2.5 biological membranes Flashcards
what is tonoplast
the membrane surrounding the vacuole
is the nuclear envelope a membrane
yes
the membrane at the outside of the cell can be called…
the plasma membrane or the cell surface membrane
membranes are - permeable
partially
cell membranes control…
what can enter and exit the cell
cell membranes are used in cell
signalling
cell membranes provide - for enzymes
attachment sites
cytosol is…
an area of cytoplasm with no organelles in it
cell membranes compartmentalise, which means that they…
produce different compartments inside cells
phospholipid heads are
hydrophilic
phospholipid tails are
hydrophobic
what are the bonds in phospholipids?
ester bonds
what is formed when phospholipids are put in water?
micelles
what did Gorter and Grendel propose and when?
that the cell membrane is formed of a phospholipid bilayer, 1925
what was Davson-Danielli wrong about?
he said that proteins formed a layer on top of the membrane, but they are actually embedded in the membrane
who proposed the fluid mosaic model?
Singer and Nicholson
what model do we use for the plasma membrane structure?
the fluid mosaic model
proteins move more freely in - phospholipids, because…
unsaturated, they are bent and less rigid
what makes ATP?
ATP synthase (in the mitochondria)
can fat soluble molecules go through the phospholipid bilayer?
yes
a glycocalyx consists of…
a lipid and a glycolipid
what proteins are present in the plasma membrane?
peripheral proteins, enzyme or signalling proteins, glycoproteins, transport proteins, integral proteins
what are the transport proteins? 4
passive carrier protein, active carrier protein, channel protein, gated channel protein
integral and intrinsic proteins…
span the whole plasma membrane
peripheral and extrinsic proteins…
are found in one layer of the plasma membrane only
channel proteins are - in the plasma membrane
pores
channel proteins allow movement of - or - molecules, eg.
large or hydrophilic, glucose
channel proteins are often gated so that…
they only allow one type of ion through
channel proteins may be gated, which means they can…
open and close to allow certain things through
carrier proteins are often used in - using - energy
active transport, ATP
carrier proteins often have a particular shape so that
specific molecules fit
a glycocalyx is a - chain
carbohydrate
glycocalyxs form - bonds with -, helping to stabilize the membrane structure
hydrogen, water
aggregating means
bringing together
glycocalyxs are involved in cell adhesion for
aggregating cells into tissues
glycocalyxs act as receptors for
chemical signals
glycolipids in the glycocalyx act as cell identity markers or -, allowing…
antigens, the immune system to recognise them as self or non-self
cholesterol is found between - of a plasma membrane
the tails in the phospholipids
the function of cholesterol in the plasma membrane is…
to regulate fluidity
at high temperatures, cholesterol makes the plasma membrane more/less fluid
less
at low temperatures, cholesterol makes the plasma membrane more/less fluid
more
the plasma membrane being more fluid when it is colder is useful as it prevents…
the membrane from freezing
lipid soluble molecules go through
the phospholipid bilayer
polar or soluble molecules go through
hydrophilic channels created by channel proteins
endocrine systems signal to cells
over large distances
panacrine systems signal to cells
to other cells locally
autocrine systems signal
within the cell or to cells of the same type
the ‘message molecule’ sent is called the - or the -
signal or stimuli
the most common types of signal or stimuli are
hormones
the detect signals, cells must have sensors called -
receptors
receptors are often
proteins
non polar signals (such as testosterone and oestrogen) are able to… and bind to …
diffuse directly through the phospholipid bilayer, intracellular receptors
polar signals must bind to the membrane bound receptors, which are the - proteins
intrinsic
5 steps of cell signalling:
- stimuli
- receptors
- transducers
- amplifiers
- intracellular responses
a ligand is the
primary messenger
hormones are - messengers transported in the -
chemical, blood
target cells are any cells with a - for
receptor, the hormone
the hormone and the receptor on the target cell bind due to
their complementary shapes
channel proteins travel to- to let - into the cell
the cell membrane, glucose
binding causes the target cell to
react in a certain way
under normal circumstances, are there any channel proteins present in the plasma membrane?
