Introduction to membranes Flashcards
Plasma membrane
a boundary that
separates living cell from its surroundings
Plasma membrane exhibits selective permeability
allowing some
substances to cross it more easily than others
Introduction to Membranes- The spherical phospholipid bilayer is
the basic structure of
all biological membranes
liposome
spherical lipid bilayer
(cross-section is shown
Membranes are made of
proteins and lipids
most abundant lipid in the
plasma membrane
Phospholipids
(Singer and Nicholson, 1972)
“Fluid Mosaic Model”
- membrane is a fluid structure with a _______ appearance because it contains different types of ______ embedded in it.
different membranes can contain ______
”mosaic”, proteins,
different proteins
Proteins of the bilayer can be classified into two main groups:
1) integral
2) peripheral
(or intrinsic) membrane proteins
- embedded in the bilayer due to at least one portion of the protein
being hydrophobic
integral - Proteins of the bilayer
(or extrinsic) membrane proteins
- attached loosely to the surface of the membrane
(usually by interacting with an integral protein)
peripheral - Proteins of the bilayer
Please label
- Integral membrane proteins
- Peripheral membrane proteins
- Hydrophilic
- Hydrophobic
- Hydrophilic
In addition to phospholipids and proteins,
membranes can contain other components:
Glycoproteins, Glycolipids, Cholesterol
membrane proteins that have a
sugar attached
- important function in cell recognition
Glycoproteins
membrane lipids that have a
sugar attached
Glycolipids
inserts between phospholipid
molecules
- influences membrane permeability and
fluidity
Cholesterol
Variability in the type and number of these different
components gives different membranes
specific properties
Please label
- Glycoproteins
- Glycolipids
- Cholesterol
Biological membranes are fluid at
physiological temperature
Phospholipids and some proteins in the membrane can
move
Please label
- Phospholipids drift laterally
- Phospholipids rarely
flip-flop transversely
Biological membranes- High temperature will cause an increase in _____. gaps in the membrane will form if ________
fluidity, temperature goes high enough
membrane can become more permeable at ___________
high temperatures
All membranes will turn solid if temperature goes _______ ,called _______.
low enough, phase transition
Temperature at which phase transition occurs depends on the composition
of the membrane:
- Length of fatty acids in the phospholipid
- “Shape” of fatty acids in the phospholipid
(influenced by double bonds)
Phase transition composition:
- Length of fatty acids in the phospholipid
- Short chains have less stable interactions with each other
- therefore, a lower temp required to keep them in a solid structure
Phase transition composition:
- “Shape” of fatty acids in the phospholipid
(influenced by double bonds)
- Double bonds cause structural kinks, decreasing ability of chains to
pack together (as discussed previously)
- Cholesterol also has an effect on
membrane fluidity
Cholesterol acts as a _______ maintain membrane fluidity at a
greater range of _______.
“fluidity buffer”, temperatures
Cholesterol interferes with the __________
lateral movement of phospholipids (reducing membrane fluidity at moderate temperatures)
Cholesterol prevents close packing of _______________________.
phospholipids at lower temperatures
(solidification occurs at a lower temperature)
-Cholesterol is very important (and prevalent) in _________ (e.g. As much as ___ of the lipid in some nerve cells is cholesterol)
- - Cholesterol is not in _________.
- animal cell membranes, 25%
- prokaryote membranes, and plant cells have very little, if any.
What are the proteins doing in the membrane?
Six major functions for membrane proteins:
- Transport of molecules
into or out of cell - Enzymatic reactions
near the membrane - Signaling via receptors
- Cell-cell recognition
- Intercellular attachment
- Attachment of the
cell to extracellular
matrix proteins
What are the proteins doing in the membrane?
Transport of molecules
into or out of cell
What are the proteins doing in the membrane?
Enzymatic reactions
near the membrane
What are the proteins doing in the membrane?
Signaling via receptors
What are the proteins doing in the membrane?
Cell-cell recognition ( e.g., blood groups A and B
result from different
glycoproteins on blood cells )
What are the proteins doing in the membrane?
Intercellular attachment
What are the proteins doing in the membrane?
Attachment of the
cell to extracellular
matrix proteins
Transport- How is the movement of various molecules across the membrane
achieved (or prevented)?
3 ways: Diffusion, Facilitated diffusion, Active transport
-Lipid bilayer is permeable to some substances, impermeable to others
-Main barrier is the Hydrophobic core of the bilayer
1) Diffusion (or Passive Transport)
- occurs best with_________.
- these are ______ in the bilayer and
can pass through quite quickly
- when such a molecule is more _______ on one side of a
membrane, __________________.
- i.e., molecules _______________.
-small hydrophobic molecules such as O2
- soluble
- concentrated
-diffusion occurs until equilibrium is reached
- “diffuse down their *
concentration gradient”
Diffusion (or Passive Transport)
- Net diffusion
- Net diffusion
- Equillibrium
Only certain molecules can pass through the membrane via ______.
diffusion
Only certain molecules can pass through the membrane via diffusion
- hydrophobic
molecules, very good - small
uncharged
polar, fair to poor - large
uncharged
polar, rarely, if ever,
pass through
4.charged
(large or small), almost never
pass through
Osmosis: a special case of _______
- diffusion of _______ across a _____________.
