Cellular Membrane Structure + Function

Question 1

What are the major components of the cellular membrane?

Answer 1

The cellular membrane is made up of mostly lipids (phospholipids) and proteins, yet carbohydrates play an important role in the membrane as well

Question 2

What does it mean that both proteins and phospholipids within the cellular membrane are amphipathic?

Answer 2

This means that both proteins and phospholipids within the cell are made up of regions which are both hydrophobic and hydrophilic

Question 3

Describe the fluid mosaic model

Answer 3

• The fluid mosaic model defines the general makeup of the cell membrane and its different components which allow for the membrane to remain fluid.
• This model consists of a phospholipid bilayer in which the hydrophilic heads of the phospholipids are exposed to extracellular and intercellular fluids while the hydrophobic hydrocarbon tails make up the inner membrane.

Question 4

Describe the difference between integral and peripheral proteins.

Answer 4

Integral proteins are those which stretch across and penetrate through the hydrophobic interior of the membrane (ex. transmembrane proteins)

Peripheral proteins are those which remain on both the extracellular and intercellular surface of the membrane.

Question 5

Why are peripheral proteins immobile?

Answer 5

Peripheral proteins found on the extracellular side are held in place by the extracellular matrix

Peripheral proteins found on the intercellular side are held in place by the cytoskeleton

Question 6

Explain the effects of cooling temperatures on the fluidity of the cell membrane.

Answer 6

Membranes which are concentrated with phospholipids with saturated hydrocarbon tails are known to solidify in lower temperatures whereas those concentrated with unsaturated hydrocarbon tails can remain fluid.

Question 7

Why are membranes rich with phospholipids made up of unsaturated hydrocarbon tails able to remain fluid in lower temperatures?

Answer 7

Unsaturated hydrocarbon tails form kinks in cooler temperatures which prevent the phospholipids from solidifying and further lower the temperature at which the membrane may solidify

Prevents the phospholipids from packing together too tightly

Question 8

Define a “fluidity buffer”

Answer 8

A steroid cholesterol found within the phospholipid bilayer is often referred to as a “fluidity buffer” as it prevents membranes in warmer temperatures from becoming too fluid, though also at lower temperatures it can hinder solidification as for its disruption to the packing of phospholipids

Question 9

Why is it important that the cell membrane maintains fluidity?

Answer 9

The significance of maintaining a fluid cell membrane is to ensure that the membrane remains semi-permeable to allow the transportation of certain substances inside and outside the cell. Also, it allows for proteins to move to where needed within the cell.

Question 10

Why do different organisms have different lipid compositions within their cell membranes?

Answer 10

This is a result of the evolution and adaptation of organisms to their environmental conditions.

Those organisms which tend to live in cooler habitats have developed phospholipids which are made up of unsaturated hydrocarbon tails for their kinking properties allow their membranes to remain fluid in these cooler temperatures.

Organisms which live in warmer habitats have other unusual properties to their hydrocarbon tails which prevent the membranes from becoming too fluid.

Question 11

What are the 6 major functions of proteins found within the cellular membrane?

Answer 11

1) Transport
2) Enzymatic activity
3) Signal Transduction
4) Cell-cell recognition
5) Intercellular Joining
6) The maintenance of cell shape and structure

Question 12

What is the major component which allows proteins to perform cell-cell recognition?

Answer 12

small chains of carbohydrates, often bound to proteins (glycoproteins) and sometimes bound to lipids (glycolipids) found on each cell membrane act as an identification tag. These tags loosely bind to the membranes of neighbouring cells in order to recognize each other.

Question 13

What is the purpose of cell-cell recognition?

Answer 13

This major function of proteins found within the cell membrane is to recognize and act as a defence system to foreign cells and allow for the organization of different cells to different organs and tissues.

Question 14

How does the lipid composition of the cell membrane and transport proteins contribute to the semi-permeability of the cell membrane?

Answer 14

The lipid composition of the cell membrane contributes to the semi-permeability of the membrane as how its hydrophobic interior only allows non-polar molecules to pass through the membrane easily whereas polar, hydrophilic molecules may only pass through if their small and slow.

Transport proteins contribute to semi-permeability as they only allow for the passage of specific molecules

Question 15

What are aquaporins?

Answer 15

Proteins which specifically transport polar water molecules across the cellular membrane

Question 16

What is passive transport and how does it take place?

Answer 16

The diffusion of a substance across a biological membrane requires no energy input. Substances naturally diffuse down a concentration gradient which favors moving in the less concentrated direction

Question 17

What is the difference between channel and carrier proteins?

