Download Proteins - Winona State University

PROTEINS
Recall:
Nutrients in the human body have three general functions:
1. They can supply energy for processes such as
growth, movement, electrical signalling, metabolism
2. They can regulate body processes such as
metabolism, growth, membrane transport,
cellular communication
3. They can provide the building blocks for making
the structures of our cells and our bodies
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Proteins in our diet serve all three functions
Proteins
1. Proteins can supply energy:
Although cells of the body prefer to use
carbohydrates and lipids as sources of energy,
many cells can also use proteins as fuel molecules
if necessary.
That means that extra dietary protein can be
converted to carbohydrate or lipid molecules and
stored for future energy needs.
Proteins
2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones
Proteins
2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones
They form “channels” in the membrane
which allow things to get into and out of cells
Proteins
2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones
They form “channels” in the membrane
which allow things to get into and out of cells
They form “junctions” on membranes
which allow cells to communicate with
each other.
Proteins
2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions
Proteins
2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions
They slide past each other to make
muscles contract
Proteins
2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions
They slide past each other to make
muscles contract
They fom the cytoskeleton which
holds organelles in place and moves
them around in the cell
Proteins
2. Proteins can regulate cellular processes:
They form antibodies all
over the body, proteins in the
blood, and many hormones.
Proteins
3. Proteins can make structures our bodies need:
Proteins such as collagen form
tendons and ligaments
Proteins
3. Proteins can make structures our bodies need:
Proteins such as collagen form
tendons and ligaments
Collagen and another protein called
elastin form the dermis is the skin.
The protein keratin forms hair and
the top layer of the epidermis.
Proteins
All of these proteins in the body must constantly be
replaced.
That means your diet must
contain the building blocks
of proteins, called amino acids
Proteins
Food sources
Meat, Chicken, Fish
Milk & cheese
Eggs
Beans, peas, grains, nuts,
seeds, vegetables
Amino Acids
Amino Acids
Amino Acids
Amino acids bond together by a
process called dehydration
synthesis.
Amino Acids
Amino acids bond together by a
process called dehydration
synthesis.
Bonding two amino acids together
forms a dipeptide
Amino Acids
Amino acids bond together by a
process called dehydration
synthesis.
Bonding two amino acids together
forms a dipeptide
Bonding many
amino acids
together forms
a polypeptide
or protein
Amino Acids
While proteins are
long, unbranching
chains of amino
acids, they do not
remain straight.
Different sidegroups cause the
chain to bend and
coil.
In fact, the three dimensional stucture of a protein is
what gives it a specific function.
Amino Acids
Changing the three-dimensional shape of a protein is
called denaturing, and changes the function of a protein,
often permanently.
Proteins can be denatured
many ways: heat
alcohol
acids or alkalis
digestive enzymes
(“proteases”)
etc.
Protein Digestion
Protein digestion begins
in the stomach.
Hydochloric acid
denatures the protein,
unfolding it so proteases
can reach the amino
acids to break the peptide
bonds between them.
Protein Digestion
Along with the
hydrochloric acid, one of
these proteases, pepsin,
begins protein digestion
in the stomach.
Protein Digestion
It is then continued in the
small intestine by
proteases secreted by the
pancreas and cells of the
intestine.
Protein Digestion & Amino Acids
Individual amino acids are
absorbed into the blood
vessels in the mucosa of
the small intestine.
They are carried first to
the liver, which can
remove excess amino
acids, after which they
enter the general
circulation and become
available to cells all
around the body.
Amino Acids
All cells of the body have the
ability to take those amino
acids out of the blood and
use them to build the proteins
they need.
Amino Acids
All cells of the body also have
the ability to break down
proteins to release the
individual amino acids back
into the blood.
Amino Acids
Thus, there is a pool of amino
acids available for building all of
the proteins the body needs.
Amino Acids
Thus, there is a pool of amino
acids available for building all of
the proteins the body needs.
