4.Transport Across Cel Membranes Flashcards
What is a plasma membrane
Membrane surrounding cells and their organelles
What is cell surface membrane for
Plasma membrane Forms boundary between environment and cytoplasm-controls movement in and out of cell
What do phospholipids do
Form bilayer
Hydrophilic phosphate heads attracted to and associate with water whereas hydrophobic tails repelled by water and form lipid soluble membrane
What’s the function of lipid soluble membrane
Only allows lipid soluble substance to pass through
Water soluble substance prevented from passing through
Makes me,brand flexible and self selecting
What are the types proteins used in the plasma membranes
Interspersed throughout
Embedded within the phospholipids
Intrinsic-carrier proteins and channel proteins, span across whole bilayer
Extrinsic-only in surface of bilayer, for mechanical support, form glycolipids, act as receptors
How do carrier and channel proteins work
Carrier-ions bind to protein then it changes shape releasing ion or molecule to other side
Channel-Water filled so only water soluble ions diffuse across membrane
What’s the function of membrane proteins
Structural support
Act as channels for transporting water soluble molecules
Active transport
Cell surface receptors for identifying cells
Help cells adhere
Receptors eg hormones
Facts about cholesterol in membranes
Embedded with phospholipid bilayer
Very hydrophobic
Pulls fatty acids tails together limiting their movement
Function of cholesterol in membranes
Reduces lateral movement
Adds strength
Makes membrane less fluid at high temp
Prevents leakage of water
What is a glycolipid
Carb covalently bonded to lipid
Carb extended from bilayer into watery environment
What’s the function of a glycolipid
Act as recognition sites
Helps cells attach to one another and form tissues
Cell surface receptors
What’s the function of glycoproteins
Act as cell surface receptors specifically for hormones and neurotransmitters
Recognition sites
Help cells attach to one another eg lymphocytes recognising self material
Why can’t most molecules freely diffuse across cell surface membrane?
Too large
Not lipid soluble
Get repelled if same charge as channel
If electrically charged have trouble passing through non polar hydrophobic bilayer
Why is the cell surface membrane related to fluid Mosaic model
Fluid-individual phospholipid molecules can move relative to one another, giving membrane a flexible structure that’s constantly moving and changing shape
Mosaic-the proteins that are embedded into the phospholipids bilayer vary in shape, size and pattern in the same way the tiles of a mosaic are
What is diffusion
The met movement of molecules or ions from a region where they are highly concentrated to a region where they are less concentrated until evenly distributed
What is simple diffusion
Passive transport
Movement is due to the kinetic energy that the particles possess
Move randomly
What’s facilitated diffusion
Passive process that requires a channel or carrier protein
What is osmosis
Passage of water from region of high water potential to a region of low water potential through s semi permeable membrane
Facts about water potential
Measured in kilopascals Standard conditions water has w.p of 0 Addition of solutes to pure water lowers its w.p Always -ve value The more solute the more -ve Water moves from less -ve to more -ve
What is a hypertonic solution
Has a lower w.p than the tissue
What’s a hypotonic solution
Higher w.p
What happens when an animal cell is put in it a hypertonic solution
The water moves out of cell into solution and so cell shrinks
What happens when an animal cell is put in a hypotonic solution
The cell undergoes lysis (bursts) as water moves from the solution into the cell
What happens when a plant cell is placed in a hypertonic solution
Cell is plasmolysed as the water leaves the cell and the protoplasm pulls away from the cell wall
What happens when plant cell is put in an isotonic solution (same water potential)
Cell in incipient plasmolysed
What happens when you put a plant celll into a hypotonic solution
Cell swell, protoplast pushes onto cell wall, cell is turgid
What is active transport
Movement of ions or molecules into or out of a cell from region of low conc to region of higher conc using ATP and carrier proteins
What is ATP used fo
Directly move molecules
Individually move molecules using conc gradient that was set up by atp in (direct)
How does direct transport work
Carrier protein span plasma membrane
Ion or molecule binds to receptor site
On inside atp binds to protein, causing it to hydrolyse into adp + pi
As result protein changes shape releasing to other side
Phosphate is released, protein reverts back to orig shape
During respiration phosphate recombined with adp
How to increase rate of movement across membranes
1-epithelial cells lining the ileum possess micro ills finger like projections
2-provide larger surface area for insertion of proteins which allow active, facilitated and simple diffusion
3-increase no of protein carriers/channels
What’s the role of diffusion in absorption
Carbs n glucose continuously digested, higher conc in ileum than blood, facilitated diffusion into blood
Cells use up carbs n glucose so it maintains the conc gradient down
What’s the role of active transport in absorption
Diffusion will result in dynamic equilibrium so not all amino acids/glucose absorbed
Co transport of na+ and glucose/amino acids maintain the conc grad
How does the na+/k+ pump work
- Na+ is actively transported out by the pump, into the blood by carrier proteins in epithelial cells
- maintains higher conc of na+ in ileum than epithelial
- na+ diffuse down grad into epithelial cells through carrier proteins
- na+ is actively transported along with either amino acids or glucose molecule
- pass int blood by facilitated diffusion
