7.4/14.1 PROTEINS
Protein’s have 4 levels of Structure:
1. Primary Structure = the order of amino acids
that make up the polypeptide; amino acids are
bonded together with peptide bonds
What
determines
the order of
amino acids?
2. Secondary Structure – the repeated, regular
structures that polypeptide chains make due
to hydrogen bonding; usually twisted alpha
helices or beta-pleated sheets
Alpha helix
Beta pleated sheet
3. Tertiary Structure – 3D shape due to the bending
and folding of the polypeptide; folds are the
result of interactions between the R groups of
amino acids
bonds include covalent
bonds (disulfide bonds
between sulfurs),
hydrogen bonds, ionic
bonds
** folding occurs after
translation
4. Quaternary Structure – when 2 or more
polypeptide chains come together to make a
protein; other elements may also be involved
Prosthetic group
Fibrous vs. Globular Proteins
• Fibrous Proteins – long, narrow, and often
insoluble in water
– Ex: keratin – skin and hair
– Ex: collagen – connective tissue
– Ex: actin - muscles
Fibrous vs. Globular Proteins
• Globular Proteins – 3 dimensional and often
water soluble
– Ex: hemoglobin
– Ex: insulin
– Ex: enzymes
– Ex: antibodies
Significance of Amino Acid Polarity
Non-Polar Amino Acids make up proteins that are typically
hydrophobic and therefore found at inner parts of cell
membrane, water insoluble
Polar Amino Acids make up proteins that are typically
hydrophilic and therefore found protruding through cell
membrane; water soluble
Enzyme-substrate specificity is also determined by polarity
Review Question!!!
What are the 6 functions
of membrane-bound
proteins?
The 6 Functions Are…
1. Channel for passive transport
2. Pump for active transport
3. Hormone binding site
4. Enzyme
5. Cell to cell communication
6. Attachment
Four Functions of Proteins:
1.
2.
3.
4.
5.
6.
Structure – collagen
Movement – myosin and actin in muscles
Gas transport – hemoglobin
Defense – antibodies
Enzyme – amylase
Pick 4 to know!
Hormone - insulin