BIO 1140 - Cell Membrane

Question 1

What are Cell Membranes?

Answer 1

Cell membranes act as selective barriers
- A living cell is a self-reproducing system of molecules held inside a container
- That container is the plasma membrane

Question 2

What is the Plasma Membrane?

Answer 2

Plasma membrane is a thin fatty film studded with proteins and coated with carbohydrates
- only membrane for SOME bacteria
- eukaryotes have internal membranes

Question 3

What is the Function of the Plasma Membrane?

Answer 3

1. Receiving information through receptor proteins
2. import and export of small molecules through transport proteins
3. capacity for movement and expansion

Question 4

What is the Plasma Membrane involved in?

Answer 4

• cell communication
• import and export of molecules
• cell growth
• motility

Question 5

What are all Cell Membranes composed of?

Answer 5

All cell membranes is composed of lipids and proteins
- The lipids are arranged in two closely apposed sheets, forming a lipid bilayer
- A type of lipid molecule called phospholipids are the major lipid components of all biological membranes
- Phospholipids have a hydrophilic head and two hydrophobic tails

Question 6

What is the Major Lipid component of all Biological Membranes?

Answer 6

A type of lipid molecule called phospholipids are the major lipid components of all biological membranes
- Phospholipids have a hydrophilic head and two hydrophobic tails

Question 7

What is the most common Phospholipid in Biological Membranes?

Answer 7

Phosphatidylcholineis themost commonphospholipid in biological membranes
- The hydrophilic head of phosphatidylcholine is composed of a choline molecule and a phosphate group
- The hydrophobic tails are composed of two fatty acids (14 and 24 carbon atoms)
- Glycerol links the hydrophilic head to the hydrophobic tail

Question 8

What are Saturated and Unsaturated Hydrocarbons?

Answer 8

The hydrocarbon tail with no double bonds is calledsaturated​

The hydrocarbon tail with double bond(s) is calledunsaturated.

Question 9

What are Amphipathic Molecules?

Answer 9

Molecules with both hydrophilic and hydrophobic parts aretermedamphipathic.
- All membrane lipids are amphipathic

Question 10

What is a Triacylglycerol?

Answer 10

Triacylglycerol is the main constituents of animal fats and plant oils
- is entirely hydrophobic

Question 11

What do Phospholipid Bilayers form?

Answer 11

Phospholipidbilayersspontaneously close in on themselves to form sealed compartments

The closed structure is stable because it avoids the exposure of the hydrophobic hydrocarbon tails to water (energetically favourable)

Question 12

What is the Fluid Mosaic Model?

Answer 12

• Cell membrane is made up of many discrete components.
• membrane structure is mosaic.
• The components can move freely.
• membrane structure is fluid.

Question 13

What does the Fluidity of a Lipid Bilayer depend on?

Answer 13

The fluidity of a lipid bilayer depends on its lipid composition
- Fluidity decreases at reduced temperatures
- Cholesterol tends to stiffen cell membranes
- Lipid bilayers with unsaturated hydrocarbon tails are more fluid
- Lipid bilayers with shorter fatty acid chains are more fluid

Question 14

Where is new Membrane synthesized?

Answer 14

New membrane is synthesized in the ER

Question 15

Where is new Membrane motified?

Answer 15

New membrane is modified in the Golgi membrane
- Certain phospholipids are confined to one side of the membrane
- This asymmetry is preserved during membrane transfer

Question 16

How are Membranes transported?

Answer 16

Membranes are transported by aprocess of vesicle budding andfusing
- Membranes retain their orientation during transfer between cell compartments

Question 17

How are Phospholipids and Glycolipids distributed?

Answer 17

Phospholipids and glycolipids are distributed asymmetrically
- Glycolipids are located mainly in the plasma membrane.
- At the plasma membrane they are at the non-cytosolic half of the bilayer

Question 18

What are Most Membrane Functions carried out by?

Answer 18

Most membrane functions are carried out by membrane proteins
- Plasma membrane proteins have a variety of functions.

Question 19

What are some functions of Plasma Membrane Proteins?

Answer 19

• Transporter
• Ion Channels
• Anchor
• Receptors
• Enzyme

Question 20

What are the Two Types of Membrane Proteins?

Answer 20

1. Integral Protein: extend through the lipid bilayer (transmembrane, associated with the lipid monolayer, or lipid-linked)
2. Peripheral Protein: interact with integral membrane proteins or phospholipids

Question 21

How can Integral Proteins be removed?

Answer 21

Integral proteins can be removed only by disrupting the bilayer withdetergents

Question 22

What is the distribution of Membrane Proteins?

Answer 22

The distribution of membrane proteins is asymmetrical

Question 23

What is a Transmembrane Protein?

Answer 23

An integral protein that extends all the way through the phospholipid bilayer is called a transmembrane protein.

Question 24

How do Cells confine particular proteins to localized areas?

Answer 24

Cells can confine particular proteins to localized areas by:
- binding the meshwork of proteins inside the cell (cell cortex)
- binding extracellular matrix molecules
- binding proteins on the surface of another cell
- restricted by diffusion barriers.

Question 25

What are Membrane Domains?

Answer 25

They can create functionally specialized regions called membrane domains.

Question 26

What is the Plasma Membrane reinforced by?

Answer 26

The plasma membrane Is reinforced by the underlying cell cortex
- Cell membrane by itself is extremely thin and fragile.
- Cell membranes are supported by a framework of proteins called the Cell Cortex

Question 27

What is the Glycocalyx?

Answer 27

All of the carbohydrate on the glycoproteins, proteoglycans, and glycolipids is located on the outside of the plasma membrane
- This sugar coating is called the carbohydrate layer or glycocalyx

Question 28

What is the Function of Glycoproteins & Proteoglycans?

Answer 28

The carbohydrates of glycoproteins and proteoglycans often function in cell recognition and adhesion.

Question 29

What do Cell Surface Carbohydrates allow?

Answer 29

Cell surface carbohydrates allow:
- cell adhesion
- neutrophils migration at sites of infection

Question 30

What are the Three Types of Cell Junction?

Answer 30

1. Tight Junction
2. Desmosomal Adhesion
3. Gap Juncrion

Question 31

What is Tight Junction?

Answer 31

Protein complex between two cells that creates a seal to prevent substances from moving through the spaces between cells
- cells lining the bladder have tight junctions so urine cannot leak out into the body cavity

Question 32

What are Desmosomes?

Answer 32

Desmosomes hold neighboring cells firmly together, acting like spot welds or rivets
- Localized spot-like adhesions
- Materials can still move around in the extracellular matrix
- This provides mechanical stability for tissues such as skin that receive physical stress
- Randomly arranged on the lateral sides of the cell

Question 33

What are Gap Junctions?

Answer 33

Gap junctions are channels that run between membrane pores in adjacent cells, allowing substances to pass
between cells
- allow the rapid spread of electric current (mediated by ions) so the heart muscle cells beat in unison