topic two - biological membrane - miss whitehouse Flashcards
why do cells need membranes?
control entry and exit of molecules
separate cell contents from outside
environment (tissue fluid)
separate cell components from cytoplasm
cell recognition and cell signalling
holding the components of metabolic
reactions in place
what percentage of plasma membrane makes up phospholipids?
phospholipids make up around 75% of plasma membranes
what four things does plasma include?
proteins
glycoproteins
cholesterol
polysaccharides
explain bilayer and why is happens this way?
the phosphate group “head” is polar and hydrophilic (water loving)
the fatty acid “tails” are non polar and hydrophobic (water hating)
the ‘head’ always faces the water and the tail goes in between the heads making sure it’s does get wet
what are the five types of molecules that make up the cell surface (plasma) membrane?
phospholipids
cholesterol
proteins – integral (go all the way through
the bilayer) and peripheral (don’t span the
bilayer)
glycoproteins
glycolipids
give some examples of differentiation?
many receptors for growth hormones in the cells of a
growing plant shoot
chlorophyll molecules in the inner chloroplast membrane
receptors to foreign bodies on the surface of white
blood cells
state the five steps of freeze fracture?
cell is rapidly frozen in liquid nitrogen
cell is cleaved along the fracture plane that splits the lipid bilayer (exposing proteins embedded in membrane)
after fracture, the two sections are coated/shadowed
with a heavy metal like platinum
acid is used next to dissolve the organic material,
resulting in a replica of the surfaces of the sample
the replicas are then viewed with an electron
microscope
explain why the model for membrane structure is known as the fluid mosaic model?
the phospholipid molecules can move freely
laterally and makes the membrane fluid.
the proteins are distributed throughout the
membrane unevenly and in a mosaic pattern
the agreed structure is based upon
experimental and chemical evidence and so is
classed as a model
label a fluid mosaic model structure?
use the olc to check answers
define and explain ‘phospholipids’?
hydrophobic centre prevents diffusion of polar molecules (some water does get through)
fatty acids can be saturated or unsaturated. Unsaturated fatty acids pack in less tightly due to a “kinked” molecular shape, meaning a more fluid
membrane
define and explain ‘cholesterol’?
regulates membrane fluidity/stability
fits between fatty acid tails and bind them together to make the barrier more complete
define and explain ‘proteins’?
enzymes catalyse reactions e.g. respiration and photosynthesis
channel proteins – allow the passive diffusion of polar
molecules (facilitated diffusion). Channel is hydrophilic
define and explain ‘glycolipids’?
phospholipids with polysaccharide attached on the OUTSIDE
cell recognition and communication
glycolipids and glycoproteins together make up the
glycocalyx layer (for cell recognition so cells group
together to form tissues)
can stabilise the membrane by forming hydrogen bonds with surrounding water molecules
define membrane permeability?
a measure of how easily molecules can cross a plasma membrane - the more permeable the easier it is for molecules to cross
state the effects of solvents on membrane permeability?
some organic solvents e.g. ethanol can dissolve the lipids in cell membrane causing the membrane to lose its structure
effects on increase in temp on membrane?
increases the fluidity and increases the kinetic energy of molecules leads to an increase in membrane permeability
effects on decrease in temp?
decrease fluidity, decreases kinetic energy of molecules leads to a decrease in membrane permeability
what does a higher proportion of unsaturated fatty acids do to the membrane?
increase fluidity, phospholipids can’t be packed as tightly
define passive transport and how it effects small and large molecules?
moving molecules down a concentration gradient and doesn’t require energy to move
small molecules e.g. co2 and o2 diffuses through the bilayer
large molecules (polar) need to be carried across the membrane by facilitated diffusion
how does water mostly move?
by osmosis
state the two passive processes and what they do?
simple diffusion - the movement of molecules/ions
from a region of high concentration
to a region of low concentration until an equilibrium is reached
facilitated diffusion - using a channel protein which forms a pore in the membrane
define net movement?
random movement of ions or molecules from high to low concentration
define the 5 factors affecting diffusion?
temp - as it increases molecules have more kinetic energy so diffusion will increase
diffusion distance - thicker the membrane across which molecules have to diffuse the slower the rate
surface area - more diffusion can take place
size of diffusing molecules - small molecules diffuse more rapidly
concentrating gradient - the steeper the gradient the faster the diffusion
define active process?
requires energy in the form of ATP to more molecules across a membrane
molecule move against the concentration gradient
