Have you ever had a chance to look inside a cell down a powerful
microscope? You will be amazed at what you find - each and every
one of our cells is alive, with the molecules inside the cell
moving about in an elaborate dance. Every molecule is continually
moving as they go about their own specialised tasks.
Every day, your cells have to move many molecules from one site
to another. Have you wondered how they do this?
Your cells use the help of two versatile motor proteins, called
kinesin and dynein. These motor proteins "walk" along a molecular
catwalk, which is made of proteins called "microtubules". Using
this catwalk, the motor proteins can carry loads several times
their size from one site to another.
Kinesin carrying a large load.
Image courtesy
Steven Block / C. Asbury
How do kinesin and dynein work?
Both motor proteins have two 'hands' and two 'feet'. The hands
and feet are 'sticky' - as sticky as post-it notes. Precious cargo,
like proteins, carbohydrates and enzymes, which need to be
transported around the cell, are first enclosed in membrane
'sacks'. Using their hands, the motor proteins grab these large
bundles as they float around the cell. The sticky patches on
the 'hands' prevent the bundle from falling off as the motor
proteins set off on their journey.
Now comes the amazing part. Just as a human can walk by
placing one foot in front of the other, the motor proteins start
'walking' along the microtubules by swinging one foot in front of
the other, much like a trapeze artist walking on a high wire. Some
scientists say that the motor proteins "walk like a drunken
sailor"! Have a look at them in action:
Each step uses a molecule of energy. The motor proteins need
125,000 steps to move 1mm along the catwalk - that is a lot of
energy!
The astonishing thing is that the feet never walk backwards,
only forwards! Once it reaches the other side, it drops its cargo
off, jumps off the microtubule, swims back to the other end, and
the whole process repeats again.
Watch this animation of a motor protein pulling a large
load:
By Zara Mahmoud, ScienceBuz