Proteins

1
Proteins

• Chapter 22

2
Goals

• Know sources and needs for protein
• Become familiar with protein structures
• Understand the significance of protein
  denaturation
• Draw a dipeptide

3
Sources

• Plants synthesize proteins from inorganic
  materials
• Animals must get protein from plants or other
  animals.
• Protein is the second most abundant molecule in
  our bodies, next to water

4
Function

• Build new cells, maintain existing cells, replace
  old cells.
• Provide energy 4 cal/g
• Regulate hormones
• Catalyze chemical reactions (enzymes)
• Transfer hereditary information (DNA)

5
What are proteins?

• Polymers of amino acids linked by a peptide bond
• Formula weight is in 1,000s of g/mol
• 20 amino acids make up proteins
• General structure of amino acid
• Amphoteric
• Most have a D or L form. Generally only the L
  form is biologically active.
• What about glycine?
• The R group determines function
• Polar - hydrophillic (water loving)
• Non-polar - hydrophobic (water hating)
• Acid or base

6
Why must we eat protein?

• Some amino acids cannot be made by the body, but
  they are required to make protein They are
  essential.
• Example cats need tryptophan

7
DNA analysis

• Isoelectric point - the pH where the protein has
  both a positive and negative charge (so the net
  charge is 0)
• Proteins are zwitterions
• Have a positive and negative charge on the same
  molecule
• Apply a voltage across a solution at a given pH,
  the proteins will migrate to electrode if -
  charge, and vice versa. Each protein moves a
  different amount.

8
Dipeptides

• Two amino acids joined by a peptide bond.
• Two different dipeptides are possible.
• How many are possible for a tripeptide?

9
Primary structure

• The order of amino acids
• determines function
• Normal Hb Thr - Pro - Glu - Glu - Lys - Ala
• Sickle Cell Thr - Pro - Val - Glu - Lys -Ala
• Some changes have no effect, some minor, some
  serious.

10
Secondary Structure

• Alpha helix, beta sheet or random coil
• Fingernails, hair and wool are alpha,
• silk is beta
• Held together by hydrogen bonds
• (like, not love)
• Determines function
• Protein wont function if we denature secondary
  structure.

11
Tertiary structure

• Secondary structure wound up on itself
• Held together by
• Covalent bonds - disulfide linkages (S-S)
• Hydrogen bonding
• Salt bridges (ionized side chains)
• Hydrophobic interactions
• (non-polar parts congregate inside protein, polar
  stay outside.)

12
Quaternary Structure

• Jumble of cords coming out the back of your
  computer
• Proteins with more than one chain fold up on each
  other
• Example - hemoglobin is 4 heme groups twisted
  together (fig 22.7 p.390)

13
Types of Protein

• Structural
• Globular hemoglobin, albumin
• Fibrous- collagen, hair, fingernails
• Lipoproteins
• HDL break down other lipoproteins
• LDL carries cholesterol in blood
• Hormones, enzymes, snake venoms

14
Properties of Proteins

• Colloids
• Pass through filter paper, not membranes
• Protein shouldnt be found in urine unless
  cellular damage
• Indicator of kidney damage
• Denaturation-
• keeps primary structure intact, changes folding
  of secondary, tertiary, structure
• May be reversible (mild condition) or
  irreversible
• A denatured protein cannot function.

15
Conditions to Denature Protein

• Alcohol 70 concentration more effective than
  100
• Heavy metal salts use egg white antidote to
  damage albumin before damages you.
• Heat gentle is reversible, strong irreversible
• Radiation - irreversible
• pH reversible and irreversible
• Oxidizing/reducing agents- bleach
• Salting out reversible, precipitate using
• a concentrated salt solution