yes
when blood glucose levels rise, the hormone - is secreted into the blood by the -
insulin, pancreas
medicinal drugs can interfere with
receptors
beta blockers block receptors to prevent…
the heart muscle increasing the heart rate if it would be dangerous for the patient
some drugs mimic natural receptors which people lack, eg in
schizophrenia
drugs blocking receptors form
drug- receptor complexes
painkillers attach to receptors and block - from travelling along the -
pain signals, nerve
drugs can do 2 things:
- mimic natural receptors
- block receptors
how does botox work?
it uses a toxin from the bacterium clostridium botulinum, the toxin binds to the receptors on muscle fibres, prevents them working and causes paralysis, reduces wrinkling of the skin
what is theory of Brownian Motion?
molecules move around randomly and bump into each other, and so tend to fill out the space that they are in
diffusion occurs down a
concentration gradient
diffusion is always
passive
diffusion can be - or -
simple or facilitated
what happens at equilibrium
the reaction rate is equal in both directions
which molecules go through channel proteins
large or polar molecules
is facilitated diffusion active
no
how wide is the phospholipid bilayer
7nm
how wide is the channel protein
0.8nm
what can move by osmosis
only water
pure water has a potential of
0
which symbol represents water potential
psi
diffusion occurs across a
partially permeable membrane
why are plant cells not haemolysed
they have a cell wall which prevents it
plant cells, water moves in so cell is
turgid
animal cells, water moves in so cell is
haemolysed
plant cells, water moves out so cell is
flaccid or plasmolysed
animal cells, water moves out so cell is
crenated
what is a hypertonic solution
something with a very low water potential
what is plamolysis
when water moves out of a cell, causing the vacuole to shrink and cytoplasm to move away from the cell wall
what is the incipient point of plasmolysis
when 50% of cells have been plasmolysed
what is bulk transport
moving large quantities of material in or out of the cell
endocytosis is
moving large quantities of material into the cell
exocytosis is
moving large quantities of material out of the cell
what type of energy does active transport need
ATP
when is active transport used
when diffusion isn’t quick enough or when the movement is against a concentration gradient
cells involved in active transport have lots of
mitochondria
why are most carrier proteins one way
because otherwise particles would want to move back by diffusion
the shape of carrier proteins is
complementary
carrier proteins are complementary so that
they only allow specific molecules to enter snd exit the cell
the two types of endocytosis are
pinocytosis and phagocytosis
pinocytosis is
the cell taking in liquids
phagocytosis is
the cell taking in solids
an example of phagocytosis is
white blood cells engulfing and digesting pathogens
is bulk transport active or passive
active
why is bulk transport active
because it uses energy to transport material in vesicles along the cytoskeleton
exocytosis example
insulin exiting the cell
endocytosis example
pathogens entering the cell
why is beetroot used to investigate the effect of temperature on cell membranes
because their red cell sap is naturally coloured and easy to see
why does temperature effect cell membranes
because phospholipids break and proteins denature, and the plasma membrane melts. The tonoplast is broken and cell sap can escape from the vacuole.
what steps happen to the cell membrane as temperature is increased
- proteins are denatured as the bonds in their tertiary structure are broken
- phospholipid membrane bonds break
- rate of diffusion increases
how do we conduct an experiment to investigate the effect of temperature on cell membranes?
- place test tubes with 10cm3 of water into water baths set at 30, 40, 50 and 70, and leave one at room temperature. Leave for 15 mins to equilibrate.
- cut beetroot into identical cylinders measured with a ruler and rinse and dry them
- place the beetroot cylinders into test tubes and leave for 10 mins
- remove the test tubes, remove the beetroot and swirl the liquid
- place liquid into cuvettes and measure light absorption, record data in table and plot graph
how do we investigate osmosis in an artificial cell?
- create a dilution series of 1.0, 0.8, 0.4, 0.2 and 0.1 mol dm3
- cut visking tubing into 5 equal sections and tie then ends in knots
- fill tubing 1/3 full with 0.4 mol dm3 solution
- measure the mass of each concentration initially
- place the artificial cells into each concentrated solution for 20 mins and then remove and weigh mass
- create a table recording concentration, initial mass, final mass, mass change, and percentage change
