Unit 3. Cell Membrane Flashcards
T or F
All cells have a cell
membrane.
T
2 functions of cell membrane
a. Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis.
b. Provides protection and
support for the cell
Cell membrane contains almost
proteins called
Membrane proteins
It is a double layer of
phospholipids
lipid bilayer
T or F
Cell membranes have pores (holes) in it.
T
Lipid Bilayer contains: (3)
a. Phosphate head is polar
• (water loving)
b. Fatty acid tails are non-polar
• (water fearing)
c. Proteins embedded in
membrane
The property of cell membrane to allow some molecules in
and keeps other molecules out.
Selective permeability
In 1972, they proposed that the
membrane is a mosaic of proteins dispersed within the
bilayer, with only the hydrophilic regions exposed to
water. (Who at what model is it?)
Seymour Jonathan Singer and Garth L. Nicolson
Fluid Mosaic Model
T or F
A molecule always flip-flop
transversely across the membrane
F
always —> rarely
T or F
Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions
T
- proteins that penetrate the hydrophobic core
- 70% of Cell membrane proteins part
and parcel of membrane structure
Integral proteins
proteins that are bound to the surface of
the membrane
Peripheral proteins
They transfer substances against Concentration/Electrical gradients
Pumps
Opened and closed by gates
Channel proteins
Involved in transport of substances
Carrier Proteins
Takes place in membrane reaction
Enzyme proteins
They bear appropriate sites for
recognition of Specific Ligands.
Receptor proteins
Which statement/s is/are true about the role of membrane carbohydrates
in cell-cell recognition?
A. Cells recognize each other by binding to surface
molecules, often containing carbohydrates, on
the extracellular surface of the plasma
membrane.
B. Membrane carbohydrates may be covalently
bonded to lipids (forming glycolipids) or more
commonly to proteins (forming glycoproteins)
C. Both statements are true.
D. None
C
Receptor and co-receptor where HIV binds.
CD4
CCR5
T or F
HIV cannot infect a cell lacking CCR5 on its surface
T
Which statement/s is/are true?
A. Hydrophobic (nonpolar) molecules, such
as hydrocarbons, cannot be dissolved in the lipid bilayer, thus, cannot pass through the membrane
• Polar molecules, such as sugars, can cross the membrane easily
C. Both statements are true.
D. None
D
- non polar can dissolve and pass through rapidly
- polar molecules cannot cross easily
allow passage of hydrophilic substances across the membrane
Transport proteins
have a hydrophilic channel that
certain molecules or ions can use as a tunnel
Channel proteins
Channel proteins that facilitate
the passage of water
aquaporins
bind to molecules and change
shape to shuttle them across the membrane
Carrier proteins
T or F
A transport protein is specific for the
substance it moves.
T
Example of Active Transport Mechanism
Primary Transport
Secondary Transport
Example of Passive Transport Mechanisms
Simple Diffusion
Facilitated Diffusion
Osmosis
Bulk flow filtration
is the tendency for molecules to
spread out evenly into the available space.
Diffusion
Substances diffuse down their __________, the region along which the density of a
chemical substance increases or decreases.
concentration gradient
T or F
No work must be done to move substances down
the concentration gradient.
T
T or F
The diffusion of a substance across a biological membrane is active transport because energy is expended by the cell to make it happen
F
- PASSIVE transport
- NO energy is expended
Factors that Influence
Diffusion Rates (5)
• Distance
• Molecular Size
• Temperature
• Steepness of Concentration Gradient
• Membrane of Surface Area
Lipophilic substances can enter cells easily because they diffuse through the lipid portion of the membrane
Simple Diffusion
■ Membrane channels are transmembrane proteins
■ Used by ions, very small water-soluble compounds
■ Much more complex than simple diffusion.
Channel-Mediated Diffusion
is the diffusion of water across a
selectively permeable membrane
Osmosis
is the ability of a surrounding solution to cause a cell to gain or lose water
Tonicity
Solute concentration is the same as
that inside the cell; no net water movement across the plasma membrane
Isotonic
Solute concentration is greater
than that inside the cell; cell loses water
Hypertonic
Solute concentration is less than
that inside the cell; cell gains water
Hypotonic
A plant cell in a hypotonic solution swells
until the wall opposes uptake; the cell is now _________
turgid (firm)
If a plant cell and its surroundings are isotonic, there is no net movement of water
into the cell; the cell becomes __________, and the plant may wilt
flaccid
(limp)
In a hypertonic environment, plant cells
lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called
plasmolysis
In _______ diffusion, transport
proteins speed the passive movement of molecules across the plasma membrane.
Facilitated
moves substances
against their concentration gradients and allows cells to maintain
concentration gradients that differ from
their surroundings
Active transport
T or F
The sodium-potassium pump is one type
of passive transport system.
F
passive —-> active
is the voltage
difference across a membrane
Membrane potential
Two combined forces, collectively called
the ___________, drive the
diffusion of ions across a membrane
electrochemical gradient
is a transport protein that
generates voltage across a membrane
electrogenic pump
The main electrogenic pump of plants, fungi, and bacteria is a
proton pump
occurs
when active transport
of a solute indirectly
drives transport of
other solutes.
Cotransport
Which statement is INCORRECT about the bulk transport across the plasma membrane that occurs by exocytosis and endocytosis?
A. Small molecules and water enter or leave
the cell through the lipid bilayer or via transport proteins
B. Large molecules, such as polysaccharides
and proteins, cross the membrane in bulk via vesicles
C. Bulk transport requires energy
D. None
D
transport vesicles migrate
to the membrane, fuse with it, and release
their contents
which many secretory cells used to export their products
Exocytosis
the cell takes in macromolecules by forming vesicles from the plasma membrane
Endocytosis
Three types of endocytosis
– Phagocytosis (“cellular eating”)
– Pinocytosis (“cellular drinking”)
– Receptor-mediated endocytosis
