Topic 2/8 - Energy and Aerobic Metabolism

Which defining characteristics of life are low energy?

cellular organization (make organelles), homeostasis (in optimal environments), reproduction (when not reproducing), heredity (cell life)

Which defining characteristics of life are high energy?

growth and metabolism, homeostasis (in nonoptimal environments), reproduction (when reproducing)

What is the solar constant?

the amount of energy the earth receives from the sun, 51% is absorbed by land and oceans while 49% is reflected back into space

What happens to the solar energy that is absorbed by the Earth?

used to maintain the temperature of the land, oceans and air (no sun = ice age), captured by autotrophs and converted into chemical bond energy (base of food webs)

What is the Urey-Miller experiment?

simulation of conditions on early Earth testing the idea that life, or more specifically organic molecules, could have formed by simple chemical reactions

What is the accepted theory of early evolution?

1. primordial soup
2. lightning (energy)
3. urey-miller experiment
4. abiogenesis

What is abiogenesis?

first life forms generated were very simple and through a gradual process became increasingly complex

What was the early atmosphere like?

anaerobic: no O2, mostly CO2, some N2

What were the first organisms to evolve?

anaerobic heterotrophs: able to get a small amount of energy from glucose without O2 (breakdown chemicals into nutrients with fewer enzymes)
early autotrophs: able to make their own molecules to get energy (H2S, then H2O)
true autotrophs: able to undergo photosynthesis (use oxygen)

What is the modern atmosphere like?

aerobic: lots of O2, mostly N2 and some CO2

What is aerobic metabolism?

metabolism in the presence of oxygen used by aerobic heterotrophs (glucose is eaten, not made)

Is evolution goal oriented?

no, it is random (due to mutations). it will never start over from scratch and will simply build on existing pathways (its inefficient but nothing else exists)

What is the energy currency of life?

ATP (adenosine triphosphate) s the preferred activation energy

How is ATP formed?

energy from the sun is stored as chemical energy in the bonds of glucose, cellular organisation converts the stored chemical energy into usable energy in high energy bonds of ATP

Why are the bonds in the phosphate group on ATP considered to be high energy bonds?

O charge on PO4 is negative, and it is harder to put negative ions together

What is the reaction for the hydrolysis of ATP?

the reaction of ATP and water yields ADP and inorganic phosphate (Pi - phosphate not attached to carbon) and releases energy (exothermic)

Is the hydrolysis of ATP exothermic or endothermic, and why?

highly exothermic as the high-energy bonds release energy when broken

Is the synthesis of ADP to ATP exothermic or endothermic, and why?

highly endothermic as putting 2 functional groups with like charges (that repel) together takes a lot of energy

How much energy is released when a high energy bond breaks?

7.3 kcal/mol of energy per bond (31 kJ/mol)

What is the activation energy of the average biochemical reaction?

3.5 kcal/mol (15.5 kJ/mol)

What is AMP?

adenosine monophosphate or nucleic acids (RNA/DNA)

What are coupled reactions?

when two reactions occur in close proximity, so the energy released by the exothermic reaction can be used to provide the activation energy needed for the endothermic reaction

What was the first way to make ATP without O2?

substrate-level phosphorylation (SLP)

What is substrate-level phosphorylation?

direct transfer of a phosphate group from an organic substrate to ADP by an enzyme (usually a kinase); this process occurs during glycolysis and the kreb cycle, but generates much less ATP during cellular respiration than oxidative phosphorylation

How is ATP made when there is O2?

chemiosmosis or oxidative phosphorylation

What is oxidative phosphorylation?

a series of reactions in which electrons are transferred from NADH and FADH2 (the molecules are oxidized) to different electron acceptors (such as oxygen) to drive the phosphorylation of ADP to ATP; this process occurs through an electron transport chain that establish a proton gradient, followed by chemiosmosis that produces ATP

What does the proton pump do?

creates an electrochemical concentration gradient across the inner mitochondrial membrane by actively transports hydrogen ions (H+) out of the cell

How many protons (hydrogen ions) go through ATP synthase to create 1 ATP?

3 (correct: 3.5)

What is ATP synthase?

an enzyme/channel protein that helps the ions cross the inner mitochondrial membrane

What is the proton motive force?

the force provided by a transmembrane hydrogen ion gradient, creating kinetic energy within ATP synthase that is converted into the chemical energy in the high energy bond in ATP

Where does SLP occur? Does it occur during aerobic or anaerobic metabolism?

cytoplasm for glycolysis and mitochondrial matrix for krebs cycle (eukaryotes), during aerobic or anaerobic respiration

Where does oxidative phosphorylation occur? Does it occur during aerobic or anaerobic metabolism?

inner mitochondrial membrane during aerobic respiration (for animals)

What is cellular respiration?

process by which all cells release the energy from the bonds of glucose into usable energy (ATP)

What are the 3 main stages of cellular respiration? Do they make ATP directly or indirectly?

glycolysis (makes ATP directly), oxidation of pyruvate (makes ATP indirectly), krebs cycle (makes ATP directly)

What is the equation for cellular respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP energy

What is glycolysis?

first stage of cellular respiration, occurs in cytoplasm, occurs with or without oxygen

What are the 3 pairs of isomers in glycolysis?

glucose/fructose, DHAP/G3P, 3PG/2PG

What are the 2 exothermic reactions in glycolysis?

