Download Proteins

Proteins
…The most diverse molecules in living
organisms!
Proteins have 2 main roles:
1. Structural building blocks (ex: spider web)
2. Functional molecules (ex: enzymes)
Images courtesy of google images
Examples of proteins:
Functional:
• Enzymes: biological catalysts
• Immunoglobulins: protect animals from foreign microbes and
cancer cells (antobodies)
• Hemoglobin: shuttles oxygen
Structural:
• Keratin: tough structures in hair, fingernails
• Fibrin: helps clot blood
• Collagen: forms protein component of bones, skin, ligaments and
tendons
Images courtesy of google images
What are they made of?
• Amino acids (a.a.) are the subunits:
R group = “side chain”
Images courtesy of google images
A bit about the amino acids…
• There are 20 a.a.’s (p42+ 43)
• 8-10 are “essential” because our body
cannot synthesize them so we need to get
them from our diet.
The amino acids:
Images courtesy of google images
No… you don’t have to memorize them… maybe in university though
How are proteins made?
• DNA directs ribosomes, RNA and enzymes to
join a.a.’s together in the correct sequence (this
is called protein synthesis)
• The aa’s are joined together by peptide bonds
(aka amide bond)
• Resulting polymer is called a polypeptide
Images courtesy of google images
Polypeptides are formed by condensation reaction
between the amino group of one amino acid and
the carboxyl group of the adjacent amino acid
Two general categories of proteins
1.
Polypeptide: a few aa in length to >1000. Usually
linear: strands or sheets
AND
2.
Globular: are made of 1 or more polypeptide chains in
a rounded, spherical shape (ex: enzymes)
Images courtesy of google images
The final shape (conformation) of a protein is
determined by a.a. sequence and can be:
• Primary: straight chain of a.a (ex: insulin)
• Secondary: The a.a. chain coils and folds making
helices and pleated sheets (ex: keratin, spider silk)
• Tertiary: A secondary protein undergoes more
folding due to environmental forces. This can be
done by a chaperone protein. Is now globular.
• Quarternary: 2 or more polypeptides come
together to make one functional protein (ex:
keratin, collagen, hemoglobin). Is also globular.
Images courtesy of google images
Denaturation
• Chemical and physical environmental factors
(temperature, pH, ionic concentration) can
cause proteins to change shape (denature) and
lose their function.
• Denaturation can be:
– Dangerous: example- prolonged fever above 39
celcius can denature critical enzymes in the brain.
– Useful: blanching of fruit, straightening hair, cooking
meat to make it easier to chew
Images courtesy of google images