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PHGY 215 Module 1 > Section 2 > Flashcards

Section 2 Flashcards

1
Q

What are the roles of the plasma/cell membrane?

A
  • helps to regulate the internal fluid composition as it can control what molecules can move in or out of a cell
  • allows nutrients to enter cells and allows waste products to leave
  • permits chemical signals released from other cells in the body to influence a cell, thus allowing cell to cell communication
  • participates in joining cells together to form tissues and organs
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2
Q

What are the three primary functions of the plasma membrane?

A
  • ensure the cell’s survival
  • maintain homeostasis
  • function cooperatively and in coordination with surrounding cells
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3
Q

describe the phospholipids in the phospholipid bilayer

A
  • a phospholipid has a POLAR head with a NEG charged phosphate group and two NON-polar fatty acid tails
  • the head is hydrophilic
  • the tail is hydrophobic
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4
Q

describe the function/location of cholesterol in the phospholipid bilayer

A
  • found tucked in between the phospholipids
  • prevents fatty acid chains from packing too tightly together and forming rigid structures
  • keeps the membrane fluid
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5
Q

describe the function/location of membrane proteins in the phospholipid bilayer

A
  • inserted into the phospholipid bilayer, can be associated with the inner side or outer side or even pass all the way through the plasma membrane
  • function to maintain cell structure, regulate cell function, allow transport across the membrane and facilitate signalling
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6
Q

describe the location/function of ion channels in the phospholipid bilayer

A
  • they are specialized membrane proteins
  • they span the entire lipid membrane
  • they permit the entry or exit of ions
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7
Q

describe the location/function of carbohydrate chains in the phospholipid bilayer

A
  • short chains
  • can be attached to either proteins or the bilayer itself
  • form glycoproteins and glycolipids
  • involved in stabilizing membrane structure, act as cell surface receptors, participate in transportation across the cell membrane, and much more
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8
Q

what makes the membrane ‘fluid’?

A
  • the phospholipid bilayer being viscous and the individual phospholipids being able to move
  • the lipid bilayer provides the membrane with fluidity and elasticity
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9
Q

what makes the membrane a ‘mosaic’?

A

because it is embedded with proteins and other molecules that perform many functions important to cell functioning

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10
Q

what are the three different means cells are held together by?

A
  1. extracellular matrix
  2. cell adhesion molecules
  3. cell junctions
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11
Q

What is the extracellular matrix (ECM)? What is its function?

A
  • a network of fibrous proteins embedded in a gel-like mixture of complex carbohydrates
  • surrounds all cells in tissues and keeps them in place
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12
Q

what is the function of the watery gel (aka interstitial fluid) in the extracellular matrix?

A
  • allows for diffusion of nutrients from the blood and the removal of wastes from the cell
  • comprised of three major protein fibres(collagen, elastin, fibronectin)
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13
Q

what are the three major protein fibres found in the interstitial fluid? What are their functions?

A
  • Collagen: forms the cable-like fibres that give the ECM its tensile strength
  • Elastin: a rubber-like protein that allows tissues to be stretched and then recoil after the stretching force is removed
  • Fibronectin promotes cell adhesion
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14
Q

The majority of the ECM is secreted by _________ located within the _________

A

fibroblasts, interstitial space

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15
Q

what are fibroblasts?

A

a type of cell that synthesizes the ECM and collagen

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16
Q

describe the interactions of cell adhesion molecules (CAMs)

A
  • they are usually transmembrane proteins
  • the intracellular side of the protein interacts with the cytoskeleton
  • the extracellular side interacts with the extracellular matrix CAMs from other cells
  • CAMs are involved in protein-protein interactions (they bind with other cells or with the ECM) and therefore CAM cells help cells stick to each other and their surroundings
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17
Q

What are the four main families of cell adhesion molecules?

A
  • cadherins
  • selectins
  • NCAMs
  • integrins
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18
Q

what is the function of cadherins?

A
  • play important roles in cell adhesion by forming adherens junctions to bind cells within tissues together
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19
Q

what are cell junctions?

A

while CAMs hold cells together, some cells can also form specialized junctions between cells

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20
Q

what are the different types of cell junctions?

