Main Final Exam Content Flashcards
6 Steps of Protein Synthesis
- Rough ER synthesises proteins to be secreted to exterior or to be incorporated into plasma membrane or other cell components
- Smooth ER packages protein into transport vesicle, which bud off and travel to Golgi complex
- Transport vesicle fuses with Golgi complex and empties contents into Golgi sac
- Proteins travel through layers of the Golgi complex
- Secretory vesicles containing finished protein bud off Golgi complex and remain in cytosol to store until signalled
- On appropriate stimulation, secretory vesicles fuse with plasma membrane, open and empty protein into cells exterior for use
Describe Desmosomes (Cell Junctions)
- join two cells together without touching
- bound by glycoprotein filaments attached to thickened cytoplasm
- prevents tearing of the tissue when stretched
- e.g. epidermis cells, cardiac cells
Describe Tight Junctions (Cell Junctions)
- membrane proteins from adjacent cells fuse together
- prevents passage of molecules between adjoining cells
- e.g. nephrons in kidney, intestine cells
Describe Gap Junctions (Cell Junctions)
- tunnels from one cell to another
- transport of ions and small molecules between cells
- e.g. some nervous system cells, cardiac cells
Describe Passive transport and list the 3 different types of passive transport
Passive transport = doesn’t require energy (ATP)
- simple diffusion
- osmosis
- facilitated diffusion (channels & carriers)
Describe Active transport and list the 3 different types of active transport
Active transport = requires energy (ATP)
- primary active transport
- secondary active transport
- vesicular transport (endocytosis & exocytosis)
Describe Diffusion
- movement of molecules from an area of high concentration to an area of low concentration
- molecules diffuse down a concentration gradient in order to reach equilibrium
Describe Osmosis
- diffusion of water across a selectively permeable membrane
- movement of water from an area of low solute concentration to an area of high solute concentration
- osmolarity = number of solute particles per litre of solution
- most body fluids are 300 mOsm/L
Describe Facilitated Diffusion
- down concentration gradient
- does not require ATP
- two types: channel or carrier
Describe Channels (Facilitated Diffusion)
- transport of small ions (Na, K, Ca, Cl) and water (aquaporins)
- can be open or closed
- open to both sides of membrane simultaneously
- allows rapid transport of molecules
Describe Carriers (Facilitated Diffusion)
- transport for larger hydrophilic molecules (glucose and amino acids)
- always open
- only open to one side of membrane
- allows slower movement of molecules
List and describe 5 things that affect Diffusion Rate
- The size of the concentration gradient
- bigger gradient = faster diffusion - Membrane surface area
- bigger surface area = faster diffusion - Size of the molecule
- small molecules diffuse more quickly than large molecules - Diffusion distance
- decreasing diffusion distance = increasing diffusion rate - Lipid solubility of the molecule
- whether the molecule can pass through the lipid part of the membrane
Describe Tonicity
Tonicity = the ability of a solution to change the shape of a cell
Isotonic = solution concentration is equal to ICF concentration = no cell change
Hypertonic = solution concentration is higher than ICF concentration = cell shrivels/shrinks
Hypotonic = solution concentration is lower than ICF concentration = cell bursts/swells
List the 6 Steps of Primary Active Transport: Na/K ATPase
- Binding of cytoplasmic Na to the pump protein stimulates phosphorylation of ATP
- Phosphorylation causes the protein to change its shape
- The shape change expels Na to outside and extracellular K binds
- K binding triggers release of the phosphate group
- Loss of phosphate restores the original conformation of the pump protein
- K is released and Na sites are ready to bind Na again,; the cycle repeats
List the 3 Steps of Secondary Active Transport: Sodium Glucose Transport
- Na/K pump creates ion gradient
- Na - glucose symport transporter loading glucose from ECF
- Na - glucose symport transporter releasing glucose to the cytoplasm
Describe Vesicular Transport
- transfer of materials between ECF and ICF within vesicles
- requires energy from ATP
- endocytosis = vesicular transport into cell
- exocytosis = vesicular transport out of cell
List the 7 Steps of Receptor - Mediated Endocytosis
- Target molecules (ligands) bind to receptors in plasma membrane
- Areas coated with ligands form deep pockets in plasma membrane surface
- Pockets pinch off, forming endosomes known as coated vesicles
- Coated vesicles fuse with primary lysosomes to form secondary lysosomes
- Ligands are removed and absorbed into the cytoplasm
- The lysosomal and endosomal membrane separate
- The endosome fuses with the plasma membrane and the receptors are again available for ligand binding
List the 3 Steps of Pinocytosis (Endocytosis)
- Solute molecules and water molecules are outside the plasma membrane
- Membrane pockets inward, enclosing solute molecules and water molecules
- Pocket pinches off as endocytic vesicle containing sample of ECF
List the 5 Steps of Phagocytosis (Endocytosis)
- Cell engulfs large solid particles (e.g. bacterium)
- The cell extends pseudopods (cytoplasmic extensions) around the object
- The resulting vesicle (phagosome) can fuse with a lysosome containing enzymes
- The enzymes break down the object
- The object is then killed and digested within the vesicles
Describe Exocytosis
- reverse of endocytosis
- secretory vesicles are released from the Golgi complex. They bind to the cell membrane, releasing their contents
Describe Membrane Potential
- difference in electric potential between the interior and the exterior of a biological cell
- separation of opposite charges across the membrane
- the resting membrane potential is negative because the Na/K ATPase pumps 3Na out and 2K in
- resting membrane potential is approximately -70mV in a human neuron
Describe the Effect of Na/K pump on membrane potential
- Na/K pump transports 3Na out for every 2K it transports in
- most of the membrane potential results from the passive diffusion of K and Na down concentration gradients
Describe an Action Potential
- occurs when the membrane potential of a specific cell location rapidly rises and falls: this depolarisation then causes adjacent locations to similarly depolarise
- action potentials assist in the propagation of signals along the axon
List the 5 Steps of an Action Potential
- Voltage gated ion channels closed
- Some Na channels open, Na in
- Many Na channels open, Na in
Depolarisation: decrease in potential; membrane less negative - K channels open, K out, Na inactivated
Repolarisation: return to resting potential after depolarisation - Na/K ATPase restore Na and K concentrations during this time it is more difficult to generate AP.
Hyperpolarisation: increase in potential; membrane more negative