01- Cell Signaling Flashcards
What is the plasma membrane and what are its functions?
The plasma membrane is a phospholipid bilayer that also contains proteins, lipids (phospholipid and cholesterol) and carbohydrates that are attached to some lipids and proteins.
- It controls traffic into and out of the cell it surrounds.
- It is selectively permeable to allow sufficient passage of oxygen and nutrients and elimination of wastes
How are phospholipids amphipatic molecules?
It has both hydrophilic (head) and hydrophobic (tail) parts
What are the three things that affect the fluidity of the plasma membrane?
Temperature, cholesterol and saturated/unsaturated fatty acids.
When the temperature is low, the straight tails of fatty acids pack tightly together therefore fluidity decreases.
When the temperature is high, the straight tails gain energy and the distance increases therefore fluidity increases.
At low temperatures, cholesterol increases fluidity by increasing the distance between phospholipids.
At high temperatures, cholesterol decreases fluidity by decreasing the distance between phospholipids.
Saturated fatty acids decrease fluidity and unsaturated fatty acids increase fluidity
What determines the fluidity of the plasma membrane?
The structure of the fatty acid tails of the phospholipids
How does cholesterol help the plasma membrane?
It reduces membrane fluidity and helps stabilize the membrane.
What do proteins do in the plasma membrane?
Proteins determine most of the membrane’s specific functions such as transport, enzymatic activity, signal transduction, cell-cell recognition, intracellular joining and attachment to the cytoskeleton and extra cellular matrix (ECM)
There are two types:
- integral proteins: embedded into phospholipids by their hydrophobic region which anchors to the hydrophobic core of phospholipid. Some extend all the way across the membrane and are called transmembrane proteins.
- peripheral proteins: are not embedded in the lipid bilayer. They are found on the outside and inside surfaces if membranes and are attached to integral proteins or phospholipids.
What do carbohydrates do in the plasma membrane?
They sort cell into tissues and organs in the embryo and reject foreign cells by the immune system. They are important in cell-cell recognition
They are usually short branched oligosaccharides that are covalently bonded to proteins.
What do intracellular junctions do in the plasma membrane?
Animal cell walls are perforated with channels called intracellular junctions that allow cells to adhere, interact and communicate.
There are three types:
- tight junctions: keeps liquid from escaping between cells
- desmosomes: pin adjacent cells together
- gap junctions: allow transport of ions, water and other substances
What are the components of the extra cellular matrix of the plasma membrane?
Collagen fibers embedded in network of proteoglycans.
Fibronectin which binds to receptor proteins called integrins which are built into the plasma membrane. The integrins bind to microfilaments on the cytoplasmic side.
Integrins anchor the cell to the extra cellular matrix
What are the two general types of cell signaling?
Direct cell-cell signaling and signaling via secretion
What are the four main forms of signaling by secretion?
- Paracrine: a cell targets a nearby cell
- Endocrine: a cell targets a distant cell through the bloodstream
- Autocrine: a cell targets itself
- Synaptic: nerve cells transmit signals
What are the main forms of direct cell-cell signaling?
- Signaling across gap junctions: a cell targets a cell connected by gap junctions
- Two cells may bind to one another because they carry complementary proteins on their surfaces. When the proteins bind to one another, this interaction changes the shape of one or both proteins transmitting a signal.
What are the two main types of receptors?
- Intracellular receptors: receptor proteins found on the inside of the cell. The ligands (chemical messengers) are usually hydrophobic since they must be able to cross the plasma membrane to reach their receptors. The primary receptors for steroid hormones are intracellular.
- cell-surface receptors: membrane-anchored proteins that bind to ligand on the outside surface of the cell. The ligand does not need to cross the cell therefore hydrophilic molecules may act as ligands.
What are the three common types of cell-surface receptors?
- Ligand-gated ion channels: ion channels that can open or close in response to the binding of a ligand. Changes in ion levels inside the cell can change the activity of other molecules (such as ion-binding enzymes and voltage-sensitive channels) to produce a response. Neurons have ligand-gated channels that are bound by neurotransmitters.
- G protein-coupled receptors (GPCR) : seven-pass transmembrane receptors. when its ligand is not present, a G protein-coupled receptor waits at the plasma membrane in an inactive state. Ligand binding activates the GPCR and causes the G protein to exchange GDP for GTP. The now active G protein separates into two pieces and these subunits can interact with other proteins triggering a signaling pathway that leads to a response. The alpha subunit will eventually hydrolysis GTP back into GDP at which point the G protein becomes inactive.
- enzyme-linked receptors: cell-surface receptors with intracellular domains that are associated with an enzyme. Receptor tyrosine kinases are a class of enzyme-linked receptors found in humans.
What is an example of the same signal producing different effects in different cells?
Acetylcholine causes skeletal muscle cells to contract, heart muscle cells to relax and secretory cells to secrete more.
