Lesson 5. Explain the term secondary structure Explain the term tertiary structure.
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PROTEINS: SECONDARY
AND TERTIARY STRUCTURE
Lesson 5
SUCCESS CRITERIA Explain the term secondary structure Explain the term tertiary structure
STARTER Draw the structure of a protein and label
it in as much detail as you can
KEY TERM: SECONDARY STRUCTURE The coiling and pleating of parts of the
polypeptide molecule
SECONDARY STRUCTURES Alpha Helix or Beta Pleated Sheet Hydrogen bonds hold the structure in
place Hydrogen bonds form between oxygen
and hydrogen atoms Although hydrogen bonds are quite
weak, as many bonds are formed they add stability to the structure of the protein
ALPHA HELIX Right hand coil, where
hydrogen bonds form between oxygen and hydrogen atoms bought into close proximity
Stabilises the protein
Alpha helix
HYDROGENBOND
BETA PLEATED SHEET Amino acid chain folds
up on itself forming anti-parallel chains
O and H atoms bought in close proximity to each other form hydrogen bonds
Stabilises the protein
Beta pleated sheet
TASK Make plasticene models of alpha helix
and beta pleated sheet Describe the structures to the person
next to you
KEY TERM: TERTIARY STRUCTURE The overall 3D structure of the protein
molecule
TERTIARY STRUCTURE The final 3D shape of the protein is
formed when the polypeptide chain with the coils and pleats fold themselves
The 3D shape is held in place byHydrophobic and hydrophilic interactionsDisulphide bonds Ionic interactions
Primary
Secondary
TertiaryQuaterna
ry
LEVELS OF PROTEIN STRUCTURE
TASK In groups of 4 each person gets a
quarter of an OHT to explain one of the following:Tertiary structureHydrophobic and hydrophilic interactionsDisulfide bonds Ionic interactions
You will then present to the class
HYDROPHOBIC AND HYDROPHILIC INTERACTIONS Many hydrophobic R groups tend to
cluster towards the interior of the protein molecule forming Hydrophobic Interactions
Hydrophilic R Groups tend to be found on the outside of proteins
DISULPHIDE BONDS R groups of two amino acids
contain sulphur atoms (e.g. cysteine)
If these atoms are in close proximity they form DISULPHIDE BONDS
IONIC INTERACTIONS Many of the carboxylic acid and
amino groups form charged groups in solution. Oppositely charged groups form IONIC BONDS
TERTIARY STRUCTURE The proteins shape is vital to each
function Three examples are
EnzymeHormone ReceptorCollagen
Why is shape important in these three cases?
ANSWERS Enzyme: fit of the active site to its
specific substrate Hormone receptor: hormone won’t bind
unless specific shape Collagen: shaped for strength
3D PROTEIN SHAPES Globular
Ball structureHydrophobic amino acids turn inwards and
hydrophilic interactions turn outwards making them water soluble
E.g. enzymes Fibrous
Form fibresRegular repetitive amino acid sequencesUsually insolubleE.g. collagen
SUCCESS CRITERIA Explain the term secondary structure Explain the term tertiary structure
PLENARY Draw the structure of a protein and label
it in as much detail as you can
HOMEWORK Complete the next part of the summary
table
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