Bioenergetics

Question 1

Def of bioenergetics

Answer 1

Is the study of energy changes associated with biochemical reactions,
It is the study of how energy is captured and transformed from one type to another
It studies utlization of energy

Question 2

Def and equation of ^ G ( Gibbs free energy change)

Answer 2

Total energy change in a system that is available for doing work.that is the useful energy , known as chemical potential

^G=G of products-G of reactants

Question 3

Sign of ^G

Answer 3

Negative ~> there is net lose of energy
The reaction is spontaneous
Exergonic reaction

Positive ~> there is net gain of energy
The reaction is not spontaneous
Endergonic reaction that need energy to happen

Question 4

What meant by ^G = 0

Answer 4

That the reactants are in equilibrium state where the reaction happens in both directions at the same rate

Question 5

What is coupling

Answer 5

Vital endergonic reactions such as synthetic one need energy so it obtain it by coupling to an exergonic reaction and is named coupled exergonic endergonic system where the overall net change is exergonic

Vital exergonic reactions are catabolism
Vital endergonic reactions are anabolism

Question 6

How ATP acts as a carrier ?

Answer 6

Catabolic reactions give energy which can be stored in the form of ATP that anabolic reactions can utilise it later through hydrolysis of ATP

Question 7

Structure of ATP

Answer 7

It has 3 components
1- nitrogenous base ( adenine)
2- sugar ( ribose)
3- 3 phosphoryl groups joined to ribose by phosphate ester bond ( covalent one) and to each other by phospho anhydride bonds

Question 8

^G of ATP

Answer 8

-7.3 kcal / mol

Question 9

Importance of ATP

Answer 9

breakdown of either phospho anydride bonds releases energy

Question 10

How ATP is generated ?

Answer 10

1- substrate level phosphorylation
• the conversion of ADP TO ATP by the use of high energy phosphate metabolites
• Some of the common phosphate-containing compounds found in cells and the energy
released by hydrolysis of their phosphate bonds under standard conditions must have ^ G >7.3

2- oxidative phosphorylation
Approximately 40% of the released energy is partly converted
into useful form . ATP formation in this process depends on the principles of oxidation-
reduction reactions (redox) reactions that occur mainly in the mitochondria.

Question 11

What ihappens in oxidative phosphorylation ?

Answer 11

•Redox reactions occurs
•Hydrogen removel of one electron is accompanied by a release of energy
•Instead of releasing a massive energy in form of heat which may destroy the living cells , hydrogen tranfers electron through different components of the redox chain ( that get more electropositive )so it is liberated in steps and small utilizable amounts
•Part of this amounts can be captured and stored by the production of ATP and this is called oxidative phosphorylation

Question 12

Major electron carriers in redox reactions

Answer 12

Dehydrogenase is used and according to the type of hydrogen carrier dehydrogenase is classified into
1- NAD LINKED DEHYDROGENASE
it is the electron acceptor in oxidation of hydroxlyted carbon atoms

2- FAD LINKED DEHYDROGENASE
It is the electron acceptor in oxidation of two adjacent carbons ( carbon -carbon double bond )

3- NADPH LINKED DEHYDROGENASE
It is a major source of reducing power for biosynthetic pathways.
In contrast to NADH, that is generated and used primarily in the mitochondria; most of the NADPH
is formed and used in extra-mitochondrial reactions.

Question 13

ETC DEF

Answer 13

it is the final common pathway in aerobic cells by which electrons carried in NADH+H AND FADH2 are transfered to oxygen to form water

The energy relaesd at specific steps in ETC is used to synthesize ATP by oxidative phosphorylation

Question 14

Location of ETC

Answer 14

Inner mitochondrial membrane

Question 15

Structure and function of complexes

Answer 15

5 complexes
1- FMN ,FE-s Transfer2 e from NADH+H to CoQ
2- FAD ,FE-S. transfer2 e from succinate to CoQ
3- Cytochrome b , c1 , FE-S. transfer 2 e from reduced CoQ to cytochrome c
4- cytochrome a, a3 , CuA , CuB. Transfer 2 e from cytochrome c to oxygen forming h2o

Question 16

Def of reduction potential

Answer 16

the tendency of a compound to be reduced
(gaining electron)

Question 17

Relation between reduction potential and electron affinity

Answer 17

The lowest electron affinity / the lowest reduction potential and vice versa

Question 18

Who has the highest reduction potential and the lowest

Answer 18

Hydrogen has the lowest
Oxygen has the highest

Question 19

What does it mean when reduction potential is - or +

Answer 19

Stronger electron acceptors have positive reduction
potential. (higher electron affinity )
Stronger electron donors have negative reduction
potential -(lower electron affinity )
Electrons will be transferred from more elecronegative to
more electropositive compounds.

