Speed Doesn’t Kill: How quickly stuff moves in our cells
A common mantra in sports, from boxing to NASCAR, is that “speed kills.” However, in our cells, tremendous speeds are in fact essential for life. Cellular processes are carried out extremely quickly; molecules zoom and whirl past each other in a cacophony of collisions. Being able to harness this speed is the key to life as we know it.
Here is some of the rapid machinery at work inside your body right now:
DNA Replication
Copying our DNA is a complex process that involves numerous proteins to unwind, break up, copy, and correct strands of the DNA molecules. Although it is complex, it occurs at amazing speeds. Bacteria can copy their DNA at a rate of 500–1000 nucleotides per second, and can finish their whole genome in 20 minutes! In humans, which are more complex eukaryotes, the process is slower, but our DNA is still copied at a rate of 50 nucleotides per second. At this rate, it would take 800 hours to copy our entire genome, but we have multiple replication start sites, which reduce the time to about 8 hours.
Here is a great video of DNA replication from the DNA Learning Center: http://content.dnalc.org/content/c16/16906/16906_replication_advanced.mp4
Building Proteins
Ribosomes are the cellular factories that translate the genetic code to the proteins which make up our cells. Proteins are made from long chains of amino acids. These amino acids are assembled at a rate of ~5–20 amino acids per second. Depending on the size of the protein, that means a new one can be made in a few seconds to a few minutes. Trillions of ribosomes are actively building proteins simultaneously in your cells; in fact, you bone marrow cells alone produce 100 trillion hemoglobin proteins per second!
Translation, from the DNA Learning Center: http://content.dnalc.org/content/c15/15501/translation_basic.mp4
Making Energy
Usable energy is produced by the mitochondria in our cells. The electron transport chain creates a proton gradient along the mitochondrial membrane. When the protons pass through the membrane, they spin a rotor. This rotor is able to combine ADP and phosphate, giving us the ATP we use for energy. This rotor can spin at 130 revolutions per second, which produces about 400 ATP per second. Each of your trillions of cells undergo this reaction about a million times per minute. The below video was created by Masasuke Yoshida and Graham Johnson.
Transport
Molecular motors are able to transport things across a cell by moving along long filaments such as actin. These motors carry their cargo across the cell at rate of a few hundred nanometers per second to a few micrometers per second. Although this seems unbearably slow to us, if we scaled up the size of a cellular vesicle (100 nm) to our size (2 m), we could run at about 45 miles per hour!
The below video from XVIVO Scientific Animation shows actin motors “walking” at 1:14, among molecules zipping around at over 200 miles per hour!
“I am not a speed reader. I am a speed understander.” — Isaac Asimov
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