1.16. Cell respiration 1

Question 1

cell respiration

Answer 1

metabolic pathway with many steps with the purpose of harvesting chemical energy from food molecules
- the oldest metabolic process in living organisms on Earth

Question 2

substrates and products in CR

Answer 2

substrates: glucose, O2 (optional - only if aerobic), NAD^+
products: CO2, H2O, ATP and NADH + H^+ (chemical energy)

Question 3

which living organisms perform CR?

Answer 3

all - Animalia, Plants, Funghi, Protocstists, Archea, Bacteria

Question 4

where does CR occur

Answer 4

in cytoplasm and in mitochondria (in most organisms - except Archea ad Bacteria)

Question 5

why is the presence of an oxidizing agent needed for cell respiration?

Answer 5

glucose is a very stable molecule (it’s inert/self-satisfied) - it needs to be destabilized to react/interact which can be achieved either by heating it, providing an enzyme or providing an oxidizing agent to oxidize it
- catabolic reaction analogy: rock rolling downhill - initial push (E invested) and then reaction continues spontaneously providing much more E than invested (2 ATP invested, 38 released)

Question 6

providing thermal E to glucose:

Answer 6

products CO2, H2O, light E and heat (useless for organisms)

Question 7

in organisms, E from glucose is released as… (efficiency?)

Answer 7

ATP (chemical energy) and heat (thermal energy) - efficiency is 40% (rest is lost as heat)

Question 8

ATP is…

Answer 8

universal energy transfer molecule

Question 9

glucose gets oxidized by…

Answer 9

oxygen

Question 10

redox reactions

Answer 10

reduction and oxidation reactions are coupled processes (one causes the other):
glucose + O2 into CO2 + H2O (ox.)
ADP + P into ATP (red.)
or
ATP into ADP + P (ox.)
a-a into polypeptide chain (red.)
- oxidation of ATP creates E for a-a polymerization

Question 11

oxidation

Answer 11

• similar to hydrolysis
• E released
• gain of O2
• loss of e-
• loss of H+
• results in many C-O bonds
• yields a compound with lesser potential energy

Question 12

reduction

Answer 12

• similar to dehydration
• E has to be invested
• loss of O2
• gain of e-
• gain of H+
• results in many C-H bonds
• yields a compound with higher potential energy

Question 13

high electronegativity

Answer 13

affinity of a substance to gain electrons (susceptible to reduction)

Question 14

how does oxidation release energy

Answer 14

transfer of electrons from a less electronegative towards the more electronegative atom releases E

Question 15

organic compounds store chem E in ___ (___) because…

Answer 15

chemical bonds, covalent bonds, they are shared e- pairs so e- in the bond are the ones possessing energy

Question 16

if cell respiration is anaerobic, it happens in…

Answer 16

cytoplasm (no mitochondria)

Question 17

energy within glucose is stored in…

Answer 17

chemical bonds: C-O, C-H, C-C - covalent bonds=electrons whose transfer produces energy - they absorb E jump to excited state and when spontaneously going back to the ground state emit light/heat

Question 18

two most important products of gradual oxidation of glucose (state full equations)

Answer 18

glucose -> (oxidizing agent) …
1|…-> (energy) P + ADP -> ATP
2|…-> (H) NAD^+ + 2H -> NADH + H^+

Question 19

NADH + H^+ is the ___ form and the NAD^+ ___ form of the electron/hydrogen carrier

Answer 19

reduced, oxidized

Question 20

why is NAD^+ an oxidizing agent?

Answer 20

because of it’s high electronegativity - it’ s hungry for electrons so it steals them from other substances

Question 21

electron/hydrogen carrier meaning

Answer 21

it carries electrons and/or hydrogen atoms/protons (H^+=p+)

Question 22

what can be done with the two products of gradual (step-by-step) oxidation of a food molecule

Answer 22

1|ATP can immediately be used to obtain energy to power anabolic processes
2|H atoms are joined with NAD^+ and NADH + H^+ is formed - little boxes storing potential energy which accumulate and get transferred to a specific site in mitochondria where they are opened in controlled way and the E released is used to create ATP - majority of E is stored in this way

Question 23

gradual oxidation also called

Answer 23

stepwise or regulated - meaning, it has multiple steps

Question 24

when is O2 used as oxidizing agent

Answer 24

only in the last step of cell respiration - in its place the cell uses NAD^+ (found in cell)

Question 25

why does oxygen have to be introduced as an oxidizing agent

Answer 25

because once NAD^+ is reduced, it is very stable so an even stronger oxidizing agent has to be introduced to turn it back to its oxidized form - this is O2

Question 26

how is water one of the products of CR? (show equations)

Answer 26

O2->2O^2-
O^2- + 2H^+->H2O

Question 27

the main electron carrier in CR is…

Answer 27

NAD^+ (nicotinamide adenine dinucleotide)

Question 28

what is the aim of many steps of CR?

Answer 28

to generate NADH+H^+ molecules because in the final step of CR they will accumulate and release energy for ATP

Question 29

molecule that stores E in the cell

Answer 29

ATP?

Question 30

most common CR substrates

Answer 30

carbohydrates (glucose - any hexose sugars), lipids, proteins (once c-h and lipids are used up)