Answer 17

Channel proteins are known to create a passageway for hydrophilic solutes to cross the membrane whereas carrier proteins change shape and carry and guide hydrophilic solutes across the membrane

Question 18

Define osmosis

Answer 18

The diffusion of water from an area of greater free water concentration to that of a lower concentration

Question 19

What is tonicity and what are the three types?

Answer 19

The ability of a cell’s surrounding solution to cause the cell to either gain or lose water.

1) Isotonic
2) Hypotonic
3) Hypertonic

Question 20

Define what would happen to a cell in an isotonic environment

Answer 20

Isotonic means that the concentration of free water inside the cell is the same as the concentration outside the cell and therefore, In an isotonic environment, there is no movement of water in or out of the cell.

Question 21

Define what would happen to a cell in a hypertonic environment

Answer 21

Hypertonic means that the concentration of solutes outside the cell is greater than that inside the cell and that there is more free water inside the cell. As a result of this water imbalance, free water will move out of the cell causing the cell to shrivel and die.

Question 22

Define what would happen to a cell in a hypotonic environment

Answer 22

Hypotonic means that there is less free water outside the cell than inside but there are more solutes inside the cell. As a result of this, water will move into the cell potentially causing the cell to swell, burst and die.

Question 23

How is osmoregulation maintained in plant cells?

Answer 23

Osmoregulation, meaning the maintained balance of water and solute concentrations in plant cells is easily maintained thanks to their rigid cell walls.

Cell walls being inelastic are unable to expand therefore creating a pressure which pushes excessive concentrations of water out of the cell

Question 24

What is turgor pressure?

Answer 24

Turgor pressure is a force experienced by plant cells through their cell walls which oppose excessive water intake

Question 25

What does it mean for a plant cell to be turgid and when does this happen?

Answer 25

The term turgid refers to the healthy state of a plant cell. A plant cell is turgid when surrounded by a hypotonic environment. When experiencing turgor pressure, plant cells become firm which is preferred by most non-woody plants as this provides the plants mechanical support. Without turgor pressure, plants may become flaccid and wilt.

Question 26

What kinds of tonicity are not ideal for plant cells to remain turgid and why?

Answer 26

For a plant cell to remain turgid, it must be surrounded by a hypotonic environment.

Tonicities which are not as ideal may include isotonic and hypertonic environments

isotonic environments are unable to provide plant cells with any mechanical support and may result in wilting as there is no movement of water in and out of the cell and therefore also no turgor pressure

Hypertonic environments, similar to animal cells will cause the plant cell to lose water, wilt and die

Question 27

How are diffusion and facilitated transport relative to one another and how are they different?

Answer 27

Diffusion and facilitated transport are both relative to one another as they are both types of passive transport meaning they don’t require the use of energy. Diffusion is the natural movement of substances across the membrane down a concentration gradient whereas facilitated transport is the transport of substances across the membrane aided by proteins such as channel and carrier proteins.

Question 28

What is active transport and how is it different from passive transport?

Answer 28

Active transport is the transport of molecules against it’s concentration gradient with the use of energy whereas passive transport requires the use of no energy as molecules may only be carried along it’s concentration gradient

Question 29

What transport proteins can perform active transport and why so?

Answer 29

The only transport proteins which can perform active transport are carrier proteins. This is because channel proteins can’t carry molecules against their concentration gradient whereas carrier proteins open and close therefore allowing the substances to move against their gradient.

Question 30

what is the major electrogenic pump in animal cells?

Answer 30

The sodium-potassium pump is the major electrogenic pump in animal cells. This is because this protein generates a voltage across the membrane for a net charge of one positive charge into the extracellular fluid from the cytoplasm with every 2 potassium ions pumped into the cell for 3 sodium ions pumped out

Question 31

How are electrogenic pumps beneficial to cells?

Answer 31

electrogenic pumps are beneficial to cells as the voltage generated helps store energy which can be used to carry out cellular processes.

Question 32

What is the difference between an electrochemical gradient and a concentration gradient?

Answer 32

The difference between an electrochemical gradient and a concentration gradient is that a concentration gradient is driven by the chemical force of an imbalance of solutes whereas an electrochemical gradient is driven by both the chemical force of the solute imbalance and an electrical force of the ions movement.

Question 33

what is cotransport?

Answer 33

Cotransport is the diffusion of a substance against its concentration gradient along with another substance moving along its concentration gradient

Question 34

Define and compare endocytosis and exocytosis

Answer 34

Endocytosis is how the cellular membrane takes in different molecules by forming vesicles which enclose the particles and carry them to where needed within the cell. Exocytosis is how vesicles carrying wastes fuse with the cell membrane and secrete certain molecules from the cell.

Question 35

What is phagocytosis?

Answer 35

Phagocytosis can also be understood as cell-eating