Why do sperm cells contain large amounts of mitochondria and glucose?

Answer 1

The motile sperm or spermatozoon uses a flagellum to move towards the egg during reproduction. The beating of the flagellum causes the sperm to "swim" towards the egg; however this beating must have an energy source for it to occur. Just as you or I need food as an energy source to swim, the sperm needs an energy source to swim.

Since the journey between the testes and the egg is a long journey for a single cell measuring 25 µm (0.0025mm) in length, a lot of energy is required for it to complete the journey. The high abundance of glucose can be explained because glucose can be used by the sperm cell to provide energy in the form of adenosine triphosphate, or ATP.

The reason why there are so many mitochondria in a sperm cell is a bit of a mystery because sperm cells produce energy mainly by a process called glycolysis, which does not require mitochondria.

Mitochondria produce energy via the process below:

Adenosine Triphosphate + ATPase ---> Adenosine Diphosphate + Pi*

*Where Pi stands for Inorganic Phosphate (orthophosphate)

OR SHORTENED REATION EQUATION

ATP + ATPase ---> ADP + Pi

Hydrolysing ATP to Adenosine Diphosphate (ADP) releases an inorganic phosphate group in an exothermic process thus "releasing" energy; therefore explaining why ATP is the "univesal energy currency" i.e. because it is possible to derive energy from ATP.

The hydrolysis of ATP releases approximately -30.5 kJ mol-1 energy (actually 30.5 kJ mol-1 energy however the negative sign denotes an exothermic reaction).

The glucose is made into energy in the following simplified process:

i) Glucose enters glycolysis in which 1 molecule of glucose is turned into 2

molecules of pyruvate. (Net increase 2 ATP + 4NADH) The process:

Glucose -> Glucose-6-phosphate -> Fructose-6-phosphate -> Fructose-1,3-bisphosphate -> { Glyceraldehyde-3-phosphate -> 1,3-bisphosphate glycerate -> 3-phospho glycerate -> 2-phospho glycerate -> Phosphoenolpyruvate -> Pyruvate } x 2

ii) Pyruvate is changed into Acetyl CoA by pyruvate dehydrogenase enzyme so that it can be utilised in the Citric Acid Cycle:

Pyruvate ----------> Acetly CoA

iii) 2x Pyruvate enters the Krebs cycle in which Acetyl Coenzyme A (Acetyl

CoA) binds with oxaloacetate to form citric acid. (Net increase 2 x 1 GTP)

Pyruvate -> Citrate -> Isocitrate -> Alpha - ketoglutarate -> Succinyl CoA -> Succinate -> Fumurate -> Malate -> Oxaloacetate (Cyclic)

iv) Electron transport chain (ETC) utilising 3x NADH + H+,1x FADH2 and 1 x ATP

from the Krebs cycle. (Net increase 24 ATP)

Protons obtained from splitting NADH + H and FADH2 e.g.

NADH + H+ ---> NAD + H2 H2 ---> 2H+ + 2e-

Using proton carriers (known as complexes):

Complex I - NADH-Q reductase

Complex II - Succinyl CoA reductase

Complex III - Cytochrome c reductase

Complex IV - Cytochrome c oxidase

Process:

Complex I + II pass electrons to Complex III which passes electrons to Complex IV

The high energy electrons that are passed between the complexes power the proton pumps in order to pump protons from the matrix of the mitochondria into the inner membrane. This creates a proton motor force (PMF) which therefore creates a chemiosmotic (or pH) gradient between the matrix and inner membrane; since protons cause acidity.

The high energy electrons then reach ATP synthase (Also known as ATPase) which utilises the energy from the protons and electrons to synthesis ATP from ADP and inorganic phosphate in the reaction previously illustrated:

ADP + Pi ---> ATP

Following this the protons are reassociated with electrons and oxygen to produce water. This explains why oxygen is essential for the ETC (Electron Transport Chain) or Oxidative Phosphorylation, to occur:

O2 + 4H+ + 4e+ ---> 4H2O

As such this clearly illustrates why oxygen is necessary for aerobic respiration to occur and therefore why carbon dioxide and water are by-products of aerobic respiration:

C6H12O6 + 6O2 ---> 6CO2 + 6H2O + ATP

Therefore one molecule of glucose produces a net. increase of 32 molecules of ATP thus allowing approximately 976kJ of energy to be produced from one molecule of glucose depending on condition variables.

Answer 2

Sperm cells need large amounts of mitochondria to provide energy for the journey through the female reproductive tract to fertilize the egg. Glucose is a source of energy that can be quickly metabolized by the mitochondria to fuel the sperm's motility.