2.1.5 biological membranes Flashcards
describe the fluid Mosaic model of membranes
fluid: phospholipid bilayer in which individual phospholipids can move which means that the membrane has flexible shape
Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded
Explain the role of cholesterol and glycolipids in membranes
cholesterol: steroid molecule in some plasma membranes, connects phospholipids and reduces fluidity to make bilayer more stable
Glycolipids: cell signalling and cell recognition
Explain the function of extrinsic and transmembrane proteins in membranes
binding sites/receptors e.g. for hormones and drugs: antigens (glycoproteins), bind cells together and involved in cell signalling
Explain the functions of intrinsic transmembrane proteins in membranes
electron carriers (respiration/photosynthesis)
Channel proteins: facilitated diffusion
Carrier proteins: facilitated diffusion and active transport
Explain the functions of membranes within cells
provide internal transport system
selectively permeable to regulate passage of molecules into and out of organelles or within organelles
provide reaction surface
Isolate organelles from cytoplasm for specific metabolic reactions
Explain the functions of the cell surface membrane
isolate Cytoplasm from extra cellular environment
selectively permeable to regulate transport of substances
involved in cell signalling/cell recognition
Name and explain three factors that affect membrane permeability
temperature: high temperature denatures membrane proteins/phospholipid molecules have more kinetic energy and move further apart
PH: changes tertiary structure of membrane proteins
Use of a solvent: may dissolve membrane
What are the three factors that affect the permeability of the cell membrane
ethanol: dissolves the lipid components of membrane, makes membrane more permeable
PH: if extreme, denatures the membranes proteins
Heat: more movement in the phospholipid bilayer which creates gaps. When cold, ice crystals damage the membrane. The kinetic energy of phospholipid bilayer increases fluidity
Describe the five functions of the cell surface membrane and give examples
partially permeable: allow small, un charged particles to pass through it
Produce different compartments inside cells: mitochondria surrounded by two membranes, which isolate the reactions taking place inside from reactions in the cytoplasm
important in cell signalling: a substance produced by one cell docs into a receptor in membrane of another, causing something to happen in second cell
can allow electrical signals to pass along them: the membrane of the axon of a motoneuron transmits action potential from the CNS to a muscle
Provides attachment sites for enzymes and other molecules involved in metabolism: the inner membrane of the mitochondrion contains my molecules need for the production of ATP. The inner membrane of a chloroplast contains chlorophyll
Describe a phospholipid
phospholipids have a hydrophilic head which contain a phosphate group connected to a glycerol by phosphodiester bond
They also have a hydrophobic tail which include 2 fatty acids that are connected to the glycerol by Ester bond
Describe cell signalling
receptor activation: the binding of a signalling molecule causes a change in receptor that activates its function
Signal transduction: the activated receptor stimulates a series of proteins that form a signal transduction pathway
Cellular response
Describe hormone receptors
Hormones are chemical messengers. Any cell with a receptor for the hormone molecules is a target cell. A hormone binds to receptor on a target cell surface membrane as they have a complimentary shape. The binding of the hormone receptor causes the target cell to respond in a certain way
What affects the rate of diffusion
temperature: the higher the temperature, the greater rate of diffusion
concentration gradient
surface area of membrane: the larger the surface area, the greater rate of diffusion
size of particle: larger the particle, slower rate of diffusion
Chemical nature of particle: nonpolar particles diffuse faster than polar
Describe simple diffusion
The net movement from high concentration to low concentration through the phospholipid bilayer. Small uncharged molecules go through e.g. carbon dioxide
Passive process requires no energy from ATP hydrolysis
Describe facilitated diffusion
The net movement from high concentration to low concentration through an intrinsic protein. Large, charged molecules can move through e.g. glucose
Passive process
Describe active transport
The movement from low concentration to high concentration. It is an energy requiring process and it moves the molecule from one side of the membrane to another. These molecules would be minerals in root hair cells or glucose in the small intestine
Describe water potential
water potential is the amount of solutes in a solvent. You cannot have a water potential higher than zero so if you have pure water it is 0 kPa.
