Lectures 1.1-1.3

Question 1

What are the basic functions and components of biological membranes

Answer 1

• is a permeable barrier that allows nutrients to pass through
• serves as a barrier between the cell and external environment
• allows selective transport in and out of cell
• allows interactions with other cells (through cell signaling and cell-cell contacts)
• allows interactions with the external environment

Question 2

What is the structure of Phospholipids?

Answer 2

amphipathic molecules that have a hydophilic polar head and hydrophobic hydrocarbon tails (usually fatty acids)

Question 3

How do Phospholipids form bilayers?

Answer 3

form spontaneously due to the hydrophobic effect. hydrophilic head groups are exposed to the aqueous environment while the hydrophobic tail groups face each other and form a weak bond that attaches the leaflets to each other.

Question 4

Structure of cholesterol?

Answer 4

rigid ring structure, a single polar hydroxyl group, and a short hydrocarbon tail.

Question 5

how does cholesterol contribute to membrane fluidity?

Answer 5

intercalates between phospholipids and helps maintain the structural integrity of the membrane. (ie maintains the correct fluidity of membrane).

Decreases permeability of bilayer to small water soluble molecules

Question 6

glycolipid

Answer 6

sphingolipids that are attached to sugar moieties

• can partition in specialized microdomains of the membrane
• protects membrane
• facilitates in cell-recognition processes
• is entry point for bacterial toxins and other human pathogens

Question 7

What are the different types of membrane proteins? and what are their roles?

Answer 7

• integral and Peripheral (and Glycocalyx)
• transport ions and polar molecules
• bind peptide and polypeptide hormones
• signal transduction across membrane
• is apart of the structural stability of bilayer
• gives cell its distinct functional properties

Question 8

glycoproteins

Answer 8

most cell-surface membrane proteins are glycosylated (i.e. the carbohydrate is attached to a hydroxyl or other functional group of another molecule)

Question 9

glycocalyx

Answer 9

the glycoproteins and glycolipids form a carbohydrate rich layer at the plasma membrane.

• protects against mechanical and chemical damage
• facilitates cell-cell recognition and interactions
• binds antigens and enzymes to cell surface
• aids in the attachment of cells to extracellular matrix components

Question 10

membrane domain

Answer 10

two broad domains: apical and basolateral

• the composition is not uniform around the cell
• each different domain has a specific function/job

Question 11

microdomain

Answer 11

small “patches” of membrane with distinct phospholipid composition found on the cell surface

• can be called lipid rafts
• enriched in sphingolipids and cholesterol
• used to localize proteins that must work together

Question 12

lipid bilayer asymmetry (how it is established and maintained)

Answer 12

• each leaflet has distinct lipid composition
• allows the two sides of the membrane to be functionally distinct
• established by specific translocating enzymes within the endoplasmic reticulum and the plasma membrane
• maintained by these enzymes (flippases, floppases, scramblases)

Question 13

why is membrane fluidity important?

Answer 13

proteins and lipids of biological membranes diffuse laterally within the membrane

Question 14

How do lipids affect membrane fluidity?

Answer 14

more saturated fatty acids = less fluid

more unsaturated fatty acids = more fluid

Question 15

amphipathic

Answer 15

hydrophilic head and hydrophobic tail

Question 16

fluid mosaic model

Answer 16

model of plasma membrane that is made up of many different macromolecules (mosaic) and allows components to move laterally throughout the memberane (fluid)

Question 17

phosphoglyceride

Answer 17

Most abundant phospholipid with a glycerol backbone, a phosphate group, and one of several head groups

Question 18

sphingolipid

Answer 18

lipid found in cell membrane with a sphingoid base

Question 19

proteoglycan

Answer 19

heavily glycosylated protein

Question 20

integral membrane proteins

Answer 20

• completely span the lipid bilayer

- can span the membrane multiple times

Question 21

peripheral membrane proteins

Answer 21

• bound to the surface of the membrane
• can be removed without dissolving the membrane
• can attach to membrane by ionic interactions or with phosopholipid head group

Question 22

single pass membrane protein

Answer 22

type of integral membrane protein

- passes one time through bilayer

Question 23

multi pass transmembrane proteins

Answer 23

type of integral membrane protein

- passes through bilayer multiple times

Question 24

tight junctions

Answer 24

separates domains on plasma membrane

- also involved in cell-cell connections

Question 25

flippase

Answer 25

enzyme that facilitates in taking molecules from inside the cell to outside the cell

