Topics 3,4,5 - Movement into Cells Flashcards
Learning Objectives
1.Explain how cell membranes create compartmentisation which regulate the flow of substances in and out of the cell
2.Descibe the passive diffusion of water across semi-permiable membranes and the role of aquaporins.
3.Describe how the cell uses the Na-K ATPase to create elecrochemical gradients
4.Explain how larger molecules and particles get in and out of cells
5.Descibe the endocrine system and hormones
6.Explain how hormones allow distant cells to communicate
7.Explain the roles of messengers and receptors in cell communication
8.Describe the difference between lipid-soluble and water soluble hormones
9.Explain the basic mechanism of steroid hormone responses
10.Explain the differences between first and second messengers, with cAMP as an example
11.Explain negative and positive feedback loops w/ examples
12.Describe an example of homeostasis
13.Describe how sensors and feedback systems operate to maintain homeostasis in negative feedback loops
14.Explain the basis of how the body regulates extracellular fluid osmolarity
15.Explain how oxytocin and ADH work
Cells
Surrounded by semi-permiable plasma membranes
- Made up of a phospholipid bilayer
- Hydpophilic Phospahte Head
- Phydrophobic lipid tail
Impermiable to most essential molecules and ions
Movement of molecules
Diffusion:
- Molecules become equally distributed with random movement
Osmosis:
- Bulk flow of water through a semi-permiable membrane into another aqueous compartment containing solute at a higher concentration
- Water “wants” to be at equilibrium
Tonicity
Osmotic pressure gradient
Isotonic
External solution that has the same solute concentration compared to the body of fluid
Hypertonic
External solution that has a high solute concentration and low H2O concentration (Gains water)
Hypotonic
External solution has a lower concentration of solute and higher H2O (loses water)
Ion Transport
Potassium pump channels in the cell membrane open w/ help of proteins allowing for K+ and Na+ ions to pass through
Intergral Membrane Proteins
Types and their functiosn
Allow for larger molecules/ particles to get in and out of the cell
Channel:
- Facilitated diffusion, allowing ions to flow down concentration gradient (no ATP required)
Transporters:
- Facilitated diffusion OR Active Transport
- Active Transport requires ATP
Aquaporins
Special water channels to allow for large amounts of water into the cell
- Kidney and gut to allow maximal function capacity
Active Vs Passive transport
Active:
- Movement against concentration gradient using ATP
Passive:
- Movement down concentration gradient via Simple diffusion or Facilitated diffusion (no ATP)
Ion Channels
Conduct charges by creating an electrochemical gradient
A membrane potential is formed when one side of the membrane has a different charge to the other.
Sodium Potassium Pump
(Na-K ATPase)
SOPI
- 3 Na+ ions bind to intracellular sites on the pump
- A phosphate group is transferred to the pump via hydrolysis of ATP
- The pump undergoes a conformational change, translocating the 3 Na+ across the membrane out of the cell
- two K+ binding sites on the extracellular surface of the pump are then opened, 2 K+ ions bind to the sites
- The phosphate group is released, causing the pump to return to its original shape
- This translocates the potassium across the membrane into the cell
Consequences of Na-K ATPase action
A membrane potential is created though 2K+ entering and 3Na+ leaving the cell, creating a negative charge.
Na-K ATPase contribute to Nerve action potentials by building a negative membrane potential threshold.
Facilitated diffusion
Transporters allow for larger molecules that are unable to freely cross the bilayer, to get into the cell
- Channel and Carrier
Carrier proteins
Integral glycoprotein that regulates the momevement of nutrients accross the membrane down concentration gradient
- Undergo conformational change to allow solute accross the membrane
- Slower rate of transportation
Channel Proteins
Integral glycoproteins containing a pore via which ions may freely pass across the membrane
- Ion selective and may be gated to regulate flow
- Moves along/ down concentration gradient
- Fast rate of transportation
Endocytosis
Cell ‘engulfing’ small bulks of substances without it passing through the membrane
- Pinocytes and Phagocytes
Pinocytosis = solid substances
Phagocytosis = liquid substances
Exocytosis
Large substances OR bulk transport of substances exit the cell without passing through the membrane
- Vessicles from golgi complex fuse w/ plasma membrane to expell its contents
- Replaces lost portions of the membrane that are used in endocytosis, maintaining its membrane size
Homeostasis
Organism or cells maintaining their internal environment w/ tolerance limits
- Governed by negative feedback loops
Feedback loops
Negative:
- A response is detected by a receptor, an effetcor is then activated to induce a reversed change to the response that is detected
- Eg. Thermoregulation, Blood sugar, Osmoregulation
Positive:
- A response is detected by a recepter, an effector is then activated and amplifies the initial stimili to move further away from its starting point.
- Eg. Contractions during child birth, Blood clotting, Milk Secretion
Endocrine system
A slower chemical based messenging system to help maintain homeostasis
- A system of ductless glands/ organs that release chimicals (hormones) into the blood stream to regulate body functions
- Has a more prolongued response compared to nervous system
Hormones
Chemical messenger transported via blood stream to act on distant or neighbouring target cells
- Hormones are specific and only activate cells/ tissues that have the appropriate taget receptor
