Ch 13 Segway Lecture

Question 1

catabolism

Answer 1

breaks down food for energy and building blocks ex: glycolysis

Question 2

anabolism

Answer 2

used energy and building blocks to make the molecules used for catabolism ex: photosynthesis

Question 3

Where does the energy we consume come from and what is the general formula

Answer 3

Sun (Energy) + 6 CO2 + 6 H2O -> (C6H12O6)n + 6 O2

Question 4

What molecules do most chemoheterotrophs use for energy?

Answer 4

reduced carbon

Question 5

∆G°’

Answer 5

free energy change of reaction when all of its reactants and products are in their standard states: 25°C, 1 atm, and unit concentrations of 1M for reactants and products at a pH of 7. This never happens in biology, so a correction from ∆G°’ to actual ∆G must be made

Question 6

∆G = (in terms of ∆G°’)

Answer 6

∆G = ∆G°’ + RT ln K_eq

To make ( RT ln K_eq ) negative (for reaction spontenuity) increase the concentration of the reactants or remove product to drive the reaction towards K_eq

Question 7

General charachteristics of metabolic pathways

Answer 7

• Individual pathways are irreversable: don’t waste energy on reactions that will revert back
• Catabolic and anabolic pathways must differ: for independent control of the two processes
• Every pathway has an early committed step
• All pathways are regualted
• Metabolic pathways in eukaryotes occur in different areas: glycolysis in cytosol and citric acid cycle in mitochondria

Question 8

Why is the ATP to ADP conversion so energetically favourable?

Answer 8

Releif of charge repulsion between phosphate groups, resonance stabilisation of product (Pi), reionisation of ADP

Question 9

Three easy ways to oxidise

Answer 9

loss of electrons, loss of hydrogen, gain of oxygen

Question 10

Three easy ways to reduce

Answer 10

gain of electrions, gain of hydrogen, loss of oxygen

Question 11

Transfer of electrions to O₂ is exergonic or endergonic and why?

Answer 11

exergonic, oxygen has a very high standard reduction potential (wants to be reduced)

Question 12

standard reduction potential

Answer 12

the affinity of a molecule to be reduced, greater is more likely to be reduced

Question 13

list the oxidation states of carbon in biomolecules and give examples of each in order from most reduced to most oxidised

Answer 13

alkane > alcohol > ketone/aldehyde > carboxcylic acid > CO₂

Question 14

coenzyme

Answer 14

a low molecular weight organic compound which in cooperation with an enzyme, facilitates a reaction

coenzyme may appear to be a substrate and/or product. many coenzymes have a part of their structure that is derived from a vitamin

this is what makes vitamins a nutritional requirement, as the cell cannot biosynthesize an adequate amount for its own use

Question 15

What is the difference between the types of reactions NAD⁺ and NADP

Answer 15

NAD+ is reduced to NADH during many oxidative reaction of catabolism

NADPH is oxidised to NADP in anabolic pathways

Question 16

What happens to NAD⁺ during catabolism? What is the function of NAD⁺ in catabolism?

Answer 16

NAD+ is reduced to NADH during many oxidative reactions of catabolism.

NAD+ collects electrons released during catabolism.

NADH is a form of stored chemical energy: it can be oxidized in aerobic cells, this oxidation provides the energy for ADP + Pi –> ATP

Question 17

H and electrons in a cell

Answer 17

H = e^- + H⁺
• A hydrogen ion is a proton
• Water dissociates to H⁺ + OH^-, so there are always lots of protons around free in the cell.
• Protons can exist free in the cell (recall pH), but electrons can’t.
• To move electrons, the cell uses electron carriers like NADH and FADH₂

Question 18

Where does reduced carbon factor into metabolism?

Answer 18

Reduced carbon (in carbohydrates, fats, or proteins) + O2 -> CO2 + H2O + Energy

Question 19

Where are polymers broken down?

Answer 19

Polymers are broken down in the intestine. Only monomers are absorbed.

Question 20

Where are monomers broken down?

Answer 20

Monomers are absorbed and broken down in the cells

Question 21

What happens to individual biomolecules during catabolism?

Answer 21

Individual biomolecules are broken down by unique pathways into universal molecules (like acetyl-CoA) that can “feed into” a common energy producing pathway called the TCA cycle

Question 22

exergonic reaction

Answer 22

Favorable reactions are exergonic and release free energy, represented by a negative ∆G

Question 23

endergonic reaction

Answer 23

Nonspontaneous reactions that absorb free energy and has a positive ∆G are called endergonic

Question 24

Favorable reactions are exergonic or endergonic? Is their ∆G positive or negative?

Answer 24

exergonic, -∆G

Question 25

Unfavorable reactions are exergonic or endergonic? Is their ∆G positive or negative?

Answer 25

endergonic, +∆G

Question 26

A reaction with +∆G is exergonic or endergonic? Spontaneous or nonspontaneous?

Answer 26

endergonic, nonspontaneous

Question 27

A reaction with a -∆G is exergonic or endergonic? Spontaneous or nonspontaneous?

