Membrane Transport

Question 1

Functions of the Plasma Membrane

Answer 1

Structural (keeps cell contents together)

Serves as the boundary between the cytoplasm and the external environment

Maintains stability and fluidity of the cell

Provides cell-to-cell communication by different mechanisms

Controls what enters and exits the cell

Question 2

Fluid Mosaic Model

Answer 2

FMM was first suggested to describe the arrangement of molecules in the plasma membrane

Fluid: Always changing shape and flexible

Mosaic: The pattern of the scattered proteins when seen from above

Model: No one knows how plasma membrane looks like, so this was constructed based off experiments on the behaviour of the membrane

Question 3

Importance of Selective Permeability

Answer 3

Helps maintain and regulate a cell’s internal environment and conditions

Permeability depends on size, charge, and polarity of molecule

Question 4

Components of Phospholipid

Answer 4

Hydrophilic Head: Made of glycerol and phosphate group and faces outwards into both the cytoplasm and external environment

Hydrophobic Tail: Made of 2 fatty acids facing each other

Phospholipid bilayer is amphipathic

Question 5

Function of Phospholipids in Cell Membrane

Answer 5

Allow lipid-soluble and polar substances to enter and exit the cell

Prevents water-soluble substances from entering and exiting the cell, acts as a hydrophobic barrier

Allows membrane fluidity and stability

Question 6

Components of Plasma Membrane

Answer 6

Phospholipid and Cholesterol

Question 7

Cholesterol

Answer 7

An amphipathic molecule that is needed for membrane fluidity and stability

Disrupts the regular packing of the tails which increases flexibility as it prevents the tails from crystalizing and solidifying

Allows membranes to function at a wider range of temperatures

Question 8

Fatty Acids in High and Low Temperatures

Answer 8

High: Stabilizes the membrane and raises the melting point

Low: Intercalates between the phospholipids by disrupting the packing of tails

Question 9

Integral Protein Location and Function

Answer 9

Location: Penetrate the phospholipid bilayer, amphipathic

Function: Pumps for active transport and channels for facilitated diffusion

Question 10

Peripheral Protein Location and Function

Answer 10

Location: Bound on the membrane surface, hydrophilic

Function: Cell to cell communication

Question 11

Glycoprotein / Conjugated Protein Location and Function

Answer 11

Location: Peripheral proteins but with carbohydrates called oligosaccharides attached, hydrophilic

Function: Cell recognition, identifies self and non-self cells, forms a layer with glycolipid called glycocalyx which binds cells together and prevents the tissue from falling apart

Question 12

Glycolipid Protein Location and Function

Answer 12

Location: Phospholipids with carbohydrates attached, hydrophilic

Function: Cell recognition, identifies self and non-self cells, forms a layer with glycoprotein called glycocalyx which binds cells together and prevents the tissue from falling apart

Question 13

The 2 Types of Integral Proteins

Answer 13

Channel Proteins: Transports most of the ions and hydrophilic molecules through facilitated diffusion

Carrier Proteins / Protein Pumps: Transport molecules by active transport using ATP

Question 14

Factors Affecting Fluidity of Membrane

Answer 14

Fatty Acid Saturation: The more saturated the fatty acid, the less movement, therefore the less fluid the membrane is

Tail Length: The longer the tail, the less fluid the membrane

Temperature: The lower the temperature, the more the membrane solidifies. Solidified membranes do not function well

Question 15

Passive Transport Features

Answer 15

Moves from high to low concentration

Substances move across a concentration gradient

Doesn’t require ATP or a protein pump

Equilibrium is reached

Examples include simple diffusion, facilitated diffusion, and osmosis

Question 16

Active Transport Features

Answer 16

Substances move from low to high concentration

Substances move against concentration gradient

Requires ATP and a protein pump

Equilibrium is NOT reached

Examples include endocytosis, exocytosis, and active transport

Question 17

Simple Diffusion

Answer 17

The passive movement of particles across a partially permeable membrane and concentration gradient from high to low concentration

Question 18

What Determines How Easily Substances can pass Membranes

Answer 18

Size: Smaller substances can enter easier

Polarity: Non-polar (hydrophobic) molecules can pass easier than polar (hydrophilic)

Question 19

Osmosis

Answer 19

The passive movement of water molecules across a partially permeable membrane through aquaporin protein channels from low solute to high solute concentration until equilibrium

Question 20

Facilitated Diffusion

Answer 20

The passive movement of molecules across the partially permeable membrane and the concentration gradient through the aid of a membrane channel

Question 21

Differences with Simple and Facilitated Diffusion

Answer 21

Simple Diffusion moves directly through the phospholipid bilayer while facilitated diffusion doesn’t move directly through

Simple diffusion doesn’t involve a channel protein while facilitated diffusion uses channel proteins

Simple diffusion transports hydrophobic molecules while facilitated diffusion transports hydrophilic molecules

Simple diffusion is slower and facilitated diffusion is faster

Question 22

Active Transport

Answer 22

The movement of substances through the membrane against their concentration gradient from low to high concentration through the use of ATP and carrier molecules

Question 23

Types of Active Transport

Answer 23

Protein Pumps

Exocytosis

Endocytosis

Question 24

Protein Pumps

Answer 24

The carrier has two sides, with one to recognize the substance to carry and one to release ATP to provide energy for the protein carriers

As a result, the protein molecule changes its shape so the target substance can be carried across the membrane

After that, the phosphate molecule is released from the protein molecule and combines with ADP to form ATP in the mitochondria

The protein then reverts back to its original shape

Question 25

Gated Ion Channels

Answer 25

Three sodium ions bind on the sodium potassium pump in the intracellular space

ATP attaches to the protein and a phosphate group is transferred to the pump via hydrolysis

This causes a change in shape for the sodium pump, thus releasing the sodium ions into the exterior

Two potassium ions bind to different regions of the protein in the exterior surface which causes the release of the phosphate group

The loss of phosphate makes the pump revert back to its original shape and releases the potassium ions into the intracellular space

Question 26

Exocytosis

Answer 26

The process by which macromolecules leave the cell

Vesicles from RER transport proteins to Golgi apparatus

These Vesicles undergo modification from the Golgi and get repackaged and sent into the plasma membrane

The vesicles carrying the protein fuse with the membrane expelling the content outside the cell

The membrane then goes back to its original state

Question 27

Endocytosis

Answer 27

The process by which macromolecules enter the cell

The membrane pulls inwards and seals back on itself forming a vesicle

The vesicle pinches off the plasma membrane

Inside of plasma membrane becomes outside of vesicle membrane, and vice versa

The vesicle enters the cytoplasm and carries the content anywhere in the cell

Question 28

Cotransport

Answer 28

The coupled movement of substances across a cell membrane via a carrier protein

A combination of facilitated diffusion and active transport

Question 29

Cell Adhesion Molecules (CAMs)

Answer 29

Cell surface proteins that are involved in the binding of cells with other cells through cell adhesion

Question 30

Function of CAMs

Answer 30

Help cells stick to each other

Crucial components in maintaining tissue structure

Play important roles in the cell’s growth