1.6 Transport Across the Cellular Membrane

Question 1

Passive vs active transport

Answer 1

Passive transport doesn’t require ATP and travels with the gradient. Active transport travels against the concentration gradient and requires ATP

Question 2

What are the four types of passive transport

Answer 2

Simple, filtrations, osmosis, facilitated diffusion

Question 3

How does simple diffusion work? what is the goal? What is the rate of flow proportional to? What inhibits the passage of certain molecules?

Answer 3

-Motion of particles from a region of high concentration to low concentration
-goal is the reach equilibrium on both sides
-the rate of flow is proportional to the concentration gradient for instance a high concentration results in a faster rate of diffusion
-size and electrical charge may inhibit the passage of certain molecules

Question 4

How do molecules travel in facilitated diffusion? what do molecules require (4)?

Answer 4

-molecules travel from a region of high to low concentration
-require transmembrane proteins which establish pores through which ions and some hydrophilic molecules can pass through
-the channels open and close by physiological needs and state of the cell
-these proteins and termed gated because they open and close

Question 5

How does filtration work? what do the molecules depend on inorder to get through the cell membrane?

Answer 5

-molecules are being forced to the other side of the membrane using hydrostatic pressure created by the cardiovascular system (heart beating)

-which molecules are allowed to pass through depends largely on the size of the molecules compared to the pores

Question 6

what is osmosis? how do the proteins transform in order to make this work?

Answer 6

-the diffusion of water across the membrane moving from an area of low to an area of high concentration

-transmembrane proteins form hydrophilic (water-loving) channels through which water molecules can move

Question 7

What is a hypertonic solution? What happens to a cell when it is placed in a hypertonic solution?

Answer 7

A solution that has a high concentration of solute compared to another solution

• when a cell is placed in a hypertonic solution that water diffuses out of the cell because water flows where there is a higher concentration of solute which causes the cell to shrivel

Question 8

What is a hypotonic solution? What happens to a cell when it is placed in a hypotonic solution?

Answer 8

A solution that has a low concentration of solute compared to another solution

-when a cell is placed in a hypotonic solution, water diffuses into the cell causing the cell to swell and possibly explode

Question 9

What are isotonic solutions? What happens to a cell when placed in a isotonic solution?

Answer 9

When a solution has the same concentration of solute compared to another solution

-since the concentration is the same inside and out of the cell, when a cell is placed in an isotonic solution, water diffuses into and out of the cell at the same rate

Question 10

What is active transport? what does it require? what does it allow the cell to do?

Answer 10

The movement of molecules against a concentration gradient from a region of low concentration to the high concentration

-since molecules are being moved against the concentration gradient, cellular energy is required

-allows a cell to maintain conditions different from the surrounding environment

Question 11

Where does cellular energy come from? which part of the ATP structure provides energy?

Answer 11

Cellular energy comes from ATP which is a multifunctional nucleotide

-contains three phosphate groups and it is this special structural characteristics that provides ATP which energetic abilities

Question 12

How is ATP produced? How is the reaction reversed?

Answer 12

Produced through cellular respiration that breaks the bonds within glucose to derived useful energy

-it is produced by the enzyme ATP synthase which links an organic phosphate into a adenosine diphosphate molecules

-the reaction is reversible and can be broken down into ADP and Pi along with a net release of free energy so it can be continually recycles by other processes that link them back together

Question 13

How does the sodium-potassium pump take in sodium and potassium? What does it require?

Answer 13

In order to carry molecules across the cell membrane that have very specific shapes that fit and bond well with sodium and potassium ions

-because the transport of these molecules are against the concentration gradient, they require a significant amount of energy

Question 14

Potassium vs sodium concentration

Answer 14

There is a higher concentration of potassium inside the cell and a higher concentration of sodium outside the cell

Question 15

what is endocytosis? How does the process work?

Answer 15

The process by which the cell takes in molecules that are too large to pass through the cellular membrane

-the cell engulfs proteins and molecules near the surface of the cellular membrane

-it can swallow large molecules, and bits of protein and or create receptor pockets through which specific types of molecules are attracted

-once the molecules are surrounded by the cellular membrane the area is pinched off to create vesicles inside the cell that holds the molecule

Question 16

Describe the process of exocytosis. what are the three steps?

Answer 16

The process by which the cell expels molecules that are too large to pass through the membrane

1. waste or other chemicals inside the cell are surrounded by a vesicle
2. then the vesicle moves to the edge of the cell and attaches itself to the cellular membrane
3. then pushes out what it’s carrying to the extracellular fluid

Question 17

What do endocytosis and exocytosis both make use of? What is this substance used for?

