Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
15 Cards in this Set
- Front
- Back
|
Draw and label a diagram to show the structure of membranes |
|
|
|
explain the structure phospholipids |
* Consist of a polar head (hydrophilic) made from glycerol and phosphate
* Consist of two non-polar fatty acid tails (hydrophobic) |
|
|
Outline the arrangement of a membrane |
* Phospholipids spontaneously arrange in a bilayer
* Hydrophobic tail regions face inwards and are shielded from the surrounding polar fluid while the two hydrophilic head regions associate with the cytosolic and extracellular environments respectively |
|
|
Explain the structural properties of phospholipid bilayer |
* Phospholipids are held together in a bilayer by hydrophobic interactions (weak associations)
* Hydrophilic / hydrophobic layers restrict entry and exit of substances * Phospholipids allow for membrane fluidity / flexibility (important for functionality) * Phospholipids with short or unsaturated fatty acids are more fluid * Phospholipids can move horizontally or occasionally laterally to increase fluidity * Fluidity allows for the breaking / remaking of membranes (exocytosis / endocytosis) |
|
|
List the functions of membrane proteins |
Transport: Protein channels (facilitated) and protein pumps (active) Receptors: Peptide-based hormones (insulin, glucagon, etc.) Anchorage: Cytoskeleton attachments and extracellular matrix Cell recognition: MHC proteins and antigens Intercellular joinings: Tight junctions and plasmodesmata Enzymatic activity: Metabolic pathways (e.g. electron transport chain) |
|
|
Define diffusion |
Diffusion: The net movement of particles from a region of high concentration to a region of low concentration (along the gradient) until equilibrium |
|
|
Define osmosis |
Osmosis: The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached |
|
|
name the two types of passive transport |
*simple diffusion *facilitated diffusion |
|
|
name the two underlying concepts that enable passive diffusion to work |
* The plasma membrane is semi-permeable and selective in what can cross
* Substances that move along the concentration gradient (high to low) undergo passive transport and do not require the expenditure of energy (ATP) |
|
|
Explain passive transport across the membrane in terms of simple diffusion |
Simple diffusion: * Small, non-polar (lipophilic) molecules can freely diffuse across the membrane |
|
|
Explain passive transport across the membrane in terms of facilitated diffusion |
Facilitated diffusion: * Larger, polar substances (ions, macromolecules) cannot freely diffuse and require the assistance of transport proteins (carrier proteins and channel proteins) to facilitate their movement (facilitated diffusion) |
|
|
Explain the role of protein pumps and ATP in active transport across membranes |
* Active transport is the passage of materials against a concentration gradient (from low to high)
* This process requires the use of protein pumps which use the energy from ATP to translocate the molecules against the gradient * The hydrolysis of ATP causes a conformational change in the protein pump resulting in the forced movement of the substance * Protein pumps are specific for a given molecule, allowing for movement to be regulated (e.g. to maintain chemical or electrical gradients) * An example of an active transport mechanism is the Na+/K+ pump which is involved in the generation of nerve impulses
|
|
|
Explain how vesicles are used to transport materials within a cell between the endoplasmic reticulum, Golgi apparatus and plasma membrane |
* Polypeptides destined for secretion contain an initial target sequence (a signal recognition peptide) which directs the ribosome to the endoplasmic reticulum
* The polypeptide continues to be synthesised by the ribosome into the lumen of the ER, where the signal sequence is removed from the nascent chain * The polypeptide within the rough ER is transferred to the golgi apparatus via a vesicle, which forms from the budding of the membrane * The polypeptide moves via vesicles from the cis face of the golgi to the trans face and may be modified along the way (e.g. glycosylated, truncated, etc.) * The polypeptide is finally transferred via a vesicle to the plasma membrane, whereby it is either immediately released (constitutive secretion) or stored for a delayed release in response to some cellular signal (regulatory secretion = for a more concentrated and more sustained effect) --- For diagrams check bioninja 2.4.7 |
|
|
Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis |
Endocytosis * The process by which large substances (or bulk amounts of smaller substances) enter the cell without travelling across the plasma membrane* An invagination of the membrane forms a flask-like depression which envelopes the material; the invagination is then sealed off forming a vesicle * There are two main types of endocytosis: * The process by which solid substances (e.g. food particles, foreign pathogens) are ingested (usually to be transported to the lysosome for break down) * The process by which liquids / solutions (e.g. dissolved substances) are ingested by the cell (allows quick entry for large amounts of substance) |
|
|
Describe how the fluidity of the membrane allows it to change shape, break and reform during exocytosis |
Exocytosis * The process by which large substances exit the cell without travelling across the plasma membrane* Vesicles (usually derived from the golgi) fuse with the plasma membrane expelling their contents into the extracellular environment |
