1.3 movement across the membrane Flashcards
what is the fluid mosaic model?
the individual phospholipid molecules can move within a layer (fluid) and the proteins embedded in the bilayer vary in shaper and size and their distributions among the phospholipids (mosaic)
what is a phospholipid bilayer?
one sheet of phospholipids opposite another.
what is a property of the phospholipid heads?
they are hydrophilic as they interact with the water in the cytoplasm inside and the surroundings of the cell outside.
what is a property of the phospholipid tails?
they are hydrophobic.
what is an intrinsic protein?
a protein that extends across both layers of the bilayer.
what are the properties of intrinsic proteins?
they include transport proteins which move molecules and ions across the membrane by active or passive transport.
what is an extrinsic protein?
a protein that sits on either surface of the bilayer.
what are the properties of extrinsic proteins?
they provide structural support and form recognition sites, by identifying cells and receptor sites for hormone attachment.
what is the role of cholesterol in the cell membrane?
it makes the membrane more stable at high temperatures and more fluid at low temperatures.
what is diffusion?
the movement of molecules or ions from a region of high concentration to a region of lower concentration down a concentration gradient.
how does the steepness of the concentration gradient affect the rate of diffusion?
the greater the difference in molecule concentration between two areas, the more molecules can diffuse in a given time.
how does the thickness of the membrane or the distance to travel affect the rate of diffusion?
the thinner the membrane or shorter the distance to travel, the more molecules can diffuse.
how does the surface area of the membrane affect the rate of diffusion?
the larger the surface area, the more molecules have room to cross in a given time.
do diffusion and facilitated diffusion require ATP?
they are passive processes - they do not require energy.
what is facilitated diffusion?
diffusion is made easier by the use of channel and carrier proteins.
what is a channel protein?
molecules with pores that are lined with polar groups.
how do ions pass through a channel protein?
the channels are hydrophilic, so ions can pass through as they are water-soluble. the channels open and close according to the needs of the cell.
what is a carrier protein?
a protein that allows the diffusion of larger polar molecules across the membrane such as sugars and amino acids.
how do ions pass through a carrier protein?
a molecule attaches to its binding site. the carrier protein changes shape and releases the molecule on the other side of the membrane before changing back to its original shape.
what is active transport?
the movement of ions/molecules from a region of lower concentration to a region of higher concentration against a concentration gradient.
does active transport require ATP?
yes.
how does active transport occur?
it occurs through intrinsic carrier proteins - it is limited by number and availability of carrier proteins.
what are some examples of processes involving active transport?
muscle contraction, nerve impulse transmission, transcription of glucose in the kidney, and in plant root hairs.
what happens in active transport?
- molecule combines with carrier protein on outside.
- ATP transfers a phosphate group to the carrier protein on inside.
- carrier protein changes shape + carries molecule across the membrane and inside the cell.
- molecule released into cytoplasm.
- phosphate ion is released into the cytoplasm + recombines with ADP to form ATP.
- carrier protein returns to its original shape.
