

-process by which messages are sent to cells -allows multicellular organisms to control / coordinate their bodies and respond to their environments -Cell signalling pathways coordinate the activities of cells, even if they are large distances apart within the organism

Answer 11

1. A stimulus or signal is received by a receptor 2. The signal is converted to a ‘message’ that can be passed on – this process is known as transduction 3. The ‘message’ is transmitted to a target (effector) 4. An appropriate response is made

Answer 12

📌 Transmission of messages in cell signalling pathways requires crossing barriers such as cell surface membranes 📌 SO membrane is very important in signalling pathways because the membrane controls which molecules (including cell signalling molecules) can move between the internal and external environments of the cell 📌 Signalling molecules are usually very SMALL for EASY transport across cell membranes 📌 Typically in cell signalling pathways, signalling molecules need to cross or interact with cell membranes

Answer 13

📌📌 -Ligands are SECRETED from a cell (the sending cell) into the extracellular space The ligands are then TRANSPORTED through the extracellular space to the target cell The ligands BIND to surface RECEPTORS (specific to that ligand) on the target cell. [these receptors are formed from glycolipids and glycoproteins] 📍 message carried by the ligand is relayed through a chain of chemical messengers inside the cell, triggering a response

Answer 14

-random movement is caused by the natural kinetic energy of the molecules or ions -As a result of diffusion, molecules or ions tend to reach an equilibrium situation (given sufficient time), where they are evenly spread within a given volume of space

Answer 15

📌 conc gradient: difference in the concentrations of the substance of both sides of the surface 📌 greater difference in concentration means a greater difference in the number of molecules passing in the two directions and therefore a faster rate of diffusion 📌 from high to low conc

Answer 16

📌Molecules and ions have more kinetic energy at higher temperatures 📌move faster, resulting in a higher rate of diffusion

Answer 17

📌 greater the surface area across which diffusion is taking place => the greater number of molecules or ions that can cross it at any one moment => faster diffusion occurs 📌surface area of cell membranes can be increased by folding (eg. microvilli in an intestinal epithelium cell or cristae in a mitochondrion) 📌Cell bigger => SA:VOLUME RATIO smaller => slows rate of diffusion through cell => bc distance required to move is too big.

Answer 18

📌 Large molecules diffuse more slowly than smaller ones as they require more energy to move 📌 Uncharged and non-polar molecules diffuse directly across the phospholipid bilayer 📌Non-polar molecules diffuse more quickly than polar ones because they are soluble in the non-polar central layer of the phospholipid bilayer NON-POLAR QUICKER

Answer 19

📌Certain substances cannot diffuse through phospholipid bilayer of cell membranes. These include: 1) Large polar molecules such as glucose and amino acids. 2) Ions such as sodium ions (Na+) and chloride ions (Cl-) 📌two types of proteins that enable facilitated diffusion: Channel proteins, & Carrier proteins - channel+carrier proteins HIGHLY SPECIFIC (they only allow one type of molecule or ion to pass through)

Answer 20

-these are WATER-FILLED PORES -allow charged substances (eg. ions) to diffuse through the cell membrane ++diffusion of these ions does not occur freely, most channel proteins are ‘gated’, meaning that part of the channel protein on the inside surface of the membrane can move in order to close or open the pore This allows the channel protein to control the exchange of ions

Answer 21

-CAN SWITCH BETWEEN 2 SHAPES -causes the binding site of the carrier protein to be OPEN to ONE side of the membrane first, and then open to the other side of the membrane when the carrier protein switches shape [-direction of movement of molecules diffusing across the membrane depends on their relative concentrations on each side of the membrane -Net diffusion of molecules or ions into or out of a cell will occur down a concentration gradient (from an area containing many of that specific molecule to an area containing less of that molecule)]

Answer 22

-DEFINITION: net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a SELECTIVELY permeable membrane ++allows certain molecules (like water) through the bilayer - bc H2O IS SMALL so can pass between phospholipids despite being polar. Larger molecules (like solute molecules) require channel or carrier proteins, which may or may not exist in a certain piece of membrane.

Answer 23

describes the tendency of water to move out of a solution DILUTE low solute conc = high water p CONC solution high solute conc = low water p 📌📌 water potential of PURE WATER (without solutes) at ATMOSPHERIC PRESSURE is 0kPa, so any solution w/ solutes will have a water potential LOWER than 0 kPa (negative value) w/ solutes = negative water potential MORE NEGATIVE wp = LOWER wp (further away it is from pure water at 0kPa)

Answer 24

-REQUIRES CARRIER PROTEINS (each carrier protein being specific for a particular type of molecule or ion) + facilitated diffusion also uses carrier protein, active transport is different as it requires an INPUT of additional energy -ENERGY is REQUIRED to MAKE the carrier protein CHANGE SHAPE, allowing it to transfer the molecules or ions across the cell membrane 📌energy required is provided by HYDROLYSIS of ATP (adenosine triphosphate), which is produced during respiration)

Answer 25

📍 Reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules 📍Absorption of some products of digestion from the digestive tract 📍Loading sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant 📍Loading inorganic ions from the soil into root hairs

Answer 26

📌 bulk transport of larger volumes of materials - endo: in ;;;; exo: out 📌eg - Large molecules such as proteins or polysaccharides ;; Parts of cells ;; Whole cells eg. bacteria 📌require energy input, so forms of active transport

Answer 27

📌process by which cell surface MEMBRANE ENGULFS material, forming a SMALL SAC (or ‘endocytic vacuole’) around it 📌2 forms: phagocytosis, pinocytosis 📌phagocytosis (solid, food): bulk intake of solid material by a cell ;; vacuoles formed = phagocytic vacuoles. ++ eg, engulfing of bacteria by phagocytic white blood cells. 📌pinocytosis (liquids, pint): bulk intake of liquids. ++ if vacuole/vesicle formed is extremely SMALL then = micropinocytosis.