Some amino acids can be used
to make other molecules such
as hormones, nucleotides, or
neurotransmitters.
Amino Acids
Cells of the liver can break
amino acids apart, separating
the amino groups (nitrogen atom
and two hydrogen atoms) from
the rest of the amino acid
molecules, called their “carbon
skeleton”, which can be used to
form lipids or carbohydrates
which can be used to produce or
store energy.
The amino groups are hooked together to form urea
Amino Acids
That urea can then safely travel
to the kidneys, where it is
removed and excreted in the
urine.
Amino Acids
Your body needs to take in new amino acids from your
diet, but this must be balanced by the excretion of
nitrogen in the form of urea.
Amino Acids
Your body needs to take in new amino acids from your
diet, but this must be balanced by the excretion of
nitrogen in the form of urea.
If your liver can’t form enough urea, the nitrogen
produced by the breakdown of amino acids can be toxic
to the body.
This is called “nitrogen balance”:
Your intake of nitrogen (in the form of proteins)
must equal
Your output of nitrogen (in the form of urea in the urine)
Nitrogen Balance
Nitrogen equilibrium
Nitrogen intake = nitrogen output
Healthy adults
Positive nitrogen balance
Nitrogen intake > nitrogen output
Necessary during growth; recovery from illness
Negative nitrogen balance
Nitrogen intake < nitrogen output
Results from injury and illness
Proteins in the Diet
Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Proteins in the Diet
Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
Proteins in the Diet
Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day
Proteins in the Diet
Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day
A 90 kg adult (198 pounds) should eat
90 x .8 = 72 grams of protein per day
Proteins in the Diet
Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day
A 90 kg adult (198 pounds) should eat
90 x .8 = 72 grams of protein per day
In the United States: protein intake > protein needs
Proteins in the Diet
Excess protein can strain kidney function
There are links between high-protein diets and
Osteoporosis
Obesity
Heart disease
Some forms of cancer
Proteins in the Diet
At the other extreme, it is possible to have too little
protein in your diet.
This can occur in diets which are not properly designed,
but it is most often associated with extreme poverty,
and occurs together with insufficient intake of fuel
molecules such as carbohydrates or lipids.
Kwashiorkor
and Marsmas
Proteins in the Diet
Not all dietary proteins are
equally useful for the body.
Proteins in the Diet
Essential AA
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanin
eThreonine
Tryptophan
Valine
Nonessential
Alanine
AA
Arginine
Asparagine
Aspartic Acid
Cysteine
Glutamic acid
Glutamine
Glycine
Proline
Serine
Tyrosine
Not all dietary proteins are
equally useful for the body.
Of the 20 amino acids which
are used to make proteins in
the human body, only 11 of
them can be synthesized.
The remaining 9 must be
obtained through the diet.
Proteins in the Diet
Protein quality:
Complete proteins supply all of the
essential amino acids
(e.g. animal proteins; soy proteins)
Proteins in the Diet
Protein quality:
Complete proteins supply all of the
essential amino acids
(e.g. animal proteins; soy proteins)
Incomplete proteins are low in one
or more essential amino acid
( e.g. most plant proteins)
Proteins in the Diet
Protein quality:
Complete proteins supply all of the
essential amino acids
(e.g. animal proteins; soy proteins)
Incomplete proteins are low in one
or more essential amino acid
( e.g. most plant proteins)
This can create problems for people
on vegetarian or vegan diets, or for
people on special diets low in meats,
milk, eggs, etc.
Proteins in the Diet
Protein quality:
You can ensure that you get all essential amino acids
by combinig two or more incomplete proteins which
are missing different ones.
These are called
complementary proteins
Proteins in the Diet
A healthy diet should include a variety of proteins from
meats, eggs, dairy, soy products, legumes and other
vegetables.
A vegetarian diet must include complementary proteins
such as those in - rice and beans
- whole grains and vegetables
- corn and beans
to ensure that all essential amino acids are available
Total protein intake should be moderated