Module 1: Principles of Cell Function Flashcards
What are the 2 main functions of Phospholipid movement?
- Lateral movement (10^7 times per second)
2. Flip-flop (once per month)
Describe 2 properties of membrane fluidity?
- Unsaturated hydrocarbon tails with kinks = fluid
2. Saturated hydrocarbon tails = viscous
Cholesterol increases fluidity, describe with reference to different temperatures:
- High temperatures stabilises and raises melting point (more viscous)
- Low temperatures prevents stiffening (more fluid)
List the 7 things that Phospholipid bilayers contain:
- Fibres of extracellular matrix (ECM)
- Glycoproteins with carbohydrates attached (surface/peripheral)
- Cholesterol (internal)
- Microfilaments of cytoskeleton (inside)
- Peripheral proteins
- Integral Proteins: (Hydrophilic regions on the outside, hydrophobic regions in the middle, N-terminus on the outside, C-terminus on the inside)
- Glycolipids
Describe the Fluid Mosaic Model
- Mouse cell and human cell combined as hybrid cell
- Mixed surface proteins within an hour due to frequent lateral movement
List the 6 major functions of membrane proteins:
- Transport (active/facilitated)
- Enzymatic activity
- Signal transduction ( receives signalling molecule, performs signal transduction)
- Cell to cell recognition (via glycoproteins/peripheral proteins)
- Intercellular joining
- Attachment to the cytoskeleton and ECM (extracellular matrix)
Describe selective permeability and transport
- lipid bilayers are impermeable to most essential molecules and ions
- only allows some water molecules and small, uncharged molecules
- not permeable to ions, hydrophilic molecules and macromolecules
Describe Passive transport
With time, due to random motion, molecules become equally distributed to eliminate concentration gradients via diffusion
Describe Osmosis
- diffusion of water through a selectively permeable membrane into another aqueous compartment containing solute at a higher concentration
- equalises concentration
Define ‘Osmotica’ and give examples
- things that are osmotically active
e. g. Ions, sugars, proteins
Define tonicity, list the 3 different types of tonicity and the differences in plant and animal cells
- Tonicity is the ability of a solution to cause a cell to gain or lose water
- Isotonic: solute conc. is the same, no net movement
- Hypertonic: solute conc. is GREATER than that inside the cell, cell loses water: cell shrivels
- Hypotonic: solute conc. is LESS than that inside the cell, cell gains water: cell bursts (or lyses)
- Animal cells can lyse (burst) or shrivel
- Plant cells can be turgid, flaccid or plasmolysed
Outline Facilitated Diffusion and list the 3 types of proteins used in this process
- transport proteins facilitate passive movement of molecules across the plasma membrane for specific proteins
Channel proteins: allow a specific molecule or ion to cross the membrane (e.g. Aquaporins - for water, Ion-gated channels)
Transport proteins: allow passage of hydrophilic substances (facilitated or active)
Carrier proteins: bind to molecules and change their shape to shuttle them across the membrane
Outline Active Transport
- against concentration gradient (requires ATP, e.g. sodium-potassium Na+/K- ATPase)
- an electrogenic pump is a transport protein that generates voltage across a membrane (Sodium-potassium pump is a major electrogenic pump of animal cells, proton pump is main electrogenic pump of plants, fungi and bacteria)
Outline Co-transport
- coupled transport by a membrane protein
- when active transport of a solute indirectly drives transport of another solute
- e.g. plants use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell (proton pump pumps H+ out of cell, sucrose-H+ co-transporter transports sucrose into the cell, puling H+ in)
- sodium-potassium pump works with Na+ glucose co-transporter to drive glucose uptake
Describe bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Endocytosis: pinches off cell membrane to transport product from outside
Exocytosis: cell membrane of vesicle fuses with cell membrane to deliver product to outside
Phagocytosis: engulfing particles
Pinocytosis: drinking particles
