Week 4: Membranes

Question 1

What is the primary function of cell membranes?

Answer 1

To keep the inside in and the outside out

Question 2

What surrounds the nucleus and mitochondria in eukaryotic cells?

Answer 2

A double membrane

Question 3

What is the structure of the plasma membrane?

Answer 3

A lipid bilayer made of lipids and proteins

Question 4

What are the two main components of biological membranes?

Answer 4

• Lipids
• Proteins

Question 5

What is the role of cholesterol in the lipid bilayer?

Answer 5

Provides structural support

Question 6

Define amphipathic molecules.

Answer 6

Molecules that are hydrophilic (water loving) and hydrophobic (water hating)

Question 7

What do lipid bilayers spontaneously form in aqueous environments?

Answer 7

• Micelles
• Bilayers
• Spherical structures

Question 8

What is the typical behavior of lipids in membranes?

Answer 8

• Fluidity
• Lateral diffusion
• Rotation
• Flexion

Question 9

True or False: Flip-flopping of lipids in the membrane is common.

Answer 9

False

Question 10

What are membrane proteins responsible for?

Answer 10

• Transport
• Structural links
• Receptors

Question 11

How many proteins are there approximately per 50 lipids in a membrane?

Answer 11

1 protein

Question 12

What type of protein can only be separated from the membrane with detergents?

Answer 12

Integral membrane proteins

Question 13

Fill in the blank: The carbohydrate layer on the cell surface is called the _______.

Answer 13

glycocalyx

Question 14

What is the purpose of the glycocalyx?

Answer 14

Involved in cell adhesion and protection

Question 15

What types of molecules are typically transported across membranes?

Answer 15

• Small water-soluble molecules
• Ions

Question 16

What do carrier proteins do?

Answer 16

Bind solutes and initiate a conformational change to transport them

Question 17

How do channel proteins function?

Answer 17

Contain a pore through the membrane that is controlled for opening

Question 18

What is the permeability of the lipid bilayer to hydrophilic molecules?

Answer 18

Barrier to most hydrophilic molecules

Question 19

What types of molecules are mostly excluded by the lipid bilayer?

Answer 19

• Uncharged polar molecules
• Ions

Question 20

What is the difference between integral and peripheral membrane proteins?

Answer 20

• Integral proteins: separated with detergents
• Peripheral proteins: separated with changes in pH or salt

Question 21

What is the role of membrane proteins in cellular signaling?

Answer 21

They allow inside things to get out and outside things to get in

Question 22

What type of protein is involved in membrane curvature in the ER?

Answer 22

Reticulons

Question 23

What type of anchor do GPI-linked proteins have?

Answer 23

Glycosylphosphatidylinositol (GPI) anchor

Question 24

What are the examples of membrane proteins that are involved in signal transduction?

Answer 24

• EGFR (epidermal growth factor receptor)
• Heterotrimeric G-proteins

Question 25

What is the purpose of maintaining different solute concentrations inside and outside the cell?

Answer 25

To protect the cell and maintain the chemistry in organelles

Question 26

Fill in the blank: Membranes act as a selective _______.

Answer 26

barrier

Question 27

What initiates a conformational change in the protein during solute transport?

Answer 27

Solute binds on one side of the membrane

Question 28

What is released on the other side after solute binding?

Answer 28

Solute

Question 29

Give an example of a transporter that binds solute.

Answer 29

Glucose transporters (GLUTs)

Question 30

How do channel proteins differ from transporters?

Answer 30

Channel proteins do not bind the solute but contain a 'pore' through the membrane

Question 31

What type of transport moves molecules from high to low concentrations?

Answer 31

Passive transport

Question 32

What type of transport moves molecules 'uphill'?

Answer 32

Active transport

Question 33

What do carrier proteins do in passive transport?

Answer 33

Bind molecules on the high concentration side and move them to the low concentration side

Question 34

What influences the passive movement of charged ions?

Answer 34

Electrical and chemical gradient

Question 35

What is a coupled carrier?

Answer 35

The transport of one molecule is 'coupled' with another

Question 36

What is an example of a symport coupled carrier?

Answer 36

Na-glucose carrier

Question 37

What do ATP-driven pumps use to drive active transport?

Answer 37

Hydrolysis of ATP

Question 38

What is an example of an ATP-driven pump?

Answer 38

Na+-K+ pump

Question 39

What is the function of the Na+-K+ pump?

Answer 39

Needed for muscle function and to maintain charge potential across the membrane

Question 40

What do ion channels facilitate?

Answer 40

Passive transport of ions through hydrophilic pores

Question 41

How many molecules can ion channels allow to pass per second?

Answer 41

10^8 molecules

Question 42

What influences the opening/closing of ion channels?

Answer 42

Gating mechanisms

Question 43

What is the selectivity of ion channels based on?

Answer 43

Narrow pore allowing contact between the ion and the pore wall

Question 44

What types of cells are voltage-gated ion channels especially useful for?

Answer 44

Nerve cells (neurones) and skeletal muscle cells

Question 45

What conditions can malfunctioning ion channels cause?

Answer 45

Epilepsy and neuromuscular conditions

Question 46

What are the main components of cell membranes?

Answer 46

* Lipid bilayer * Membrane proteins * Sugar coat

Question 47

Fill in the blank: The lipid bilayer is a _______ barrier.

Answer 47

selective

Question 48

Name two ways small molecules cross the membrane barrier.

Answer 48

* Carrier proteins (passive or active transport) * Channel proteins (ion channels - passive transport only)