“The Variety of Proteins”
Different types, with different tasks
Review
 What
determines the behavior
of a molecule?
 Like Legos, if we change the
shape, we change its use and
how it attaches to others.
 Different
shapes allow the
Legos to do different jobs,
just like different shapes
allow proteins to do
different jobs.
 Proteins in our tendons
are 10x as long as they
are wide, forming stiff,
strong structures.
What is collagen?
 “The
protein collagen acts like
glue between cells.”
 As we get older and lose our
ability to make collagen, our
skin wrinkles and sags.
 “Enzymes
are
proteins that
change other
substances
chemically.”
 Digestive
enzymes, for
example.
 Some
work alone, while
others need to work together.
 Hemoglobin is made of four
smaller protein strands; each
holds iron for the blood.
It also turns our blood red.

Methemoglobinemia
How so much variety?
 As
we’ve mentioned, it’s all about
the combination of the 20 amino
acids.
 You could compare this to a Lego
set, with 20 bricks.
 Imagine all of the different
shapes you could make…
 Your body contains 10,000
different proteins.
Inherited Amino Acid Sequences
 Remember
that the
amino acid
sequence is
specified by
heredity.
 “In sickle-cell
disease, one aa is
wrong, changing
the shape of
hemoglobin.”
Gene Expression
 “When
a cell makes a protein, the
gene for that protein has been
‘expressed.’”
 So if you received a blond hair
gene from mom and a brown hair
gene from dad,
 And your hair turns out brown,
 The brown hair gene was
expressed.
Can what I eat change my DNA?
 “Nutrients
don’t change DNA.”
 “They do influence expression.”
 So perhaps consuming a
nutrient could trigger you to
express a hidden gene!
 Ghost in Your Genes: New
science!
So How Much Protein Do We
Need to Eat?
 “Nutritionists
say we should
get a minimum of 10% of
calories from protein.”
 If you’ll remember, the
specific amount was “0.8
grams of protein per kilogram
of body weight.”
What about athletes?
 Athletes
may need slightly
more, but the increased need
is well covered by most
Americans’ diets.
 So most of us are already
eating more than we need.
“Nitrogen Balance”
 So
why are the recommendations
what they are?
 In order to figure out how much
protein we need, we have to look
at the nitrogen we eat and
compare it to the nitrogen we
need to excrete.
 “In
healthy adults, nitrogen-in
(consumed) = nitrogen-out
(excreted).”
 How can we measure someone’s
nitrogen excreted?
 Under controlled conditions, we
can examine the nitrogen totals in
urine, sweat, feces.
 Then we can calculate what the
person needs to consume to
make up for these losses.
Balance of Nitrogen Value
 “Normal
adults: nitrogen
equilibrium.”
 There are other situations,
where one is greater than the
other,
 We’ll take a look at who this
would be.
 “Nitrogen-in>nitrogen-out:
person
is making more proteins than they
are losing.”
 Who might be in this situation?
 “growing child, person building
muscle, pregnant woman”
 “Nitrogen-in<nitrogen-out:
losing protein.”
 Who might be in this situation?
 “sick person, astronaut”
 Why an astronaut?
“Complimentary Proteins”
 So
if we need all of the amino
acids, and no food contains
them all, what would be a
logical way to construct a
diet?
 “A diet should contain
different proteins, so that all
aa’s are consumed.”
 “When
we eat multiple aa-rich
foods, our bodies build
complementary proteins.”
 This means that what we don’t get
from one food, we get from
another.
 This
plan is called mutual
supplementation.
 In this example, legumes and
grains go together because they
supply different aa’s.
Benefit of Living Here
 In
the U.S., we have access to
all different proteins!
 In countries where food is
limited, they may have
adequate quantity, but they
may only have one type of aa.
 That can cause malnutrition.