A
  • desmosomes
  • tight junctions
  • gap junctions
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21
Q

what are desmosomes?

A
  • a type of cell junction
  • aka “adherens junctions”
  • used to anchor together two adjacent cells that are not otherwise in direct contact
  • composed of dense intracellular thickenings (plaques) that are connected by glycoprotein filaments containing cadherins to attach the neighbouring plaques together
  • desmosome containing cells are able to stretch due to the network of strong fibres that forms when other cytoskeletal anchoring proteins attach to the plaque area
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22
Q

what are tight junctions?

A
  • a type of cell junction
  • aka “impermeable junction”
  • creates a very tight seal between cells, preventing movement of molecules from cell to cell
  • they are formed by long strings of junctional proteins between neighbouring cells aligning in the plasma membrane (where they meet is called a kiss site)
  • found primarily in epithelial tissues and allows them to form highly selective barriers between compartments with different chemical composition
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23
Q

What is the area where opposing junctional proteins from neighbour cells meet called?

A

A kiss site

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24
Q

Provide an example/function of tight junctions in epithelial tissues.

A

The lining of the digestive tract
- prevents blood vessels from being directly exposed to digestive juices and enzymes
- nutrients absorbed by the epithelial cells are then transported directly to the blood, because tight junctions even prevent substances moving between adjacent epithelial cells

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25
Q

what are gap junctions?

A
  • a type of cell junction
  • aka “communicating junctions”
  • six connexin protein subunits form one half of a gap junction (a connexon) which then aligns with the connexon of an adjacent protein and forms a tunnel that connects their intracellular spaces and allows them to communicate directly
  • they are common in cardiac and smooth muscle cells that need to spread the wave of excitation (electrical activity)
  • they also allow the spread of secondary messengers between connected cells which provides a mechanism for cells to act in a cooperative manner
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26
Q

describe the tunnel that forms from the alignment of connexons from two adjacent cells

A
  • the diameter in this tunnel is very narrow meaning only small, water soluble substances can pass through the junction
  • the tunnels can be opened and closed as needed to control cell to cell communication
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27
Q

___________ create a very tight seal between cells, preventing the movement of molecules between cells. The area where opposing junctional proteins from neighbouring cells meet is called a ___________. These junctions are primarily found in _______________.

A

Tight junctions, Kiss site, Epithelial tissues

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28
Q

___________ are composed of dense intracellular thickenings known as plaques that are connected by glycoprotein filaments containing ___________. These junctions are aka _____________. These junctions are often found in _________.

A

Desmosomes, cadherins, adherens junctions, skin

29
Q

Connexon proteins form _____________. These are common in ______________. They are aka _____________.

A

Gap junctions, cardiac muscle cells, communicating junctions

30
Q

The plasma membrane is:
a) permeable
b) semi-permeable
c) impermeable

A

b) semi-permeable

31
Q

What are two main factors for a molecule that determine membrane permeability?

A
  1. Size: small substances like ions can enter through the membrane spanning ion channels, whereas larger substances (e.g glucose) require transport proteins
  2. Solubility: if the molecule is lipophilic or lipophobic. Uncharged or nonpolar molecules are usually very lipophilic and can readily cross the plasma membrane. Charged or polar substances are lipophobic and cannot pass through the plasma membrane unaided
32
Q

What is lipophilicity, and what are some examples of lipophilic/lipophobic molecules?

A
  • Lipophilic is tending to combine with or dissolve in fats
  • Uncharged or nonpolar molecules (O2, CO2, fatty acids) are usually very lipophilic and can readily cross the plasma membrane
  • Lipophobic compounds are not soluble in lipids or other non-polar solvents
  • Charged or polar substances (Na+, Ca2+, glucose) are lipophobic and cannot pass through the plasma membrane unaided
33
Q

What is the difference between passive and active transport?

A

Passive does not require cellular energy, while active does

34
Q

Label the following as either passive or active transport:
- facilitated diffusion
- carrier mediated
- vesicular transport
- diffusion

A

Passive:
- Diffusion or facilitated diffusion

Active:
- Carrier mediated or vesicular transport

35
Q

What forces drive substances to cross the membrane?