Receptor-mediated endocytosis: coated vesicles form from receptors receiving signals, which are carried inside vesicle (may be alongside other particles)
Outline local signalling
Paracrine signalling: secreting cells discharge molecules of a local regulator into the extracellular fluid of a target cell
Synaptic signalling: a nerve cell releases neurotransmitter to the post-synaptic neutron, triggering an action potential
Outline long-distance signalling
Hormonal signalling: specialised endocrine cells secrete hormones into body fluids, e.g. blood, that can reach virtually any cell
Describe the 3 stages of cell signalling
- Reception: a receptor protein in the plasma membrane receives a signalling molecule
- Transduction: relay molecules translate the signal in a signal transduction pathway
- Response: a cellular response is activated
Give 2 types of Reception
- Hydrophilic signalling molecule and cell-surface receptor
- Carrier protein: small hydrophobic signalling molecule and intracellular receptor
List 3 types of responses
- Gene activation
- Enzyme stimulation
- To rearrange the cytoskeleton
List and describe the 3 types of Ion Channel Receptors in order of speed
- Ion Channel Receptors: Na+ channel opened by ligand: fast neurotransmitter
- G Protein-Coupled receptors: 7 transmembrane-spanning regions: applies to all aspects of physiology and pharmacology
- Tyrosine Kinase Linked Receptors (e.g. Insulin receptors): metabolism, cell growth, cell reproduction
List and describe the 1 type of Intracellular receptors
- Steroid Receptors (e.g. testosterone): long-distance signalling that can persist in blood stream from hours to months
Outline 3 points of G-Protein Coupled Receptors
- largest family of receptors
- activated by: light, ions, odourants, neurotransmitters, hormones, peptides, proteins, etc.
- interact with G-proteins to control cellular response
Outline the 7 steps of how G-Protein coupled receptors work:
- Signal molecule (adrenaline) binds to G-protein coupled receptor
- It facilitates a G-protein to gain energy from a GTP molecule, converting it to GDP (di instead of tri)
- The G-protein uses this energy to send a signal to adenyl cyclase
- Adenyl cyclase converts ATP into cyclic AMP (cAMP)
- Phosphodiesterase regales the duration of activity of cAMP by converting it to its inactive form, AMP
- One of cAMP’s various activities is that it can activate protein kinase A (PKA)
- PKA can in turn produce cellular responses specific to the signal molecule (adrenaline in this case)
Outline 2 points with regards to Tyrosine kinase linked receptors:
- phosphorylation cascades mediated by enzymes called kinases transfer phosphate and activate or inactivate target proteins
- Phosphorylation results in: conformational change, protein-protein interactions, change in cellular location
Outline 1 point with regards to Insulin receptors (part of Tyrosine kinase linked receptors):
- insulin’s role is to increase glycogen synthesis. One pathway is via PI- 3 kinase
Outline the 7 steps of how Tyrosine kinase linked receptors work (in particular: the inactivation of glycogen synthase kinase 3 to indirectly increase glycogen synthesis):
- Insulin binds to insulin receptor
- Insulin receptor substrate I (IRS1) activates PI- 3 kinase
- PI-3 kinase converts PIP2 to PIP3
- PIP3 indirectly activates protein kinase B via phosphorylation, which can itself perform phosphorylation on a range of target proteins
- One such protein is glycogen synthase kinase 3 (GSK -3), the role of which is to inactive glycogen synthase (GS)
- Phosphorylation inactivates GSK-3, so that it cannot phosphorylates GS and make it inactive
- This is an inhibitory pathway that inhibits another inhibitory pathway. Indirectly, insulin increases glycogen synthesis
Outline 5 points with regards to Steroid hormones:
- Steroid hormones are hydrophobic, and must therefore be transported inside the cell membrane by HORMONE RECEPTOR COMPLEXES
- They require specific carrier proteins in the blood, unlike hydrophilic proteins
- They travel freely in the extracellular fluid and through the plasma membrane
- Within the cytoplasm, they require being carried by hormone receptor complexes
- They are carried to the nucleus where they are received by a receptor and promote the synthesis of a specific protein
