Week 7 Part 1: Membrane Structure (Lipids)

Question 1

What parts of an animal cell are animal cell specific?

Answer 1

Extracellular Matrix, Lysosome

Question 2

What is the name for the part of an animal cell that is the specialized material outside the cell?

Answer 2

Extracellular Matrix

Question 3

What happens within the lyososome?

Answer 3

Degredation of cellular components that are no longer needed

Question 4

In plant cells, what is the function of the cell wall?

Answer 4

Holds cell shape and acts as protection against mechanical stress

Question 5

What are the two types of vacuoles within plant cells?

Answer 5

A vacuole for degredation (like an animal cell’s lysosome) and a vacuole for storage (small molecules and proteins)

Question 6

What is the chloroplast?

Answer 6

The site of photosynthesis

Question 7

What is the cytoplasm? What does it include?

Answer 7

The cytoplasm are the contents of the cell outside the nucleus. This means that this includes all the organelles except the nucleus

Question 8

What is the name for the aqueous part of the cytoplasm?

Answer 8

Cytosol (this does not include membrane bound organelles, but it does incude things like ribosomes, cytoskeleton, etc.)

Question 9

What is lumen?

Answer 9

The inside of organelles (usually in between the membranes)

Question 10

What model for membrane bilayers did Singer and Nicolson propose in 1972?

Answer 10

The Fluid Mosaic Model of the Membrane

Question 11

When considering the name of the 1972 model of a membrane bilayers, what does “Fluid” and “Mosaic” mean?

Answer 11

Fluid refers to the mobility of the lipids and some of the proteins that the membrane is composed of. Mosaic refers to the many different lipids and many different proteins.

Question 12

Why are lipids amphipathic?

Answer 12

They have hydrophilic (or polar) heads, and hydrophobic tails

Question 13

What are the different types of lipids that a membrane is composed of?

Answer 13

Phospholipids, sterols, gycolipids

Question 14

What is the name for a phospholipid with a glycerol group?

Answer 14

Phosphoglycerides

Question 15

What does a general phosphoglyceride consist of?

Answer 15

Different groups + phosphate (polar head group), glycerol, hydrocarbon tails (non polar/hydrophobic)

Question 16

What are the characteristics of a phosphoglyceride’s hydrocarbon tails?

Answer 16

They’re usually 14-24 carbon atoms long and they can be saturated/unsaturated

Question 17

What is a kink? (In a phosphoglyceride)

Answer 17

It is a tail that is unsaturated and it contains a cis-double bond

Question 18

Where do membrane bilayers usually form?

Answer 18

In water

Question 19

In an aqeuous environment, phospholipids ____________ ________-_________ into a bilayer

Answer 19

spontaneously self-associate

Question 20

In a membrane bilayer, what does each layer interact with?

Answer 20

The polar/hydrophilic head interacts with water. The nonpolar/hydrophobic tails interact with other hydrophobic tails.

Question 21

What is a liposome?

Answer 21

Artificial lipid bilayer

Question 22

What are the three uses of liposomes?

Answer 22

1. Study lipid proteins
2. Membrane protein properties
3. Drug delivery into cells (either via the water within the spherical compartment or within the hydrophobic layer)

Question 23

Because a planar phospholipid bilayer causes hydrophobic tails to be exposed to water, what formation does the phospholipid bilayer adopt? Is this energetically favourable?

Answer 23

The planar phospholipid bilayer curls inward forming a spherical sealed compartment which shields hydrophobic tails from water. This is energetically favourable

Question 24

True or False: Cell membranes are not fluid

Answer 24

False

Question 25

Can a membrane be deformed without causing damage?

Answer 25

Yes it can. An example of this is a technique called live cell imaging where laser tweezers are used to manipulate the membrane.

Question 26

What are the three kinds of movement that phospholipids within each leaflet rapidly do?

Answer 26

1. Diffuse laterally 2. Rotate 3. Flex

Question 27

Which movement do phospholipids rarely do?

Answer 27

They rarely move from one leaflet to the other (**flip-flop**) on their own

Question 28

Describe lateral diffusion

Answer 28

While the phospholipid can move from side to side in one plane (i.e. on an x axis) it can also move deeper within the plane (i.e. on a z axis)

Question 29

Why is cell membrane fluidity carefully regulated?

Answer 29

It is carefully regulated because it is important for its function

Question 30

What are examples of the functions of membrane proteins?

Answer 30

Transport, enzyme activity, signaling

Question 31

What are factors affecting membrane fluidity?

Answer 31

Temperature and composition

Question 32

What happens to molecules at lower temperatures?

Answer 32

They are more viscous and less fluid -- you want to avoid this as it is supposed to be fluid

Question 33

Describe the effect of cis-double bonds at lower temperatures

Answer 33

Cis-double bonds **increase** fluidity at lower temperatures

Question 34

What does shorter phospholipid lengths cause?

Answer 34

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

Question 35

What does addition of cholesterol cause in animal cell membranes?

Answer 35

It stiffens membrane, makes it less permeable to water

Question 36

What ratio can cholesterol and phospholipids exist in? What does this mean for the membrane?

Answer 36

1:1 ratio. This means that cholesterol is a big part of the membrane.

Question 37

What does cholesterol cause in phospholipid tails?

Answer 37

It decreases mobility of phospholipid (stiffens membrane)

Question 38

Why does having cholesterol in plasma membranes make it less permeable to polar molecules?

Answer 38

It's because parts of the cholesterol are hydrophobic

Question 39

What is the function of **scramblase**

Answer 39

It catalyzes rapid flip-flop of **random** phospholipids from one leaflet to the other

Question 40

Why is scramblase needed?

Answer 40

Phospholipids are synthesized in **cytosolic** leaflet of endoplasmic reticulum and must be moved to the **lumen facing leaflet** for **symmetric growth** of both halves of bilayer

Question 41

Which enzymes in the golgi membrane flip lipids from one leaflet to the other?

Answer 41

Flippases

Question 42

What do flippases do?

Answer 42

They catalyze the rapid flipflop of **specific** phospholipids to the cytosolic leaflet. Some can bind **cytosolic** proteins at the plasma membrane

Question 43

What is the purpose behind the job of flippases?

Answer 43

Flippases flip lipids so that in the membrane they are the right orientation

Question 44

True or False: Proteins flip-flop

Answer 44

Mega false

Question 45

How are glycolipids and glycoproteins formed?

Answer 45

They are formed by adding sugar groups to lipids/proteins on **luminal** face of Golgi

Question 46

Which way do glycolipids and glycoproteins face? What is their purpose?

Answer 46

Glycolipids and glycoproteins face the noncytosolic side **always**. Their purpose is to protect the membrane from hash environments.