proteins

• proteins overview

  • Proteins are the principal constituents of organs and soft structures of the animal body
  • A continuous supply is needed from food sources throughout life for growth and repair
  • Proteins have more functions than any other macromolecule group and are instrumental in about everything an organism does
  • Humans have tens of thousands of different proteins
  • – each is unique with its own structure and function
• protein synthesis occurs in two stages, transcription (DNA → RNA) and translation (RNA → protein)
• a key concept for protein

  Form (structure) fits function

  • The shape of a protein is directly related to how it functions
• protein functions

  • Structural support
  • Enzymatic Functions
  • Defense against foreign substances
  • Transport Molecules
  • Storage
  • Movement
  • Regulating cellular processes
• Protein structure

  • Proteins are polymers constructed from amino acids (aa for short) - the universal monomer unit of proteins
  • A protein’s 3-D structure determines its function in an organism
  • Protein polymer chains typically have 100-200 aa’s
  • Many proteins have more than one polymer chain
• Amino Acids

  All amino acids have the same basic structure

  Contains central asymmetric carbon (α carbon) –

  bonded to four different covalent partners (except

  glycine)

  They all have an amino group traditionally shown

  on the left side of the asymmetric carbon, a

  hydrogen atom on the top, and a carboxyl group

  on the right

  Generally polar
• what is structure is the diagram below?

  amino acid

  
• Amino Acids: Structure

  They have a basic

  amino group

  When dissolved in water, the

  carboxyl group donates an H

  ion to the amino group

  Result: Carboxyl group

  is negatively charged

  and the amino group

  becomes positively

  charged
• Amino acids vary by what is attached by the

  fourth bond to the asymmetric = ‘R’ group or side

  chain
• There are 20 different amino acids because

  there are 20 different R groups found in

  organisms
• The physical and chemical characteristics of the

  R group determine the unique characteristics of

  the amino acid it belongs to

  There are 3 classes of amino acids:

  Nonpolar (hydrophobic)

  Polar (hydrophilic)

  Electrically charged (acidic or basic)
• one group of amino acids has a hydrophobic R group?

  alanine (Ala) and Glycine (Gly)
• group of amino acids who has polar R groups, making them Hydrophilic

  Serine(ser) and Cysteine (cys)
• what amino acids are electrically charged (ionized) at cellular pH(some R groups are bases and some are acids) acidic

  electrically charged: Aspartic Acid (asp) Basic: Lysine (Lys)

  
• Amino acids are divided into two nutritional

  categories:

  • Essential: those the animal cannot synthesize in sufficient quantity to support maximum growth, typically dietary in nature
  • Nonessential: synthesized by animal body, typically non-dietary in nature
• Essential AA

  for humans

  lysine (LYS)

  methionine (MET)

  isoleucine (ILE)

  leucine (LEU)

  threonine (THR)

  tryptophan (TRY)

  phenylalanine (PHE)

  valine (VAL)
• • Amino acids join together with a peptide bond to form a polypeptide.
  • a linear polymer of amino acids is called a polypeptide

  
• How many possible proteins can be made from amino

  acids? length of about 300
• How many amino acids are in one polypeptide

  chain?

  more than about 50 amino acids long
• How many different amino acids are there?

  20 different amino acids
• For a polypeptide chain that is 10 aa’s long, how

  many possible proteins can we make? 10 to the power of 50
• A protein’s function depends on

  its specific shape
• A functional protein consists of one or more

  polypeptides that have been precisely twisted,

  folded, and coiled into a unique shape
• It is the order and type of amino acids that

  determines what the three-dimensional

  conformation will be
• • primary: the unique sequence of aa’s forming the protein (20200 possibilities!) 🡪 peptide bonds
  • secondary: folding of polypeptide chains (e.g., α helix or β pleated sheet) 🡪 H-bonds
  • tertiary: intermolecular bonding between side chains (R groups) that results in irregular contortions; gives 3-D appearance
  • quaternary: packing of polypeptide chains together (globular proteins chains that take on a rounded shape)
• what structure is this?

  20 Structure

  • The growing polypeptide chains (10 Structure) coils and folds at various locations
  • Two types of folding:
  • α helix
  • β-pleated sheet

  
• Tertiary structure is determined by a variety

  of interactions among R groups and between R

  groups and the polypeptide backbone

  • These interactions include hydrogen bonds among polar and/or charged areas, ionic bonds between charged R groups, and hydrophobic interactions among hydrophobic R groups
• what structure is this?

  30 Structure

  * Interactions

  between “R”

  groups of amino

  acids in

  polypeptide

  chains

  
• While these three interactions are relatively weak,

  disulfide bridges, strong covalent bonds that form

  between the sulfhydryl groups (SH) of cysteine amino

  acids, stabilize the structure

  
• what structure is this?

  40 Structure

  * Two or more polypeptide subunits

  come together to form a functional

  protein

  
• What is responsible for folding

  proteins?

  Molecular chaperones!
• Name each structure

  a

  A) pleated sheet

  B) (a) primary structure

  C) (b) secondary structure

  D) (c) tertiary structure

  E) (d) quaternary structure

  
• Changing the sequence

  by ONE amino acid can

  drastically alter the final

  shape of a protein…
• Denaturation

  * A protein’s conformation can change in response to its

  physical and chemical conditions

  *Alterations in pH, salt concentration, temperature,

  harmful chemicals or other factors can unravel or

  denature a protein

  *These forces disrupt the hydrogen bonds, ionic bonds,

  and disulfide bridges that maintain the protein’s shape

  *Some proteins can return to their functional shape after

  denaturation, but others cannot, especially in the

  crowded environment of the cell
• what is this process called (look at both arrows)?

  denaturation and Returation