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AEBI 210 > LEC 4: THE CELL WALL > Flashcards

LEC 4: THE CELL WALL Flashcards

1
Q

What scientist was the first to report what a cell looked like?

A

Robert Hooke

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2
Q

How did scientists FIRST differentiate plant and animal cells?

A

Plant cells had a distinctive cell wall surrounding the cell content while animal cells did not.

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3
Q

What are the 4 main functions of the cell wall

A
  1. provide rigidity/structure to the cell AND the plant
  2. limit the expansion of the cell
  3. create turgor pressure in vacuoles and in the cell
  4. are a physical and live barrier for metabolic activity
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4
Q

What is a plant cell that does not have a cell wall called?

A

Protoplast

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5
Q

True or False: Cell walls are degraded while the nuclear genome of the plant replicates and divides

A

False, the cell wall stays in tact as chromosomes separate

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6
Q

What ancestral organisms had/have cell walls?

A
  1. Bacterial ancestors
  2. Green algae
  3. Land plants
  4. Fungi
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7
Q

What is the cell wall of bacteria made of?

A

Peptidoglycan

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8
Q

Do green algae and land plants have the same cell wall composition?

A

No, although green algae and land plants have a cell wall made of cellulose land plants have more complex proteins and molecules that accompany the wall

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9
Q

What is the cell wall of fungi made of?

A

Chitin-glucan

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10
Q

What is the primary cell wall of plant cells made of?

A

cellulose, hemicellulose, pectin

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11
Q

What is cellulose?

A

A long string of polymeric compounds that make microfibrils

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12
Q

How are cellulose and hemicellulose alike, but different from pectin?

A

Cellulose and hemicellulose are both hydrophobic while pectin is hydrophilic

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13
Q

What function does hemicellulose hold in the construction of the cell wall?

A

Hemicellulose tethers itself to cellulose to limit the extensibility of the cell wall and regulate cell expansion.

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14
Q

How are pectin and ripe fruits related?

A

Pectin structures change as the plant ripens, causing the pectin to break down making the fruit easier to eat (more elastic)

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15
Q

What function does pectin serve in the cell wall?

A

Its hydrophilic properties allow the cell to be elastic and mobile, but simultaneously regulates how elastic the cell can be

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16
Q

What is the Middle Lamella’s function in plants?

A

It acts like a glue between adjacent cells

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17
Q

What is the middle lamella made of?

A

Pectin

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18
Q

What use does a secondary cell wall serve?

A

It adds rigidity to cells that need to be structurally withstanding (xylem, woody tissues etc)

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19
Q

What other molecules does the secondary cell wall contain?

A

Lignin, suberin and cutin

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20
Q

What are two components of the primary cell wall that are essential to the plant?

A
  1. Primary cell walls have enzymes that complete metabolic functions
  2. Primary cell walls have chemicals that can be toxins used to defend the plant from invaders
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21
Q

What is the most abundant macromolecule in the world?

A

Cellulose

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22
Q

What is the basic unit of cellulose? What linkage binds these units?

A

D-glucose units are bound by a Beta 1-4 linkage

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23
Q

What term is given to units of glucose that are strung together and aligned to form threads?

A

Microfibrils

24
Q

What happens when glucose units align perfectly in the cell wall?

A

Crystalline structures are formed

25
Q

What are the crystalline structures formed by glucose units called?

A

Micelles

26
Q

What allows plants to withstand the strength of turgor pressure induced by vacuoles?

A

The rigidity of the cell wall

27
Q

What differentiates hemicellulose from cellulose?

A

Cellulose can perfectly align to create a straight chain of glucose units.

Hemicellulose has hydrogen bonds between units that create kinks

28
Q

What creates limited extendibility in the cell wall?

A

The zig-zagged arrangement of hemicellulose around cellulose

29
Q

What makes pectin such a dynamic component of the cell wall?

A

It creates elasticity for the cell wall but also limits that plasticity

30
Q

How does pectin encourage plasticity?

A

Hydrophilic properties of pectin allow the cell to elongate and become elastic

31
Q

How does pectin discourage plasticity?

A

Calcium cross linkages provided by pectin stop the cell from stretching any further than necessary

32
Q

A cell is able to pass material to another cell through what structure?

A

Plasmodesmata

33
Q

What connects two adjacent cells together?

A

The pit membrane along the middle lamella

34
Q

A shared endoplasmic reticulum between two cells is called what?

A

Desmotubule

35
Q

What must occur (mostly) before a secondary cell wall forms?

A

The cells must stop growing or die

36
Q

What is the secondary cell wall made of?

A

Cellulose, hemicellulose

37
Q

What does the primary cell wall have that the secondary cell wall does not have? Why?

A

Pectin, proteins, plasmodesmata, pit membrane.

Because cells are not alive, they no longer need to be elastic or complete metabolic functions. Since they do not need to exchange material and no longer need to be connected there is no plasmodesmata or pit membrane

38
Q

What creates rigidity in primary and secondary cell walls?

A

The orientation of cellulose microfibrils

39
Q

If cellulose microfibrils are arranged amorphously, what shape will the cell take?

A

Amorphous = no direction. Cell will be spherical

40
Q

If cellulose microfibrils are arranged in a horizontal direction, what shape will the cell take?

A

The cell will grow vertically upward

41
Q

What molecule allows the cell wall to loosen for elongation?

A

Expansins

42
Q

What do expansins control

A

They control dynamic growth/elongation of the cell

43
Q

What enzyme is used to generate cellulose cell wall?

A

Cellulose synthase

44
Q

What substrate is used by cellulose synthase?

A

UDP glucose, or Uridine Disphosphate Glucose

45
Q

What is the product of cellulose synthase and UDP glucose enzyme-substrate?

A

A polymeric cellulose molecule made of glucose linked with beta 1-4 linkages

46
Q

What are the main substances present in the matrix of a plant cell?

A

Hemicellulose, pectin and glycoproteins

47
Q

How are other matrix components delivered?

A

Secretory vesicles produced in the Golgi Apparatus

48
Q

Increased pectin concentrations in the matrix of a cell creates what conditions?

A

More elastic conditions

49
Q

Increased hemicellulose concentrations in the matrix of a cell creates what conditions?

A

More rigid conditions

50
Q

What determines cell type/differentiation

A

The cells location

51
Q

What is true about lignin deposition in the cell wall of plants over time?

A

As the plant develops more lignin is deposited to increase structural rigidity

52
Q

What is an example of a plant species and toxin that holds chemicals in their cell walls?

A

Sanguinarine is held in the cell wall of California Poppys

53
Q

What does it mean if a substance is cytotoxic?

A

It is toxic to the cell that produces it and to those that come in contact with it

54
Q

When scientists tested sanguinarine presence in California Poppys, what did they do to prove the toxin was only present in the cell wall?

A

They plasmolyzed the cell - or created a hypertonic solution so the plasma membrane and vacuoles collapsed on themselves.

Since the cell was essentially empty, they could see that sanguinarine was only present in the cell wall

55
Q
A

AEBI 210 (5 decks)

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