Membranes and Osmosis Flashcards
What is the purpose of intracellular membranes?
Compartmentalisation. - Separates and organises enzymes and substances. - Ensure ideal conditions for reactions.
Explain the meaning of the fluid mosaic model.
Viscous layer of phospholipids and proteins moving around each other - Proteins RANDOMLY DISPERSED in layer. - It’s a model and-so is still a theory.
What is CH3
CH3 is a Methar group and is hydrophobic.
What are the 2 intrinsic proteins?
Channel and carrier proteins.
What word describes how different ends have different properties?
Amphipathic.
Why are the weak hydrophobic/philic interactions in phospholipid bilayers important?
They cause membrane fluidity and allow the membrane to break and reform in endo/exocytosis.
What causes substances to be unable to enter the membrane?
They’re polarity and size. Large and polar molecules struggle to enter cell.
What is the role of cholesterol?
Cholesterol increases the integrity and mechanical stability of the membrane, by pulling the heads and tails together by interacting with them. They only appear in animals and can also effect steroid hormones.
How thick is a phospholipid bilayer?
7.5nm
What holds phospholipids together?
weak interaction (associations)
Why do phospholipids form bilayers?
-Phospholipids are amphipathic, they have polar hydrophilic heads and non-polar hydrophobic fatty acid tails; the tails are repelled from aqueous solutions and-so are repelled by both the environment and the cytoplasm, causing the fatty acid tails to face each other.
Difference between intrinsic and extrinsic proteins:
Intrinsic proteins go through entire bilayer, whilst extrinsic only embed in one layer.
Describe a channel protein:
- Polar interior -> Hydrophilic and allows entry of polar solutions.
- Non-polar exterior-> Directly associates with fatty acid tails.
Membranes are ________ permeable.
Membranes are partially permeable.
Where are glycolipids and what do they do?
Glycolipids are attached to a glycoprotein and act as antigens or cell markers; They help with cell recognition, adhesion and act as a receptor and binding site for chemical signals, allowing for direct or cascade responses. (Open glycoprotein)
What type(s) of transport do carrier proteins operate?
Mostly Passive. Some use active transport, requiring ATP (energy) to change the shape of the substance.
What is diffusion?
Net movement of particles from a region of higher concentration to a region of lower concentration.
What is osmosis?
The diffusion of water across a partially permeable membrane,
What is Bulk transport?
Active movement of large molecules. (Endo/exocytosis)
What is Active transport?
Movement of molecules or ions into/ out of a cell up a concentration gradient.
What is facilitated diffusion?
Movement down a concentration across a membrane through channel or carrier proteins. This is utilised by molecules which are unable to freely cross membrane.
What 3 factors increase the rate of diffusion?
Temperature, Concentration Gradient and SA:V ratio.
What factor decreases the rate of diffusion?
The membrane thickness.
What is Fickes Law?
(Surface Area x Gradient)// thickness = rate of diffusion.
What molecules can’t go through membranes?
Ions, large uncharged molecules and polar molecules.
What molecules can go through membranes?
Gases, small non-polar molecules and small polar molecules (H20, glycerol and ethanol)
Channel Proteins IN DEPTH:
Integral lipoproteins which contain a pore.
Channel proteins are ion-selective and may be gated to regulate the passage of ions.
Channel proteins can only transport molecules down a concentration gradient.
Channel proteins are faster than carrier proteins.
Carrier Proteins IN DEPTH:
Integral glycoproteins which bind to solute and undergo CONFORMATIONAL CHANGE to translocate the solute across the membrane.
Carrier proteins will only bind to a specific molecule via an attachment similar to an enzyme-substrate interaction.
Carrier proteins may move molecules against a concentration gradient in presence of ATP.
Carrier proteins much slower than channel proteins.
What are gated channels called?
ligand gated ion channels
What is the general name for molecular interactions.
van de waals interactions
Alpha helix make up what membrane structure
Recognition receptors.
Beta barrel make up what membrane structure
Transporters (channel proteins)
Helical Bundles make up what membrane structure
Enzymes, transporters and receptors
What does hypertonic mean?
There’s a higher concentration of solute and-so a lower water potential.
What does Hypotonic mean?
There’s a lower concentration of solute and-so a higher water potential.
What direction does water travel (in terms of water potential)
Water moves from a high water potential to a low water potential.
Water potential is the potential for the water to leave the area.
What 2 factors effect water potential in plants?
The solute potential and pressure potential.
What is a protoplast?
A protoplast is the entire cell except for the cell wall.
What is the tonoplast?
The membrane of the vacuole.
Why does increasing temperature increase membrane permeability?
The extra kinetic energy makes it easier for molecules to move across.
Why are non-polar solvents harmful?
Disrupt membrane by disrupting fatty acid tails. Strong acid can associate with fatty acid tails, dissolving the membrane.
What are the 2 types of endocytosis?
Phagocytosis - Solids
Pinocytosis - liquids.
What is plant cell turgor caused by?
The water pressure against the cell wall.
What is meant by plasmolysis?
The a plant’s protoplast is pulled from the cell wall.
What is the purpose of osmoregulation?
To stop the alteration of cell size/ shape.
What feature of fatty acids contributes to cell structure.
Hydrophobic fatty acids face away from aqueous solutions, forming bilayer; Therefore splitting aqueous solutions.
How do hydrophobic tails of phospholipids contribute to the stability of the plasma membrane?
Their hydrophobic interactions help stability by forming a bilayer which separates separate aqueous regions.
What are 3 roles of cell membranes in cells?
- Act as a barrier between areas (main role)
- provides compartmentalisation of enzymes to provide ideal conditions for specific reactions
- Site of some chemical reactions
- Aids cell signalling (extracellular)
Why does facilitated diffusion require no metabolic energy?
The particles have their own energy and so they will move down the concentration gradient, therefore they don’t need additional energy.
Why can’t glucose pass through a cell membrane by simple diffusion?
Glucose is polar and is to large to fit through the phospholipid bilayer.
During a practical on how sucrose concentration effects the change in mass of a potato during osmosis. What could cause a smaller change in mass?
Not drying the potato after osmosis has taken place would lead to a greater end mass measured.