-passive transport
- water, selectively permeable membrane
-
Please label-Water (solvent) follows the solute:
- Water molecules can
pass through membrane,
but sugar cannot - Fewer
solute
molecules - Water clusters
around the solute
4.More
solute
molecules - Osmosis- Water moves from high to low free water concentration
(or low to high solute concentration)
the relative concentration of a solute in two solutions separated by a
membrane that it cannot cross. If water can pass freely, the solute [conc.] difference
determines whether cells gain or lose water.
Tonicity
Pls label
- Hypotonic, Lysed, Turgid (normal)
- Isotonic, Normal, Flaccid
- Hypertonic, Shriveled, Plasmolyzed cell shrinks, membrane pulls away
from the cell wall = plasmolysis
-Facilitated Diffusion: _____________.
- specific molecules that are ______.
-Passive Transport Aided by Proteins
- impeded by the membrane but diffuse
passively with the aid of a transport protein
Two types of transport proteins are used for facilitated diffusion:
1) Channel proteins:
2) Carrier proteins:
1) Channel proteins:
- A specific channel protein usually
allows only one type of _______.
- __________ determine if the
channel is open or closed.
-molecule or
ion to pass through.
- Cellular conditions
________are a type of channel protein that facilitates _______. Water
moves across the membrane ________ if it goes through a channel.
- Aquaporins
- osmosis
- faster
________ allow specific ions through. (i.e., usually a different protein for
each ion)
Ion channels
Channel proteins can be ______, turned on or
off by __________.
-“gated”
-different stimuli (voltage, ligands, etc.)
Please label
- Down the
[conc.]
gradient - a “pore” or
channel
2) Carrier proteins:
- These undergo a subtle _________ to translocate a _________.
- change in shape
(conformational change) - solute
across the membrane.
2) Carrier proteins:
- specific for the _________
- solute also________
- protein has same_______
-molecule being transported
- diffuses down its concentration gradient
- affinity for target molecule on both sides of
the membrane (i.e., movement can occur in either direction, but
always down the concentration gradient)
3) Active Transport: used to move a substance _________.
-Why do cells do this?
- To concentrate_______
-To expel_____
- To establish_____
-against the
concentration gradient
- nutrients in the cell
- waste
- voltage/chemical gradients
3) Active Transport:
-Proteins involved in this type of transport are all_______.
- _________ for each substance.
- Carrier proteins
- specific carrier protein
3) Active Transport:
- Compared to its surroundings, an animal cell maintains a high internal _________.
- to do this, a cell uses a ________ and __________.
- conc. of K+ and low Na+
- “sodium-potassium pump”
- energy stored in a molecule called ATP
- ATP = ________.
- breaks down to _______
- ADP = _______.
- Pi = ______.
- adenosine triphosphate
- ADP + Pi and
releases energy - adenosine diphosphate
- phosphate
Active transport allows cells to establish and maintain________.
concentration
gradients that might not occur naturally
Please label
- The sodiumpotassium pump
is one type of active
transport system
Please label the sodium potassium pump
-sodium potassium pump
- Starts with _____________.
- Ends with _______________.
- 3 Na+ (in) + 2 K+ Start (out) + ATP
- 3 Na+ (out) + 2 K+ (in) + ADP + Pi
3 Na+ go out, and 2 K+ come in ____________.
- creating an imbalance in charge
across the membrane (inside is more negative than outside)
Please label
- Fewer “+” ions
- More “+” ions
3.Voltage - Voltage = difference
in electric potential - membrane
All cells exhibit a ______ across their plasma membranes
voltage
The _____ distribution of ________ across
the plasma membrane is
called the__________.
-The inner side of the membrane is _______.
- unequal
- anions and/or cations
- membrane
potential.
-negative
e.g., cells typically have a membrane potential of _______
-50 to -200 mV
For ions, two forces drive their diffusion across the membrane
- a difference in their ________
– a difference in _________
- So ________ flow down their ________________.
- concentration (chemical force)
- total charge (electrical force)
= electrochemical gradient
-charged molecules
-electrochemical gradient
(Not simply their conc. gradient)
The pumps that are responsible for creating__________ are called _________.
-electrochemical gradients
- electrogenic pumps.
-An important electrogenic pump in animal cells is the _______________.
- Plants, fungi and bacteria mainly use a _______.
- sodium-potassium pump
- proton pump
Please label.
1.proton pump
Another type of Active Transport: Cotransport (or coupled transport)
-_________ couple the _______ transport of a solute to the _______ transport of a _________
- Cotransporters
- “downhill”
-“uphill” - second substance against its own concentration gradient
please label the sucrose transport in a plant cell.