A
  • their concentration gradient
  • their electrical gradient
36
Q

What is dynamic equilibrium?

A

substance movement occuring at the same rate in both directions (no net movement)

37
Q

What does diffusion depend on?

A

whether or not the membrane is permeable to the substance

  • if permeable there will be net diffusion of substance passively down its concentration gradient, across the membrane until equilibrium is reached
  • if not permeable, no diffusion and concentration gradient remains in place
38
Q

What is osmosis?

A

It is water moving down its concentration gradient by diffusion (balances out unequal concentrations of water on different sides of a membrane)
- water molecules are small enough that they can readily cross the plasma membrane by moving between the phospholipid molecules, also aquaporins are channels present in many cell membranes that allow water molecules to freely pass

39
Q

What is the difference between a penetrating and non penetrating solute in osmosis? Why is this important?

A

in a penetrating solute, both the molecules of water and solute move across the membrane to balance out the concentrations.

in a non penetrating solute, only the water molecules move, and balance it out by having the same concentration of water on each side.

It is important because for non penetrating solutes the volumes are not the same on each side of the membrane and can cause cells to either shrink or swell, depending on which way the net movement of water occurs

40
Q

What are the two forces that underlie the movement of water?

A

Osmotic pressure and hydrostatic pressure

Sometimes we can achieve equal pressures on both sides, but with different concentrations (a concentration gradient still exists but there is no net movement of water)

41
Q

What is hydrostatic pressure?

A

the force created by a given volume of water

the greater the volume, the greater the hydrostatic pressure

41
Q

What is osmotic pressure?

A

the underlying force that moves water down its concentration gradient

the greater the gradient, the greater the osmotic pressure trying to move water across the membrane

41
Q

What are the two types of carrier mediated transport, and explain both.

A
  1. Facilitated diffusion: does not require energy and uses a carrier to assist in the transport of a substance down its concentration gradient
  2. Active transport: also uses a carrier protein but moves the substance against its concentration gradient, thus requires energy in the form of ATP
41
Q

Provide an example of facilitated diffusion

A

The transport of glucose into cells. The plasma membrane is impermeable to glucose, so glucose carrier proteins bind to glucose to move it into the cell. Because glucose is constantly being consumed to produce ATP, a cell maintains the concentration gradient to move glucose inside

41
Q

Provide an example of active transport

A

Na+-K+-ATPase pump. The Na+ concentration is much higher outside the cell, whereas the concentration of K+ is much higher inside.

These concentration gradients are maintained by the NA+-K+-ATPase pump, which transports Na+ out of a cell and bring K+ in.

42
Q

Does the carrier protein change conformation once a solute molecule binds in facilitated diffusion?

A

Yes, it changes conformation so that the binding site is exposed to a region of lower solute concentration. (Basically closes on one side and opens on the other to let the molecule pass)

43
Q

Make sure you know the process of active transport step by step (its on the slide 22 of section 2 of module 1) or you can watch a video

A

Be happy

44
Q

What are the three important characteristics that determine what will be transported across the membrane in carrier mediated transport?

A
  1. Specificity: carrier proteins are specialized to recognize and transport a specific substance. often, structurally related substances may share the same transporter
  2. Saturation: There is a max amount of substance that can be transported at a given time (Tm). Once this max is reached, no other forces can increase the amount of that substance being transported
  3. Competition: when several related substances are recognized by a carrier protein, no individual substance will be able to achieve its own Tm.
45
Q

What is vesicular transport?

A

When cells transport substances bt wrapping them in a membrane enclosed vessel. (endo or exocytosis)

It requires energy and is therefore considered a form of active transport

46
Q

What are the three forms of endocytosis?

A
  1. Pinocytosis
  2. Receptor-mediated endocytosis
  3. Phagocytosis
47
Q

What is pinocytosis?

A

When the cell membrane engulfs and internalizes a small droplet of extracellular fluid. Membrane-deforming coat proteins on the inner side of the plasma membrane cause the formation of an endocytic pouch that is pinched off by the protein dynamin. The result is an internalized vesicle filled with extracellular fluid.

