Unit 1: Membranes Flashcards
Name some functions of membranes
provide selectively permeable barriers compartmentalisation localising reactions in the cell transport of solutes signal transduction
what is a membrane?
fluid bilayer of phospholipids with an interspersed mosaic of proteins
what is the purpose of the hydrophobic centre of the phospholipid bilayer?
forms a barrier to the passage of polar molecules and ions
How does cholesterol alter membrane fluidity?
the structure of cholesterol - OH is hydrophilic and four rings are hydrophobic - reduces fluidity at warmer temperature but it prevents crystallisation at low temperature
cholesterol breaks up van der waals and the close packing of phospholipid tails
what is a peripheral (extrinsic) protein?
those that are easily removed from the membrane on the lab using ionic washes
how are peripheral proteins held in membrane?
on the surface held by charged or polar amino R groups
what are Integral (intrinsic) proteins?
cannot be washed from the membrane in the lab as they are firmly in place in the membrane by strong hydrophobic interactions with lipids tails
give the two types of integral proteins
transmembrane or embedded in one side of the bilayer only
what are glycoproteins?
proteins with a carbohydrate chain
what are glycolipids?
phospholipids with a carbohydrate chain
name functions of membrane proteins
passive transport proteins active transport proteins enzymes receptor proteins attachment proteins cell recognition proteins structural proteins
what does the term crenated mean?
when an animal cell is placed in hypertonic solutions and it shrinks
what does plasmolysis mean?
when a plant cell is placed in hypertonic solutions and the cell contents pulls away form cell wall
What are passive transport proteins?
They are transmembrane (integral) proteins that transport molecules across the membrane down a concentration gradient
why do channel proteins have a pore?
to facilitate or speed up diffusion
what is a passive carrier protein?
bind to specific molecules to allow the passage of molecules across the membrane
what are active transport proteins?
they pump ions and molecules against a concentration gradient and requires energy (ATP)
what provides the energy for active transport proteins?
hydrolysis of ATP for the phosphorylation and conformational change of protein pump
what is the function of a receptor protein?
they are in the plasma membrane, hydrophilic signalling molecules cannot cross hydrophobic regions in membrane, when there is a signal, the receptor proteins respond within the cell -
what are attachment proteins?
provide cytoskeleton attachment points within the membrane for the structural support of the cell
what is cell to cell recognition?
distinguishing between own cells and the cells of another organism by its ability to recognise glycoproteins (antigenic markers). to do with the different carbohydrate chains on the glycoprotein
what are the three main types of cell junction in animal cells?
spot desmosome, tight junction and gap junction
plants have one type of cell junction, what is it?
plasmodesmata
what is a spot desmosome?
dense deposits of protein holding adjacent cells together
what is a tight junction?
adjacent membrane proteins bonded together preventing passage of materials in spaces between cells
what is a gap junction?
doughnut shaped proteins from each cell join together to form tiny channels allowing passage of small molecules
what is plasmodesmata?
channels lined by cell membrane bridging the gap between cells
what does the rate of diffusion depend on?
the size of the molecule and its solubility. the more hydrophobic and the smaller, the faster the rate of diffusion
what is passive diffusion?
molecules are lipid soluble and pass straight through the phospholipid bilayer
what is facilitated diffusion?
molecules are dependent on a carrier protein to allow its passage through a membrane
