Membrane Structure and Transport

Question 1

semi-permeable membrane

Answer 1

• allows certain things in and out

- Used to organize internal organelles and spaces

Question 2

railroad tracks

Answer 2

• how the membrane looks
• intercellular space in between
• phospholipid heads facing in and out, tails face in

Question 3

3 most common lipids in membranes

Answer 3

1. Phosphatidylethanolamine (PE)- biggest (fatty acids, glycerol)
2. Phosphatidylcholine (PC)
3. Phosphatidylserine (PS)

Question 4

Galactocerebroside (glycolipic)

Answer 4

• found in membrane of brain
• 2 fatty acid tails, head
  Ga1 attached

Question 5

cholesterol

Answer 5

• steroid arrangement of rings, OH at one end (ampipathic), fit into phospholipid bilaryers and arrange so OH sticks out to fact water side, and embedded in bilayer

Question 6

distribution of membrane lipids

Answer 6

• nonrandom
• asymmetric distribution
  (ex. brain has unique distribution, different from other tissues)

Question 7

Glycolipids

Answer 7

• sugars attached to nonpolar tails of fatty acids
• sugar is always facing out–> types of sugars facing out represents signal for the types of cell it is
• arrangement and types of sugars–> give information important for cell communication
  ex. liver cell near other liver cells can detect that, might act differently next to a non-liver cell

Question 8

fluidity

Answer 8

• types of lipid affects fluidity
• phospholipid can move around in membrane
  1. unsaturated- more fluid b/c not tightly packed
  2. cholesterol- the more cholesterol, the more fluid, but if too much then becomes gooey (less fluid- NOT a linear relationship)
  3. length of fatty acid tails- longer tend to stick together and are less fluid

Question 9

protein fluidity (human and mouse cells)

Answer 9

put marker on mouse and humans antibodies and fuse cells together–> after 40 min, proteins from both mice and humans are mixed

Question 10

fluid mosaic model

Answer 10

• complex relationship- proteins embedded in the membrane, some in the inner leaf some in just outer leaf
• supported by freeze fracture- showed that proteins were embedded in membrane
  4 layers- inner spectrin cortex, phospholipids, proteins, sugars (face out)
  **just AS MANY proteins as phospholipids

Question 11

integral proteins

Answer 11

• when proteins go through bilayer

- usually an alpha helix

Question 12

peripheral proteins

Answer 12

• just associated with inner and outer membrane

Question 13

linker (channel)

Answer 13

• hooked up to something inside and outside (ex. integrin/spectrin when attached, structures cannot move freely)

Question 14

receptors

Answer 14

• integral protein that goes through bilayer and has a binding site that faces out
• has a signal tool for ligands to bind to
• ligand not brought in, but sends message to cell
• ex. growth hormone

Question 15

enzyme

Answer 15

• recognizes ligand, changes shape, converts something into something else
• ex. phosphorylation- often will put a phosphate on X which becomes Y

Question 16

transmembrane

Answer 16

• alpha helices sometimes arrange in a way to create a pore
• beta barrel- sometimes sheets in opening
• have hydrophobic regions (alpha helix)
  hydrophilic parts (R groups) anchor protein to membrane

Question 17

aqueous pores

Answer 17

• some transmembrane proteins create pores–> that allow water to flow though
• side chains (R groups) face into pore
• nonpolar (hydrophobic) parts face out

Question 18

cortex

Answer 18

• area beneath the outside surface of a cell or organ

Question 19

spectrin

Answer 19

• Network of protein molecules inside of the cell to help support the plasma membrane
• also attachment proteins

Question 20

glycocalyx

Answer 20

• (sugar halo) acts as a distinctive covering of the cell and is composed of oligosaccharides linked to membrane components
• important for cells during recognition of neighbors

Question 21

Not all proteins can move freely

Answer 21

1. spectrin- in cortex w/ transmembranes anchored
2. proteins attached to extracellular matrix
3. junction proteins holding one cell to another
4. polarized cell (epithelial cell with 2 jobs)- proteins on top can’t get to bottom and vv

Question 22

selective permeability

Answer 22

• transport across membrane is selective
• small hydrophobic, or nonpolar uncharged molecules get through
• larger ones get through w/ channels

Question 23

aquaporin

Answer 23

• H2O channel
• important in tissues that move a lot of water (kidneys)
• also glycerol and ethanol (drinking- alcohol reached stomach)

Question 24

facilitated diffusion

Answer 24

• passive transport
• specific protein acts as a carrier or channel to facilitate movement across the membrane
• no energy requirement
• specific recognition
• saturable–> each protein has a finite capacity (rate) that it can allow things to pass
• direction- only works w/ concentration gradient
  1. carrier transport
  2. channel protein

