Membrane Proteins Flashcards
What describes the structure of the plasma membrane?
Fluid mosaic model
Some integral proteins are…
Transmembrane proteins
What are transmembrane proteins?
Span entire width of the membrane e.g. channels, transporters and many receptors
What is facilitated diffusion?
Passive transport of substances across the membrane through specific transmembrane proteins, used by channel and transporter proteins
what are the proteins involved in transporting substances?
Channel
Transporter
Protein pumps
Function of plasma membrane
Surrounds cells and controls entry and exit of materials
Plasma membrane is composed of…
Phospholipids and proteins
What gives the membrane it’s fluid quality?
Phospholipids are constantly changing position
Structure of phospholipids
Charged, hydrophilic head and uncharged, non-polar, hydrophobic tail
Integral proteins react extensively with…
hydrophobic region of membrane phospholipids
Membrane proteins are either…
Integral (within membrane) or peripheral (on surface of membrane)
How are integral proteins held within the phospholipid bilayer?
Regions of hydrophobic R groups allow strong hydrophobic interactions
Peripheral 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 proteins interact with…
The surface of integral proteins
The phospholipid bilayer is a barrier to…
Ions and most uncharged polar molecules
Small molecules such as oxygen and carbon dioxide can pass through membrane by…
Simple diffusion
What are channel proteins?
Multi-subunit proteins with subunits arranged to form water filled pores that extend across membrane
Most channel proteins in plants and animals are…
Highly selective
Some channel proteins are…
Gated- change conformation to allow/prevent diffusion
What are ligand-gated channels controlled by?
Binding of signal molecules, correct binds>gate opens>allows flow of ions through, have chemical stimulus
What are voltage-gated channels controlled by?
Changes in ion concentration, have electrical stimulus
How do transporter proteins transfer the solute across the membrane?
Bind to specific substance to be transported and undergo conformational change
Transported proteins alternate between… so that…
2 conformations, the binding site for the solute is sequentially exposed on one side of the membrane and then the other
What are pumps that carry out active transport?
Transporter proteins coupled to an energy source
Active transport uses..
Pump proteins that transfer substances across the membrane against their concentration gradient so require a source of metabolic energy
Some active transport proteins…
Hydrolyse ATP directly using ATPases to provide energy for the confrormational change require to move substances across the membrane
What does the electrochemical gradient determine?
Transport of a solute e.g. where and how far it goes
What is the concentration gradient?
Difference in concentration of a solute across the plasma membrane
What is the electrical potential difference?
Created when there is a difference in electrical charge on the 2 sides of a membrane
For a solute carrying a net charge, what combines to form the electrochemical gradient?
Concentration gradient and electrical potential difference
What does the sodium-potassium pump account for?
A high proportion of the basal metabolic rate in many organisms
Sodium-potassium pump actively transports…
3 sodium ions out and 2 potassium ions in cell (per ATP hydrolysed)
Function of ATP hydrolysis in SPP
Establishes and maintains ion gradient
Ion pumps such as the SPP transports ions…
Against a steep concentration gradient using energy directly from ATP hydrolysis
How does the SPP work?
- Pump has high affinity for sodium ions inside cell so binding occurs
- Pump hydrolyses ATP and phosphate attaches (phosphorylation by ATP), conformation of protein changes
- Affinity for sodium ions decreases so released outside cell
- Pump has high affinity for potassium ions outside cell so binding occurs
- Dephosphorylation causes the protein to change conformation
- Potassium ions are taken into cell and affinity returns to start
In intestinal epithelial cells of the small intestine, the SPP generates a…
sodium ion gradient across the plasma membrane, this gradient drives the active transport of glucose
What is the protein that transports glucose called?
Glucose symport
Glucose symport is responsible for…
The active transport of glucose and sodium ions at the same time and in the same direction.
Sodium ions enter the cell down their concentration gradient and the simultaneous transport of…
Glucose pumps glucose into the cell against its concentration gradient
