Lecture 3: Intro to membranes

Question 1

why are membranes composed of a phospholipid bilayer?

Answer 1

b/c of their geometry (cylindrical) and their chemistry (amphipathic)
- Amphipathic nature allows phospholipids to spontaneously form membranes

Question 2

Define a micelle and describe differences b/t micelle and bilayer

Answer 2

Micelle= forms an aggregate with the hydrophilic “head” regions in contact with surrounding solvent, with the hydrophobic single-tail regions in the micelle centre.

• Micelles are single tailed phospholipids, bilayers are double
• phospholipids spontaneously form a bilayer because they’re cylindrical
• micelles form (a circle) because phospholipids are conical (cones)

Question 3

Phospholipids can move freely laterally because they’re only associated based on hydrophobicity, and no ____ bonds

Answer 3

covalent

Question 4

What’s the effect of high temp of membrane fluidity? Name the 3 adaptations

Answer 4

more kinetic energy at high temps = move faster, gap increases between them

1) increase HC tailing (increases hydrophobicity)
2) decrease C=C bonds (double)- the kink prevents close packing
3) increase cholesterol content (increases hydrophobicity and acts as a pylon to slow them)

Question 5

What’s the effect of low temp of membrane fluidity? Name the 3 adaptations

Answer 5

less kinetic energy at low temps = move slower, gap decreases between them

1. increase C=C (double) b/c kink physically pushes them apart
2. decrease tail length (decrease hydrophobicity)
3. increase cholesterol: acts as a spacer b/w phospholipids

Question 6

What are the 2 types of membrane associated proteins

Answer 6

integral membrane proteins and peripheral membrane proteins

Question 7

many protein-protein interactions in membranes are hydro____

Answer 7

hydrophobic

Question 8

How can you tell the difference b/w an animal and plant membrane?

Answer 8

animal membrane contains cholesterol

Question 9

The fluid mosaic model states that:

Answer 9

the membrane is a fluid structure (phospholipids) with a mosaic of different proteins embedded in or attached to a double bilayer of phospholipids

Question 10

____ have different functions within the bilayer; for every role of the membrane there’s a ___ involved

Answer 10

protein

protein

Question 11

name 6 of the different types of proteins in a membrane

Answer 11

1. transporter
2. enzymes
3. cell-cell recognition
4. cell-cell attachment
5. signal receptors
6. attachment to extracellular matrix

Question 12

what substances are permeable to the membrane?

Answer 12

small, uncharged molecules

Question 13

Impermeable substances cannot cross the hydrophobic core because they’re either too ___ or too ___

Answer 13

large

polar

Question 14

____ are the least permeable to the membrane. Why?

Answer 14

Ions

- b/c whenever there’s a proton, there’s an entourage of water, making a big, polar molecule

Question 15

Water is polar but diffuses readily by osmosis (is permeable). why?

Answer 15

it undergoes a dipole moment: the unequal charge distribution disappears long enough to cross the membrane
*but water diffuses by osmosis very slowly

Question 16

osmosis is the ___ diffusion of water

Answer 16

passive

Question 17

Passive transport (for ____ (permeable/impermeable) substances) is diffusion that’s not active or involved in any way. Define diffusion

Answer 17

permeable

• diffusion= movement of molecules from an area of high concentration to an area of [low] until an equilibrium is reached
• molecules have thermal motion and can diffuse

Question 18

water follows ___

Answer 18

solute

Question 19

what’s the risk in an animal cell if too much water rushes in?

Answer 19

the cell can burst! = osmotic lysis

Question 20

describe a hypotonic enviro in an animal and plant cell

Answer 20

H20 rushes into the cell (increase [solute] inside the cell)

• animal cell may burst (b/c no cell wall)
• in a plant cell, the cell wall prevents bursting

Question 21

describe a isotonic enviro in an animal and plant cell

Answer 21

no net water movement
[solute] inside cell = [solute] outside cell
-“perfect” enviro

Question 22

describe a hypertonic enviro in an animal and plant cell

Answer 22

H20 rushes out of the cell (increase [solute] outside the cell)
risk= cell shrinks
- in plant cells, plasmolysis can occur (pulling away of membrane from cell wall)

Question 23

____ are a protein that’s a transmembrane water channel. This speeds up osmosis

Answer 23

aquaporins

Question 24

Facilitated diffusion involves
- ____ energy input
- transport __(up/down) concentration gradient
example?

Answer 24

no
down
example= aquaporin

Question 25

2 types of facilitated transporters

Answer 25

1. Channel protein

2. Carrier protein

Question 26

Describe channel proteins

Answer 26

• used to move molecules down their conc. gradient
• it’s an integral membrane protein
• allows transport of a specific solute without changing the shape
• can tell difference b/w different molecules, so very specific with what molecules are allowed across

Question 27

Describe carrier proteins

Answer 27

• used to move molecules down their conc. gradient
• spans bilayer (integral membrane protein)
• allows transport of a specific solute by changing shape

Question 28

transport proteins are ____ and can be ____ (open or close in response to a stimuli)

Answer 28

specific

gated

Question 29

active transport requires ___

- solute moves __(up/down) gradient

Answer 29

energy

up

Question 30

why perform active transport? list 3 reasons

Answer 30

1. to concentrate nutrients in the cell
2. to expel waste
3. to maintain a voltage and/or [gradient] across membrane

Question 31

an example of active transport is the ____/___ ___

Answer 31

sodium/ potassium pump

Question 32

what’s an example of cotransport?

Answer 32

cotransport= 2 molecules use the same transporter 
example = Na/ K pump

Question 33

explain the Na/K pump

Answer 33

SOPI PONI (sodium out, potassium in; positive out, negative in)
3Na+ out and 2 K+ in 
net negative charge inside the cell (resting membrane potential)

Question 34

symport vs antiport

Answer 34

(in cotransport)
symport= 2 molecules moved in same direction
antiport= 2 molecules moved in different directions

Question 35

molecule that need to pass the membrane but are too large must be transported using a _____ transport mechanism.
This involves the formation of ____

Answer 35

bulk

vesicles

Question 36

bulk transport can either undergo ____ (secretion) or _____(“bringing into cell”)

Answer 36

exocytosis

endocytosis

Question 37

receptor mediated endocytosis is the ____ of a specific ligand (anything that binds a receptor).

• receptor = ______
• receptors congregate at ____-____ pits

Answer 37

endocytosis
receptor= integral membrane protein that recognizes and binds a specific ligand
clathrin- coated pits (clathrin recruits receptors)