This is non-selective transport as the vesicle will contain whatever substances were close to the membrane at the time.

48
Q

What is dynamin?

A

An enzyme that aids in the formation of the endocytic vesicle

49
Q

Is pinocytosis selective or non-selective?

A

Non-selective transport as the vesicle will contain whatever substances were close to the membrane at the time.

50
Q

What is receptor-mediated endocytosis?

A

similar to pinocytosis except the trigger to create a vesicle is dependent upon the binding of a substance to a specific-receptor on the cell surface. (target molecule is transported in the vesicle)

51
Q

What is phagocytosis?

A

Involves the internalization of large multimolecular particles and only occurs in a few specialized cell types, such as white blood cells.

52
Q

Describe the process of phagocytosis

A
  1. Pseudopods begin to surround prey
  2. Pseudopods close around prey
  3. Prey is enclosed in endocytic vesicle that sinks into cytoplasm
  4. Lysosome fuses with vesicle, releasing enzymes that attack material inside vesicle
53
Q

Describe the process of pinocytosis

A
  1. solute and water molecules are outside the plasma membrane
  2. membrane pockets inward, enclosing solute and water molecules
  3. pocket pinches off as endocytic vesicle containing sample of ECF
54
Q

Describe the process of receptor-mediated endocytosis

A
  1. Substances attach to membrane receptors
  2. Membrane pockets inward
  3. Pocket pinches off as endocytic vesicle containing target molecule
55
Q

Which two organelles use exocytosis?

A

Endoplasmic reticulum (network of tubules inside the cell responsible for protein and lipid synthesis) and the Golgi complex (responsible for protein folding, modification, and packaging)

56
Q

What two purposes do the Golgi complex and endoplasmic reticulum use exocytosis for?

A
  1. As a mechanism to release large polar molecules, such as protein hormones, that cannot cross the plasma membrane. Often the release of the vesicles is dependent on a cell receiving a particular signal to release the substance within the vesicles
  2. To enable a cell to move proteins such as carrier proteins, ion channels, and receptors. When the vesicle membrane fuses with the plasma membrane any protein in the vesicle membrane becomes part of the plasma membrane
57
Q

What are the steps of exocytosis?

A
  1. Secretory vesicle formation: recognition markers in the membrane of the outermost Golgi sac capture the appropriate cargo from the Golgi lumen by binding only with the sorting signals of the protein molecules to be secreted. The membrane that will wrap the vesicle is coated with coatomer, which causes the membrane to curve, forming a bud.
  2. Budding from the Golgi: the membrane closes beneath the bud, pinching off the secretory vesicle
  3. Uncoating: The vesicle loses its coating, exposing the v-SNARE docking markers on the vesicle surface
  4. Docking at plasma membrane: the v-SNAREs bind only with the t-SNARE docking-marker acceptors of the targeted plasma membrane, ensuring that secretory vesicles empty their contents to the cell’s exterior
  5. Exocytosis occurs!
58
Q

What type of transport is the following, and does it require ATP?

The internalization of large multimolecular particles that only occurs in a few specialized cell types, such as white blood cells.

A

Phagocytosis

Requires ATP

59
Q

What type of transport is the following, and does it require ATP?

The use of a carrier protein to assist in the transport of a substance down its conc gradient.

A

Facilitated diffusion

no ATP

60
Q

What type of transport is the following, and does it require ATP?

Membrane-enclosed vesicle that was formed within the cell fuses with the plasma membrane and releases its contents into the extracellular environment.

A

Exocytosis

Requires ATP

61
Q

What type of transport is the following, and does it require ATP?

The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.

A

Pinocytosis

Requires ATP

62
Q

What type of transport is the following, and does it require ATP?

The use of a carrier protein to assist in the transport of a substance against its conc gradient.

A

Active transport

Requires ATP

63
Q

What type of transport is the following, and does it require ATP?

The movement of water molecules across a semi-permeable membrane down a conc gradient.

A

Osmosis

no ATP

64
Q
A

PHGY 215 Module 1 (6 decks)

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