ATP losing PO4 to become ADP in reactions 1 and 3

How many ATP are used and produced in the energy investment phase of glycolysis?

2 ATP used, 0 are made

What is the final product of the energy investment phase of glycolysis?

2 molecules of G3P

Where is the redox reaction in glycolysis?

reaction 6 where G3P becomes 1,3-BPG

What are 2 examples of SLP in glycolysis?

reaction 7 and 10 where ADP becomes ATP

What does phosphorylation accomplish?

adding phosphate group (via kinase) makes new molecule unstable, so another reaction will occur soon after

What is the most common hydrogen/electron carrier? What does it become?

NAD+ (nicotinamide adenine dinucleotide) becomes NADH + H+

How much energy is in the bonds of glucose?

686 kcal/mol

How much usable energy has been extracted during glycolysis?

from 2 ATP (2 high energy bonds x 7.3 kcal/mol = 14.6 kcal/mol)
energy yield in glycolysis/chemical potential energy in glucose = 14.6/686 = 2%

How much ATP is produced in glycolysis?

4 ATP, 2 are used so net 2 ATP

Where does the chemical potential energy in glucose go in glycolysis?

2% in ATP, 98% in bonds of pyruvate molecules

If glycolysis is so inefficient, why is it still around?

it works despite being inefficient so that's all there is: evolution

What are the limitations of glycolysis?

glycolysis will eventually convert all NAD+ to NADH unless there is some way to remove the electrons; if the cell runs out of NAD+, glycolysis will stop and the cell will run out of energy

What are the 2 ways to recycle NADH (after glycolysis)? Which evolved first and why?

fermentation (evolved first since it does not require oxygen) and oxidative respiration (evolved later since it requires oxygen)

What is fermentation?

an ATP-generating process in which organic molecules act as both donors and acceptors of electrons, works under both aerobic and anaerobic conditions; another organic molecule removes the hydrogen (electrons) from NADH to recycle the NAD+

What is ethanol fermentation?

performed by yeast cells or bacteria; conversion of pyruvate to ethanol under aerobic or anaerobic conditions; used in baking and alcohol brewing

What is lactic acid fermentation?

performed by animal cells, some bacteria (lactobacilli) and fungi when deprived of O2; occurs under anaerobic conditions; catalyzed by lactate dehydrogenase

How is lactic acid produced in the body?

when the body cannot provide enough oxygen to the muscle cell, the body builds up lactic acid, causing fatigue and cramping; this lactic acid is then carried to the liver and converted back to pyruvate

What is oxidative respiration?

occurs under aerobic conditions in the mitochondria; pyruvate is oxidized and oxidative respiration continues

What is oxidation of pyruvate?

second stage of aerobic metabolism aka link reaction; catalyzed by pyruvate dehydrogenase; 3 main tasks: decarboxylation, oxidation of pyruvate to create acetyl group, addition of co-enzyme A

What is the Krebs cycle (citric acid cycle)?

third stage of aerobic metabolism; first reaction produces citrate/citric acid; cycle beginning with oxaloacetate (4C molecule that is regenerated); entry point for other metabolic processes (proteins, fats, lipids are turned into acetyl groups and enter Krebs cycle when digested)

How many times will the cell go through the Krebs cycle for each molecule of glucose? How many ATP are produced per molecule of glucose?

2 times, 1 ATP by SLP each time (2 ATP total)

Where are the decarboxylation reactions in the Krebs cycle?

reactions 3 and 4

Where are the redox reactions in the Krebs cycle?

reactions 3, 4, 6, 8

What is the most exothermic reaction in the Krebs cycle?

succinyl CoA --> succinate (reaction 5)

What are the two electron carriers in the Krebs cycle?

NAD+, FAD

What is the pair of isomers in the Krebs cycle?

citrate/isocitrate

What are NAD+ and FAD?

co-enzymes or electron carriers with high electron affinity so they removed hydrogen atoms and their electrons to oxidize other molecules and create reactive intermediates

What is NAD+/NADH? Where is it found?

(nicotinamide adenine dinucleotide) found in the cytoplasm and mitochondria, cannot cross the mitochondrial membrane

What is FAD/FADH2? Where is it from?

