B2.1 Membranes and Membrane Transport

Question 1

State that phospholipids naturally form continuous sheet-like bilayers in water.

Answer 1

When added to water phospholipids naturally form bilayers

Question 2

List locations of lipid bilayers in cells.

Answer 2

Nucleus, mitochondria, and chloroplast

Question 3

Outline the location of aqueous solutions in relation to the lipid bilayer.

Answer 3

The cytoplasm is located within the lipid bilayer and other aqueous solutions are located outside the lipid bilayer

Question 4

State the primary function of the cell membrane.

Answer 4

Separating the cytoplasm and cell contents from the environment

Question 5

Explain why the hydrophobic core of a lipid bilayer has low permeability to large molecules and hydrophobic particles.

Answer 5

In order to not ruin the internal chemistry of the cell

Question 6

Describe simple diffusion.

Answer 6

the passive transport of particles from a region of high concentration to low concentration

Question 7

Outline the impact of concentration gradient, particle size and polarity or charge of molecules on the rate of diffusion across a lipid membrane.

Answer 7

Higher concentration gradients, smaller particle sizes, and non-polar characteristics promote faster diffusion and vice versa

Question 8

Explain two examples of simple diffusion of molecules into and out of cells.

Answer 8

Oxygen moves from an area of higher concentration (such as the external environment or capillaries) to an area of lower concentration (inside the cell).

The higher concentration of carbon dioxide inside the cell creates a concentration gradient, and CO2 molecules move from inside the cell to an area of lower concentration (such as the bloodstream or extracellular space).

Question 9

Compare the location of integral and peripheral proteins in the membrane.

Answer 9

Integral proteins are permanently attached to the plasma membrane, peripheral proteins are temporarily attached to one side of the membrane

Question 10

Outline how the hydrophobic and hydrophilic structures of proteins impact their anchoring to the membrane.

Answer 10

The hydrophobic section of the integral protein anchors the protein in the bilayer, whereas the peripheral protein has no hydrophobic part and isnt anchored to the protein

Question 11

List at least four functions (with example) of membrane bound proteins.

Answer 11

Transport GLUT2
Cell signalling EGFR
Enzymatic activity ATP
Cell adhesion Cadherin

Question 12

Define osmosis.

Answer 12

Osmosis is the passive transport of water molecules from a region of low solute to a region of high solute concentration

Question 13

Outline the structure and function of aquaporin proteins.

Answer 13

Aquaporins are integral channel proteins that selectively transport water rapidly through membranes.

Question 14

Describe the structure and function of channel proteins.

Answer 14

Channel proteins are specific to the molecule that can pass through them making cell membranes more selective

Question 15

Define facilitated diffusion.

Answer 15

The passive transport of molecules from a region of high concentration to a region of low concentration through channel proteins.

Question 16

Outline the specificity of channel proteins for ions.

Answer 16

size, charge, and coordination chemistry

Question 17

List types of gates on channel proteins

Answer 17

Gated channels open in response to stimuli whereas voltage gated channels open and close based on potential difference across membranes

Question 18

Describe one example of facilitated diffusion through a protein channel.

Answer 18

GLUT1 a transmembrane protein that facilitates the passive transport of glucose molecules across the cell membrane.

Question 19

Describe the structure and function of pump proteins, including the role of specificity, conformational change and ATP.

Answer 19

Pump proteins are integral membrane proteins that function as active transporters by utilizing energy from ATP to move ions against their concentration gradient with high specificity.

Question 20

Compare active transport using a pump protein to facilitate diffusion using a channel protein.

Answer 20

Channel proteins requires no energy, has no conformational change, goes with the concentration gradient and are a lot less selective.

Question 21

Explain one example of active transport of molecules into and out of cells through a protein pump.

Answer 21

The sodium potassium pump an integral membrane protein that transports three sodium ions out of the cell while also moving 2 potassium ions into the cell

Question 22

Define selective permeability.

Answer 22

Allowing certain substances to pass while restricting others from crossing

Question 23

Outline how channels and pumps in the membrane allow for selective permeability.

Answer 23

Because they only allow specific particles to pass or transport through.

Question 23

State the simple diffusion is not selective and depends only on the concentration gradient, particle size and polarity or charge of molecules.

Answer 23

Simple diffusion is not selective and depends only on concentration gradient, particle size and polarity or charge of molecules.

Question 24

Outline the structure of glycoproteins and glycolipids.

Answer 24

Glycoproteins are membrane proteins with a carbohydrate chain attached

Glycolipids are phospholipids with a carbohydrate chain attached.

Question 25

Describe the role of glycoproteins and glycolipids in cell adhesion and cell recognition.

Answer 25

glycoproteins are sometimes responsible for direct attachment between neighboring cells. The carbohydrates of glycoproteins and glycolipids can form an extracellular matrix with their neighboring cells, leading to stable cell adhesion

The carbohydrate chains that form on glycoproteins and glycolipids have specific shapes allowing the immune system to recognise the cells as self. Glycoproteins and glycolipids act as antigens if the carbohydrate chain isn’t recognized.

