Biological membranes Flashcards
What are all cell membranes and organelle membranes composed of?
-a phospholipid bilayer
What do cell membranes provide?
-a partially permeable membrane and they’re the sites of chemical reactions and have a role in cell communication
What is the fluid mosaic model?
mixture and movement of the phospholipids, proteins, glycoproteins and glycolipids the membrane is made of.
What do the phospholipids align as and why?
-As a bilayer due to the hydrophilic heads being attracted to the water and the hydrophobic tails being repelled by the water
What do extrinsic proteins provide?(peripheral proteins)
-mechanical support or they make glycoproteins/glycolipids. The function of these is cell recognition or receptors
-they have hydrophilic R groups
What are intrinsic/integral proteins?
-they are also transmembrane proteins
-protein carriers or channel proteins involved in the transport of molecules across the membrane
-they have amino acids with hydrophobic R groups on their external surfaces which interact with the hydrophobic core of the membrane, keeping them in place.
What do protein channels fill with?
-water to enable water soluble ions to diffuse
What do carrier proteins do?
They bind with other ions and larger molecules such as glucose and amino acids and change shape to transport them to the other side of the membrane
What does cholesterol do?
-restricts the lateral movement of other molecules in the membrane
-controls fluidity and permeability of the membrane
-prevents water and dissolved ions from leaking out of the cell
what factors affect membrane structure and permeability? (temperature)
-temperature-high temperatures increase the kinetic energy of the phospholipids so that they move even more. This increases the fluidity of the membrane, increasing the permeability and the structure can start to break. It makes it easier for particles to move across the membrane
-it also denatures the carrier and channel proteins in the membrane
What factors affect membrane structure and permeability?(solvents)
Organic solvents such as alcohol can dissolve the phospholipid bilayer in membranes. This damage causes the fluidity of the membrane to increase and become more permeable
Simple diffusion
-the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.
-process does not require ATP
-for molecules to diffuse across the membrane, they have to be lipid soluble and small
Facilitated diffusion
- a passive process, down the concentration gradient, through proteins
-movement of ions and polar molecules, which cannot simply diffuse, can be transported across the membranes by facilitated diffusion using protein channels and carrier proteins
Osmosis
-the movement of water from an area of higher water potential to an area of lower water potential(more negative) across a partially permeable membrane
What is a hypotonic solution?
-when the water potential of a solution is more positive(closer to zero) than the cell
-cell could eventually swell or burst
What is an isotonic solution?
-when the water potential of the solution is the same in the solution and the cell within the solution
-has no overall impact on the cell’s shape
What is a hypertonic solution?
-when the water potential of a solution is more negative than the cell so water moves out of the cell
-cell could shrivel up (crenation in animal cells and plasmalized in plant cells).
Active transport
-the movement of molecules and ions from an area of lower concentration to an area of high concentration(against the concentration gradient) using ATP and carrier proteins
-selective as only certain molecules will bind to the receptor site on the carrier proteins. ATP will bind to the protein on the inside of the membrane and will be hydrolysed into ADP and Pi.
-protein will change shape and open towards the inside of the membrane so molecule can be released to the other side of the membrane
-Pi molecule is then released from the protein, resulting in the protein to revert back into its original shape.
Endocytosis
-type of active transport. It is the bulk transport of molecules into a cell
-cell surface membrane bends inwards around a molecule surrounding it to form a vesicle
-vesicle pinches off and moves within the cytoplasm
-can be classed as phagocytosis when a solid particle is being taken in or pinocytosis when a liquid is being taken in
-requires energy from ATP for cell to engulf and change shape around the material
Exocytosis
-this is a bulk transport of molecules out of a cell
-vesicles move towards the cell surface membrane. fuse with the membrane and then the content of the vesicle is released outside of the cell
-requires energy because ATP is required to move the vesicle along the cytoskeleton
What are the functions of glycoproteins?
-intrinsic proteins
-embedded within the cell surface membrane with an attached carbohydrate chain
-play a role in cell adhesion and as receptors for chemical signals(cell signalling)
-receptors for neurotransmitters or hormones
What are the functions of glycolipids?
-they’re lipids with an attached carbohydrate chain
-can be recognised by the cells of an immune system