(flavin adenine dinucleotide), only found in mitochondria

Where do electron carriers NAD+/FAD carry electrons?

from electron transport chain to a series of proton pumps

What is the cristae of the mitochondria? What occurs here?

folds of the inner membrane, electron transfer chain and chemiosmosis occur here

How are electrons from NADH passed to FAD inside the mitochondria?

electrons from NADH can enter the mitochondrial ETC from reducing DHAP to G3P (oxidized intermediate); G3P is reoxidized by electron transfer to an FAD prosthetic group in membrane bound G3P dehydrogenase; electrons then enter the ETC

Why is it important for electrons but not NAD+ to pass the mitochondrial membrane?

maintains supply of NAD+

What is the electron transport chain?

a cluster of membrane proteins (cytochrome complexes) arranged in order of increasing electronegativity along the inner mitochondrial membrane; receive electrons from NADH/FADH2 and pass them along until they reach oxygen, the final electron acceptor

How many electrons are made in the electron transport chain?

2 electrons made

What happens there is no O2 in the electron transport chain?

if there was no O2 present in the mitochondria, the electrons could not be removed from the system, and the entire ETC would back up and stop (electrons would not be removed from NADH/FADH2); mitochondria would be unable to generate new ATP this way, and the cell would ultimately die from lack of energy

What is one of the products of cellular respiration made in the ETC?

H2O

What are the names of all complexes in the ETC?

complex 1: NADH reductase complex (e- from NADH to Q)
Q: ubiquinone, motile e- carrier (e- from NADH reductase or FADH2)
complex 2: cytochrome B complex (e- from Q to cyt. C)
cytochrome C: motile e- carrier
complex 3: cytochrome oxidase complex (e- from cyt. C to O2 making H2O)

How many protons does each cytochrome complex pump out?

3-4 protons

How are the ETC and ATP synthase related?

electrons are passed along driven by a drop in free energy, energy lost pumps protons actively against concentration gradient; this creates huge concentration gradient; ATP synthase molecules create 1 ATP for every 3H+

Does the ETC make ATP?

not directly, but indirectly helps by creating the concentration gradient where 3H+ then make 1 ATP in chemiosmosis

How are triglycerides metabolized?

hydrolyzed by lipases into glycerol and fatty acids (have tons of energy/gram)

How is glycerol metabolized?

can be converted into glucose via gluconeogenesis (glycerol+glycerol=glucose)

How are fatty acids metabolized?

transported into mitochondrial matrix to undergo B-oxidation (broken into acetyl groups), then enter Krebs cycle (each cleavage uses 1 ATP and produces 3 NADH and 1 FADH2)

What is B-oxidation?

first step in fatty acid oxidation, in which fatty acids are broken into separate two carbon units of acetic acid, each of which is then converted to acetyl CoA

How much ATP is lost and gained from metabolizing lipids?

loss: - (number of acetyl groups)
gain: 11 x (number of acetyl groups)

How are monosaccharides metabolized?

aerobic metabolism

How is starch metabolized?

hydrolyzed by amylase into monosaccharides, then aerobic metabolism

How is glycogen metabolized?

removed from the liver and muscle cells to undergo glycogenolysis (break apart glycogen) to increase blood glucose

How is excess glucose metabolized?

converted to glycogen via glycogenesis (glucose to glycogen) and stored in the liver

How are polypeptides metabolized?

hydrolyzed by pepsin in stomach (main enzyme that breaks peptides into amino acids)

What is deamination?

all NH3 (amine groups) are removed from proteins are excreted as urea

Where do the remaining carbon skeletons from amino acids, sugars and nitrogenous bases enter aerobic metabolism?

can become acetyl CoA (krebs cycle) or pyruvate

How are nucleic acids metabolized?

negligible digestion; hydrolyzed into nucleotides which are usually recycled into new nucleotides but can be used as an energy source if absolutely necessary

ATP determines the fate of acetyl groups... What happens if there is low ATP?

acetyl groups are picked up by CoA and enter cellular respiration

ATP determines the fate of acetyl groups... What happens if there is high ATP?

acetyl groups are picked up by CoA that converts them into fatty acids for storage; phosphofructokinase is inhibited (adds P to fructose-6-phosphate)

What happens if there is high NADH in cellular respiration?

non-competitive inhibitor of pyruvate decarboxylase

What was Earth like before photosynthesis?

it was a reducing environment (gain electrons)... less than 2% oxygen

Did photosynthesis or cellular respiration evolve first? Why?

photosynthesis happened first since it doesn't require oxygen, and cellular respiration requires oxygen

What started photosynthesis?

cyanobacteria started photosynthesizing 2.5 bya, oxygen was a byproduct of the photolysis of water (breakdown of molecules by light)

What time period did oxygen levels rise?

750 mya to present - oxygen levels have risen from 2% to roughly 20% because of photosynthesis

What are the implication of oxygen production?

1. oxygen production led to the formation of the ozone layer, this made Earth livable since it reduced UV exposure allowing more life to survive and evolve
2. oxygen in the atmosphere led to oxidized compounds such as iron oxides that have formed rock depositions on the ocean floor