Calvin Cycle and PPP

Question 1

where is CO2 fixed to and by what?

Answer 1

RuBisCO attaches a CO2 to ribulose 1,5-bisphosphate (RuBP) turning gas into a carbohydrate

Question 2

After Rubisco carboxylates RuBP, what is the transient 6C intermediate split into, and how many?

Answer 2

Into two 3-phosphoglycerates

Question 3

What does the active site of rubisco utilize to attach CO2 to RuBP

Answer 3

A carbamylated lysine residue and a Mg2+

Question 4

Why is RuBisCO slow? (more than accidently binding O2)

Answer 4

Stabilization of the late transition state to differentiate between O2 and CO2 creates a sort of product inhibition, so releasing the product and completing the reaction

Question 5

What is the reverse reactions of steps 6&7 of glycolysis?

Answer 5

Reduction of 3PG to GAP

Question 6

What drives the reduction from 1,3-bisphophoglycerate to glyceraldehyde-3-phosphate?

Answer 6

Cleavage of the acyl-phosphate bond

Question 7

How many CO2s go through the cycle to make 6 GAP?

Answer 7

3

Question 8

Where do the majority of GAPs go to in the cycle, and how many? Where does the rest go to, and how many?

Answer 8

5 are used to regenerate 3 RuBP. 1 goes to net carbohydrate synthesis

Question 9

For each 3 turns you start with __ carbons from __ RuBPs, add in __ C from __ CO2s, and siphon off __ carbons in __ GAP to make sugars

Answer 9

For each 3 turns you start with 15 carbons from 3 RuBPs, add in 3 C from 3 CO2s and siphon off 3 C in 1 GAP to make sugar

Question 10

Which two enzymes change the number of carbons in the calvin cycle?

Answer 10

aldolase and transketolase

Question 11

Which two enzymes move things around within the molecule in the calvin cycle?

Answer 11

isomerases and epimerases

Question 12

What happen between GAP and DHAP and which enzyme does this?

Answer 12

isomerized by TIM

Question 13

What combines one 3C aldose and one 3C ketose into a 6C carbohydrate?

Answer 13

aldolase

Question 14

What enzyme transfers 2C from a ketose to an aldose acceptor?

Answer 14

transketolase

Question 15

What cofactor is part of transketolase

Answer 15

TPP

Question 16

What enzyme adds a 3C DHAP to the 4C E4P to make the 7C SBP

Answer 16

aldolase

Question 17

What enzyme transfers 2C from S7P to GAP to make two 5C molecules

Answer 17

transketolase

Question 18

What are R5P and Yu5P converted to and how many?

Answer 18

3 RuBPs

Question 19

What enzyme converts R5P?

Answer 19

(ribose phosphate) isomerase

Question 20

What enzyme converts Xu5P?

Answer 20

(phosphopentose) epimerase

Question 21

What is the delta C for aldolases? for transketolases?

Answer 21

3 for aldolase, 2 for transketolase

Question 22

What are the regulated steps in the calvin cycle?

Answer 22

rubisco and the kinase/phosphatases

Question 23

Is biophosphatase reduced or oxidized to become active?

Answer 23

reduced

Question 24

What reduces biophosphatase?

Answer 24

Thioredoxin

Question 25

How many ATPs and NADPHs does the calvin cycle burn?

Answer 25

9 ATPs and 6 NADPHs

Question 26

2 GAPs from 2 turns of the calvin cycle are used to make what?

Answer 26

hexoses

Question 27

Where is sucrose formed?

Answer 27

cytoplasm

Question 28

Is sucrose a long term or short term energy storage?

Answer 28

short term

Question 29

Where is amylose formed?

Answer 29

stroma

Question 30

Is amylose a long term or short term energy storage?

Answer 30

long term

Question 31

What is the pentose phosphate pathway?

Answer 31

oxidation of glucose in the cytosol

Question 32

Where does the PPP occur?

Answer 32

everywhere but especially in anabolic tissue like the liver and adipose tissue

Question 33

How many NADHs does the first stage of the PPP produce?

Answer 33

2

Question 34

During the first stage of the PPP which substrate has 2 carbons oxidized to generate the 5C sugar Ru5P?

Answer 34

glucose-6-phosphate

Question 35

What are two key enzymes that move carbons around in the PPP?

Answer 35

transketolase and transaldolase

Question 36

What does stage 2 convert 3 Ru5Ps to in the PPP?

Answer 36

2 F6Ps and 1 GAP

Question 37

What cofactor does transaldolase use to transfer 3C from a ketose onto an aldose?

Answer 37

no cofactor- reaction is catalyzed by a lysine side chain that forms a schiff base

Question 38

What is the difference between aldolases and transaldolases?

Answer 38

aldolase sticks a proton onto the carbanion intermediate, while transaldolase sticks an aldose on

Question 39

What is an important use of NADPH

Answer 39

protects cell from oxidative damage through reduction of glutathione

Question 40

Which pathway is the main source of cytoplasmic NADPH in eukaryotes?

Answer 40

PPP