Question 20

^ E =?

Answer 20

^E=E acceptor -Edonor

Question 21

What is the relationship between ^G and ^E

Answer 21

^G = -n F ^E

Question 22

How can i make non spontaneous reaction ( endergonic) spontaneous

Answer 22

By changing its products and reactants concentration

Question 23

^G in forward and backward reactions are …….

Answer 23

Are equal

Question 24

Places where substrate level phosphorylation occurs

Answer 24

Cytosol
Mitochondria

Question 25

All the members of the respiratory chain are ….. except …… which is ……

Answer 25

1- protein
2- CoQ
3- lipid

Question 26

The members of ETC can be separated into

Answer 26

4 fixed complexes
2 mobile components ( CoQ and cyto c)

Question 27

What are the other names of complex 1,2,4

Answer 27

1- NADH+H dehydrogenase
2- Succinate dehydrogenase
4- cytochrome oxidase

Question 28

Talk about complex v

Answer 28

1- it consists of 2 complex
~ Fo complex :
Presents in inner mitochondrial membrane
Forms a proton channel

~ F1 :
Projects into mitochondrial matrix
Attached to Fo
Contain ATP synthase enzyme

Question 29

Def of oxidative phosphorylation

Answer 29

The flow of electrons from NADH to oxygen (oxidation) results in ATP synthesis by
phosphorylation of ADP (phosphorylation). Therefore, there is a
coupling between oxidation and phosphorylation.

Question 30

Talk about chemiosmotic hypothesis

Answer 30

(also known as the Mitchell hypothesis) explains how the free energy generated by electron transport by the ETC is used to produce ATP

• Proton pump: The transport of electrons through the ETC gives energy. This energy
is used to transport H* from the mitochondrial matrix to the inter-membrane space
(from inside to outside the inner mitochondrial membrane). This is done by complexes I, IlI
and IV in case of NADH+H and III AND IV in case of FADH2 ,This process creates across the inner mitochondrial membrane:

a.electrical gradient; (with more positive charges on the outside than on the inside).
b. A pH gradient: the outside of the membrane is at lower pH than the inside).
c. The energy generated by this proton gradient is sufficient for ATP synthesis.
• ATP synthase (complex V):
The protons outside the inner mitochondrial membrane can re-enter
the matrix by passing through channel in Fo to pass by ATP synthase
enzyme which is present in F1 subunit. This results in the synthesis of ATP from ADP .At
the same time decrease the pH and electrical gradients.

Question 31

Inhibitors of complex 1

Answer 31

Barbiturates
Insecticides
Fish poison rotenone

Preventing passage of e from FMN to CoQ

Question 32

Inhibitors of complex II

Answer 32

Malonate

Question 33

Inhibitors of complex III

Answer 33

Antimiycin A
dimercaprol.

Preventing passage of e from cytochrome b to cytochrome c

Question 34

Inhibitors of complex IV

Answer 34

H2s
Cyanide
Carbon monoxide

Preventing passage of e from cytochrome a& a3 to O2

Question 35

Inhibitors of complex V ( ATP SYNTHASE)

Answer 35

Oligomycin
Binds to Fo subunit and prevents re entry of protons into the mitochondrial matrix. The increased proton
gradient across the inner mitochondrial membrane eventually leads to diminished electron transport

Question 36

Uncouplers of oxidation and phosphorylation

Answer 36

Uncouplers make membrane permeable to protons thus abolish proton gradient, It allows oxidation to happen but prevent phosphorylation. So, electron transport is
unaffected, but ATP synthesis cannot occur because the energy resulting from electron transfer cannot be used as it is dissipated as heat. This explains the cause of
hotness after intake of these substances. Examples:
• 2,4 Dinitrophenol: It increases the permeability of the inner mitochondrial membrane to
proton causing decrease proton gradient.

• Calcium and high doses of aspirin: this explains the fever that accompanies toxic
overdoses of these drugs.

• lonophores: e.g. antibiotics
“valinomycin and Nigericin. They have the ability to make a complex with cations as potassium “K+” and
facilitate their transport into mitochondria and They inhibit
phosphorylation because they decrease both electrical and pH gradient.
d. Thermogenin, which is found in the mitochondrial membrane of brown fat ,
surrounds the major blood vessels of the neonate, where it functions to keep the blood warm

Question 37

What is P:O ratio

Answer 37

ATP made per O atom reduced )
It is 3:1 in NADH+H as it synthesize 3 ATP DUE TO ACTIVATION OF H PUMB IN 1-3-4

It is 2:1 in FADH2 as it synthesize 2 ATP DUE TO ACTIVATION OF H PUMB IN 3-4