week 3 notes Flashcards
__________ are the major lipids of plasma
membranes
phospholipids
Phospholipids are orientated so that
a. polar fatty acid tails face towards
water
b. nonpolar fatty acid tails face towards
water
c. polar ‘head’ groups face towards
water
d. nonpolar ‘head’ groups face towards
water
c. polar ‘head’ groups face towards
water
True or False
Individual phospholipids in a membrane are
not permanently attached to adjacent
phospholipids?
true
Vesicles are small structures within a cell, consisting of fluid enclosed by a lipid bilayer involved in transport, buoyancy control, and enzyme storage.
What would you predict are
some useful attributes of cell
membranes
- Controls traffic in & out of
the cell: Selectively Permeable meaning it allows some substances to
cross more easily than
others - self sealing; they get bigger, and they can be flexible to have the right fluidity
- expandable
- flexible and have appropriate/ideal fluidity
what does the plasma membrane seperate?
The plasma membrane
separates a living cell from
nonliving surroundings
water is a …. molecule
Water is a polar
molecule therefore Water can participate in
hydrogen bonding
what do Phospholipids spontaneously form?
Phospholipids spontaneously form micelles or
lipid bilayers.
how do micelles or
lipid bilayers form?
form spontaneously and
cluster the hydrophobic regions of the
phospholipid toward the inside and leave the
hydrophilic regions exposed to the water
environment.
what are the basis of biological
membranes.
Lipid bilayers are the basis of biological
membranes.
Lipids associate via ________ interactions
non-covalent
This means that they are free to move around
in the bilayer – the membrane is ________ .
fluid
As temperatures cool, membranes ________
switch from a fluid state to a solid state.
what is The temperature at which a membrane solidifies
The temperature at which a membrane solidifies depends on the types of
lipids.
what consistency must membranes be to work properly?
Membranes must be fluid to work properly, having a consistency similar to
salad oil
what membranes are more fluid than other?
Membranes rich in unsaturated fatty acids are more fluid that those rich in
saturated fatty acids.
Saturated fatty acids =
Saturated fatty acids – less fluid
unsaturated fatty acids =
unsaturated fatty acids – more fluid
Warm temperatures =
Warm temperatures = more fluid
Cold temperatures =
Cold temperatures = less fluid
cold-adapted organisms such as certain fish have …..
greater
proportion of unsaturated fatty acids in their membrane
phospholipids
Most membranes also contain …..
sterols
……. Increase or decrease in fluidity depending on temperature:
sterols - cholesterol
at cold temps sterols - cholesterol …..
at cold temps it reduces packing of phospholipids
maintaining fluidity
At higher temperature cholesterol …..
restrains movement
of phospholipids making the membrane less fluid
where are sterols-cholesterol often found?
Often found on the inner and outer leaflet of animal
membranes
are sterols-cholesterols hydrophobic or philic
Hydrophobic – sits between the fatty acid chains
what do lipid droplets consist of …..
These
lipid droplets contain fats
as well as other
hydrophobic lipids
including modified
cholesterol
Can you see how a structure that is similar to a micelle
can be used to store fat in the cytosol of cells?
Based on the structure of cholesterol can you see an issue with it being stored
in the core?
Do you think cholesterol may need to be modified to be stored in the lipid
droplet?
Major barrier to crossing a
biological membrane:
- Major barrier to crossing a
biological membrane is
the hydrophobic interior
that repels polar
molecules but not
nonpolar molecules - Nonpolar molecules
will move until the
concentration is equal
on both sides - Limited permeability to
small polar molecules - Very limited
permeability to larger
polar molecules and
ions
WHAT IS Passive Diffusion
Movement of molecules across
membrane
* No energy required
* Concentration gradient
Diffusion
* From high concentration to low
concentration
* Continues until concentration
same
* Oxygen
* Nonpolar organic molecules
The Bilayer is more than lipids as …..
Membrane proteins are inserted into the
phospholipid bilayer
Fluid Mosaic Model
what is Facilitated Diffusion?
- Molecules that cannot cross membrane easily may move through proteins
- Move from higher to lower concentration
- Channel proteins: Hydrophilic channel when open
- Carrier proteins: Bind specifically to molecules transported
what are Carrier Proteins and functions?
- Transport both ions and other solutes:
-Some sugars
-Amino acids - Concentration gradient across membrane
- Carrier must bind molecule
- Saturation:
-Rate limited by number of transporters - Specific binding:Carrier shape change
Active Transport Across Membranes involves ….
- Requires energy: ATP used directly or indirectly
-Moves substances: From low to high concentration - Highly selective carrier proteins
-Uniporters: Move one molecule at a time - Symporters: Move two molecules in same direction
- Antiporters: Move two molecules in opposite directions
- Same terms for facilitated diffusion carriers
Na+–K+ Pump cycle
Coupled Transport
Coupled Transport Across Membrane requires….