Answer 27

exergonic, spontaneous

Question 28

What is true about a reverse reaction's ∆G compared with the forward reaction?

Answer 28

It has the same magnitude but inverses the sign

Question 29

NAD⁺ structure

Answer 29

Nicotinamide adenine dinucleotide, like all dinucleotides, consists of two nucleotides joined by a pair of bridging phosphate groups. The nucleotides consist of ribose rings, one with adenine attached to the first carbon atom (the 1' position) and the other with nicotinamide at this position. The nicotinamide moiety can be attached in two orientations to this anomeric carbon atom. Because of these two possible structures, the compound exists as two diastereomers. It is the β-nicotinamide diastereomer of NAD+ that is found in organisms. These nucleotides are joined together by a bridge of two phosphate groups through the 5' carbons

Question 30

ln (natural log) of anything \<1 is negative or positive

Answer 30

negative

Question 31

What is one way biological systems can make a reaction with positive ∆G°' spontaneous?

Answer 31

When products are quickly removed from the reaction by rapidly using them in a sequential reaction, making the second term in the equation for actual ∆G negative (products lower than reactants)

Question 32

What is the structure of adenosine?

Answer 32

Question 33

What is the structure of adenosine, and how does it relate to ATP?

Answer 33

Question 34

What type of bond forms upon the conversion of adenosine to AMP?

Answer 34

phosphoester bond

Question 35

What type of bond forms upon the conversion of AMP to ADP?

Answer 35

phosphoanhydride bond

Question 36

what bond forms on upon the conversion of ADP to ATP?

Answer 36

phosphoanhydride bond

Question 37

phosphoanhydride bond vs phosphoester bond vs phosphodiester bond and an example of where they are found

Answer 37

phosphoanhydride bond: P-O-P, found linking the last two Pi groups in ATP phosphoester bond: C-O-P, found linking the first Pi group with adenosine in ATP phosphodiester bond: C-O-P-O-C, found along the DNA backbone linking nucleotides

Question 38

NAD⁺: anabolism or catabolism energy carrier?

Answer 38

NAD⁺ collects electrons released during **catabolism**

Question 39

How do coupled reactions work?

Answer 39

Using shared intermediates to take advantage of the free energy from an exergonic reaction to drive an endergonic reaction

Question 40

NADPH: anabolism or catabolism?

Answer 40

NADPH is a stored form of reducing power, it is used to drive the reductive biosynthetic reaction of **anabolic** pathways

Question 41

What is responsible (either directly or indirectly) for all work performed by a cell?

Answer 41

the flow of electrons in redox reactions

Question 42

What is the general path of electrons through the cell?

Answer 42

Electrons move from electron rich molecules (food) to metabolic intermediates to electron carriers to oxygen

Question 43

loss of hydrogen: oxidation or reduction?

Answer 43

oxidation

Question 44

loss of electrons: oxidation or reduction?

Answer 44

oxidation

Question 45

gain of oxygen: oxidation or reduction?

Answer 45

oxidation

Question 46

Can a reaction be either an oxidation reaction or a reduction rection?

Answer 46

No, they occur together, one species is being oxidised while another is reduced

Question 47

gain of hydrogen: oxidation or reduction?

Answer 47

reduction

Question 48

gain of electrons: oxidation or reduction?

Answer 48

reduction

Question 49

loss of oxygen: oxidation or reduction?

Answer 49

reduction

Question 50

When NAD⁺ is converted to NADH, how many electrons are transferred? How many protons? Oxidation or reduction? Give an example of a reaction that would compliment this.

Answer 50

2 electrons (both stay with NADH), 2 protons (only one stays with NADH), reduction

Question 51

what is the general rule for oxidation of carbon in an organic compound?

Answer 51

more C-O bonds means more oxidised

Question 52

What is being reduced while carbon is being oxidised (the forward reaction shown)?

Answer 52

NAD⁺ + 2e^- + 2H⁺ -\> NADH + H⁺

Question 53

explain the NAD⁺ to NADH conversion

Answer 53

RH2 + NAD⁺ -\> NADH + H⁺ + R; From the hydride electron pair, one electron is transferred to the positively charged nitrogen of the nicotinamide ring of NAD⁺, and the second hydrogen atom transferred to the C4 carbon atom opposite this nitrogen. The midpoint potential of the NAD⁺/NADH redox pair is −0.32 volts, which makes NADH a strong reducing agent. The reaction is easily reversible, when NADH reduces another molecule and is re-oxidized to NAD⁺. This means the coenzyme can continuously cycle between the NAD+ and NADH forms without being consumed.

Question 54

what does NAD⁺ stand for?

Answer 54

Nicotinamide Adenine Dinucleotide

Question 55

Why do molecules like NADH or FADH₂ exist in cells the first place?

Answer 55

H = e^- + H⁺ * A hydrogen ion is a proton, a hydrogen molecule is a proton+electron * Water dissociates to H⁺ + OH^-, so there are always lots of protons around free in the cell. * _Protons can_ exist free in the cell (recall pH), but _electrons can’t_. * **To move electrons, the cell uses electron carriers like NADH and FADH₂**