- proton pump
- sucrose-H+ cotransporter
- active transport has enough energy to pull the sucrose in
- using the protons falling through the electrochemical force that also moves the sucrose in
Bulk Transport
- Big molecules (e.g. polysaccharides) must be transported using a _______.
- involves _______.
- Membrane is ______ and can bend into different shapes including _________
- transport mechanism
- formation of vesicles
- flexible
- pinching off into vesicles. This requires energy.
– exporting substances out of the cell
Exocytosis (secretion)
Please label
Endocytosis (importing substances)
3 main types:
1.) Phagocytosis
(cell “eating”)
- 2) Pinocytosis
(cell “drinking”) - receptor-mediated
3) receptor-mediated
Recall that receptors are a specific type of________ Receptors receive __________ This involves a _________ Each receptor only binds ___________.
- membrane protein.
- chemical signals from outside the cell
- physical interaction between ligand and receptor
- to ligands of a particular structure (often, only one type of molecule will bind
to a specific receptor).
Please label
Please label
Receptor-mediated endocytosis
- Receptors bind to a__________ that the cell needs to________. ___________ binds to these receptors on the ________, gathering them and the membrane into a ____ shape that eventually forms a ________. the particle (ligand) is used/consumed, and the receptors _________ back to the membrane
-Substance(ligand)
-Uptake
-Clatharin
-Inside of the cell
-pit
-Vesicle
-makes their way back
An example of receptor-mediated endocytosis:__________
- _________ transport fats to cells via the__________.
- Fat delivery to cells
-Lipoproteins
-Bloodstream
Label the lipoprotein
specific proteins (called apolipoproteins) associate with the_________
- the proteins differ, depending on the_______.
- receptors on the recipient cell recognize the _______.
-fat droplet
- lipoprotein
- apoprotein and promote endocytosis (involving coated-pits) and uptake of the fats.
Too much cholesterol can build up in __________.
arteries and form plaques
LDL (low density lipoprotein) low in _____,but highest in _______.
-LDL cholesterol is often referred to as
-density
-cholesterol.
- “bad” cholesterol
HDL (high density lipoprotein) highest in density due to high ________.These particles can remove excess ________.
- HDL cholesterol is often referred to as ______.
-protein/lipid ratio
cholesterol from
blood vessels (and transport to it the liver for removal).
- Good cholesterol
-Clathrin is a _____ protein that
helps facilitate ______.
-coat
- vesicle formation
High levels of LDL vs. HDL can indicate higher risk of
cardiovascular disease
Transporter Definitions
- systems that perform active transport using ATP directly
mediate
-“primary active transport” (e.g., the Na+/K+ pump)
Transporter Definitions
- systems __________ that use carrier proteins
driven by ion gradients are said to mediate _______.
- (such as sucrose-H+, above)
- “secondary active
transport”
the carrier or transport proteins used in facilitated diffusion
or active transport are sometimes described as:
a) uniporters (those that
transport only one type of
molecule)
the carrier or transport proteins used in facilitated diffusion
or active transport are sometimes described as:
b) symporters (transport two
different molecules in the same
direction)
the carrier or transport proteins used in facilitated diffusion
or active transport are sometimes described as:
c) antiporters (transport two
different molecules in the
opposite direction)
Review of Membranes and Transport:
Cellular membranes are fluid mosaics of_________
lipids and
proteins
Review of Membranes and Transport:
Membrane structure results in________
selective permeability
Review of Membranes and Transport:
Passive transport is diffusion of a substance across a
membrane with __________
no energy investment
Review of Membranes and Transport:
Active transport uses _________
energy to move solutes against
gradients
Review of Membranes and Transport:
Bulk transport across plasma membranes uses_________
exocytosis and endocytosis
Bacterial Cell Walls
-provide _____,________ from bursting in_______ environments.
-Bacterial cells, like_______, contain a much higher ________, compared with their ________.
-shape
-protection
-hypertonic
-animal cells
-concentration
of many molecules
-environment
Bacterial Cell Walls
-Almost all bacterial cell walls contain __________
-Most bacteria belong to one of two major classes, as
defined by their________
- The two types are distinguished by the_________ A procedure developed by _________.
- peptidoglycan.
- cell wall structure
- Gram stain
- Hans Gram (late 1800s)
Pls label
1.Gram positive
2.gram negative
Please label
Please label
Peptidoglycan
- a thin sheet composed of:
1. Chains of a repeating __________composed of two ________
i)_____________
ii)____________
2._________
-attached to ________
- bonds formed between________
-disaccharide
-monosaccharides
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
-Small peptides
-NAM subunits of the chains
-peptides on adjacent chains
cross-link the chains and gives strength to the structure
Peptidoglycan is a polymer of _____ and _______
-N-acetylglucosamine (NAG)
-N-acetylmuramic acid (NAM)
Please label
Please label
For both Gram-positive and Gram-negative bacteria,
peptidoglycan is not _______
-a barrier to solutes.
Peptidoglycan is synthesized only in
growing cells.
