Week 7 - Membrane Structure

Question 1

Define Cytoplasm.

Answer 1

Contents of the cell outside of the nucleus (includes other organelles).

Question 2

Define Cytosol.

Answer 2

Aqueous part of the cytoplasm; does NOT include membrane bound organelles - DOES include ribosomes and cytoskeleton

Question 3

Define Lumen.

Answer 3

Insides of organelles.

Question 4

What are the 6 cell functions at the membrane?

Answer 4

1. Compartmentalization
2. Scaffold for biochemical activities
3. Selectively permeable barrier
4. Transporting solutes
5. Responding to external signals
6. Interactions between cells

Question 5

Membrane lipid bilayers have what properties?

Answer 5

1. Amphipathic (hydrophilic/polar head groups and hydrophobic tails)
2. Have 2 layers (leaflets)

Question 6

What is the fluid mosaic model?

Answer 6

Of the membrane bilayer; Lipids are FLUID and some Proteins are MOBILE; MOSAIC of many different lipids and proteins

Question 7

Membrane lipids structure?

Answer 7

• polar, hydrophilic head group

- 2 hydrocarbon, hydrophobic tails

Question 8

In an aqueous environment, phospholipids spontaneously self-associate into what?

Answer 8

Spontaneously self-associate into a bilayer

Question 9

Hydrocarbon tails of membrane lipids interact with what?

Answer 9

Other hydrocarbon tails

Question 10

What is in artificial lipid bilayers?

Answer 10

liposomes

Question 11

Experimental uses of a Liposome? (3)

Answer 11

1. Study lipid properties
2. Membrane protein properties
3. Drug delivery into cells

Question 12

Most energetically favourable structure of a liposome?

Answer 12

Spherical sealed compartment formed by phospholipid bilayer

Question 13

Types of membrane lipids?

Answer 13

1. Phospholipid (i.e. Phosphoglyceride)
2. Sphingolipids (less abundant)
3. Steroids (i.e. Cholesterol in animal cells)

Question 14

What is the Phosphoglyceride structure?

Answer 14

• Variable head group (R)
• phosphate group
• glycerol group
• 2 hydrocarbon tails.

Question 15

Hydrocarbon tails have what structure properties?

Answer 15

• saturated or unsaturated (the latter with a kink from a cis double bond)
• 14-24 carbons in length

Question 16

What is the Steroid (cholesterol) structure?

Answer 16

• polar head group
• rigid steroid ring structure (like a wedge)
• 1 non-polar hydrocarbon tail

Question 17

The 1;1; ratio of cholesterol to phospholipids can decrease what?

Answer 17

• decrease mobility of phospholipid tails

- decrease plasma membrane permeability

Question 18

Phospholipids diffuse and move in what directions?

Answer 18

• laterally
• within each leaflet
• rotationally
• with flexion (often)

Question 19

Phospholipids RARELY diffuse in what way?

Answer 19

transversely (flip-flopping) without other influences

Question 20

At lower temperatures, lipid bilayers become what?

Answer 20

become rigid (gel)

Question 21

The presence of cis-double bonds allows the membrane to remain what?

Answer 21

remain fluid at lower temperatures

Question 22

Kinks in hydrocarbon tails allow for what?

Answer 22

Kinks in hydrocarbon tails allow for more space and less hydrophobic interactions

Question 23

Shorter hydrocarbon tails increase what?

Answer 23

Shorter hydrocarbon tails increase fluidity at lower temperatures (the tails interact less)

Question 24

Phospholipid translocators catalyze what?

Answer 24

They catalyze the rapid flip-flop of phospholipids from one leaflet to the other

Question 25

Why is it necessary to have some phospholipid flip-flopping?

Answer 25

Phospholipids are synthesized in the cytosolic leaflet of the endoplasmic reticulum but are needed on both the cytosolic and exoplasmic faces

Question 26

What are the 2 leaflets of the lipid bilayer of one membrane?

Answer 26

Cytosolic and exoplasmic

Question 27

What does the inner membrane of the nucleus have?

Answer 27

The inner membrane has a cytosolic face that faces into the nucleus. It is continuous and bends around the nuclear pore.

Question 28

What does the outer membrane of the nucleus have?

Answer 28

The outer membrane has an "exoplasmic face", although it faces inter membrane space

Question 29

What organelles have 2 membranes?

Answer 29

The nucleus and mitochondria

Question 30

Where does the exoplasmic face of the mitochondria face?

Answer 30

It faces inter membrane space.

Question 31

Where does the cytosolic face of the mitochondria face?

Answer 31

It faces the matrix of the mitochondria, and it is discontinuous.

Question 32

What are the bilayers of the vesicles like?

Answer 32

They are continuous and stay consistent.

Question 33

Is the lipid bilayer symmetrical or asymmetrical?

Answer 33

Asymmetrical

Question 34

Glycolipids and glycoproteins found on the exoplasmic leaflet are formed by what?

Answer 34

Formed by adding sugar groups.

Question 35

Glycolipids and glycoproteins protect what?

Answer 35

They protect the membrane from harsh environments.

Question 36

Phospholipids are distributed in what manner?

Answer 36

Asymmetrically

Question 37

Phospholipids can bind to what?

Answer 37

Some can bind to cytosolic proteins.