KA1.3 - Membrane Proteins Flashcards
Unit 1 (47 cards)
What is the cell membrane primarily composed of?
A bilayer of phospholipid molecules with proteins embedded throughout the two layers.
Describe the “head” region of a phospholipid molecule.
Charged region, which is hydrophilic.
Describe the “tail” region of a phospholipid molecule.
Uncharged non-polar region, which is hydrophobic.
How do the hydrophilic and hydrophobic parts of phospholipids arrange themselves in the cell membrane?
Hydrophobic tails are shielded from the inter/extracellular environments, while the hydrophilic heads are exposed to those environments.
Why is the cell membrane described as being a “fluid mosaic”?
Because the phospholipids are constantly changing position, and the proteins are arranged in a patchwork throughout the bilayer.
Define an ‘integral protein’
A protein which is embedded within the phospholipid bilayer
Describe the characteristics of integral membrane proteins.
- Interact extensively with the hydrophobic region of membrane phospholipids.
- Some are transmembrane proteins
- Contain regions of hydrophobic R groups allowing strong hydrophobic interactions that hold them within the phospholipid bilayer.
Define a ‘transmembrane protein’
A integral protein which spans the entirety of a cell membrane
i.e. it is in contact with both the intra and extracellular environment
Define a ‘peripheral protein’
A protein located on the surface of the membrane (either intra/extracellularly)
Describe the characteristics of peripheral membrane proteins.
- Have hydrophilic R groups on their surface.
- Bound to the surface of membranes, mainly by ionic and hydrogen bond interactions.
- Many interact with the surfaces of integral membrane proteins
What types of molecules is the phospholipid bilayer a barrier to?
Ions and most uncharged polar molecules
What small molecules can pass directly through the phospholipid bilayer by simple diffusion?
Oxygen and carbon dioxide
Define facilitated diffusion
The passive transport of substances across the membrane through specific transmembrane proteins.
What is a key characteristic of the majority of transmembrane proteins involved in facilitated diffusion in animal and plant cells
They are highly selective
Describe the structure of channel proteins.
Multi-subunit proteins with subunits arranged to form water-filled pores that extend across the membrane.
Describe what a gated channel is?
Channel proteins that change conformation to allow or prevent diffusion
Describe the types of stimuli that can open or close a gated channel.
They respond to a stimulus that may be chemical (ligand-gated) or electrical (voltage-gated)
How do transporter proteins move solutes across the membrane?
They bind to the specific substance and undergo a conformational change to transfer the solute. They alternate between two conformations, exposing the binding site sequentially on one side of the bilayer, then the other.
Does transport by transporter proteins (in facilitated diffusion) require energy?
No, it is passive and requires no energy.
Define active transport.
Uses pump proteins that transfer substances across the membrane against their concentration gradient.
Both simple and facilitated difussion rely on which concentration gradient?
High concentration to Low concentration
Explain the difference between simple and facilitated diffusion?
- Simple diffusion = uses no proteins
- Facilitated diffusion = uses proteins
What is required for active transport?
A source of metabolic energy is required
Explain how some pump proteins are powered.
Some active transport proteins hydrolyse ATP directly to provide energy. They are known as an ATPase.
