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BIO130 Final > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

How do epithelial cells interact with each other and the extracellular matrix?

A

through junctions to form tissues

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2
Q

What do sheets of epithelial cells do?

A

they cover the external surfaces and organs, line internal body cavities

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3
Q

What are all the junctions present in epithelial cells?

A
  • tight junctions
  • adherens junctions
  • desmosomes
  • gap junctions
  • hemidesmosomes
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4
Q

When are cells arranged in a specific order? What is this order?

A

polarized epithelial cells
- tight junctions (apical most)
- adherens junctions (cell-cell anchoring junctions)
- desmosomes (cell-cell anchoring junctions)
- gap junctions
- hemidesmosomes (cell-ECM anchoring junction)

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5
Q

What is the primary function of tight junctions?

A

Create a tight deal between cells and prevent the mixing of extracellular environments (like apical membrane proteins and basolateral membrane proteins)
serve as barriers to prevent the leakage of water-soluble molecules between neighboring cells

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6
Q

What are the main proteins involved in forming tight junctions?

A

claudins and occludins, extracellular domain in one cell interacts with the extracellular domain in neighbour cell (always occludin - occludin and claudin - claudin)

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7
Q

How do tight junctions work in the intestinal epithelial cell?

A

it prevents the Na+-glucose symporter (on apical membrane) to pass through to the basolateral membrane which has the GLUT2 uniporter and Na+-K+ pump

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8
Q

How do epithelial sheets act as barriers?

A

Tight junctions prevent racer molecules from inside the lumen from passing through into the extracellular space

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9
Q

How do tight junctions maintain the polarity of membrane proteins?

A

restrict the movement of membrane proteins between apical and basal lateral domains, thus maintaining their polarity

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10
Q

How are cells sealed together by tight junctions?

A

by branching strands of transmembrane proteins (claudins and occludins) in the plasma membranes of interacting cells

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11
Q

What are anchoring junctions and what are their function?

A
  • cell-cell anchoring junctions (adherens junctions, desmosomes which link cytoskeletons of neighboring cells)
  • cell-ECM anchoring junctions ( hemidesmosomes that link the cytoskeleton to the basal lamina)

they provide mechanical strength to the epithelium

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12
Q

What are transmembrane adhesion proteins in adherens junctions?

A
  • transmembrane proteins with extracellular domains that interact with the adhesion protein of neighboring cells or extracellular matrix. They also have intracellular domains that interact with linker proteins, which are linked to cytoskeletal filaments
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13
Q

What are intracellular linker proteins?

A

cytosolic proteins, they link transmembrane adhesion proteins to cytoskeletal filaments

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14
Q

What are adherens junctions?

A

they form an adhesion belt, that encircles the inside of the plasma membrane

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15
Q

Which transmembrane adhesion proteins is involved with adherens junctions?

A

cadherin proteins which interact with neighboring cells, and intracellular linker proteins link cadherin to the actin filaments

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16
Q

Where do cadherin proteins become concentrated?

A

at sites off cell-cell interactions from adherens junctions

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17
Q

How do tight junctions differ from adherens junctions?

A

Tight junctions seal gaps between cells to prevent substances from passing through, while adherens junctions form an adhesion belt between cells to stick them together

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18
Q

How are desmosomes and hemidesmosomes similar?

A

both link to intermediate filaments (keratin filaments)
Intermediate filaments provide the most structural strength

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19
Q

How do desmosomes and hemidesmosomes differ?

A

Desmosomes: linked to keratin filaments and connect to neighboring cells

hemidesmosomes: anchor keratin filaments to the basal lamina

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20
Q

How do desmosomes link cells together?

A

through transmembrane adhesion (nonclassical cadherin proteins) proteins called desmogleins and desmocollins. These proteins interact with similar proteins on adjacent cells to form a strong adhesive bond (bind homophilic and heterophilic). Intracellular linker proteins link desmoglein and desmocollin to keratin filaments inside the cell

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21
Q

What are hemidesmosomes?

A

specialized junctions that anchor epithelial cells to the underlying basal lamina

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22
Q

Where are hemidesmosomes found?

A

prevalent in epithelial cells, specifically at the interface between the cell and the basal lamina

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23
Q

How do hemidesmosomes attach epithelial cells to the extracellular matrix?

A

make connections between transmembrane adhesion proteins (integrins) on the cell surface and intermediate filaments inside the cell, such as keratin filaments. Intracellular link proteins link integrin to keratin filaments inside the cell

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24
Q

What is the function of hemidesmosomes?

A

provide mechanical strength and stability to epithelial tissues by anchoring them to the underlying basal lamina

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25
Q

What are desmosomes?

A

specialized cell structures that function in cell-to-cell adhesion. They are important in tissues that experience mechanical stress, such as the skin and heart muscle.

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26
Q

What is the function of gap junctions?

A

allow for communication between cells. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to pass freely between cells.

