#### Transcript Homer`s Hair

```Homer’s Hair
Arrggh! Where’s my hair gone?
Ohhh! Why won’t it grow faster?
What is this hair stuff anyway?
Homer’s Hair Structure
The main component
of hair is keratin.
Keratins are proteins
(polymers) of amino
acids. They account
for approximately
85% of Homer’s hair
with the remainder
comprising water,
fats, vitamins and
trace elements.
Homer’s hair seen under an
electron microscope.
Homer’s hair structure.
Homer’s Amino acids
Amino what?
Where are they?
Will they hurt me?
Homer’s Amino Acids
Amino-acids are small biomolecules. There are 16 different amino acids found in keratin.
Hydrogen
Carboxyl
group
Amino
group
‘R’ group
Homer’s Amino Acids
So, how many do I need?
Can I eat them?
Mmmmmm amino acids.
How many amino acids
does it take for 1 hair
to grow for 1 second?
Let’s do the Calculation
What shape is your hair Homer?
Cubic
Cylindrical
OK we agree it is a cylinder. So we can work out a volume of
hair grown per month using
пr2h
For this we need to know the length of hair grown per month
and the radius of a hair
Choose a length (mm)
1
10
100
1
0.05
0.0001
Volume of Hair per month
You grow about 10 mm of hair per month and the radius of one
hair is about 0.05 mm (it takes about the width of 10 hairs is
Therefore the Volume of hair grown per month is
= П x (0.05)2 x 10
= 0.0785 mm3
Mass of Hair
We now need to transform this volume into a mass. What relates mass and
volume?
Refractive index
Density
Body Fat Index
So we need to know the density of hair – does it float or sink in water?
Well it does a bit of both (surface tension is a problem) which suggests
the density of hair is about the same as water which is 1 g/cm3 – careful of
the units Homer, convert it into g/mm3
1 g/cm3 = 0.001 g/mm3
So the mass of hair grown per month is
Mass = density x volume
= 0.001 g/mm3 x 0.0785 mm3
= 0.000 0785 g
Mass per second
OK so we know how much mass each hair puts on per
month, but we need to know how much mass per second.
How many seconds in a month Homer?
About 30 days, 24 hrs per day, 60 minutes per hour, 60
seconds per minute
30 x 24 x 60 x 60 = 2592000 seconds per month
Therefore
Mass of hair per sec = 0.000 0758 / 2592000
= 0.000 000 000 0302 g
Moles
So now we have a mass of hair per second we need to
work out the number of molecules.
To work out the number of molecules we first need to
work out the number of moles.
number of moles = mass of hair / RMM
As you know Homer hair is made of keratin which is a
protein made up of amino acids. To work out the number
of moles of amino acids per second we need to know the
relative molecular mass (RMM) of amino acids. As this is
a rough calculation we will use the average RMM of 135
g/mole.
Moles to Molecules
OK Homer are you ready for this.
Number of moles of amino acids
= 0. 000 000 000 0302 g
135 g/mole
= 0.000 000 000 000 224 moles
Not much Hey? Now to convert it into molecules
Moles to Molecules
Avogadro was the first to work out
how many molecules were in a mole.
He found that in one mole there are
603 000 000 000 000 000 000 000
Molecules
We now call this Avogadro’s Number
= 0.000 000 000 000 224 x 603 000 000 000 000 000 000 000