3.2.3 Cell Membranes Flashcards
Structure of cell membrane
Fluid mosaic model
- phospholipid bilayer
- proteins (channel, carrier,receptor)
- glycoproteins
- glycolipids
- cholesterol
Characteristic of cell membrane
partially permeable
function on cell membrane
allows selected molecules in and out
Role of phospholipid bilayer
- hydrophobic tail and hydrophilic head
- head out (attract to H2O in cytoplasm/surrounding) , tail in (repel)
- centre is hydrophobic, doesn’t allow water soluble sunstances in (e.g. ions)
role of cholesterol
- controlling membrane fluidity
- regulating cell temperature
- maintain shape of animal cells
diffusions rate of small,non polar molecules (O2, CO2)
rapid
diffusion rate of small, polar molecules (water, urea)
steady
function of channel protein
water filled tubes allow water soluble ions to diffuse across the membrane (facilitated diffusion)
function of carrier protein
binds to ions or molecules which then changes shape to allow the molecules to move across membrane (active transport & facilitated diffusion)
glycoprotein function
- recognition sites
- binding cells together
- cell signalling
glycolipid function
- cell signalling
- cell recognition
receptor proteins
on cell surface membrane which allow cell to detect chemicals released from other cells
how does temperature affect permeability
affects how much the phospholipids in the bilayer can move
temps below 0
- v little energy
- phospholipids barely move, tightly packed together
- channel proteins & carrier proteins denature (increase permeability)
- ice crystals form & pierce membrane (highly permeable)
temps between 0 & 45
- phospholipids can move a little - not tightly packed as more kinetic energy
- membrane is partially permeable
temps above 45
- bilayer begins to melt (more permeable)
- water inside cell expands putting pressure on membrane
- channel proteins & carrier proteins denature (cannot control what enters/leaves cell) so membrane more permeable
simple diffusion
The movement of particles (molecules or ions) from a region of high concentration to a region of low concentration
facilitated diffusion
involves presence of protein carrier molecules to allow passive movement of substances (large, polar, charged molecules) across a plasma membrane
factors that affect rate of diffusion
- concentration gradient
- thickness of exchange surface
- surface area of exchange surfaces
factors affecting facilitated diffusion
- concentration gradient
- number of channel/carrier proteins
osmosis
Movement of water from an area of high water potential to an area of low water potential
isotonic
a solution which has the same water potential as the cell within it
hypotonic
solutions with a higher water potential than the cell, cell swells
hypertonic
solutions with lower water potential than cell, cell shrinks
factors affecting osmosis
- water potential gradient
- thickness of exchange surface
- surface area of exchange surface
active transport
movement of a substance from low concentration to a region where it is in a high concentration. Requires energy (ATP)
process of active transport
1) molecule/ion binds to receptor site of carrier protein in plasma membrane
2) ATP binds to the protein on the other side, causing it to split by by hydrolysis into ADP and Pi, releasing energy
3) protein changes shape and opens on the opposite side of the membrane
4) the molecule/ion is released on the other side of the membrane
5) ATP is reformed and protein reverts to its normal shape
factors affecting rate of active transport
- speed of individual carrier proteins
- number of carrier proteins
- rate of respiration/availability of ATP
co-transport of glucose in the ileum
- sodium ions actively transported out of epithelial cells into ileum
- higher concentration of sodium in the ileum
- sodium diffuses back into epithelial cell through sodium-glucose co transporter, so the sodium also moves glucose into the epithelial cell
- a high concentration of glucose inside the epithelial cell so diffuses into blood by facilitated diffusion
why co-transport works
the concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient
Types of bulk transport
Endocytosis and exocytosis
Endocytosis
moving into a cell
(pinocytosis-liquids)
(phagocytosis- solids)
Exocytosis
moving out of cell
( secretion-useful)
(excretion- useless)