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27
Q

What is the structural unit that forms a gap junction?

A

2 connexons for an intercellular channel
1 connexon = 6 connexins (1 subunit is a connexin)

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28
Q

How do substances pass through gap junctions?

A

Substances pass through gap junctions via channels formed by aligned connexons from adjacent cells that allow small molecules and ions to move directly from one cell’s cytosol to another’s

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29
Q

Which types of molecules typically move through gap junctions?

A

Ions and metabolites <1000 daltons (cAMP, nucleotides, glucose, amino acids)
but not larger molecules (macromolecules, proteins, nucleic acids)

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30
Q

Can the opening or closing of gap junction channels be regulated? If so, how?

A

Yes, the opening or closing of gap joint channels can be regulated in response to extracellular or intracellular signals
- dramatic increases in cytosolic Ca+ (closes gap junction)
- membrane damage: Ca leaks into the damaged cell (Gap junction closes), this prevents the loss of metabolites from adjacent cell

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31
Q

Why do plant cells lack cell junctions found in animal cells?

A

they are surrounded by cell walls which hold the cells together and provide mechanical strength

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32
Q

What are plasmodesmata?

A

channels that traverse the cell walls of plant cells and some algal cells, facilitating transport and communication between individual plant cells

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33
Q

How do substances travel through plasmodesmata?

A

substances can move through the cytoplasmic sleeve of plasmodesmata via simple diffusion or sometimes facilitated by active transport mechanisms

34
Q

What types of molecules typically pass through plasmodesmata?

A
  • small soluble molecules (<1000 daltons) move freely (sugars, ions, essential nutrients)
  • controlled trafficking of large complex molecules (gating of proteins, regulatory RNAs)
35
Q

How do plasmodesmata differ from gap junctions in animal cells?

A

Plasmodesmata in plant cells allow for direct cytoplasmic connections between adjacent cells with a continuous plasma membrane lining the channel. In contrast, gap junctions in animal cells facilitate intercellular communication by forming pores that connect adjacent cell membranes without continuity of the plasma membrane

36
Q

What is an example of plasmodesmata gating?

A
  • blocking the movement of large complex molecules
  • enhanced callose deposition
  • callose is a plant polysaccharide
  • permeability control through reversible callose deposition
37
Q

What are animal tissues composed of?

A

cells and extracellular matrix
- epithelium, basal lamina and connective tissue

38
Q

What are some examples of epithelial tissue?

A

intestinal lining, skin epidermis

39
Q

What is the epithelium?

A

also known as epithelial tissues
- composed of cells closely associated and attached to each other with a limited extracellular matrix (thin basal lamina)

40
Q

What provides resistance to mechanical stress in the epithelium?

A

cytoskeletal filaments

41
Q

What are some examples of connective tissues?

A

skin dermis, bone, tendon, cartilage

42
Q

What is connective tissue?

A

cells that are rarely connected to each other but are attached to the matrix, with a plentiful extracellular matrix

43
Q

What provides resistance to mechanical stress to connective tissues?

A

extracellular matrix

44
Q

What is the primary component in connective tissues?

A

extracellular matrix

45
Q

Why are there different compositions of the extracellular matrix?

A

it gives tissues different properties

46
Q

What are the major classes of macromolecules in the extracellular matrix?

A
  • glycosaminoglycans (GAGs) and proteoglycans
  • fibrous proteins (collagen, elastin)
  • glycoproteins (laminin, fibronectin)
47
Q

What are glycosaminoglycans (GAGs)?

A

long negatively charged disaccharide chains made of repeating disaccharide units, which attract Na+ and water

48
Q

Where are GAGs usually found?

A

Extracellular matrix of animal cells

49
Q

What is the primary function of GAGs?

A

to resist compression and provide strength to the extracellular matrix, due to a hydrated gel formed

50
Q

Where are GAGs synthesized?

A

most are synthesized inside the cell and released by exocytosis

51
Q

What is Hyaluronan?

A

a simple GAG
long chain of repeating disaccharide subunits. It’s spun directly from the cell surface by a plasma membrane enzyme complex

52
Q

What are proteoglycans and where are they commonly found?

A

a group of glycoproteins that are heavily glycosylated with long polysaccharide chains known as glycosaminoglycans (GAGs). They have at least one sugar side chain, which must be a GAG. They are commonly found in the extracellular matrix of animal tissues.

53
Q

What are some examples of proteoglycans?

A
  • perlecan
  • decorin
  • aggrecan
  • aggercan-hyaluronan aggregate
54
Q

What is the primary structural protein found in the extracellular space in various connective tissues?

A

collagen

55
Q

How do collagen molecules assemble?

A

single collagen polypeptide chains assemble into triple-stranded collagen molecules, which then assemble into collagen fibril, which pack together to form collagen fibers

56
Q

What is collagen?

A

a fibrous protein that provides tensile strength and resists stretching

57
Q

What is an example of a typical collagen?