Answer 17

They both make use of vesicles for molecular transport which are small membrane bound sacs that move around the cell

-they are used for storage and transport

Question 18

What makes the special characteristic of a vesicles?

Answer 18

Because they are entirely enclosed by a membrane, inside they can have a completely different composition than that of their cell

Question 19

what is the process of phagocytosis?

Answer 19

a type of endocytosis when a cell uses its membrane to engulf a large particle creating an internal compartment called a phagosome. A cell that performs phagocytosis is called a phagocyte

Question 20

what is the process of pinocytosis?

Answer 20

a type of endocytosis process in which tiny particles suspended in the extracellular fluid is brought into the cell through the invagination of the cell membrane resulting in particles within a small vesicle inside the cell.

Question 21

what is the process of receptor-mediated endocytosis?

Answer 21

a process in which the cell binds to absorb hormones, metabolites, and proteins by cell surface receptors and in some cases viruses by invagination. It forms vesicles and once it is in the cytoplasm the clathrin molecules coat the outer edge of the vesicle leaves and associate with new receptors on the plasma membrane. The uncoated vesicles fuse with an endosome and the ligands and receptors separate connecting at opposite ends of the endosome. Sections of the endosome containing unbound receptors pinch off forming transport vesicles that return the receptors to the plasma membrane. the ligands fuse with a lysosome containing digestive enzymes. the digestive enzymes break the ligands down into smaller molecules which are released into the cytoplasm of the cell and are used in a number of cell processes.

Question 22

how is cholesterol carried through the cell membrane?

Answer 22

it is carried in tiny droplets called lipoproteins

Question 23

what are regulated secretory pathways used for? what do they form? what causes the contents of these vesicles to be released?

Answer 23

It is used for proteins that are stored and secreted on demand

-such proteins form proteins aggregates surrounded by vesicles and are called dense core secretory granules

-the contents of these vesicles are released due to specific stimuli

-insulin is produced by the beta cells of the pancreas and stored in dense secretory granules when blood sugar increases to a threshold level, insulin-containing secretory granules fuse with the plasma membrane releasing insulin to the blood

Question 24

what are the four functions of exocytosis?

Answer 24

-release enzymes, glucose, hormones, and proteins for other parts of the body to use

-neurotransmitters

-communicate defence measures against a disease

-expel cellular waste

Question 25

what are the four functions of endocytosis?

Answer 25

-receive nutrients

-entry for pathogens

-cell migration and adhesion

-signal receptors

Question 26

what is the main difference between endocytosis and exocytosis?

Answer 26

endocytosis creates vesicles and exocytosis destroys vesicles

Question 27

what are the different types of passive transport?

Answer 27

filtration, osmosis, simple, facilitated

Question 28

what are the different types of active transport?

Answer 28

endocytosis and exocytosis

Question 29

how do electrolytes move through the cell membrane?

Answer 29

Electrolyte ions require facilitated diffusion and active transport to cross the semi-permeable membrane

Question 30

how does water move through the cell membrane?

Answer 30

Water moves across cell membranes by diffusion, in a process known as osmosis. Osmosis refers specifically to the movement of water across a semipermeable membrane, with the solvent (water, for example) moving from an area of low solute (dissolved material) concentration to an area of high solute concentration.

Question 31

how do macromolecules and lipids move through the cell membrane?

Answer 31

These molecules pass across membranes via the action of specific transmembrane proteins, which act as transporters.

Question 32

how does iron pass through the cell membrane?

Answer 32

facilitated diffusion or by a carrier-mediated transport process

Question 33

how does cholesterol pass through the membrane?

Answer 33

diffuses into the outer leaflet of the plasma membrane and then use the protein channel to flip to the inner leaflet or enter the cytosol to be bound by a carrier protein

Question 34

how do waste molecules enter the cell membrane?

Answer 34

Cells use both facilitated diffusion and osmosis to get rid of their wastes

Question 35

how does insulin enter the cell membrane?

Answer 35

binds to receptors on the cell’s surface, causing GLUT4 molecules to come to the cell’s surface. As their name implies, glucose transporter proteins act as vehicles to ferry glucose inside the cell

Question 36

how do lipids enter the cell membrane?

Answer 36

simple diffusion

Question 37

how do proteins pass through the cell membrane?

Answer 37

facilitated diffusion