Question 26

net diffusion

Answer 26

- occurs down chemical and electrical gradients | - described by Fick's Law

Question 27

what is the role of chemical and electrical gradients during diffusion across a biological membrane

Answer 27

affect net diffusion as molecules what to move down the gradient in a energetically favorable manner

Question 28

osmosis

Answer 28

diffusion of water from a lower solute concentration to a higher solute concentration

Question 29

osmotic pressure

Answer 29

hydrostatic pressure produced by a difference in concentration between solutions on the two sides of a surface

Question 30

difference between channels and transporters

Answer 30

- channels form aqueous pores that allow solutes to pass through them passively - transporters bind to specific solutes and undergo transformational changes to transfer the solutes. may be passive or active

Question 31

distinction between active and passive transport

Answer 31

- Passive is driven by concentration gradient with electrochemical gradient - coupled to a source of metabolic energy to move up the electrochemical gradient

Question 32

uniporter

Answer 32

transporter that carries only one type of molecule

Question 33

primary active transport

Answer 33

use energy direct metabolic energy

Question 34

secondary active transport

Answer 34

metabolic energy is indirect. ATP creates an ion gradient and as one solute is moved down the gradient, this provides energy for another molecule to move up the gradient - transport is coupled

Question 35

types of pump proteins

Answer 35

use energy derived from the hydrolysis of ATP to transport molecules across the membrane

Question 36

mechanism of Na-K ATPase

Answer 36

pump that transports sodium and potassium against their electrochemical gradients 3 Na+ out of cell 2 K+ in to cell

Question 37

cotransport

Answer 37

couple the uphill transport of one solute across the membrane to the downhill transport of another

Question 38

distinction between symporters and antiporters

Answer 38

symport = solute moves in the same direction across the membrane antiport = solute moves in the opposite direction across the membrane

Question 39

how are ion gradients established across cell membranes

Answer 39

by active transporters (Na+ -K+ -ATPase)

Question 40

why is Na+ gradient a good source of potential energy

Answer 40

Na+ is highly concentrated outside of the cell thus, it is energetically favorable to move down the electrochemical gradient in to the cell

Question 41

ABC transporter

Answer 41

- transmembrane proteins that function in the transport of a wide variety of subtrates across the membrane - ATP-binding "cassettes" help pump small molecules - exports substance from the cytosol to extracellular space or to a membrane bound intracellular compartment (i.e. endoplasmic reticulum) - critical for many diseases and drug resistance

Question 42

ion channel selectivity and gating

Answer 42

selective of the molecules it transports and uses different gating mechanisms to open/close

Question 43

how does a semipermeable plasma membrane lead to a membrane potential?

Answer 43

as one ion moves across the semipermeable membrane, a gradient will start to form thus leading to a membrane potential

Question 44

osmolarity

Answer 44

number of osmoles / liter of solution

Question 45

isotonic

Answer 45

when two solutions have the same osmotic pressure across the semipermeable membrane

Question 46

hypotonic

Answer 46

concentration of solutes is greater inside the cell than outside of it

Question 47

hypertonic

Answer 47

concentration of solutes is greater outside the cell than inside of it

Question 48

voltage-gated

Answer 48

ion channels that are activated by changes in the electrical membrane potential near the channel. Membrane potential alters the conformation of the channel protein

Question 49

ligand-gated

Answer 49

ion channels that open when a chemical messanger (ie ligand) binds to them

Question 50

mechanically gated

Answer 50

ion channel that opens when physical force acts on the membrane

Question 51

sodium-potassium ATPase

Answer 51

enzyme found in the plasma membrane of cells that pumps sodium out of the cell while pumping potassium into the cell

Question 52

MDR protein

Answer 52

(Multi drug resistance) over expression of MDR can make cells resistant to a variety of chemically unrelated cytotoxic drugs and make cells resistant to anticancer drugs

Question 53

diffusion potential

Answer 53

potential difference generated across a membrane bc of a concentration difference of an ion (can only be generated if the membrane is permeable to the ion)

Question 54

equilibrium potential

Answer 54

the membrane potential where he net flow through any open channels is 0