Cell Membranes, Transport Of Small And Large Molecules Lectures 2.1-2.3

Question 1

What are cell membranes?

Answer 1

-selectively permeable barriers
-maintain constant internal environment and enclose cell contents
-very thin

Question 2

Phospholipid molecule:

Answer 2

-has a dynamic structure so components are free to move around
*amphipillic: both hydrophilic and hydrophobic parts
*polar head: negatively charged phosphate group
*non polar tail: no charge
*phospholipid: “self-assembles” to create the bilayer. They migrate but rarely flip

Question 3

What are the two different types of tails?

Answer 3

Saturated and Unsaturated
Saturated: single bonds only
Unsaturated: at least one double bond
Double bond creates a kink in the fatty acid chain of the tail

Question 4

What do higher concentrations of saturated fatty acids cause?

Answer 4

Reduces cell membrane fluidity

Question 5

What do higher concentrations of unsaturated acids cause?

Answer 5

They promote membrane fluidity

Question 6

What does concentrations of unsaturated phospholipids affect?

Answer 6

It affects membrane fluidity

Question 7

What are the two types of carbohydrates?

Answer 7

*glycolipids
*glycoproteins

Question 8

Three major roles of carbohydrates:

Answer 8

-maintain membrane stability and cell protection and aids in cell adhesion and recognition.

Question 9

Tell me about cholesterol:

Answer 9

-is a lipid (approx 20% of the membrane lipid is cholesterol)
-has polar and non polar regions
-wedges itself between the phospholipid tails
-is able to migrate and flip between the membrane layers

Question 10

Proteins:

Answer 10

-proteins are able to serve different functions such as:
Enzymes, carrier proteins, channel proteins, receptors, cell adhesion and recognition.

Question 11

Two main types of proteins?

Answer 11

Integral and peripheral

Question 12

Integral proteins:

Answer 12

-firmly inserted into the membrane
-span the bilayer of the membrane
-transmembrane protein is hydrophobic
-extracellular and cytosolic portions are hydrophilic
-carrier proteins and channels are integral proteins

Question 13

Peripheral proteins:

Answer 13

-loosely attached to the membrane
-can be removed from the membrane with minimal disruption

Question 14

What is membrane fluidity affected by?

Answer 14

-extreme temperatures; either hot or cold
-concentration of unsaturated fatty acids
-cholesterol levels

Question 15

Membrane fluidity: what does a low temperature cause?

Answer 15

Less kinetic energy, phospholipids pack together and membranes have less fluid

Question 16

Membrane fluidity: what does a high temperature cause?

Answer 16

More kinetic energy, phospholipids move further away and membranes have more fluid

Question 17

Membrane fluidity: what does having cholesterol cause?

Answer 17

It maintains fluidity by preventing lipids from getting too close together or too far apart from each other.

Question 18

Red blood cells?

Answer 18

Equal amounts of lipid, protein and a small amount of carbohydrate

Question 19

Nerve cells?

Answer 19

Higher amounts of lipid in the cell membrane (80%)

Question 20

Passive transport?

Answer 20

-moves down a concentration gradient
Three types: simple diffusion, facilitated diffusion and osmosis
-uses inherent kinetic energy

Question 21

Active transport?

Answer 21

-moves against a concentration gradient
-has directionality
-requires a specific carrier protein
Two types: primary and secondary
-needs external energy source

Question 22

Simple diffusion?

Answer 22

-small, uncharged non polar molecules
Properties:
-no metabolic energy is required
-uses kinetic energy
-the rate of diffusion is proportional to the concentration gradient

Question 23

Facilitated diffusion?

Answer 23

-small polar molecules; H2O, glucose etc
-uses specific proteins
-the rate of diffusion is proportional to the concentration gradient

Question 24

Simple diffusion and facilitated diffusion kinetics:

Answer 24

Simple diffusion= linear relationship between concentration and rate of diffusion
Facilitated diffusion= the rate of diffusion reaches a plateau since the proteins become fully occupied

Question 25

What is osmosis?

Answer 25

-net movement of water down a concentration gradient
-water is highly polar however some small amounts can ‘sneak’ through the membrane
-water moves freely and reversibly via a specific protein channel; aquaporins
-bulk movement of water is facilitated diffusion

Question 26

Primary active transport:

Answer 26

-movement of Na+ and K+ uses the Na+/K+/ATPase pump
-maintains ion concentration differences inside the cell
-hydrolysis of ATP results in= phosphorylation of the pump —> results in conformational change of pump
-causes transport of 3Na+ out and 2K+ into the cell

Question 27

Secondary active transport (co-transport):

Answer 27

movement of two substances at the same time;
*A substance against its concentration gradient—> active transport
*Ion movement down its concentration gradient—> usually facilitated diffusion
-energy used for secondary active transport comes from the electrochemical gradient across the membrane.

Question 28

What are the two types of secondary active transports?

Answer 28

Symport;
*transported substances move in the same direction
*Na+/Glucose transporter
-Antiport;
*Transported substances move in the opposite direction
-Na+/Ca2+ exchanger- uses the Na electrochemical gradient to transport Ca2+ out of the cell.

Question 29

What is endocytosis?

Answer 29

Moves large molecules into the cell
Three types: phagocytosis, pinocytosis and receptor- mediated

Question 30

What is exocytosis? And what is it used for?

Answer 30

Moves large molecules out of the cell
*Used for: hormone secretion, neurotransmitter release and mucous secretion

Question 31

What are vesicles? And what are they made up of?

Answer 31

-vesicular transportation of large molecules
*bubble-like membranous sacs
*made up of phospholipid bilayer containing fluid
*transport bubble
*protects substances being transported

Question 32

Endocytosis- phagocytosis

Answer 32

ingestion of large particles by specialised cells (phagocytes -> immune system)
-macrophages
-certain white blood cells
*used for removing bacteria and debris
*when bacteria binds to a phagocyte the cell membrane wraps itself around the particle= results in a phagosome containing the particle

Question 33

Endocytosis- pinocytosis

Answer 33

-occurs in most cells
*process used to take in extracellular fluid with dissolved substances
*droplet enters the cell and fuses with an endosome (sorting vesicle)

Question 34

Endocytosis- receptor mediated

Answer 34

*main mechanism for specific uptake of macromolecules
*very selective method
*uptakes substances (hormones, cholesterol) found in small amounts
*receptors for this are specific membrane proteins

Question 35

Exocytosis

Answer 35

*substances are being moved out the cell—> hormones and waste products
*process is stimulated by a cell-surface signal that results in these steps:
• substance is enclosed in a vesicle
• Transported to plasma membrane
• Vesicle attaches to the ‘docking’ sites on the membrane
• Fuses with membrane and ejects substances