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
define active transport?
moves molecules against a concentration gradient and requires both ATP and carrier proteins
state how a carrier protein works?
ATP transfers a phosphate group to the carrier protein on the inside of the membrane
carrier protein changes shape
molecule is carried through to other side of the membrane
when molecule is released the carrier protein returns to its original shape
use of active transport?
minerals are essential for plant growth and are found in the soil
active transport moves the minerals into the root hair cells
what are the two main types of endocytosis?
phagocytosis- cell eating (solid material)
pinocytosis- cell drinking (liquid materials)
what is exocytosis?
the vesicles fuse with the plasma membrane to release the vesicle content
define a channel protein?
opens up space across the membrane and allows entry or exit
define carrier protein?
they are able to allow the diffusion across the membrane
difference and similarities with facilitated and simple diffusion?
differences - active transport against the gradient
facilitated is down the gradient
similarities - both use proteins
why are some membranes up to 100x more permeable?
because of the presence of aquaporins - specialised channel of proteins
what is water potential measured in and what does pure water equal?
kPa - kilopascals
pure water - 0kPa
what does dissolving solutes do?
lowers the water potential, so it becomes more negative
how does water move (in terms of + & -)
moves from less negative to more negative potential
what does water potential equal?
solute potential + pressure potential
what is solute potential?
is the concentration of dissolved substances in the cell - a measure of reduction in water potential due to water molecules being negative
define pressure potential?
pressure exerted on the cell contents by cell wall or membrane
what happens when you place cells in pure water?
osmosis - water moves from outside to inside the cell
what happens when plant cells are placed in water?
in a plant cell, the cytoplasm and vacuole
swell until the cell wall resists the increasing
osmotic pressure – no more osmosis occurs
(turgor)
what happens when animal cells are placed in water?
in an animal cell, the cell may burst as there is no
cell wall to withstand the increasing pressure
(haemolysis)
what happens when plant cells are placed in a concentrated solution?
in plant cells the plasma membrane is pulled
away from the cell wall as the cytoplasm shrivels
plant cells become plasmolysed
what happens when animal cells are placed in concentrated solution?
cell shrinks and appears wrinkled - it is crenated
review the osmosis potato practical?
OLC
why do fresh water fish take in water through osmosis?
there blood is more concentrated then the surrounding water
where does a fresh water fish take in water and why?
through the gills because they have thin membranes
like fresh water fish, sea water fish take up water by osmosis through the gills, suggest how they keep the concentration constant in sea water fishes?
the gills expel the excess salt from the blood
what happens in cell signallling?
how cells communicate with each other, using signal
molecules
some signals take place inside cells, while other signals carry messages from one cell to another
state four uses cell signalling?
cell signalling controls many cellular processes, including cell division, cell death and cell differentiation
which type of molecule usually acts as a receptor?
protein molecules
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djehhjeh
define hormones?
hormones are chemical messengers made by glands and carried in the bloodstream to act on target organs
what do hormones form part of?
form part of an animal’s endocrine system they can trigger different responses in different cells
what are the two types of hormones?
steroid
protein and peptide
what is a steroid hormone?
sex hormones such as testosterone, progesterone,
oestrogen, mineralocorticoids, glucocorticoids
can steroid hormones pass through the plasma membrane?
yes – diffuse through the phospholipid bilayer
where are the receptor of steroid hormones found?
within the cell - have an effect on synthesis of
proteins
examples of protein and polypeptide and where they derivatives from?
derivatives of amino acids
e.g insulin, glucagon, adrenaline
can protein and polypeptide pass through the membrane and how do they act on the cell?
no – proteins are hydrophilic
must bind to cell surface receptors
what shapes are drugs?
they have complementary shapes to the cell surface receptors
what shape are drugs?
they have a complementary shape to the cell surface receptor
what are drugs used for?
can be used to block receptors to inhabit cell activity and to unlock cell receptors to simulate cell activity and trigger a response
what is morphine and how does it work?
a drug is relieve pain
the body naturally produces chemicals called endorphins to relieve the pain
what do beta blockers treat?
treat arrhythmia (irregular heart rate), heart failure and hypertension (high blood pressure)
how do beta blockers work and what they do?
beta receptors in the heart muscle usually receive impulses that increase heart rate
beta blockers block beta receptors to reduce heart rate and blood pressure
what are histamines?
histamines are chemicals released following cell damage, causing inflammation in neighbouring cells by binding to receptors
what do antihistamines do?
antihistamines block histamine receptors to prevent
inflammation and reduce pain, redness and swelling
what is Botox?
toxin from the bacterium Clostridium botulinum
how does plasma work?
binds to receptors on plasma membranes of muscle cells
blocks binding of neurotransmitters such as
acetlycholine – leads to paralysis of muscle
permanent relaxation prevents formation of wrinkles
what does throazine treat?
drug used to treat schizophrenia
what is schizophernia?
disturbances in areas of brain associated with thought,
perception, attention, motor behaviour and emotion
what is dopamine and what could imbalances of dopamine cause?
dopamine is a neurotransmitter
imbalances in dopamine levels are thought to lead to
schizophrenia
what is insulin?
a protein hormone produced by cells in the pancreas in response to high blood glucose levels
state the effects of insulin on the liver?
activates enzymes that change glucose molecules so they can’t leave the cell
increase permeability of liver cells to glucose
activates hormones that convert glucose into the storage molecule glycogen
muscle cells also have insulin receptors, suggest what the binding of insulin does to the muscle cells?
the binding of insulin increase the number of glucose channels in the membrane for increased uptake
what do viruses do?
they enter the cell by binding to the receptors on the plasma membrane of the host cells
an example of viruses binding to receptors?
the HIV virus enters the cells of the immune system - its shape is complementary to the receptor