Question 26

Compare and contrast the structure, melting point and relative fluidity of saturated and unsaturated fatty acids in lipid bilayers.

Answer 26

Saturated fatty acids have no C-C double bonds resulting in a straight and close packing of phospholipids, with a higher melting point and a higher viscosity. Unsaturated fatty acids have C-C double bonds, resulting in kinks in the fatty acid tails, with lower melting points and lower viscosity

Question 27

Outline an example of adaptation in membrane composition in relation to habitat.

Answer 27

As the temperature decreases steelhead trout have a higher concentration of unsaturated fatty acid

Question 28

Describe the structural placement of cholesterol within the cell membrane.

Answer 28

Cholesterol is located between fatty acid tails of phospholipids in cell membranes

Question 29

Outline how temperature affects cell membrane fluidity.

Answer 29

Higher the temperature the less fluid the cholesterol is and vice versa

Question 30

Describe the function of cholesterol as a modulator of membrane fluidity.

Answer 30

It allows for the stability of the membrane as at higher temperatures it increases the melting point and at lower temperatures it maintains the fluidity

Question 30

Outline the structure and function of vesicles in cells.

Answer 30

Vesicles are small membrane bound structures involved in the transport of materials within cells

Question 31

State that the fluid properties of the cell membrane allow for the formation of vesicles.

Answer 31

The fluid properties of the cell membrane allows the formation of vesicles

Question 32

Outline the formation of a vesicle within the cell.

Answer 32

Through the enclosing of materials required to be transported or stored

Question 33

Describe the formation of a vesicle via endocytosis.

Answer 33

The large particle is entering the cell and is surrounded by the plasma membrane, which buds off inside the cell to form a vesicle.

Question 33

Describe the transport of materials within a cell using vesicles.

Answer 33

Proteins to be secreted are synthesized by ribosomoes and attached to the RER
The RER forms a vesiclle containing protein and sends it to the Golgi Apparatus
The vesicle then fuses with the Golgi Apparatus and the Golgii modifies the protein, it packages the protein in a secretory vesicle which moves towards the plasma membrane, where it fuses with plasma membrane releasing it outside of the cell.

Question 34

Outline two examples of materials brought into the cell via endocytosis.

Answer 34

bacteria and viruses to eat and destroy

Question 35

Describe the release of materials from cells via exocytosis.

Answer 35

Exocytosis involves the fusion of a vesicle with the plasma membrane releasing content outside of the cell.

Question 36

Outline two examples of materials released from a cell via exocytosis.

Answer 36

Neurotransmitters released from neurons for intercellular communication.
Hormones released from endocrine cells to regulate body functions.

Question 37

State the effect of endocytosis and exocytosis on the area of the cell membrane.

Answer 37

Endocytosis increases, exocytosis decreases the cell membrane area

Question 38

Contrast secretion with excretion.

Answer 38

Secretion is the release of specific substances synthesized by cells into body fluids or external environment, whereas excretion is the elimination of waste products or excess substances from the body.

Question 39

Outline the structure, function and specificity of voltage-gated channels.

Answer 39

Integral proteins allowing specific ions to pass through facilitated diffusion in response to changes in membrane potential difference

Question 40

Describe the function of the voltage-gated potassium channel.

Answer 40

A voltage gated channel located along the neurons

Question 41

Outline the structure, function and specificity of ligand-gated channels.

Answer 41

Integral proteins allowing specific ions to pass through facilitated diffusion in response to a ligand attached to the channel

Question 42

Describe the function of the ligand-gated sodium channel in the postsynaptic cell membrane (AKA the nicotinic acetylcholine receptor).

Answer 42

It allows sodium ions to enter a neuron

Question 43

State the function of an exchange-transporter proteins.

Answer 43

To facilitate silmutaneous movement of 2 different molecules or ions across a membrane in opposite directions

Question 44

Describe the structure and function of the sodium-potassium pump.

Answer 44

An integral membrane protein which allows 3 sodium ions out of the cell and 2 into the cell against their respective concentration gradients.

Question 45

Outline the role of the sodium-potassium pump in maintaining neuronal resting potential.

Answer 45

By contributing to the negative charge inside the cell and the positive charge outsidem which is crucial for proper electrical signalling in neurons.

Question 46

Outline the function of cotransporters in indirect active transport.

Answer 46

They facilitate the transport of molecules across cell membranes by harnessing the energy stored in the electrochemical gradient of one molecule to drive the transport of another molecule against it’s concentration gradient

Question 47

Describe the role of glucose cotransport proteins in the small intestine and kidney nephron.

Answer 47

SGLT1 in the small intestine and SGLT2 in the kidney nephron play a vital role in contributing to the homeostatis of glucose in the body.

Question 48

Outline the role of CAMs in the formation of tissues.

Answer 48

They mediate cell-cell adhesion and cell-matrix interactions. They also regulate tissue dvelopment, differentiation and maintenanc of tissue architecture