Cell communication Flashcards
Ch. 7, 11
What is selective permeability
Some substances can cross a barrier while others cannot
What deos amphipathic mean
A substance with both a hydrophobic and a hydrophillic region
What is the fluid mosaic model
The membrane is a mosaic where the phospholipids are the liquid and the embedded proteins are the mosaic pieces
What type of bonds hold together the phospholipid bilayer
Hydrophobic interactions
Weaker than covalent bonds
What are two ways in which we can increase membrane fluidity
- Increase temperature
- Increase amount of unsaturated fatty acids
How does cholesterol act in plasma membranes
Cholesterol acts as a fluidity buffer as it hinders the close packing of fatty acids in the membrane
Why must a membrane be fluid to work properly
The fluidity affects the permeability and ability of membrane proteins to move
What are integral proteins
Proteins that penetrate the membrane and have hydrophobic regions that are found inside the membrane
Some span the entire membrane while others do not
What are transmembrane proteins
Integral proteins that protrude on both sides of the plasma membrane
What are peripheral proteins
Proteins that are loosely bound to membrane surface and are often bound to integral proteins
What are the 6 functions of membrane proteins
The red elephant crossed an island
- Transport
- Receptors
- Enzymes
- Cell-cell recognition
- Intercellular joining
- Attachment to cytoskeleton
Explain how membrane proteins function as transport proteins
Proteins may provide selective passage through hydrophilic channels,or else shuttle through shape-changing proteins
Explain how membrane proteins function as enzymes
Enzymes with active sites exposed to a substance may carry out steps of metabolic pathways
Explain how membrane proteins function in a signal transduction pathways
Receptor proteins may have binding site with specific chemical messangers. These may cause proteins to change shape, relaying message inside the cell
Explain how membrane proteins function in cell-to-cell recognition
Glycoproteins may serve as ID tags to be specifically recognized by proteins of other cells
Explain how membrane proteins function through intercellular joining
Proteins of adjacent cells may hook together (gap/tight junctions)
Explain how membrane proteins function in cytoskeleton attachement
They help mainain shape / stabilize location of other proteins (eg fibronectins). They coordinate intra/extracellular changes
What kind of molecules can pass through the lipid membranes easily
Small and hydrophobic
Hydrophillic / polar molecules canNOT pass
What are channel proteins
Hydrophillic channels that certain molecules or ions use as a tunnel through the membrane
What is an aquaporin
A channel protein that facilitates H2O movement through membrane
What are carrier proteins
A protein that holds substances and change shape to shuttle substances across membrane
True or false:
Transport proteins are specific to the substances they shuttle
True
What is diffusion
The movement of particles* of any substance so that they spread out randomly into available space
This does not require energy and is therefore a passive transport
- This is because of thermal energy of individual molecules
What is a concentration gradient
The region along which the density of a chemical substance increases / decreases
What is osmosis
The diffusion of free H2O across a selectively permeable membrane
What does isotonic mean
Balanced H2O molecule concentration on either side of a plasma membrane
H2O may move across membrane but with no net movement
What does hypertonic mean
The solution in a cell has a high solute concentration and therefore a low H2O concentration
H2O will move to a hypertonic region
What does hypotonic mean
The solution in a cell has a low solute concentration and a high H2O concentration
H2O will leave the hypotonic region
What is osmoregulation
The regulation of H2O : solute concentrations
What does turgid mean
The healthy state for most plants → The plant cell wall is hypotonic and therefore the inside of the cell has an excess amount of water and exerts a pressure against the cell to maintain pressure
What does flaccid mean
Plant is limp; wilted → Isotonic surroundings and no net flow of water
What is plasmolysis
The plant cell dies → The cell is in a hypertonic solution and the cell membrane pulls away from the cell wall
What does lysed mean in animal cells
The cell surroundings are hypotonic, meaning water will enter the cell, leading to a burst
What does shrivelled mean in terms of animal cells
The cell is placed in a hypertonic solution and water leaves the cell, leading to the shrivelling of the cell
What is facillitated diffusion
Passive transport through membrane proteins of polar (hydrophillic) molecules and ions
What is an ion channel
Channel protein that transports ions
What are gated channels
