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Cells > Mod6 - Interactions Between Cells in Multicellular Systems > Flashcards

Mod6 - Interactions Between Cells in Multicellular Systems Flashcards

1
Q

What are the 4 major tissue types of the body?

A

Connective, Epithelial, Muscular, Nervous

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2
Q

Describe the amount of ECM in each of the 4 tissue types and how this relates to tissue strength

A

Epithelial, Muscular and Nervous: little ECM, intermediate filaments and cell-cell junctions provide strength
Connective: few cells, lots of ECM provides strength

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3
Q

Name the 5 types of cellular junctions in animals

A

Tight junctions, Adherens junctions, Desmosomes, Gap junctions, Hemidesmosomes

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4
Q

Describe the function of tight junctions

A

Seals adjacent cells together in an epithelial sheet to prevent leakage of extracellular molecules between them (also helps polarise cells)

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5
Q

Describe the function of adherens junctions

A

Joins an actin bundle in one cell to a similar bundle in a neighbouring cell

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6
Q

Describe the function of desmosomes

A

Joins the intermediate filaments in one cell to those in a neighbour

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7
Q

Describe the function of gap junctions

A

Form channels that allow small, intracellular, water-soluble molecules (e.g. ions and metabolites) to pass from cell to cell

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8
Q

Describe the function of hemidesmosomes

A

Anchor intermediate filaments in a cell to the basal lamina

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9
Q

Which type of cellular junction do plants have, and which animal junction is it most comparable to?

A

Plasmodesmata -> Gap Junctions

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10
Q

Describe the structure of vertebrate tight junctions

A

Formed of strands of occludin and claudin proteins, which allow lipids in the plasma membrane to diffuse freely, but not membrane proteins

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11
Q

How are tight junctions related to cell polarisation?

A

They allow the apical and basolateral membranes to be different in composition and function, as lipids in the membrane can diffuse but proteins cannot)

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12
Q

What type of protein is found in adherens junctions and desmosomes (and which ion is required for this to work)?

A

Cadherins (calcium, Ca2+)

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13
Q

What type of protein is found in hemidesmosomes?

A

Integrins

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14
Q

Describe the structure of adherens junctions, and the grander structure they can be involved in?

A

Cadherins link to actin filaments in two neighbouring cells via linker proteins; a continuous band of AJs forms an ADHESION BELT and an actin network across the epithelium (this CAN be contractile because of the presence of myosin II)

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15
Q

What is the function of contractile actin networks when myosin II is involved?

A

Allow epithelial sheets to move, invaginate, form tubes, etc., e.g., neurulation to generate neural tube

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16
Q

Describe the structure of desmosomes

A

Cadherins link to cytoplasmic plaque made of intracellular linker proteins; this cytoplasmic plaque has keratin filaments anchored to it

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17
Q

Where are desmosomes found in the body?

A

Abundant in tissues under high shear stress e.g., heart muscle (in addition to epithelia ofc)

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18
Q

What are the effects of desmin mutations?

A

Desmosomes in adjacent muscle cells are linked to DESMIN intermediate filaments; desmin is expressed in cardiac, smooth and skeletal muscle, and desmin mutations can cause muscular dystrophy and cardiac myopathy

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19
Q

Describe the structure of hemidesmosomes

A

Integrins in the basal plasma membrane bind to both laminin (NOT LAMIN) in the basal lamina, and cytokeratin intermediate filaments inside the cell (via linker proteins)

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20
Q

What is the function of cadherins and how do they achieve this?

A

Define which cells can interact with each other to form tissues; cadherins are transmembrane proteins in the plasma membrane which bind to an IDENTICAL CADHERIN in the next cell

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21
Q

What are the two types of cadherin mentioned, and where are they found?

A

Epithelial cells express E-CADHERIN
Muscle cells express N-CADHERIN

22
Q

How are cadherins and cancer related?

A

Cancer cells often no longer express the specific cadherins that would normally keep a cell in the right place (e.g., expressing N-cadherin instead of E-cadherin makes cells highly motile)

23
Q

What may cancerous cells secrete an increased amount of?

A

Matrix proteases which can digest the ECM, helping them to escape through the basal lamina

24
Q

Where are connexon channels found and what do they do?

A

GAP JUNCTIONS - connexon channels allow direct transfer of ions and small water-soluble molecules (<1000 daltons) between cells

25
Q

What is the main functional difference between plant plasmodesmata and animal gap junctions?

