3) a) membrane proteins Flashcards
what is the plasma membrane comprised of?
Membranes are comprised of a bilayer of phospholipid molecules and a patchwork of protein molecules.
Describe the head and the tail of a phospholipid
The head region of a phospholipid molecule is charged and, therefore, hydrophilic (attracted to water).
The tail region is uncharged and non-polar, and, therefore, hydrophobic (repelled by water).
Describe Integral Proteins
Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer.
Integral membrane proteins interact
extensively with the hydrophobic region of membrane phospholipids.
Some integral proteins are ___________ _________, this means that they ______ the _______ _______ of the ____________.
Some integral membrane proteins are transmembrane, this means that they span the entire width of the membrane.
Examples of Integral, transmembrane proteins
Examples of transmembrane proteins include
- channels
- transporters
- (many) receptors.
Describe Peripheral Proteins
Peripheral membrane proteins have
hydrophilic R groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions.
Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.
The phospholipid bilayer is a ________ to ______ and most ____________ ______ molecules.
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules
What can pass through the bilayer by simple diffusion
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion
Define Facilitated Diffusion
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins
Phospholipid bilayer is a ______ to ______ (such as _________________) and most uncharged _______ molecules (such as ________ and _______)
Phospholipid bilayer is a barrier to ions (such as H+, Na+ and amino acids) and most uncharged polar molecules (such as glucose and water)
To ________ _________ __________, different cells have different _________ and ___________ proteins.
To perform specialised functions, different cell types have different channel and transporter proteins
Describe how an ion or polar molecule can pass across the membrane
An ion or polar molecule can pass across the membrane only through a
-specific channel protein
-transporter protein
Define Channel Proteins
Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane.
What is an example of a molecule that cant pass through the hydrophobic regions so must resort to another method of diffusing across the plasma membrane
Water is a polar molecule so it cant pass through the hydrophobic regions of the plasma membrane.
Water can pass across the plasma membrane by diffusing through the phospholipid bilayer or through water channels which are called aquaporins.
Some channel proteins are _______ and ________ ____________ to allow or prevent __________.
Some channel proteins are gated and
change conformation to allow or prevent
diffusion
Gated channels respond to a __________ which causes them to _____ or ______.
Gated channels respond to a stimulus which causes them to open or close.
Ligand gated channels are ___________ by the _________ of ______ molecules.
Voltage gated channels are ____________ by _______ in ion concentration.
Ligand-gated channels are controlled by the binding of signal molecules, and voltage gated channels are controlled by changes in ion concentration
- How does a ligand gated channel work?
- The gate remains closed until a ligand binds to the receptor site.
- When the ligand binds to the receptor site, the gate opens and specific ions flow through the channel and rapidly changes the conformation of that particular ion inside the cell. (This can affect the activity of the cell).
- When the ligand dislocates from the receptor site, the gate closes and ions cant enter the cell anymore.
Hydrophilic/polar R groups mostly found at the _______ of the cell.
Hydrophilic/polar R groups mostly found at the surface of the cell
Transporter proteins bind to the ________ __________ to be ___________ and _________ a ___________ change to transfer the solute across the membrane
Transporter proteins bind to the specific
substance to be transported and undergo a conformational change to transfer the solute across the membrane
Transporters ________ between ____ conformations so that the _________ ______ for a _______ is sequentially ________ on one side of the bilayer, then the other.
Transporters alternate between two
conformations so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other.
Active transport uses ______ proteins that _________ substances across the __________ against their ____________ gradient.
Active transport uses pump proteins that
transfer substances across the membrane against their concentration gradient
Pumps that ______ active transport are ____________ _________ coupled to an _________ __________.
Pumps that mediate active transport are
transporter proteins coupled to an energy source.
A source of __________ _______ is required for active transport.
A source of metabolic energy is required for active transport
