Chapter 2 Flashcards
Cell membranes are held together by …. interactions, about … nm thick
non-covalent, 5 nm
non-covalent = weak, no sharing of electrons
Lipid bilayer = A %, membrane proteins = B%
Lipid bilayer: provides basic fluid structure. impermeable for C molecules
a = 50
b = 50
c = water-soluble
Functions of membrane proteins
- Transport
- Receptor
- Catalysis (e.g. ATP synthesis)
- Structural (link cytoskeleton to extracellular matrix or
other cell) - Cellular recognition
Lipid molecules are amphiphilic = ?
Hydrophobic non-polar end
* Hydrophilic polar end
Lipid bilayer consists of …. (75%), …. (5%) and …… (20%)
phospholipids
glycolipids
cholesterol
What are liposomes?
Phospholipid membranes spontaneously
close to form a sealed compartment:
liposomes.
* It is the energetically most favorable
arrangement.
Phospholipid molecules change places with their neighbors in a
monolayer very rapidly (107 times / s): true/false
true
Are cholesterol molecules amphiphilic?
yes queen they are in the bilayer : heads to heads, tails to tails
glycolipids: where and what do they do
Sugar-containing lipid molecules.
* Constitute 5% of total lipid molecules in the
outer monolayer.
Functions:
* Membrane protection
* Cell-recognition
* In nerve cells: membrane electrical propieties.
cell membrane is symmetric with different phospholipid compositions in each of the bilayer leaflets:true/false
false
Fluidity of a lipid bilayer depends on….. and ….
composition (fatty acid
composition and cholesterol amount)
and temperature
Cholesterol makes the lipid bilayer stronger/weaker but less firm/fluid at normal body
temperature.
stronger, less fluid
According to the fluid mosaic model of the membrane structure, membranes are
two-dimensional fluids in which protein are inserted into lipid bilayers.
okay
Functions of cell membrane?
- Diffusion barrier: regulates entry and exit of substances.
- Vesicle transport (glandular secretions).
- Cell identification: surface proteins allow identifying a cell.
- Communication: proteins act as receptors for hormones.
- Intercellular connections: cells can be in contact or linked by special
complexes.
ECF: has more A and B than intracellular fluid
A) K+
B) proteins
Given enough time, virtually almost any molecule will diffuse across a proteinfree lipid bilayer down its concentration gradient: molecules move from more to
less concentration (downhill). True/false
True, but will take very long
Rate of diffusion across membrane depends on…
- size of molecule
- polarity (more phobic, more easily)
Lipid bilayers are essentially impermeable to
charged molecules (ions).
Passive diffusion: depends on
concentration imbalance
Size molecule
Polarity
Set the following molecules from fast diffusion - no doffusion through membrane
- Large uncharged polar
- small uncharged polar
- ions
- small nonpolar
- small nonpolar
- small uncharged polar
- Large uncharged polar
- ions
Which 3 transport methods across membrane are there? passive or active?
- simple passive diff (passive)
- channels (passive)
- transporters (can be active or passive)
tonicity: ?
Osmolarity of the solution compared to
the plasma osmolarity
what types of tonicity are there?
isotonic: same in & out
hypotonic: solution lower osm
hypertonic: solution higher osm
differences channels and transporters?
channels: strictly passive, weaker interactions. faster transport rate,
transp: active or passive, undergo conformational changes
ion channels are also highly ….. and ….
highly selective
gated (most are close and open in response to stimulus)
recall three types of stimuli for ion gate to open
- voltage
- mechanical stress
- ligand binding (neurotransm, ion, nucleotide)
two gradients control the movement of ions through cell membrane
- conc gradient
- ELECTROCHEMICAL GRADIENT.
Typically, the inner surface of the plasma
membrane is more A charged
and the outer surface is more X
charged.
A negatively
X positively
The combined influence of the concentration gradient and the electrical gradient
on movement of a particular ion is referred to as its x gradient.
electrochemical
ion channels are responsible for the electrical
excitability of x cells
muscle
ion channels mediate most forms of electrical signaling in the x system
nervous
two other words for transporters?
carriers/permeases
true or false: each transporter only binds and translocates a single solute type
true
two steps for a transporter to get a molecule across?
- recognition
- conformational change
Which 3 states does a transporter have?
- outward-open
- occluded
- inward state
which 3 types of active transporters are there?
- uniport (one side to other side)
- symport (simultanious transfer in same direction)
- antiport (simultanious transfer in opposite direction)
endocytosis: passive or active?
active
What two main pathways for endocytosis are there?
- Phagocytosis: Large particles
- Pinocytosis: molecules and water
Phagocytosis:
- requires A through specific membrane receptors (B process)
- It is a(n) passive/active and highly regulated process
A recognition
b selective
- active
Phagocytosis: Once the phagosome is formed,
it will fuse x
* The content will be digested by
…. enzymes.
x lysosomes.
x lysosomal
In mammals phagocytosis occurs in specialized cells, such as…
Functions: defense against
pathogens and cleaning cell
debris.
- macrophages
- monocytes
- neutrophils
- dendritic cells
Pinocytosis:
is a form of endocytosis involving X
* In pinocytosis, the cell repeatedly takes in X from the surrounding environment
using tiny vesicles.
* Pinocytosis occurs in X cell types
X fluids containing small solutes.
X fluid
X many
What subtypes of pinocytosis are there?
- large: macropinocytosis
- small (clathrin, caveolin and clathrin + caveolin dependent)
Macropinocytosis:
- A (requires receptor activation).
- Requires reorganization of the B of the
cytoskeleton. - A protrusion is used like an arm
A Selective
B actin filaments
Clathrin-dependent:
X coat the vesicle to initiate endocytosis
The vesicle with the cargo
is transported into the cell
and fuses with endosomes
and lysosomes.
X process: ligand-receptor
Requires X
X Clathrin protein
X selective
X energy
Caveolin-dependent endocytosis
- Caveolae are small
X - Endocytosis of X and
X - In humans, this process
occurs in cells lining the
small intestine and is used
primarily for absorption. - Require much X and the process is
X invaginations of the cell’s
plasma membrane.
X fluids and solutes
X energy.
X Nonspecific.
In what types of cells is exocytosis especially important?
- secretory cells
- nerve cells