- Uses ATP indirectly
- Uses energy released when a molecule moves
by diffusion to supply energy to active
transport of a different molecule - Symporter
- Glucose–Na+: Captures energy from Na+ diffusion and Moves glucose against concentration gradient
what is osmosis?
Osmosis is the diffusion of a water
through a semi-permeable membrane
explain water attraction
The slight negative charge
on water attracts positive
charges (Na!).
The slight positive charge on
water attracts negative
charges (Cl”).
what is Osmosis?
- Net diffusion of water
across membrane toward
higher solute
concentration - Against solute
concentration gradient
what is Osmotic Pressure and its purpose? Osmotic Pressure table
- Force needed to stop osmotic flow
- Cells in hypotonic solution (less solute outside) gain water
causing cells to swell – creates pressure - If the membrane is strong enough there is a
counterbalance situation: - Osmotic pressure driving water in
- Hydrostatic pressure driving water out
- If membrane is not strong enough the cells burst of lyse
(the process is called cell lysis): - Animal cells must be in isotonic environments
- Prokaryotes, fungi, plants, protists
- Cell walls stop plasma membrane expanding
- Hydrostatic pressure (turgor pressure) = osmotic pressure
exocytosis diagram
endocytosis diagram
What are phospholipids and
what are their key attributes?
- Phospholipids are a class of lipids whose molecule has a hydrophilic “head” containing a phosphate group and two hydrophobic “tails” derived from fatty acids, joined by an alcohol residue.
What are the driving forces
that maintain a lipid bilayer?
The main driving force for the formation of the lipid bilayer is hydrophobic interactions. The hydrophobic domains of a phospholipid, are trying to question away from the polar hydrophilic water molecules. Therefore lipid bilayers form with the hydrophobic interiors pointing toward each other.
Describe the fluid mosaic model of the plasma membrane. What is
(are) the important concepts this helps us learn about membranes?
The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. Plasma membranes range from 5 to 10 nm in thickness.
A- transmembrane proteins
B- cholesterol
C- hydrophillic phospholipid heads
D- hydrophobic phospholipid heads
How does the tonicity
of a solution affect
diffusion of water
across a selectively
permeable barrier?
The tonicity of a solution refers to its relative concentration of solutes compared to another solution, typically a reference solution like the cytoplasm of a cell. The tonicity of a solution can be classified into three main categories: isotonic, hypotonic, and hypertonic. These tonicity conditions have distinct effects on the diffusion of water across a selectively permeable barrier, such as a cell membrane.
Here’s how each type of tonicity affects the diffusion of water:
Isotonic Solution: An isotonic solution has the same concentration of solutes as the solution on the other side of the selectively permeable barrier. In this case, water molecules move in and out of the cell at roughly equal rates. There is no net movement of water across the membrane, so the cell’s size and shape generally remain stable.
Hypotonic Solution: A hypotonic solution has a lower concentration of solutes compared to the solution on the other side of the barrier. In this situation, there is a higher concentration of water outside the cell compared to inside. Water molecules will move into the cell through the selectively permeable barrier in an attempt to equalize the solute concentrations on both sides. This can lead to the cell swelling or even bursting (lysis) if not regulated by mechanisms like osmoregulation.
Hypertonic Solution: A hypertonic solution has a higher concentration of solutes compared to the solution on the other side of the barrier. This means there is a higher concentration of water inside the cell compared to outside. Water molecules will move out of the cell through the selectively permeable barrier, leading to the cell shrinking and potentially becoming dehydrated or shriveled.
If a blood cell (0.9% NaCl) shrivels when placed in a NaCl
solution, was the concentration of salt of the solution likely to
have been higher or lower than the concentration of salt
(and/or similar polar ions) inside the cell? Explain why the cell shape changed
This external solution is hypertonic compared to the cell’s interior.
The process that leads to the change in cell shape is called osmosis. Osmosis is the diffusion of water across a selectively permeable membrane (like the cell membrane) from an area of lower solute concentration to an area of higher solute concentration. In this case, the hypertonic solution outside the cell has a higher concentration of NaCl (salt) than the isotonic solution inside the cell. As a result, water from inside the cell moves outwards, aiming to dilute the higher salt concentration in the external solution. This loss of water causes the cell to shrink and shrivel, leading to the observed change in cell shape.
To summarize:
The external solution (hypertonic) has a higher concentration of NaCl compared to the internal solution (isotonic) of the cell.
Water moves out of the cell through the cell membrane in an attempt to balance the concentration of salt between the cell and the external solution.
The loss of water from the cell causes it to shrink and change its shape.
This phenomenon highlights the importance of maintaining osmotic balance and the significance of tonicity when dealing with solutions and their effects on cells.
