lecture 6

Question 1

what are the two main types of polysaccharides in cell walls

Answer 1

hemicellulose and pectins

Question 2

whats the most abundant macromolecule on earth

Answer 2

cellulose

Question 3

what is cellulose monommer

Answer 3

glucose only

Question 4

what are the two phases of making the primary cell wall

Answer 4

Phase one is the crystalline microfibrillar phase- cyrstaline as its so organised
Phase two is the non-crystalline matrix. Less organised, two sugar types
Pectin and hemicellulose
Protein called extensin

Question 5

describe hemicellulose

Answer 5

Hemicellulose has a long glucose backbone with many small side chains, different side chain monomers. Relatively rigid

Question 6

describe pectin

Answer 6

Pectin, not so strong, gel like, absorbs water, whats used to make jam. It has negative charged which allows it to absorb water

Question 7

what controls the expansion of a cell.

Answer 7

Expansion of the cell wall is controlled by extensin protein cross linkage

Question 8

how does extensin linking work

Answer 8

extensin crossing dehydrates the cell, making it less extensible and increases the cell strength. Extensin cross links pectin and cellulose.

Question 9

whats the three main roles of the cell wall

Answer 9

Cell wall does 3 main things:
Influences cell morphology
Provides structural support
Prevents excessive water uptake, which prevents lysing

Question 10

what does the middle lamella do

Answer 10

Middle lamella between cells sticks the adjacent cells together.

Question 11

primary Cell wall synthesis: this involves the co-ordinated synthesis and delivery of 3 things and where are they made

Answer 11

1: cellulose microfibrils made at the plasma membrane
2: Pectin & hemicellulose made in the golgi, transported to the well in vesicles
3: Cell wall proteins, extensins, made in ER, vesicle transports this to the cell wall

Question 12

whats a rosette

Answer 12

an enzyme filled structure. The enzymes in this sac are cellulose producing enzymes

Question 13

how does a rosette work

Answer 13

This move through the plasma membrane parallel along the cortical microtubules, microtubules under the plasma membrane. The rosettes move along them creating cellulose fibres behind it.

Question 14

If the microfibrils are oriented randomly

Answer 14

then the cell wall expands equally in all directions.

Question 15

If the microfibrils are at right angles to the cell long axis

Answer 15

the cell will expand longitudinally a long said axis.

Question 16

whats the protoplast

Answer 16

everything within the cell wall.

Question 17

when does wilting occur

Answer 17

Wilting of cell wall occurs when the protoplast is shrunken and not pushing onto the cell wall. This occurs when not enough water is in the cell. As protoplast volume decreases protoplast pressure decreases.

Question 18

difference between secondary cell wall and primary cell wall

Answer 18

2nd cell wall is formed once the cell has stopped growing. 2nd cell wall has ligand. 1st cell wall has more pectin and hemicellulose and less cellulose. 2nd has many layers of microfibrils

Question 19

what does ligand do

Answer 19

Ligand is the second most abundant macromolecule:
Complex polymer
Acts to exclude water in the cell wall, contributing to its strength.
Confers the strength and rigidness of the cell wall.

Question 20

Plasmodesmata does what

Answer 20

Creates intercellular connections which allow intercellular communication
These are big enough to allow small molecules, ions, to exchange between cells
Small enough to prevent organelles from moving across them, vesicles from rER do go through tho.

Question 21

dry weigths of the cell wall

Answer 21

On dry weight cellulose is 40% weight of cell wall, hemicellulose is 20% pectins 30% and glycoproteins are 10% .

Question 22

What is hemicellulose role?

Answer 22

(ii) Non-crystalline phase: Hemicellulose acts to bind cellulose microfibrils.

Question 23

What are the two primary cell wall phases?

Answer 23

cyrstalline matirx: cellulose
and non crystalline matrix: hemicellulose and pectin

Question 24

What is cellulose role

Answer 24

Crystalline phase: Cellulose microfibrils give the wall strength and flexibility.

Question 25

What is Pectin role

Answer 25

(iii) Non-crystalline phase: Pectin acts as a glue (binds water to have gel-like properties).

Question 26

what is Extensin’s role

Answer 26

(iv) Non-crystalline phase: Extensin (protein) controls the extensibility of cells through crosslinking cellulose and pectin.

Question 27

plasmodesmata creates a what

Answer 27

continuous plasma membrane between cells.

Question 28

why does a cell need energy

Answer 28

(i) Mechanical work (e.g. motor proteins)
(ii) Making new materials (e.g. for growth and replacement)
(iii) Transport (e.g. across membranes)
(iv) Maintaining order

Question 29

what does the central vacuole do?

Answer 29

The vacuole regulates turgor pressure (together with the cell wall) within the cell allowing the plant cell to tolerate large changes in osmotic potential. This interplay of the two also determines cell shape. It also stores solutes and removes cellular wastes. A high tugor pressure gives plants their rigidity

Question 30

whats the cell equivalent of the cytoplasm

Answer 30

the protoplast

Question 31

what is the difference between the cytoplasm and the cytosol

Answer 31

cytoplasm is the fluid within the cell and all the organelles within the animal cell, cytosol is the fluid itself