Lecture 15 - Membranes

Question 1

Bacteriophages Attacking a Bacteria:

Answer 1

1- BP recognizes specific proteins and binds
to a cell through its tail fibers

2- Sheath contracts, injecting the viral DNA
into the cell through the spikes on the
bottom of the structure

3- the viral DNA inserts itself into the
bacterial genome and highjacks the cellular
machinery to make more viral proteins and
DNA which assembles into more BPs

4- Will cause the cell membrane to rupture
(killing the cell)

Question 2

Virus Life Cycle: Lysogenic life cycle

Answer 2

1- Envelope has glycoproteins on it that
recognize and bind to specific plasma
membrane receptors on the cell

2-Virus undergoes endocytosis and enters
the cytosol

3- Virus fuses with the endosome and this
releases the capsid

4- the RNA is translated by host cell
machinery, the RNA is replicated by a viral
specific RNA pol.

5- Capsid proteins are made on free ribosomes in the cytosol and the glycoproteins that are going to insert into the plasma membrane are made on the ER and moved through the endomembrane system

6- Capsid forms around RNA, moves towards the plasma membrane, interacts with the viral glycoproteins are undergoes exocytosis

Question 3

Functions of Biological Membranes

Answer 3

1) Define cell boundary

2) Define enclose compartments

3) Control movement of material into and out
of cell / organelles

4) Allow response to external stimuli

5) Enable interactions between cells

6) Provide scaffold for biochemical activities

Question 4

the trilaminar structure is a ______ _______

Answer 4

lipid bilayer

Question 5

The lipid bilayer is made up of

Answer 5

phospholipids

Question 6

Proteins are embedded in or associated with the

Answer 6

phospholipid
bilayer

Question 7

components are mobile

Answer 7

Fluid

Question 8

diverse ‘particles’ like proteins, carbohydrates, and cholesterol penetrate the lipid layer; Components can interact

Answer 8

Mosaic

Question 9

phospholipids consist of a

Answer 9

glycerol backbone bound by:
– Two non-polar fatty acyl
molecules (“fatty acid chains”)
– A polar head group linked by a phosphate residue

Question 10

Phosphatidyl….

Answer 10

ethanolamine
choline
serine
inositol

Question 10

Phospholipids are amphipathic

Answer 10

– Hydrophilic - attracted to / binds water
– Hydrophobic - repelled by water

Question 11

Lipid molecules, like phospholipids,
spontaneously aggregate to bury their

Answer 11

hydrophobic tails in the interior and expose
their hydrophilic heads to water.

Question 12

A molecule will always be in a conformation
in which it is the most

Answer 12

stable

Question 13

Micelles are
usually formed by fatty acids with only

Answer 13

one hydrophobic chain

Question 14

Synthesis occurs in

Answer 14

pre-existing membrane

Question 15

Synthesis occurs in a multistep process at the interface of the

Answer 15

cytosol and outer endoplasmic reticulum membrane

Question 16

ER membrane contains all the

Answer 16

molecular machinery (enzymes) for synthesis and distribution

Question 17

Three classes of membrane proteins

Answer 17

INTEGRAL
PERIPHERAL
LIPID-ANCHORED

Question 18

INTEGRAL membrane proteins span

Answer 18

the lipid bilayer

Question 19

PERIPHERAL membrane
proteins associate with the

Answer 19

surfaces of the lipid bilayer

Question 20

LIPID-ANCHORED proteins attach to a

Answer 20

lipid in the bilayer

Question 21

Different integral (transmembrane)
proteins have different functions
For instance:

Answer 21

1) Transport of nutrients and ions.
2) Cell-cell communication (gap
junction)
3) Attachment

Question 22

Lipids move easily, laterally within

Answer 22

leaflet

Question 23

Lipids movement between leaflets is

Answer 23

difficult and slow

Question 24

Membrane proteins diffuse

Answer 24

within the bilayer

Question 25

Movement of proteins is

Answer 25

restricted

Question 26

Rapid movement is _____ ______ Long range diffusion is _____

Answer 26

spatially limited, slow

Question 27

Biochemical modification can alter

Answer 27

protein mobility in the membrane—an
important feature for signal transduction.

Question 28

All membranes share common properties:

Answer 28

• Approximately 6 nm thick (with water)
• Stable
• Flexible
• Capable of self assembly

Question 29

Membranes also have unique features:

Answer 29

• Different membranes contain different types of lipids and proteins, giving them different functions.
• Differences between cells as well as within organelles
  within a cell

Question 30

The ____ ______of ________
contains a _____ ____ concentration of
protein necessary for electron transport
chain and ATP synthesis.

Answer 30

inner membrane, mitochondria, very high

Question 31

Myelin sheath simply consists of layers of
plasma membrane wrapped around

Answer 31

a neuron’s axon. This serves as insulation and
increases the speed at which electrical impulses propagate along the myelinated fiber

Question 32

Myelin sheaths have low amounts

Answer 32

of protein

Question 33

what are asymmetrical

Answer 33

biological membranes

Question 34

Two leaflets have distinct lipid composition in many plasma membranes, the
outer leaflet contains _______ and _______ (lipids and proteins with
__________ attached to them).

Answer 34

glycolipids, glycoproteins, carbohydrates

Question 35

Temperature is an important variable affecting the

Answer 35

fluidity of biological membranes

Question 36

Warming _______ fluidity

Answer 36

increases (liquid crystal)

Question 37

Cooling _______ fluidity

Answer 37

decreases (crystalline gel)

Question 38

Membrane fluidity is crucial to

Answer 38

cell function

Question 39

Membrane fluidity is determined by the nature of lipids in membrane:

Answer 39

– Unsaturated lipids increase fluidity

– Saturated lipids reduce fluidity

Question 40

In response to changes in temperature, lipid composition of membranes can be
changed by:

Answer 40

1) desaturation of lipids
2) exchange of lipid chains

Question 41

BALANCE between ordered (rigid) structure and disordered structure
allows:

Answer 41

• Mechanical support and
  flexibility
• Membrane assembly and
  modification
• Dynamic interactions between membrane components (e.g.,
  proteins can come together reversibly)

Question 42

Cholesterol modulates

Answer 42

membrane fluidity

Question 43

Cholesterol acts as a _______ regulator of membrane fluidity

Answer 43

bidirectional

Question 44

At ______ temperatures, Cholesterol stabilizes the membrane and raises its melting point

Answer 44

high

Question 45

At _____ temperatures, Cholesterol intercalates between the phospholipids and
prevents them from clustering together and stiffening

Answer 45

low

Question 46

the ______ structure of cholesterol allows it to pack tightly with phospholipids

Answer 46

amphithetic

Question 47

cholesterol alters

Answer 47

packing and flexibility of lipids

Question 48

If cholesterol is added to a liquid crystal membrane

Answer 48

fluidity will decrease

Question 49

If cholesterol is added to a crystalline gel membrane

Answer 49

fluidity will increase

Question 50

FLUID MOSAIC MODEL describes

Answer 50

membrane properties