A

fibril-forming collagen
- 3 chains wound around in a triple helix
- assemble into ordered polymers to form collagen fibrils ( which can pack and form into collagen fibers)

58
Q

What is the precursor form of collagen called?

A

procollagen

59
Q

What role do procollagen proteinases play in collagen assembly?

A

Procollagen proteinases cut off terminal extensions from procollagen to allow assembly into fibrils after secretion into the extracellular space

60
Q

Why don’t cells assemble collagen molecules intracellularly before secretion?

A

to prevent premature assembly and avoid becoming choked with their own products, cells secrete procollagen with obstructive peptide extensions that prevent assembly until after secretion

61
Q

What are fibroblasts and osteoblasts and what is their function related to collagen?

A

connective-tissue cells and bone cells that manufacture and secrete collagen and other components of the extracellular matrix

62
Q

What are the steps to make collagen?

A
  • collagen is secreted as procollagen by fibroblasts and osteoblasts
  • once procollagen is secreted outside
  • procollagen proteinase cleaves terminal procollagen entensions
  • giving a collagen molecule
  • self-assembly into fibrils
63
Q

How is collagen organized in the extracellular matrix?

A

connective tissue cells organize collagen by binding to it through integrin (cell surface adhesion receptors) and fibronectin (glycoprotein)

64
Q

What does fibronectin bind to?

A

It’s a dimer that it binds to collagen (extracellular matrix binding site) and integrin (cell attachment site)

65
Q

What does integrin bind to?

A
  • binds to fibronectin (extracellular domain)
  • binds to adaptor proteins - actin filaments (intracellular domain)
66
Q

What is elastin?

A

a fibrous protein found in the extracellular matrix of tissues, such as skin, arteries, and lungs. It forms elastic fibers that allow these tissues to stretch and recoil without tearing

67
Q

How are elastin molecules structured?

A

formed from relatively loose and unstructured polypeptide chains that are covalently cross-linked into a rubber-like elastic meshwork

68
Q

What is the basal lamina and what are its main components?

A

a thin, tough sheet of the extracellular matrix that mainly consists of type IV collagen and laminin proteins, which underlies all epithelia. It provides adhesive sites for integrin molecules in the basal plasma membranes of epithelial cells. It influences cell polarity (apical-basal)

69
Q

What role does laminin play in the structure of the basal lamina?

A

Laminin serves a linking role by providing adhesive sites for integrins, which helps to anchor epithelial cells to the basal lamina.

70
Q

What is the roles of the basal lamina?

A

separates epithelia from underlying tissue
- prevents fibroblasts in underlying connective tissue from interacting with epithelial cells, yet allows passage of macrophages and lymphocytes

71
Q

What makes up the basal lamina?

A
  • anchored by hemidesmosomes
  • organized by lamina (glycoprotein)
  • interacts with other components of ECM
  • links integrin (transmembrane adhesion protein) to type iv collagen (fibrous protein)
72
Q

How are all the proteins attached to the epithelial tissue?

A
  • hemidesmosomes anchor epithelial cells to basal lamina
  • transmembrane adhesion proteins (integrin) bind to laminin in the basal lamina
  • intercellular linker protein link integrins to keratin filaments inside the cell
  • integrins interact with laminin to organize the basal lamina
73
Q

What are the main components of the plant cell wall?

A

more rigid than the extracellular matrix in animal cells
- cellulose and pectin

74
Q

How does cellulose contribute to the rigidity and strength of plant cell walls?

A

interwoven with other polysaccharides and some structural proteins in the plant cell wall, creating a complex structure that resists compression and tension

75
Q

How does the orientation of cellulose microfibrils affect plant cell growth?

A

determines the direction in which a growing cell will expand due to their tensile strength; cells tend to elongate perpendicular to the orientation of these microfibrils

76
Q

How is cellulose synthesized differently from most other extracellular macromolecules?

A

Unlike most extracellular macromolecules that are made inside cells then exported by exocytosis, cellulose is synthesized directly on the outer surface of the plant cell by enzyme complexes embedded in the plasma membrane.

77
Q

What role does pectin play in plants?

A

plays a crucial role in maintaining the integrity and structure of plants by contributing to the mechanical strength and firmness of tissues

78
Q

What is the composition of the middle lamella?

A

rich in pectins, which are polysaccharides that help to glue cell walls together.

79
Q

Where is the cell wall synthesized?

A

in the Golgi and exported by exocytosis

80
Q

How are cellulose chains synthesized?

A
  • occurs at the plasma membrane of plant cells by cellulose synthase complexes, which transport sugar monomers across the plasma membrane and incorporate them into growing polymer chains, making cellulose microfibrils. The orientation of these microfibrils is determined by the paths followed by the enzyme complexes and is guided by microtubules located just underneath the plasma membrane. This process ultimately influences cell shape and organ development in plants.

BIO130 Final (7 decks)

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