Question 25

saturation in facilitated diffusion

Answer 25

• curve shows a plateau
• Transport by specific proteins demonstrates “saturation” because each protein molecule has a finite capacity (rate) at which it can allow molecules to pass

Question 26

Ion concentrations inside/outside cell

Answer 26

• Na+ 10X more concentrated outside cell
• K+ much higher inside
• Ca2+ more outside
• -> difference represent potential energy

Question 27

Fixed anions

Answer 27

• usually organic molecules- proteins that are generally negative charge

Question 28

Active Transport

Answer 28

• requires energy
• against concentration gradient
• saturable and specific
  1. coupled transporter
  2. ATP-driven pump
  3. light-driven (bacteria)

Question 29

ATP driven pump

Answer 29

• ATP binds to substance–> causes to change shape

- Pump for moving H+ into lysosomes

Question 30

coupled transporter

Answer 30

• allows things to bind that DO follow the concentration gradient, and another substance AGAINST the concentration gradient will couple with it
• this will change the confirmation and allow the one against gradient to move in
• source of E is gradient

Question 31

light-driven pump

Answer 31

• absorbed energy from light

- ex. beta barrel absorbs light and can change confirmation that will allow things in

Question 32

electrochemical gradient

Answer 32

• if things in concentration gradient are charged

Question 33

types of transport carriers

Answer 33

• uniport- single thing brought across in one direction, ATP driven
• symport- bringing two things in, in the same direction (coupled)
• antiport- one thing in, one thing out (coupled)

Question 34

Hydrolysis of ATP

Answer 34

• phosphate is removed- breaking high energy bond
• releases energy, ADP
• exergonic, 7.3 kcal/mol
• Equilibrium lies very far towards ADP + Pi because they are lower in energy than ATP

Question 35

The Na+/K+ ATPase Pump

Answer 35

• Complex protein–> ATPase
• enzyme that acts upon ATP (bind and breaks in ADP + Pi)
• With each cycle, 3K+ go out, 2 Na+ go in
• Energy from ATP hydrolysis drives movement of 3 Na+ out, and 2 K+ in, both against their concentration gradients
• Binding sites for Na+, K+ & ATP
• Covalent attachment of phosphate to the protein (and subsequent removal) cause conformational changes that drive the process

Question 36

Na+/glucose Symport

Answer 36

• facilitiative diffusion (NOT active)
• Na+ concentration is higher outside cell than inside–> movement into cytoplasm is favorable
• Carrier is designed to only allow Na+ to enter if glucose goes along too–> coupled
• so glucose is pumped out AGAINST its gradient

Question 37

gut glucose (symport)

Answer 37

• symport example
• epithelial cell with microvilli in intestinal lumen, and other side is blood/body tissue
• use coupled symporter (w/ Na+) to bring glucose into epithelial cell, and then into the blood
• Use Na+/K+ pump to balance [Na+] in epithelial cell
• use uniport (passive) when enough glucose is in cell to pass to blood

Question 38

ion channels (3)

Answer 38

1. voltage gated- charges on both sides and as membrane voltage changes, gate will open at a certain voltage
2. ligand gated (intracellular)- substances bind form inside to open channel
   - ligand gated (extracellular)- substances bind from outside to open channel
3. stress activated- open when stressed (temp, UV)

Question 39

bulk transport/endocytosis/exocytosis

Answer 39

• final step in secration- secretory vessel w/ lipid bilayer and “cargo”
• fuses with membrane, open up–> everything what was inside goes outside
• lipid bilayer fusion
• vesicle inversion- phospholipids on interior of vesicle because exterior when fused
  endocytosis- vesicle comes into cell
  exocytosis- vesicle leaves cell

Question 40

endocytosis (opposite of secretion)

Answer 40

• put membrane around matter outside the cell and bring inside
• the area of membrane is often lines with protein called clathrin (involved in infolding and production of the endosome)
  1. phagocytosis (cell eating)- food/ old cell parts are brought in and vesicle fuses with lysosome
  2. pinocytosis (cell drinking)- cell brings in extracellular fluid for nutrients
  3. receptor-mediated endocytosis- receptors bind to molecules, which helps with the infolding of vesicle, Clathrin lines the membrane where receptors are, when receptors are full, clathrin held with the infolding (coated pit), clathrin leaves, receptors are recycled (move to one side of endosome and break off), ligands go to golgi and then lysosome–> facilitated diffusion

Question 41

LDL receptor-mediated endocytosis

Answer 41

• LDL- core is nonpolar, particles circulate through the blood
• RME is how LDL is taken out of the blood–>
• receptors recognize LDL an when full, folds inwards–> brought in and lysosome breaks it down

Question 42

cell membrane function

Answer 42

1. boundary and permeability barrier for protection
2. organization
3. transport process
4. signal detection
5. cell to cel lcommunication

Question 43

endosome

Answer 43

• membrane bound compartment