Lecture 11: Alternate Metsbolic Strategies Flashcards
Glucose is not the only fuel that is able to be oxidised as a source of energy.
Other sources include:
Other carbohydrates Fats Proteins Other organic compounds Other inorganic compounds All of these can act as electron donors
O2 is not the only electron acceptor, a number of organic and inorganic compounds can acts as electron acceptors.
List and discuss them
-several species of bacteria are capable of anaerobic respiration
-substrates are oxidised but O2 is not used as the electron acceptor
-inorganic compound are reduced instead:
Sulphate reducing bacteria: SO4(2-) -> H2S we are adding (+e-)
Methanogenic bacteria: CO2 -> CH4
Nitrate reducing bacteria: NO3- -> NO2-
Denitrifying bacteria: NO2- -> N2
Organisms can be subdivided on the basis of the type of metabolism of which they are capable.
There are three types, what are they?
Obligate (strict) aerobes: these organisms have an absolute need for O2 and lack the capacity if survive by fermentation alone. We humans are.
Obligate (strict) anaerobes: these organisms can only grow in the absence of O2; not only are they incapable of aerobic respiration but cannot tolerate O2 and they are killed by it
Facultative anaerobes: these organisms can grow either in the presence or absence of O2 but always undergo fermentation.
Also in this group are the aero tolerant anaerobes (eg lactic acid bacteria) these can grow in presence or absence of O2 but they always ferment.
Diversity of substrate utilisation:
Many bacteria possess enormous flexibility as to the range of substrates they can use as any energy source. Eg one bacteria can use 200 different organic compounds as fuel
Some cells are very selective eg nerve cells and red blood cells rely almost exclusively on glucose catabolism.
Other bacteria can use unexpected source of energy
These include:
-herbicides (biodegradable)
-sewage
-car tyres
-petroleum oils
Alternative carbohydrates
Which disaccharides yield which monosaccharides?
Maltose -> 2 glucose
Sucrose -> glucose + fructose
Lactose -> glucose + galactose
We’re does fructose feed in to glycolysis?
We’re does galactose feed into glycolysis?
Fructose feeds in at step 5
Fructose is phosphorylated to fructose-1-phosphate which is then cleaved into dihydroxyacetone and glyceraldehyde
Galactose feeds in at step 2: galactose is phosphorylated to galactose-1-phosphate then converted to glucose-1-phosphate which is isomerised to glucose-6-phosphate
Both have same energy requirements and energy yield
Disaccharides: these need to be hydrolysed to their constituent monosaccharides
In bacteria there are specific transport systems for the uptake of these disaccharides into their cells, they are the hydrolysed intracellularly
In higher organisms, disaccharides must be hydrolysed prior to absorption (done in digestive system)
Polysaccharides
Eg starch, glycogen, cellulose
Too large to cross the cell membrane and must be hydrolysed extracellularly
-in higher organisms it occurs in the digestive system
-where as bacteria secrete digestive enzymes into the surrounding area and absorb the breakdown products
Amylase- breaks down starch and glycogen
Cellulose is only broken down by cellulase enzyme (humans can’t digest, ruminants depends on bacteria)
Fats (triglycerides)
Tri-3fatty acids
Glycerides (glycerol)
Concentrated store of energy because they are anhydrous (no water) so can store a lot more per gram of weight
Triglycerides are split into two
Tri-3 fatty acids which is converted to acetyl CoA then to TCA cycle
Glycerides- glycerol-> glycerol-3-phosphate -> dihydroxyacetone then to glycolysis
Proteins
Can’t store them, excess amino acids must be utilised by metabolism. For each amino acid there is complicated series of reactions…
First NH2 group is removed by process called deamination
-the resulting keto acid is converted to a glycotic or TCA intermediate
