Plant Toxins

Question 1

what are the main toxins released from plants

Answer 1

ribosome inactivating proteins (RIPs)

Question 2

how many types of RIPs are there

Answer 2

2

Question 3

what is the main example of type 2 rip

Answer 3

ricin

Question 4

what is the size of the A and B chains of ricin

Answer 4

3kDa

Question 5

what is the function of the A chain

Answer 5

warhead

Question 6

what is the function of the b chain

Answer 6

Binding

Question 7

in what year was georgi markov killed in londn using ricin

Answer 7

1978

Question 8

how many polupeptide chains do type 1 RIPs have

Answer 8

1

Question 9

what is the first step in the mechanism of action of Ricin

Answer 9

bchain binds b-1,4-linked galactose in membrane glycoproteins and glycolipids which are common to all cells of the body

Question 10

after binding the membrane, how does ricin endter the cell

Answer 10

by the endocytic pathway

Question 11

what happens to ricin once it is endocytosed

Answer 11

it is transferred toearly endosomes

Question 12

hwhat percentage of the toxin is recycled and degraded by lysosomes

Answer 12

95%

Question 13

what happens to the 5% which is not degraded

Answer 13

transferred to the golgi network

Question 14

where is ricin transported to from the golgi

Answer 14

ER

Question 15

how is ricin transported to the ER

Answer 15

by binding a protein with KDEL sequence

Question 16

once in the ER what occurs

Answer 16

reductive cleavage of disulphide bond

Question 17

how/why is the A chain translocated into the ER

Answer 17

treated as a misfolded protein

Question 18

how does the A chain block protein synthesis

Answer 18

it targets the 28s rRna of the 60s ribosomal subunit tand splits the glycosidic bond of one adenine base at a critical site causing the loss of binding of elongation factors

Question 19

what other cytotoxic actions can the A chain carry out aside from DNA aand RNA deadenylation

Answer 19

lyase activity to catalyse the fragmentation of DNA