A

Plasmodesmata allow larger molecules through (e.g., SER, proteins, mRNAs)

26
Q

Name the two proteins that link the cytoplasm with the nucleus

A

SUN and KASH

27
Q

What characteristic is correlated with increased collagen content?

A

Increased tissue stiffness?

28
Q

What are the two main components of the basal lamina?

A

Laminin and Collagen IV

29
Q

What types of cells produce collagen?

A

Connective tissue cells (osteoblasts in bone and fibroblasts in skin/tendons)

30
Q

State the 4 stages of collagen synthesis and where they occur

A
  1. Procollagen polypeptide chain
  2. Triple-stranded helical procollagen molecule (trimerisation occurs in the ER)
  3. Collagen fibril (OUTSIDE THE CELL)
  4. Collagen fibres (OUTSIDE THE CELL)
31
Q

What vitamin is required for procollagen trimerisation?

A

Vitamin C (ascorbic acid) -> hence scurvy when deficient

32
Q

What happens to convert procollagen to collagen?

A

Procollagen cannot assemble into fibrils until it is cleaved by a PROTEASE (which mainly happens outside the cell)

33
Q

Describe how collagen is organised as it is synthesised (idk how to phrase this better)

A

Collagen fibres must be properly aligned:
- cells deposit collagen in an oriented way
- cells rearrange the fibres after secretion by pulling on them

34
Q

Name 3 types of diseases due to ECM protein mutations

A

Abnormally stretchy skin, Brittle bone disease, Skeletal abnormalities (e.g. achondroplasia)

35
Q

Describe the function of integrins (apart from those found in hemidesmosomes)

A

Focal Adhesions: they link the Extracellular Matrix to the Cell’s Cytoskeleton

36
Q

What is the linker protein by which cells attach to collagen?

A

Fibronectin

37
Q

Describe the role of fibronectin

A

It is the linker protein which links collagen to integrins - the integrins then bind to actin filaments inside the cell via adaptor proteins

38
Q

In what two ways is integrin function regulated

A
  1. Binding to an intracellular protein - or an extracellular matrix molecule - causes integrins to switch to an activated state
  2. Phosphorylation can INACTIVATE integrins (e.g. in mitosis)
39
Q

What is in the “spaces” between collagen in the ECM?

A

Gels of polysaccharide (Glycosaminoglycans) and glycoprotein (Proteoglycans)

40
Q

Describe the structure of Glycosaminoglycans (GAGs)

A
  • Large, negatively charged polysaccharides
  • Strongly hydrophilic
  • Occupy a large volume for their mass
41
Q

Describe the structure of proteoglycans

A

They are extracellular (secreted) proteins with covalently-linked GAGs, forming a “toilet brush” structure

42
Q

How do GAGs and collagen make cartilage tough and resistant?

A

GAGs generate swelling pressure because they bind water molecules; this pressure is resisted by collagen fibres

43
Q

How and where are proteoglycans synthesised?

A

Protein component is made in the ER, where glycosylation starts; Glycosylation is completed in the Golgi apparatus; proteoglycan is delivered to plasma membrane by constitutive secretion

44
Q

Which proteoglycan is made by a different synthesis process, and why?

A

Hyaluronan - it is made of ONLY carbohydrate, containing no protein at all

45
Q

Why must plants have cell walls to provide strength, while animal cells do not?

A

PLANT CELLS LACK INTERMEDIATE FILAMENTS

46
Q

Describe the structure and function of plant cell walls

A

They resist turgor pressure (both compression and tension); long fibres are oriented along the lines of stress

47
Q

Distinguish between primary and secondary cell wall structure in plants

A

Primary: relatively thin, laid down first and allows the cell to grow (cell expansion is driven by turgor pressure)
Secondary: laid down after, composition determines cell properties (e.g., hard and thick in wood due to lignin; thin, flexible and waxy in leaves)

48
Q

What molecules/structure actually gives the plant cell wall its tensile strength?

A

Cellulose fibres (these are interwoven with other polysaccharides, e.g., pectin for compression resistance and lignin in wood)

49
Q

What is the role of pectin in plant cells?

A

It fills spaces, resists compression and sticks neighbouring cells together

50
Q

Describe the process of cellulose synthesis in plants

A

Cellulose fibres are synthesised at the cell membrane (similar to hyaluronan synthesis in animals):
Cellulose Synthase is made in the ER and transported via the Golgi to the plasma membrane, where it makes many cellulose molecules and assembles them into a microfibril

51
Q

State how cellulose is ORGANISED in the plant cell wall

A

Microtubules inside the cell determine the orientation of fibre deposition outside the cell

Cells (8 decks)

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