1.4 membrane structure Flashcards
what are the different ways of transport particle move across membranes
- simple diffusion
- facilitated diffusion
- osmosis
- active transport
the membrane is ‘semipermeable’
what does semipermeable mean
to allow some, but not all molecules through.
- controls what goes in and out of the cell
what is passive transport
a form of transport which does not require energy as the molecules move from a high to low concentration->down the concentration gradient
examples of passive transport
- diffusion
- factiliated diffusion
- osmosis
what is active transport
transport through the membrane which does require require energy as the molecule move from a low to high concentration–> moves against the concentratioon gradient
examples of active transport
- ion pumps
- phagocytosis
what is a concentration gradient
where the concentration is different across an area
-i.e high and low concentration
what is the difference between passive and active transport
- passive doesn’t require energy and goes from high to low concentration
- active does require energy and goes from low to high concentration
Diffusion is a form of what type of transport
passive transport
what is diffusion
passive movement of particles
- down the concentration gradient
- higher to lower concentration
- requires no energy
how does diffusion occur
occurs as the consequence of random motion of particles
why can’t all substances diffuse
- the mebrane is semi-permeable so many substances can’t diffuse due to size or polarity
steep gradient
large difference in concentration between the two areas
what affects the speed of diffusion
- the steepness of the concentration gradient
- steeper concentration gradient= faster diffusion - size of the molecules
- temperature
examples of substances that move via diffusion
mostly gases
- oxygen
carbon dioxide
-glucose
facilitated diffusion
passive transport of molecules or ions across a cell membrane
- done through transmembrane integral proteins which transport the molecules
polar molecules
- cannot freely diffuse due to the hydrophobic nature of the fatty acid tails of the phospholipids
- are transported by proteins in the form of transmembrane
examples of factilated diffusion
- glucose sodium ions - chloride ions - amino acids - nucleosides
ion channels
facilitated diffusion that involves channel proteins
- opens a channel to allow smaller molecules instead of binding to molecules
examples of molecules that ion channels allow through
- sodium
- potassium
- calcium
- chlorine
why do some molecules use factilated diffusion
the lipid bilayer is impermeable to them
e.g. the glucose molecule is to large to pass through unassisted
what is osmosis
the movement of water molecules from an area of higher water concentration to an area of lower concentration through a semi-permeable membrane.
osmosis is a form of passive transport
does not require energy
through osmosis, will water move to the hypertonic or hypotonic area and through what type of transport
the hypertonic area ( the low water area)
through osmosis
what is osmolarity
the measure of a solutes concentration
what osmolarity does water have
zero
turgid
when a cell is placed in a low salt/ high water solution, the cell gains water as it is hypertonic and swells- becoming turgid.
turgid in a plant cell vs animal cell
plant cell: optimal condition- turgid
- will be contained by the cell wall
animal cell/protist:
no cell wall so therefore may burst, killing the cell -lysed
isotonic
when the solution and cell have the same concentration
if the cell and the solution have the same concentration then it is isotonic and they remain unchanged
isotonic saline solutions are used in medical procedures such as transporting kidneys.
- they mast be in a solution with the same osmorlatiy as a a human cytoplasm to prevent osmosis
in fresh what cells tend to gain/lose water via what transport and why
gain
through osmosis
the cytoplasm contains dissolved substances and is therefore hypertonic to the fresh water which is hyoptonic
potassium ion channels
they are the most common type of ion channel and are found in most cell types.
they form potassium selective pores that spend the cell membrane.
potassium ion channels are used to move K+ ions across the membrane
the channels work with the sodium-potassium pump in the axons of neurons
the axons of neurons
transmit electrical impulses by translocating ions to create a voltage difference across the membrane
when at rest, the sodium-potassium pump expels sodium ions from the nerve cell, while potassium ions gather within the cell
when the neuron fires, these ions swap locations via facilitated diffusion through the sodium and potassium channels
what type of transport is used when the neuron fires
facilitated diffusion via the sodium and potassium channels
active transport
the movement of particles from an area of low concentration to and area of high concentration,going against the concentration gradient and requiring energy(ATP).
examples include:
the uptakes of glucose in the intestines of humans,
the exchange of Na and K+ ions in the nerve axons
uptake of mineral ions into root hair cells of plants.
what are the two main types of active transport
protein pumps
- only transport specific substances and in a specific direction,
- substance binds to the protein
- and energy(ATP) Is used to move the substance along
use of vesicles
- the fluidity of the membrane allows materials to be taken into cells by endocytosis or released exocytosis
- vesicles move materials within the cells.
sodium-potassium pumps in nerve axons
nerve cells conduct nerve impules via a ‘mexican wave’ of Na+ and K+ ions in and out of the nerve.
axons contain a pump protein that moves Na+ and K+ ions across the membrane.
