Protein Protein Chapter 17 What is by ewghwehws


Chapter 17
        What is Protein?
Protein molecules are very large and
complex. Made up of:
    – Hydrogen, carbon, oxygen ,nitrogen and
      sometimes other elements
    – Because of protein large size, protein molecules
      are often called macromolecule
          Macromolecule = large molecule containing
          many atoms.
    – Nitrogen is a crucial part of protein
          Nitrogen is the site of the chemical bond that
          gives proteins their variety and versatility
      Structure of Protein
Protein is made of chains of amino
– Amino Acids = type of organic acid.
    – Organic acids are molecules that contain a
      carboxyl group, plus the amino acids also contain
      an amine group.
    – Amine group = composed of two atoms of
      hydrogen and one atom of nitrogen.
    – (Look on page 258, figure 17-1, both carboxyl
      group and the amine group are attached to a
      central carbon.)
    – With four bonds needed and one is left open, this
      is what makes one amino acid different from
            Peptide Bonds
Peptide bonds = bonds between
the nitrogen of one amino acid and
the carbon of a second amino acid.
  (example is on page 258, figure 17-3)
   Through peptide bonds, amino acids chain
   together, creating a polypeptide.
   Polypeptide = single protein molecule
   containing then or more amino acids linked
   in peptide chains
     – Peptide bonds hold chains of amino acids
       together, that are called helixes (ex. page 259,
       figure 17-4)
Protein Structure and Function
Protein’s shape determine its
   Protein molecules that form rope-like fibers
   are called fibrous protein ex is collagen and
   Protein molecules that can be compared to a
   ball of steel wool are called globular proteins
     – The shape makes them convenient carriers ex
       hemoglobin (transports oxygen in the blood)
    Denaturation of Protein
Denaturation = this process changes the
shape of a protein molecule without
breaking its peptide bonds
    As the molecule unfolds, some of the protein’s
    original properties are diminished or lost.
    This change is unique to protein and because each
    protein is unique the process varies from one
    molecule to the next.
    Denaturation in the first step in the process of
    Coagulation = changes a liquid into a soft, semisolid
    clot or solid mass. (look pg. 260, figure 17-6)
     – Ex is scrambled eggs. Beating the egg denatures its
       protein. The protein coagulates as the egg cooks.
Other Means of Denaturation
Heat is the most common agent in
denaturing protein.
    The temperature is significant, the degree of
    denaturation increase 600 times for every 10°C.
Protein molecules may unfold in reaction
to the following:
    Freezing, pressure, and sound waves
    Mechanical treatment, such as beating eggs and
    kneading bread
    Very high or very low pH. (adding lemon juice for
    example can sour milk, causing the milk to separate
    from the liquid – forming curds and whey)
    Certain metal ions
             Protein in Eggs
   Complex biological system, containing almost every
   vitamin and mineral you need. All that lacks is vit. C
   and calcium which is found in the egg shell
   Look on pg. 262, figure 17-7 for a diagram of an egg
       – Albumen = egg white – substance makes up 54% of
         the inner contents of an egg
       – Chalaza = a twisted, ropelike structure that keeps the
         egg yolk centered
       – Egg Yolk – main component of the yolk include the
         globular protein livetin and both high-and-low-density
       – Do not exposed eggs to light and temperature changes
            Eggs lose quality as compounds in the egg white
            break down, forming water
         Protein in Meat
Muscle tissue, the lean part of meat,
is about 15-20% protein
– Other components include: water, fat
  and minerals
– Muscle is composed of fibrous proteins
  called actin and myosin. These proteins
  form bundles of fiber, which are held
  together by connective tissue made of
  collagen and elastin
Protein in Fish, Nuts and Legumes
 – Shorter segmented muscle fibers are layered
   between thin sheets of connective tissue. This
   is why some books say fish is cooked when
   you can “flake with a fork”
 – Far less connective tissue than meat, it’s also a
   type that liquefies easily
Nuts and Legumes
 – Cholesterol free, but fat content ranges
 – Soybeans are excellent source of protein,
   they’re composed of 40% protein, high in fiber
   and polyunsaturated fatty acids. Soybeans
   have also been associated with reducing the
   risk of coronary heart disease
        Protein in Cooking
    Certain proteins contain amino acids that our polar.
    One end is attracted to water (forming a hydrogen
    bond), the other end avoids water and bonds with oil.
    This is why an egg can emulsify oil and lemon juice
    Foam = air bubbles incorporated and trapped in a
    protein film by whipping
     – Foam begins when a protein-containing liquid (egg
       whites or cream) are whipped, introducing air and
       denatures the protein molecules
     – Fats can be trouble for foams, they keep protein
       molecules from bonding with each other, making the
       end product watery
Protein in Cooking Continued
    Used to set desserts and thicken meat sauces in
    animal protein
    Made by using heat and water to hydrolyze the
    collagen on the inner layer of hides and bones
    Gelatin can bind 100 times its weigh in water
    Gluten = an elastic substance formed by mixing
    water with the proteins found in wheat
    Gluten includes both fibrous and globular proteins,
    making the reactions between the water and proteins
    both stretch and springy
    Gluten is developed as dough is kneaded, denaturing
    the protein molecules
         Protein in the Body
During digestion, proteins are denatured by
hydrochloric acid in the stomach, making the
peptide bonds easier for enzymes to break.
Most proteins enter the bloodstream as amino
acids (the body creates ALL of its proteins from
20 different amino acids)
Functions of Body Proteins
– Structural protein is needed by every cell in the body
– New growth requires a continuous supply of protein to
  replace and repair cells
– Some proteins pick up, deliver and stores nutrients in
– Proteins called antibodies help you ward off disease
     Antibodies = very large proteins that weaken or destroy
     foreign substances in the body.
     Essential Amino Acids
Of the 22 amino acids the body
needs to build protein, it
manufactures 18 the other 9 needs
to be digested. Look on pg 269, figure 17-8
– Complete Protein = a protein that contains
  all the essential amino acids ex. ground beef
– Incomplete protein = lacking one or more
  essential amino acids, among plants only
  soybeans provide complete protein
    High-quality Protein = contains all the essential
    amino acids in proportion to the body’s need for them
   Protein Allowances
The RDA for a healthy adult is 0.8g of high-
quality protein per kilogram of ideal body
mass (take your weight in kg and multiply
by 0.8 gives you the amount of protein
needed in a day (young males under 18
multiply by 0.9)
RDA for children ages 11-14 is higher 1.0g
of protein per kg of body mass
Most people in the US get enough protein
Look on page 270 figure 17-9 for a list of
protein contents in certain food choices.
1. Why are amine groups important to
2. Compare peptide bonds and hydrogen
   bonds in protein formation.
3. Describe the two basic protein shapes.
   What is the main function of each?
4. What occurs during Denaturation?
5. Can proteins coagulate without
   denaturation? Why or why not?
6. How does the egg yolk compare in
   composition to the egg white?
           Questions Continued
7.    A friend refrigerates eggs still in their carton
      immediately after returning form the
      supermarket. Explain whether this is a good
8.    Compare the protein structure of meat to that
      in fish.
9.    Suppose your egg whites aren’t making a very
      impressive foam. What might be some
10.   Why is kneading the dough an important step
      in making bread?
11.   Why might injury and illness be more serious
      for someone with a long-term protein
12.   Should you be concerned if your diet lacks just
      one essential amino acid? Explain.
13.   Can a diet of fruits, vegetables, and grains
      supply all of the essential amino acids?

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