Answer 28

📌engulfed 📌phagocytic vacuole formed 📌LYSOSOMES containing digestive enzymes FUSE WITH PHAGOCYTIC VACUOLE 📌digested [undigested remains of bacterium removed by exocytosis]

Answer 29

📌 process by which materials are removed from, or transported out of, cells. + materials eg enzymes, hormones or cell wall building materials 📌released substance packaged into secretory vesicles formed from the Golgi body 📌 vesicles then travel to the cell surface membrane and fuse with the cell membrane and release their contents outside of the cell 📌eg secretion of digestive enzymes from pancreatic cells

Answer 30

-active transport, endocytosis and exocytosis all require the input of energy. This energy is provided by the hydrolysis of ATP produced during respiration. -SPECIFICALLY STATE EXO/ENDO OR BETTER FOR ENDO eg PHAGO/PINO/MICROPINO/MACROPINOCYTOSIS

Answer 31

📌surface area refers to the total area of the organism that is exposed to the external environment. Volume refers to the total internal volume of the organism (total amount of space inside the organism) ;; smaller cell has the largest surface area-to-volume ratio of the two shapes. This allows efficient diffusion into / out of the cell. 📌surface area and volume of an organism increase (and therefore the overall ‘size’ of the organism increases), the surface area : volume ratio decreases ++volume increases much more rapidly than surface area as size increases

Answer 32

📌 Obtaining necessary resources eg, oxygen, glucose, amino acids 📌Eliminating waste products eg. carbon dioxide, urea 📌Acquiring or dissipating thermal energy (heat) 📌Otherwise exchanging chemicals and energy with the surroundings eg. absorbing hormones at the cell surface in the hormone's target organ

Answer 33

1. cube: SA 6s², V s³, 2. cuboid: SA = 2lh+2lw+2wh, V = LxWxH, 3. cylinder: SA = 2πrh + 2πr², V = πr²h, & nm to um is /1000

Answer 34

It is possible to investigate the effects of immersing plant tissue in solutions of different water potentials and then use the results to estimate the water potential of the plant tissue itself The most common osmosis practical of this kind involves cutting cylinders of potato and placing them into solutions with a range of different water potentials (usually sucrose solutions of increasing concentration – at least 5 different concentrations are usually required)

Answer 35

📌-If a plant cell is placed in pure water or a dilute solution, water will enter the plant cell through its selectively permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential than the plant cell 📌water enters the VACUOLE (lower wp) of the plant cell, the volume of the plant cell increases 📌 expanding protoplast (living part of the cell inside the cell wall) pushes against the cell wall and pressure builds up inside the cell – the inelastic cell wall prevents the cell from bursting 📌 pressure created by the cell wall also stops too much water entering and this also helps to prevent the cell from bursting 📌plant cell is fully inflated with water and has become rigid and firm, it is described as fully turgid This turgidity is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant – making the plant stand upright with its leaves held out to absorb sunlight 📌plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts

Answer 36

📌 solution with a lower water potential than the plant cell (such as a concentrated sucrose solution), water will leave the plant cell through its selectively permeable cell surface membrane by osmosis 📌water leaves the vacuole of the plant cell, the volume of the plant cell decreases 📌protoplast gradually shrinks and no longer exerts pressure on the cell wall 📌begins to pull away from the cell wall = PLASMOLYSIS

Answer 37

-animal cells do not have a supporting cell wall (unlike plant cells), the results of this loss or gain of water on the cell are more severe -solution with a lower water potential than the cell (such as a concentrated sucrose solution), water will leave the cell through its selectively permeable cell surface membrane by osmosis and the cell will SHRINK (NOTNOTNOTTT "plasmo....") and shrivel up - when the cell is in a HYPERtonicenvironment -CYTOLYSIS/HYPOTONIC: cell is placed in pure water or a dilute solution, water will enter the cell through its selectively permeable cell surface membrane by osmosis, as the pure water or dilute solution has a higher water potential The cell will continue to gain water by osmosis until the cell membrane is stretched too far and the cell bursts (cytolysis), as it has no cell wall to withstand the increased pressure created This occurs when the cell is in a hypotonic environment ++why a constant water potential must be maintained inside the bodies of animals -an animal cell is in an ISOTONIC environment (the solution outside of the cell has the same solute concentration as the inside of the cell), the movement of water molecules into and out of the cell occurs at the same rate (no net movement of water) and there is no change to the cells

Answer 38

animal: no cell wall; solution w/ lower wp/high solute, water leaves cell thru membrane by osmosis, volume of cell decreases, cell shrinks. & high wp, low solute, volume increase -> no cell wall to resist increased pressure created -> cell membrane overstretched eventually and bursts. PLANTS 📍low wp/high solute: water leaves; volume decreases; protoplast shrinks, pulls away from cell wall; plasmolysed 📍high wp/low sol: water enters; volume increases; protoplast expands, pushes against cell wall; cell wall withstands increased pressure created; pressure increases until cell is rigid and turgid. ;; cell fully inflated with water & no more can enter.

4 cell membranes & transport Flashcards

(63 cards)