The most solvents, the lower the kPa is
At high water potential, water molecules have more energy because they are less restricted by the presence of solutes and vice versa. More water molecules can diffuse from high to low more than low to high
Define osmosis
The net movement of water from an area of high water potential to a low water potential across a partially permeable membrane
What is water potential measured in
kPa
What is the water potential of pure water
0 kPa
How does osmosis affects plant and animal cells
animal: when there is too much water red blood cells will burst (lysis). When there is not enough water the red blood cell will become crenated and shrivel
plant: when there is too much water the plant will become turgid as the protoplast swells. When there is not enough water the plant becomes flaccid and this occurs due to plasmolysis when the membrane comes away from the cell wall
define hypertonic
this is when the solution is more concentrated: more solute : water ratio
lower water potential as less water
Describe endocytosis
Food particles/even whole cells, are taken into the cell and digested
Define exocytosis
Large amount of some substances transported out of the cell and requires energy
What is it meant by cell signalling
The process of cellular communication within the body by cells releasing and receiving hormones and other signalling molecules
How do hormones and drugs bind to target cells
A hormone will have a specific shape for the receptor(complimentary binding)
Describe the role of phospholipids
Provide barriers in cellular membranes to protect the cell
describe the role of cholesterol
Maintains fluidity of membrane and gives the membrane of some eukaryotic cells mechanical stability
describe The role of proteins (intrinsic)
Channel proteins move ions and large molecules down diffusion gradient and carrier proteins transport large molecules against a concentration gradient
Describe the role of glycoproteins
Cell to cell recognition and adhesion
Describe the role of glycolipids
Maintain stability of cell membrane and facilitate cellular recognition
outline how colorimetry Could be used to investigate membrane permeability
use plant tissue with soluble pigment in vacuole. Tonoplast and cell-surface membrane disrupted which increases permeability and pigment diffuses into solution
select colorimeter filter with complimentary colour
use distilled water to set colorimeter to 0. Measure absorbance/percentage transmission value of solution
High absorbance/low transmission means there’s more pigment in solution
ppq: Suggest why galactose and glucose cannot pass through the plasma membrane by simple diffusion through the phospholipid bilayer
They are too large
ppq: What two substances are required To break the glycosidic bond in lactose
Enzymes and water
ppq: Which component of the plasma membrane act as a barrier to mineral irons entering the cell
Phospholipid bilayer
ppq: Describe roles of the membrane in single celled organisms e.g. amoeba
Compartmentalisation and controls what enters and exits organelles
ppq: Describe the structure of a plasma cell surface membrane
hydrophilic phosphate heads point outwards, hydrophobic fatty acid tails point inwards
There is cholesterol in amongst it (between phospholipids) and also has extrinsic and intrinsic proteins on the surface
ppq: One molecule that crosses membranes easily is the steroid hormone progesterone which is produced in the ovaries from cholesterol. Explain why progesterone can move across membranes
Because they are fat and soluble and they are hydrophobic which means they can diffuse through the phospholipid bilayer
ppq: describe the arrangement and functions of two named components of a cell surface membrane
phospholipid bilayer: phospholipid hydrophobic tails point inwards and hydrophilic heads point outwards. this provides a barrier to large polar molecules
proteins embedded in the bilayer are for active transport/facilitated diffusion
cholesterol molecules fit within the bilayer and they regulate fluidity
Glycoproteins/glycolipids on the surface for cell signalling
ppq: Which component of a cell membrane becomes more fluid as temperature increases
Phospholipid bilayer
ppq: Which component of a cell membrane denatures as temperature increases
Proteins e.g. glycoproteins
ppq: State the term used to describe a membrane through which some substances can pass freely but others cannot
Partially permeable
ppq: Complete the following paragraph about cell membranes
The model of cell membrane structure is called the ____ ___ model. phospholipid bilayer is with specific membrane proteins account for the ability of the membrane to allow both passive and ____ transport mechanisms. ions and most polar molecules are insoluble in the phospholipid bilayer. However, the bilayer allows diffusion of most nonpolar molecules such as ___. protein channels, which may be gated, and _____ proteins and able to sell to control the movement of most polar substances
Fluid Mosaic
Active
Oxygen
Carrier
ppq: Explain how cell-surface membranes contribute to the process of cell signalling
The release of signal molecule by exocytosis. Proteins e.g. glycoproteins or glycolipid have receptors and this receptor is specific. The shape of receptor and signal are complimentary and the attachment of the signal molecule causes change and the cell surface membrane allows entry of some signal molecules
ppq: State three roles of membranes inside cells
to make compartments for organelles within a cell
to isolate the contents of an organelle e.g. hydrolytic enzymes
Provide selective permeability
Site for attachment of enzymes
How do you find percentage change
Find the difference, divide by original, multiplied by 100
define isotonic
same amount of water : solute ratio
define hypotonic
solution is less concentrated. There is more water : solute ratio
ppq: The proteins embedded in the membranes of vesicles have different functions. COPI and COPII proteins are known as “address proteins”. vesicles that transport materials from the golgi to the rer are coated in COPI proteins. vesicles that transport materials to the golgi from the RER are coated in COPII proteins
suggest how these proteins ensure that a vesicle is transported to the correct target organelle
The receptor is found only on the correct target. The address protein provides a way of labelling/identifying the vesicles. The COPI has a specific shape and therefore the address proteins are complimentary to the receptor and the receptor will then fit the shape of the protein (COPI)
ppq: State two examples of active transport in cells. For each example, you should name the substance that is transported and the cell involved
mineral ions e.g. into root hair cells
hydrogen ions out of companion cells
Mineral ions e.g. across endodermis
ppq: State how each of these substances crosses the cell surface membrane
release of enzymes into the gut
plant cell taking up water
calcium ions entering a nerve cell down a concentration gradient
Oxygen entering a red blood cell
bulk transport
Osmosis
facilitated diffusion
Diffusion
ppq: Describe the routes that water molecules take through the cell surface membrane
water molecules fit between phospholipid is through the phospholipid bilayer via Protein channels
ppq: explain why plant cells do not burst when they are left in pure water
Due to the cell wall which provides strength and limits the uptake of water
ppq: Explain how a glycoprotein can act as a receptor
Receptors have a specific shape and I’ll complimentary to the shape of trigger and this trigger binds to receptor
