Lecture 7: Introduction To Cellular Energy Generation

Question 1

In order to grow, cell require?

Answer 1

Energy
Building blocks- most important is carbon, from carbon cells manufacture macromolecules they need eg proteins, glycogen, triglycerides. To build these from carbon building blocks an input of energy is needed. On the basis of how they obtain their carbon we divide cells into their 2 groups:
a) autotrophs
b) heterotrophs

Question 2

What is the difference between autotrophs and heterotrophs, explain them both and give examples

Answer 2

Autotrophs: ‘self feeding’
They obtain their carbon from CO2. On the basis of how they obtain their energy to convert this CO2 into larger compounds, we subdivide autotrophs into 2 groups.
a) Photosynthetic organisms: energy obtained from the sun eg green plants, photosynthetic bacteria ie photosynthesis
b) Chemosynthetic organisms: energy obtained from the oxidation of inorganic molecules eg
NH3 (reduced) is reduced with O2 to NO2- (oxidised) which gives energy in the form of glucose

Heterotrophs: ‘feeding of others’
These cells obtain their carbon and energy they need from assimilated compounds such as glucose. Heterotrophs break these compounds down thus releasing the energy contained in the bonds and then use this energy to recycle the carbons into macromolecules. Heterotrophic cells include animal cells, most bacteria and non-green plant cells.

Question 3

Cell metabolism

What is the definition of metabolism, and what are the two forms of metabolism?

Answer 3

Metabolism: all the enzyme reactions occurring in a cell
It’s divided into two phases
1. Catabolism: breaking larger compounds into smaller ones. These reactions release energy in the form of ATP
Eg glucose -> 6CO2 + 6H2O

2. Anabolism: building larger compounds from smaller ones, responsible for cell growth and repair processes. These reactions require an input of energy

Question 4

What is ATP, how is it used? How is it produced?

Answer 4

Adenosine triphosphate is an energy carrier or transmitter (not an energy store); it is a nucleoside triphosphate.
When energy is required a high energy phosphate bond of ATP is broken, converting ATP to ADP + inorganic phosphate and the energy contained in the phosphate bond is released:
ATP -> ADP + Pi + 30.5 kj (energy)
How is it produced?
There are 2 main ways of obtaining energy as ATP during catabolism:
1. Fermentation
2. Aerobic respiration

Question 5

What is fermentation and what is aerobic respiration. What are the conditions each function in, and give the energy yields and bi products of each

Answer 5

1. Fermentation: this is an anaerobic process, involves conversion of high energy compounds into smaller, lower energy compounds. During this process ATP is produced directly by substrate level phosphorylation.
   Eg lactic acid fermentation, which occurs in muscle cells when O2 isn’t available. Refer to pg 32 of unit reader for diagram
   Or ethanol fermentation which occurs in yeast cells when O2 isn’t available.
2. Aerobic respiration: this is an aerobic O2 requiring process. Fuel molecules like glucose are completely oxidised to CO2 and H2O and ATP is produced by both substrate level phosphorylation and by oxidative phosphorylation
   In aerobic respiration hydrogen ions and their associated electrons are transferred from fuel molecules to O2 reducing it to H2O while the fuel molecules are oxidised to CO2
   The hydrogen ions and electrons aren’t transferred directly to O2; intermediate electron acceptors are involved. These are:
   FAD: flavin adenine dinucleotide
   NAD+: nicotinamide adenine dinucleotide
   These intermediate electron carriers accept the hydrogen ions and electrons and become reduced to NADH + H+ and FADH2 which are subsequently reoxidised by passing the hydrogen ions and electrons down the electron transport chain that is located in the inner mitochondrial membrane. The last component of this electron transport chain is O2, which is the ultimate electron acceptor and in accepting the H+ and electrons it becomes reduced to H2O.
   As the hydrogen ions and electrons are passed down the chain, ATP is produced. (Oxidative phosphorylation)
   For each mole of NADH + H+ = 2.5 moles of ATP
   For each mole of FADH2 = 1.5 moles of ATP