Lecture 27: Starch and Sucrose

Question 1

what is the most abundant storage carbohydrate in plants

Answer 1

starch

Question 2

starch

Answer 2

long branched or unbranched chains of many glucose molecules

Question 3

where is synthesized starch stored

Answer 3

in the stroma of the chloroplast

Question 4

when is starch accumulated and degraded

Answer 4

accumulates during the day
degraded during the subsequent night

Question 5

2 forms of starch

Answer 5

amylose and amylopectin

Question 6

what enzymes are required to complete development of the starch granule

Answer 6

starch-branching enzyme I and II

Question 7

hydrolytic pathway

Answer 7

primary mechanism for starch degradation

Question 8

key enzymes for hydrolytic starch degradation

Answer 8

a-amylase
B-amylase
limit dextrinase

Question 9

what bonds do a-amylase target in starch

Answer 9

targeting endo a-1,4-glycosidic bonds

Question 10

what bonds do B-amylase target in starch

Answer 10

target exo a-1,4-glycosidic bonds at the non-reducing end of starch chains

Question 11

what bonds do limit dextrinase target in starch

Answer 11

target the branch point of starch

Question 12

key enzymes of sucrose biosynthesis

Answer 12

1. sucrose 6-phosphate synthase
2. sucrose 6-phosphate phosphatase

Question 13

what synthesizes sucrose and starch and where

Answer 13

both sucrose and starch are synthesized by Triose phosphate
Sucrose = cytosol
Starch = chloroplast

Question 14

sucrose synthase

Answer 14

reversible catalysis for both sucrose synthesis and degradation

Question 15

what does sucrose synthase generate

Answer 15

UDP-glucose

Question 16

what does cellulose synthase generate

Answer 16

a long cellulose chain outside the plasma membrane

Question 17

what do microtubules do

Answer 17

direct movement of cellulose synthase complexes along the plasma membrane

Question 18

2 isoforms of D-glucose

Answer 18

a-D-glucose (component of starch)
B-D-glucose (component of cellulose)