The ions are moved in opposite directions(antiport).
one energy(ATP) molecule is enough to transport three Na+ out and two K+ ions in.
what are nerve cells
axons
there are two states the sodium-potassium pumps have
In one there is more ‘binding site attraction’ for K+ ions outside the membrane.
- in this state K+ moves in and Na+ moves out.
In the other state the reverse occurs
- K+ moves out and Na+ moves in
ATP energy cause the change from one state to another
how does ATP cause the change in the sodium-potassium pump’s states
it helps to establish a net charge across the plasma membrane with the interior of the cell being negatively charged with respect to the exterior.
this prepares nerve and muscle cells for propagation of nerve
what are vesicles
usually small vacuoles containing proteins, that bud off from the endoplasmic reticulum or the Golgi bodies and then travel to the cell membrane
exocytosis
secrection
when a vesicle fuses with the cell membrane, the contents are expelled and the membrane flattens out again
e.g.
secrection in substances: hormones, contractile vacoules in paramecin
endocytosis
part of the cell membrane is pulled inward, the material in engulfed and the vesicle is pinched off
phagocytosis: is engulfing solid material
pinocytosis: is engulfing fluid material
what are the molecules that make up living things
C.L.P.N.M.W
Clay lions paint nails mysteriously well
carbohydrates: glucose, starch, cellulose
Lipids: fats, waxes, oils
Proteins: enzymes, hormones, collagen, muscle
Nucleaic acids: DNA
Minerals: calcium, iron, sodium
Water
carbon in living things
carbon is contained in organic compounds which are found in living things.
each carbon atom can form four covalent bonds: allows a great diversity of compounds to exist
the most common type is C-C and C-H.
covalent bonds
hydrogen forms one covalent bond
oxygen and sulfer form two
nitrogen form three
Carbon can form four covalent bonds
additional groups added to the C-C molecule give the organic compound it’s properties.
covalent bonds are relatively strong so molecules are stable. weaker bonds can form between molecules.
covalent bonds
hydrogen forms one covalent bond
oxygen and sulfer form two
nitrogen form three
Carbon can form four covalent bonds
additional groups added to the C-C molecule give the organic compound it’s properties.
covalent bonds are relatively strong so molecules are stable. weaker bonds can form between molecules.
life is based on carbon compounds including carbohydrates
the theory of vitalism
it used to be thought that living organisms were composed of organic molecules that could only be produced by a ‘vital force’- made by a living thing
this was proved false through biochemistry discoveries which explained the living process: e.g. photosynthesis and respiration, in terms of the chemical substances and chemical reactions.
- In 1828 Fredich Wohler synthesised urea artificially using silver isocyanate and ammonium chloride.
the structure of DNA has further explained living processes including protein synthesis, inheritance and evolution.
synthesis of urea
Urea was discovered in human urine during the 18th century
the theory of vitalism would have meant that it could have only been made in living organisms with a vital force.
In 1828 Fredich Wohler synthesised urea artificially using silver isocyanate and ammonium chloride which disproved the the theory of vitalism.
chemical synthesis
a key aspect to organic chemistry.
today most organic compounds that make up living organisms can be synthesised.
this is often used by pharmaceutical companies to. identify compounds from plants and animals and artificially synthesise them for use
e.g. hormones, enzymes, painkillers.
metabolism
metabolism is the web of all the enzyme-catalysed reactions in a cell or organism.
reactions may be anabolic or catabolic.
a metabolic pathway is a series of chemical reaction within a cell.
anabolism
the synthesis of complex molecules from simpler molecules including the formation of complex molecules including the formation of macromolecules from monomers via condensation reactions.
examples include the synthesis of sugar from CO2, (photosynthesis), the synthesis of large proteins from amino acid building blocks, and the synthesis of new DNA strands from nucleaic acid building blocks
anabolic steriods build muscle and protein
catabolism
The breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
example
respiration where glucose is broken down. into carbon dioxide and water to produce energy(ATP)
