Carbohydrate Metabolism 1- Glycolysis, Glycogen, Gluconeogenesis, and Pentose Pathway

Question 1

Acetyl-CoA

Answer 1

Contains a high-energy thioester bond that can be used to Reactions of the Citric Acid Cycle
drive other reactions when hydrolysis occurs.

Question 2

Acetyl-CoA Formation:

Answer 2

Can be formed from fatty acids, which enter the
mitochondria using carriers. The fatty acid coupled with CoA in the cytosol to form fatty acyl-CoA, which moves to the intermembrane space. The acyl (fatty acid) group is transferred to carnitine to form acyl-carnitine, which
crosses the inner membrane. The acyl group is transferred to a mitochondrial CoA to re-form fatty acyl-CoA, which can undergo b-oxidation to form acetyl

Question 3

Acetyl-CoA Formation

Answer 3

Can also be formed from the carbon skeletons of ketogenic amino acids, ketone bodies, and alcohol.

Question 4

Pyruvate Dehydrogenase

(PDH):

Answer 4

Oxidizes pyruvate, creating CO2; it requires thiamine pyrophosphate (vitamin B1, TPP) and Mg2+

Question 5

Dihydrolipoyl

Transacetylase

Answer 5

Oxidizes the remaining two-carbon molecule using lipoic acid, and transfers the resulting acetyl group to CoA, forming acetyl-CoA.

Question 6

Dihydrolipoyl

Dehydrogenase

Answer 6

Uses FAD to reoxidize lipoic acid, forming FADH2. This FADH2 can later transfer electrons to NAD+, forming NADH that can feed into the electron transport chain.

Question 7

Pyruvate Dehydrogenase

Kinase

Answer 7

Phosphorylates PDH (pyruvate dehydrogenase) when ATP or acetyl-CoA levels are high, turning it off

Question 8

Pyruvate Dehydrogenase

Phosphatase

Answer 8

Dephosphorylates PDH (pyruvate dehydrogenase) when ADP levels are high, turning it on.

Question 9

Acyl Carnitine Translocase

Answer 9

Mechanism for Acyl CoA to enter 
the mitochondrial matrix. The 
mitochondrial matrix is where Acyl 
CoA can undergo b-oxidation to 
form Acetyl-CoA.

Question 10

Where does the citric acid cycle take place?

Answer 10

In the mitochondrial matrix

Question 11

What is the purpose for the citric acid cycle?

Answer 11

Its main purpose is to

oxidize carbons in intermediates to CO2 and generate high-energy electron carriers (NADH and FADH2) and GTP.

Question 12

Citrate

Synthase

Answer 12

Couples acetyl-CoA to oxaloacetate and then hydrolyzes the

resulting product, forming citrate and CoA-SH

Question 13

What regulates citrate synthase?

Answer 13

Negative feedback from ATP, NADH, succinyl coA and citrate

Question 14

Aconitase

Answer 14

Isomerizes citrate to isocitrate

Question 15

What is the rate limiting step of the citric acid cycle?

Answer 15

Isocitrate dehydrogenase

Question 16

What are the inhibitors and activators of isocitrate dehydrogenase?

Answer 16

ATP and NADH are inhibitors and ADP and NAD+ are activators

Question 17

Isocitrate

Dehydrogenase

Answer 17

Oxidizes and decarboxylates isocitrate to form a-ketoglutarate

Question 18

a-Ketoglutarate
Dehydrogenase
Complex

Answer 18

Acts similarly to PDH complex, metabolizing a-ketoglutarate to form succinyl-CoA.This enzyme generates the second CO2 and
second NADH of the cycle

Question 19

What inhibits and activates alpha-ketoglutarate dehydrogenase complex?

Answer 19

It is inhibited by ATP, NADH, and

succinyl-CoA; it is activated by ADP and Ca2+

Question 20

Succinyl-CoA

Synthesis

Answer 20

Hydrolyzes the thioester bond in succinyl-CoA to form succinate
and CoA-SH. This enzyme generates the one GTP generated in the
cycle.

Question 21

Succinate

Dehydrogenase

Answer 21

Oxidizes succinate to form fumarate. This flavoprotein is anchored
to the inner mitochondrial membrane because it requires FAD,
which is reduced to form the one FADH2 generated in the cycle.

Question 22

Fumarase

Answer 22

Hydrolyzes the alkene bond of fumarate, forming malate

Question 23

Malate

Dehydrogenase

Answer 23

Oxidizes malate to oxaloacetate. This enzyme generates the third
and final NADH of the cycle.

Question 24

Proton-Motive

Force

Answer 24

The electrochemical gradient generated by the electron transport
chain across the inner mitochondrial membrane. The
intermembrane space has a higher concentration of protons than
the matrix; this gradient stores energy, which can be used to form
ATP via chemiosmotic coupling.

Question 25

ATP Synthase

Answer 25

The enzyme responsible for generating ATP from ADP and Pi
F0 Portion: An ion channel, allowing H+ to flow down the gradient
from the intermembrane space to the matrix
F1 Portion: Uses the energy released by the gradient to
phosphorylate ADP into ATP.

Question 26

Where does the electron transport chain take place

Answer 26

Takes place on the matrix-facing surface of the inner

mitochondrial membrane.

Question 27

What is the oxidizing agent of the ETC?

Answer 27

NADH

Question 28

What is the name of complex 1 of the ETC?

Answer 28

NADH-CoQ Oxidoreductase

Question 29

Complex 1:

Answer 29

NADH-CoQ Oxidoreductase. Uses an iron-sulfur cluster to transfer electrons from NADH to flavin mononucleotide (FMN), and then to CoQ, forming CoQH2. 4 H+ ions are translocated by Complex I.

Question 30

What is the name of complex 2?

Answer 30

Succinate-CoQ Oxidoreductase

Question 31

Complex 2 ETC

Answer 31

Uses an iron-sulfur cluster to
transfer electrons from succinate to FAD, and then to CoQ,
forming CoQH2. No H+ pumping occurs at complex II.

Question 32

What is the name of complex 3 in the ETC?

Answer 32

Cytochrome C Oxidoreductase

Question 33

Complex III:

Answer 33

CoQH2-Cytochrome C Oxidoreductase. Uses an iron-sulfur cluster
to transfer elcetrons form CoQH2 to heme, forming cytochrome
C as part of the Q cycle. 4 H+ ions are translocated by complex III.

Question 34

What is the name of Complex 4 of the ETC?

Answer 34

Cytochrome C oxidase

Question 35

Complex IV:

Answer 35

Cytochrome C Oxidase. Uses cytochromes and Cu2+ to transfer
electrons in the form of hydride ions (H-
) from cytochrome c to
oxygen, forming water. 2 H+ ions are translocated by complex IV.

Question 36

Can NADH cross the mitochondrial membrane?

Answer 36

NADH cannot cross the inner mitochondrial membrane. Therefore, one of two
available shuttle mechanisms to transfer electrons in the mitochondrial matrix must
be used.

1. ) Glycerol 3- phosphate shuttel
2. ) Malate Aspartate