1.3 Flashcards
Describe the structure of the phospholipid bilayer of the plasma membrane
The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer.
The fatty acid tails of phospholipids are exposed to the interior of the membrane and the phosphate heads are exposed to the exterior aqueous side.
What hold integral membrane proteins in the phospholipid bilayer
Regions of hydrophobic R groups allow strong, hydrophobic interactions that holds integral membrane proteins within the phospholipid bilayer.
The integral membrane proteins interact extensively with the hydrophobic region of membrane phospholipids.
Link between integral and transmembrane proteins
Some integral membrane proteins are transmembrane proteins
Describe peripheral membrane proteins
Peripheral membrane proteins have hydrophilic R groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bonds interactions
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What do many peripheral membrane proteins interact with?
Many peripheral membrane proteins interact with the surfaces of integral membrane proteins
Functions of peripheral membrane proteins
Peripheral/extrinsic proteins have fewer hydrophobic R-groups interacting with the phospholipids and are responsible for cell-cell interactions
What does the phospholipid bilayer act as?
The phospholipid bilayer acts as a barrier to ions, and most uncharged polar structures.
What transports large, charged and hydrophilic molecules across the cell membranes?
Transmembrane proteins - This process is called facilitated diffusion
What can transmembrane proteins act as
Transmembrane proteins can act as channels or transporters
How do you small molecules such as oxygen and carbon dioxide passed through the phospholipid bilayer
Diffusion
Describe, facilitated diffusion
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins
What do different cells have to perform specialised functions
To perform, specialised functions, different cell types have different channel and transporter proteins
Describe channels
Most channel proteins in animal and plant cells are highly selective.
Channels are multi-subunit proteins with the subunits arranged to form water filled pores that extend across the membrane
Describe how transport occurs across channels
Transport across the channels is always passive and specific to one type of ion or molecule (facilitated diffusion). Solute passage can be gated or ungated.
Describe Passage through an ungated channel protein
Passage through an ungated channel protein does not require a change to the conformation of the protein.
Movement of molecules as passive, and is specific to the ions or molecules that are being allowed to pass across.
Describe passage through a gated protein channel
Gated protein channels, change confirmation to allow or prevent diffusion.
Gated channels respond to a stimulus which causes them to open or close. The stimulus may be chemical (ligand gated) or electrical (voltage gated).
Describe how ligand gated channels and voltage gated channels are controlled
Ligand gated channels are controlled by the binding of signal molecules, and voltage gated channels are controlled by changes in ion concentration
Describe how transporter proteins work
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.
Transporters alternate between two confirmations, so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other.
What are the types of transport?
Facilitated diffusion or active
What does the conformational change an active transport require?
Energy from the hydrolysis of ATP by ATPases
Describe how active transport works
Active transport uses pump proteins that transfer substances across the membrane against a concentration gradient.
Explain pumps involved in active transport
Pumps that mediate active transport transport of protein coupled to an energy source
What is required for active transport?
A source of metabolic energy is required for active transport
How is an electrochemical gradient formed
For a solute carrying a net charge, the concentration gradient and the electrical potential difference combine to form the electrochemical gradient that determines the transport of the solute.
