Chapter 5- Membranes Flashcards
Arrangement + function of phospholipids in CSM?
- forms phospholipid bilayer w hydrophilic heads pointing out + hydrophobic tails pointing in
- only allows small/ non polar molecules to pass through
Arrangement + function of proteins in CSM?
- proteins form channel proteins + carrier proteins
- for facilitated diffusion + active transport
Arrangement + function of cholesterol in CSM?
- fit between phospholipids
- stabilise membranes + regulate fluidity
Arrangement + function of glycoproteins in CSM?
- stick out from surface of CSM
- receptor sites for chemical signals/ cell signalling
Arrangement + function of glycolipids in CSM?
- stick out from surface of CSM
- antigens used for recognition
Describe effects of high temperature on structure of membrane
- phospholipids have more KE
- increases size of gaps between phospholipids
- bilayer becomes fluid
- glycoproteins denature
Functions of membranes within cells?
- forms vesicles
- separate contents of organelles from cytoplasm (compartmentalisation)
- controls what substances enter + leave organelles
- provides surface for attachment
Describe structure of CSM
- phospholipid bilayer with hydrophilic heads pointing outwards+ hydrophobic tails pointing inwards
- contains intrinsic + extrinsic proteins
- glycoproteins + glycolipids stick out of membrane
- cholesterol molecules between phospholipids
Added alkaline NH3 to sample with acidic cells. No colour change.
What can you conclude about permeability of CM?
-not permeable to NH3
State the term to describe a membrane through which some substances can pass freely but others cannot.
Partially permeable
The model of cell membrane structure is called?
Fluid mosaic model
What molecules does the bilayer allow to diffuse through it?
- oxygen
- CO2
- fats
- fat soluble vitamins
One function of membranes is cell signalling. What is this?
Communication between cells
Explain how cell surface membranes contribute to the process of cell signalling
- release of signal molecules by exocytosis
- glycoproteins acts as receptor
- receptors are specific
- shape of receptor + signal are complementary
- attachment of signal causes change inside cell
- CSM allows entry of some signal molecules
Describe how vesicles are moved from one organelle to another
-move along microfilaments + microtubules using ATP
Suggest how the proteins embedded in CSM of vesicles ensure the vesicle is transported to correct target organelle
- receptor found only on target organelle
- protein has a specific shape
- shape of receptor and protein are complementary
Describe how extracellular enzymes are secreted from cells
- exocytosis
- vesicles fuses with CSM releasing enzymes
List 3 components of CSM
- phospholipids
- cholesterol
- proteins
Do not say phospholipid bilayer
What is active transport?
Mov meant of substances against a conc. gradient using ATP
2 examples of active transport in cells?
- mineral ions into root hair cells
- H+ ions out of companion cells
What is the mechanism for a plant cell taking up water?
Osmosis
What is the mechanism for oxygen entering a RBC?
Diffusion
What is the mechanism for calcium ions entering a nerve cell down a concentration gradient?
Facilitated diffusion
Describe the route water molecules take through CSM
Through phospholipid bilayer through channel proteins
Why plant cells don’t burst when left in pure water?
Have cell walls that provide strength and withstand pressure
Membranes allow recognition by other cells. Why is this important in relation to the immune system?
- glyclipids allow identification of the cell as own cell so white blood cells don’t attack
- allows identification of foreign cells via antigens on CSM
Functions of membranes?
- cell communication: chemical detection via receptors
- barrier between internal + external environment: maintains the 2 environments
Identify organelles w a membrane + state why presence of membranes important in its function
- mitochondria : increases SA for reactions
- nucleus: protects DNA
- lysosomes: keeps hydrolysis enzymes separate from cell interior
- RER: allows ribosomes to attach for protein synthesis
Describe structure of membrane using ‘phospholipid bilayer’ + ‘fluid mosaic model’
- membrane is a bilayer of phospholipid molecules
- phospholipid is a glycerol molecule attached to phosphate group + 2 fatty acids tails
- arranged so hydrophilic heads point onwards towards interior+ exterior environments of cell
- hydrophobic tails point inwards
- membrane surface called mosaic because embedded w proteins
- called fluid as phospholipids are flexible + move to allow movement of substances across membrane
Why is it key that there isn’t too much or too little cholesterol in membrane?
- too much will make membrane too rigid + exchange less efficient
- too little will make membrane too fluid +break up
How the membrane acts as a barrier to water soluble molecules?
- Arrangement of phospholipids makes it difficult for water soluble molecules to pass through
- Hydrophilic heads face out
- Hydrophobic tails face in
How could temp below 0c affect membrane permeability?
- initially membrane becomes more rigid so permeability decreases
- proteins could be denatured so increased permeability
- ice crystals could pierce membrane further increasing permeability
What happens to CSM when temp v high?
- proteins denature
- phospholipid bilayer more fluid
- membrane more permeable
Why stained cells lost colour at high temperatures?
-membrane permeable to stain so stain leaked out of cell
Functions of glycoproteins (inc. glycolipids)
- act as antigens as allow identification of cells as self
- cell signalling: receptor binding site for chemical signals
- attach to water molecules to stabilise membrane
What is cell signalling?
- communication between cells
- allows cells to work together
how glycoprotein acts as a receptor?
-has specific shape complementary to molecule
How to improve beetroot experiment?
- pieces blotted after cutting
- more intermediate temperatures
- same part of beetroot used
- same vol of water in water bath
- all samples same size
why no transmission of light after beetroot placed in water at 100c
-CSM damaged so pigment leaks out
What happens to plant cell when placed in sugar solution?
- water moves out of cell by osmosis
- cell has higher water potential than surrounding solution
- water moves down water potential gradient
How small/ non polar molecules enter CSM?
Diffuse through phospholipid bilayer
How polar substances enter CSM?
Facilitated diffusion through channel proteins
How large substances enter CSM?
Though carrier proteins
Routes that water molecules take through CSM?
-through phospholipid bio aye through aquaporins
How student could use graph to get better estimate of water potential?
- plot sucrose conc on x axis
- % plasmolysed on y axis
- read down from 50% plasmolysed to sucrose conc and look up equivalent water potential
How to make results more results more reliable?
- count more cells
- identify anomalous results
- calculate mean
How to make results more accurate?
- use more intermediate conc
- take photographs and mark cells as counting
Histamines make capillary walls more permeable. What effect does this have in surrounding tissues?
- more tissue fluid formed
- inflammation
- larger molecules pass into tissue fluid
Roles of Membanes inside cells?
- compartmentalisation
- site of attachment for enzymes
- provides selective permeability
