L3-Metabolism and Cell Culture Growth

Question 1

What essential macronutrients do most cells need to live?

Answer 1

C,(O, H,) N, P, S, K, Mg, Ca, Na

Question 2

What important micronutrients do cells need and why?

Answer 2

¬Vitamins function as coenzemes/nonprotein components of enzymes.

Question 3

How can cells sequester iron from their environment?

Answer 3

Cells produce iron-binding molecules called siderophores. These bind to Fe 3+ from insoluable minerals and transport it into the cell. After the iron-hydroxamate complex reaches the cytoplasm, iron is reduced/released and hydroxamate is excreted and can be used again for iron transport.

Question 4

What does a negative delta G of a compound mean?

Answer 4

Compound forms spontaneously

Question 5

What is a catalyst and how does it aid in reducing activation energy?

Answer 5

Catalysts lower the activation energy (to increase the reaction rate) by making it more likely that two reactants will collide usually by fixating one of the reactants in a specific conformation. Also, it aligns the substrate to the active amino acids to put strain on a bond for breakage.

Question 6

How can you determine whether something is a better electron donor than another?

Answer 6

Better electron donors have a lower reduction potential (measured in volts in reference to standard substance H2).

Question 7

How is energy stored?

Answer 7

Energy is stored in bonds of insoluble prolymers that can be catabolized later for the production of ATP. Ex. glycogen, poly-B-hydroxybutyrate, starch, lipids

Question 8

How are redox reactions mediated by NAD/NADH?

Answer 8

NAD+/NADH is a good electron and proton carrier. NAD+ can accept electrons whereas NADH can donate electrons. When NADH donates an electron to a final electron acceptor (such as O2), energy is released.

Question 9

Provide examples of catabolic reactions.

Answer 9

• • Fermentation-an organic compound is both an electron donor and acceptor and ATP is produced by substrate-level phosphorylation
• • Respiration- a compound is oxidized with O2 as the terminal electron acceptor , usually accompanied by oxidative phosphorylization

Question 10

Explain the generation of the proton motive force during aerobic respiration.

Answer 10

Generally speaking, there are three features characteristic of all electron transport chains. 1)arrangement of carriers in order of increasingly more positive E0’, 2) alternation of electron-only and electron plus proton carriers in the chain and 3)generation of a proton motive force.

Question 11

How do electron transport reactions generate proton motive force?

Answer 11

Generally speaking, there are three features characteristic of all electron transport chains. 1)arrangement of carriers in order of increasingly more positive E0’, 2) alternation of electron-only and electron plus proton carriers in the chain and 3)generation of a proton motive force.

Question 12

What structure in the cell converts the proton motive force to ATP and how does it function?

Answer 12

ATP synthase/ATPase-Pmf-drive H+ ¬movement through F0 causes movement of c protein rotary. This torque is transmitted to F1 via coupled proteins. This causes the B subunit to bind to ADP+P¬I and when the B subunit returns to original conformation, energy is released to drive ATP synthesis.

Question 13

What are the main roles of glycolysis and the TCA cycle?

Answer 13

• • Glycolysis-to consume glucose, produce ATP and generate fermentation products (anaerobic respiration) or send excess electrons to power proton motive force for more ATP generation (aerobic respiration)
• • TCA cycle-breaks down glucose to eventually create ATP, generates small compounds such as alpha-ketoglutarate and oxalacete which are precursors to several amino acids.

Question 14

Provide an example and explain chemolithotrophy, anaerobic respiration and phototrophy?

Answer 14

• Chemolithotrophy-use H2s, H2, Fe2+ and NH3 as electron donors. CO2 is used as the carbon source. Therefore autotrophs.
• Anaerobic respiration-Under anoxic conditions, electron acceptors rather than oxygen can be used to support respiration. Ex. of electron acceptors:No2-, sulfate, carbonate, and some organic compounds. Less energy is released when they are reduced
• • Phototrophy-Two types oxygenic and anoxygenic. Both reactions lead to formation of a proton motive force and utilize oxidative phosphorylization.

Question 15

Be able to calculate specific growth rate, division rate, doubling time, and number of generations per unit time in an exponentially growing culture.

Answer 15

• • N=N₀2ⁿ (N=final number of cells, N0 is the initial cell number, n=# of generations during the period of exponential growth)
• • g=t/n, g=generation time, t=duration of exponentially growing population, and t is the duration of growth in days, hours or minutes
• • n=3.3(log N-log N₀)
• • specific growth rate (¬k)-0.301/g
• • division rate(v)-1/g
• • number of generations per unit time-1/g

Question 16

Why does lag phase occur in microbial cultures?

Answer 16

A lag phase occurs when

1) inoculum is taken from an old stationary phase culture and transferred into the same medium
2) the cells are damaged or
3) the population is transferred from a rich culture medium to a poorer one.

In the first situation, cells are depleted from essential constituents and time is required for their biosynthesis. Damaged cells must have time for repair and cells in nutrient poor medium must synthesize essential metabolites not present in that medium.

Question 17

Why do batch cultures enter a stationary phase?

Answer 17

One or both of two situations limit growth:

1) an essential nutrient of the culture medium is used up or
2) a waste product of the organism accumulates in the medium and inhibits growth