Channel proteins that open and close in response to stimuli
What is active transport
Transport of a substrate against a concentration gradient and requires energy
What reaction supplies most of the energy required in active transport
ATP hydrolysis
The cytoplasmic side of the plasma membrane has what kind of charge and from where does this charge come
The cytoplasmic side has a negative charge that comes from an imbalanec in cations and anion concentrations
What is the voltage potential
The voltage across a membrane
What is an electrical chemical gradient
As cations and anions move towards their oppositely attracted regions they create an electrical gradient
What is an electrogenic pump
A transport protein that generates voltage across the membrane
What is a proton pump
A transport protein that moves H+ out of the cell
What is cotransportation
The coupling of “downhill” diffusion of one substance with the “uphill” transport of another against a concentration gradient
What is exocytosis
The fusion of vesicles to plasma membrane where inside substances leave the cell
Ex. cells in pancreas secreting insulin
What is endocytosis
The uptake of substances into a cell by forming vesicles from the plasma membrane
What are the three types of endocytosis
- Phagocytosis - cell engulfs food particles
- Pinocytosis - cell engulfs liquids
- Receptor mediated - substance binds to receptors and cell engulfs substance upon recognition
BULK TRANSPORT
What is endocrine signaling
Long-distance cell signaling in an organism
What is paracrine signaling
Local cell signaling in an organism
What is a growth factor
A local signal molecule in organisms that stimulate cell growth and division
What is synaptic signaling
An electrical signal that passes through neural cells in organisms
What are hormones
Plant and animal cell signaling molecules
What is a ligand
A signaling molecule that specifically binds to a receptor molecule which causes a cascade of reactions in a cell
GPCRs are what type of protein
Cell-surface, transmembrane protein that works with GTP
Describe how a GPCR works when bound by a ligand
- When a ligand binds to the G protein-coupled receptor, causing activation and shape change, the affinity for G-proteins increases and
- they come together and GTP replaces GDP.
- The now-active G protein dissociates and binds to an enzyme, leading to further cell responses
Describe how a RTK works when bound by a ligand
- The binding of a ligand causes dimerization in a receptor-tyrosine kinase, forming a dimer complex
- This activates tyrosine kinase regions as each region gains a phosphate group from ATP
- The fully active RTK is now recognized by other relay proteins which will lead to a cell response
Explain how an ion-channel gated receptor works when bound by a ligand
- When a ligand binds to the channel, this causes a shape change to “open”, allowing certain ions to flow through, leading to a cell response
A ligand must be one of two things to cross the hydrophobic barrier:
- Hydrophobic enough
- Small enough
What are the three ligand molecules that are small enough and hydrophobic enough to cross the bilayer
- Steroid hormones
- Thyroid problems
- NO (nitric oxide)
What is a protein kinase
An enzyme that transfers phosphate from ATP to proteins (typically a serine or threonine kinase)
What is a phosphorylation cascade
A series of proteins in a path are phosphorylated in turn, with each protein adding a phosphate group to the next in line
What is a protein phosphatase
An enzyme that removes phosphate from proteins (dephosphorylation) and deactivates the protein
What is a second messanger
A small, non-protein, aqueous molecule involved in a signal transduction pathway (eg. cAMP, Ca2+)
Explain how cAMP can act as a second messanger in an STP
The enzyme adenylyl cyclase embedded in the plasma membrane can covert ATP into cAMP. cAMP is broadcasted into the cytoplasm, sending signals from outside the cell (eg. from a ligand)
Explain how IP3 and DAG are involved in the release of Ca2+ in the cell
A ligand signal travels to a phospholipase that cleaves an IP3 from the plasma membrane (initially IPI2) which diffuses and reaches the smooth ER and acts as a signal molecule for an IP3 gated Ca2+ channel, releasing Ca2+ into the cytoplasme
Name four ways in which signal transduction pathway responses can be regulated
- Amplification → Multiple proceeding enzymes may be catalyzed at once
- Control points → Different cells have different proteins are thus respond differently to stimuli
- Scaffolding proteins → Large relay proteins may bind several relay proteins all together
- Signal termination → Proteins can change from active to inactive form
What is apoptosis
Controlled cell suicide
What is a death signal
A signal that comes from inside or outside the cell that signals for the cell to self destruct → activation of nuclease and capase
