Download Protein_hierarchy

If I make a 5-bead necklace and
I have 20 different colours of
bead. How many different
necklaces can I make?
3.2 million!!!
Learning goals:
• (b) describe, with the aid of diagrams, the structure of an amino
acid;
• (c) describe, with the aid of diagrams, the formation and
breakage of peptide bonds in the synthesis and hydrolysis of
dipeptides and polypeptides;
• (d) explain, with the aid of diagrams, the term primary
structure;
• (e) explain, with the aid of diagrams, the term secondary
structure with reference to hydrogen bonding;
• (f) explain, with the aid of diagrams, the term tertiary
structure, with reference to hydrophobic and hydrophilic
interactions, disulfide bonds and ionic interactions;
• (g) explain, with the aid of diagrams, the term quaternary
structure, with reference.
The structure of amino acids.
Amino acids.
• Proteins are made from 20 types of
amino acids.
• Each amino acid has a different R-group
R-group
How do the R-groups differ?
Where do we get amino acids
from?
• “Non essential” amino acids are made by
the body.
• “Essential” amino acids need to be eaten
in our diet.
How do they form proteins?
Condensation reaction
-OH from
carboxyl group
-H from amino
group
Forms peptide
bond
Peptides
• When two amino acids join together a dipeptide is
formed.
• Three amino acids form a tripeptide.
• Many amino acids form a polypeptide. e.g.
• In a polypeptide there is always one end with a free
amino (NH2) group, called the N-terminus,
and one end with a free carboxyl (COOH) group,
called the C-terminus.
Structure of proteins
• Primary
• Secondary
• Tertiary
• Quarternary
The sequence of amino acids in a
polypeptide chain is called the
primary structure of a protein.
Secondary structure
• The protein’s secondary structure is
formed when a chain of amino acids coils to
form an alpha helix or folds into a betapleated sheet.
• Both require H-bonding.
Alpha helix
• Every backbone
N-H group
donates a
hydrogen bond to
the backbone C=O
group of the
amino acid four
residues along.
Beta pleated sheet
• Hydrogen bonds
form between
chains lying next
to one another.
Beta sheet challenge
Tertiary structure
• Further folding or twisting of the whole
polypeptide chain.
• Bonds form between R groups in the
polypeptide chain.
• Include disulphide
bonds, ionic bonds,
hydrogen bonds,
hydrophobic
interactions.
Disulphide bonds
• Form between R-groups containing
sulphur atoms e.g. cysteine and
methionine.
Ionic bonds
• Form between R groups with charges e.g
positive and negative charges.
Hydrophobic interactions
Non polar R-groups tend to cluster together in water. These weak
associations are called hydrophobic interactions. When the polypeptide
chain folds, the hydrophobic R-groups tend to be close to each other in
the interior of the folded chain, whereas hydrophilic R-groups tend to
be on the outside, attracted to water.
Label the diagram to show the
bonds and interactions in the
tertiary structure.
Quarternary structure
• Almost all working proteins are actually composed of
more than one polypeptide chain, and the arrangement
of the different chains is called the quaternary
structure. There are a huge variety of quaternary
structures e.g.:
• The primary structure of a protein
is the sequence of amino acids,
joined by peptide bonds
• The secondary protein structure
occurs when the sequence of amino
acids are linked by hydrogen bonds
in an alpha helix or beta pleated
sheet.
• The tertiary structure describes
the folding of a polypeptide chain
that result from the molecular
interactions among the R groups of
the different amino acids( H,
disulphide, ionic bonds)
• The arrangement of two or more
polypeptide chains in a protein make
up its quaternary structure
Answer the summary
questions on amino acids.
Amino acids join together into polypeptide chains by ..........................
bonds which are formed by ........................... reactions. The linking bonds
are formed between the ................ and ................. groups of the amino
acids when ........................ is released from the reaction.
The polypeptide chains may be folded into secondary structures, such as
the ........................... and ........................... . Secondary structures may
be
further folded into tertiary structures, such as the ........................... .
Polypeptides are combined together to give the ..........................
structure
of the protein. These three dimensional shapes of the protein are held
firmly in place by ionic bonds, ...................... bonds and covalent
..................... bonds. Disruption of these bonds, by extremes of pH or
exposure to ........................... causes ........................... of the protein.
• peptide; condensation; acid/amine;; water;
alpha helix,beta pleated sheet;; globular/coil
type/shape; quaternary; hydrogen; sulphur;
high temperatures; denaturation