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Many types of proteins exist, and they perform a variety of functions.
Name eight common functions of proteins.
- Structure: skin, hair, nails...
- Catalysis: enzymes
- Movement: Muscles
- Transport: hemoglobin carries oxygen from lungs to cells and CO2 from cells to lungs...
- Hormones: insulin, erythropoietin, human growth hormone (HGH)
- Protection: Antibodies (proteins in the body protect us from Antigens (foreign proteins)
- Storage: Casein in milk and ovalbumin in eggs store nutrients for newborns
- Regulation: Some proteins control the expression of genes, thus regulating the kind of proteins synthesized in cells while also dictating when such manufature takes place.
The main structural material for plants is cellulose.
What is the main structural material for animals?
We can classify proteins into two major groups.
What are they?
- 1. Fibrous proteins (structural)
- 2. Globular proteins (nonstructural)
Fibrous proteins are (soluble/insoluble) in water and are used mainly for (structural/nonstructural) purposes.
Fibrous proteins are insoluble in water and are used mainly for structural purposes.
Globular proteins are (soluble/insoluble) in water and are used mainly for (structural/nonstructural) purposes.
Globular proteins are more or less soluble in water and are used mainly for nonstructural purposes.
An organic compound containing an amino group and a carboxyl group.
The 20 amino acids commonly found in proteins are called_____________
Alpha amino acids
- 1. Alanine / Ala / A
- 2. Arginine / Arg / R
- 3. Asparagine / Asn / N
- 4. Aspartic acid / Asp / D
- 5. Cysteine / Cys / C
- 6. Glutamic acid / Glu / E
- 7. Glutamine / Gln / Q
- 8. Glycine / Gly / G
- 9. Histidine / His / H
- 10. Isoleucine / Ile / I
- 11. Leucine / Leu / L
- 12. Lysine / Lys / K
- 13. Methionine / Met / M
- 14. Phenylalanine / Phe / F
- 15. Proline / Pro / P
- 16. Serine / Ser / S
- 17. Threonine / Thr / T
- 18. Tryptophan / Trp / W
- 19. Tyrosine / Tyr / Y
- 20. Valine / Val / V
On the basis of polarity, amino acids can be classified into what four groups?
- 1. Nonpolar (hydrophobic)
- 2. Polar, uncharged (hydrophilic)
- 3. Acidic (hydrophilic)
- 4. Basic (hydrophilic)
Nature makes only one of the two possible enantiomers for each amino acid, and it is virtually always the ______.
L-isomer (except for glycine which is achiral)
Compounds that have a positive charge on one atom and a negative charge on another are called zwitterions.
Amino acids are zwitterions, not only in water solution but also in the solid state.
What are the primary properties of amino acids?
All amino acids are solids with high melting points and the 20 most common amino acids are fairly soluble in water.
Isoelectric Point (pl)
A pH at which a sample of amino acids or protein has an equal number of positive and negative charges.
Every amino acid has a different isoelectric point, however 15 of the 20 most common have an isoelectric point at or near ____ ?
The three basic amino acids have higher isoelectric points and the two acidic amino acids have lower values.
A compound that is both an acid and a base.
A solution that neutralizes both acid and base is a buffer solution.
Amino acids are _________ compounds and aqueous solutions of them are _________.
Amino acids are amphiprotic compounds and aqueous solutions of them are buffers.
Amphiprotic - a compound that is both an acid and a base
Buffer - a solution that neutralizes both acid and base
An amide bond that links two amino acids.
The --COO- group of one amino acid molecule combines with the --NH3 group of another amino acid.
Note it is the universal custom to write peptide and protein chains with the N-terminal residue on the left.
The sequence of amino acids in a protein.
The primary structure of a protein determines to a large extent the native (most frequently occurring) secondary and tertiary structures.
A repetitive conformation of the protein backbone.
- The two most common secondary structures encountered in proteins are the α-helix and the β-pleated
A secondary protein structure in which the backbone of two protein chains in the same or different molucules is held together by hydrogen bonds.
A secondary structure where the protein folds into a coil held together by hydrogen bonds parallel to the axis of the coil.
Protein conformations that do not exhibit a repeated pattern.
The tertiary structure of a protein is the three-dimensional arrangement of every atom in the molecule.
Unlike the secondary structure, it includes interactions of the side chains, and not just the peptide backbone.
Tertiary structures of proteins are stabilized in what five ways?
- 1. Covalent Bonds
- 2. Hydrogen Bonding
- 3. Salt Bridges
- 4. Hydrophobic Interactions
- 5. Metal Ion Coordination
Certain proteins in living cells, called chaperones, help a newly synthesized polypeptid chain assume the proper secondary and tertiary structures that are necessary for the functioing of that molucule and prevent foldings that would yield biologically inactive molecules.
A protein that helps other proteins to fold into the biologically active conformation and enables partially denatured proteins to regain their biologically active conformation.
The spatial relationship and interactions between subunits in a protein that has more than one polypeptide chain.
The loss of the secondary, tertiary, and quaternary structures of a protein by a chemical or physical agent that leaves the primary structure intact.
Protein conformations are stabilized in their native states by secondary and tertiary structures and through the aggregation of subunits in quaternary structure. Any physical or chemical agent that destroys these stabilizing structures changes the conformation of the protein. We call this process denaturation.
NOTE! Denaturation changes secondary, tertiary, and quaternary structures. It does NOT affect primary structures (that is, the sequence of amino acids that make up the chain).
What are the functions of (a) ovalbumin and (b) myosin?
- (a) Ovalbumin - Storage
- (b) Myosin - Movement
What is the function of an immunoglobulin?
Protection (antibodies that protect us from antigens are immunoglobulins)
Why is it necessary to have proteins in our diets?
Proteins supply most of the amino acids we need in our bodies.
Why are all amino acids solids at room temperature?
Amino acids are zwitterions; therefore they all have positive and negative charges. These molucules are very strongly attracted to each other, so they are solids at low temperatures.
Explain why an amino acid cannot exist in an unionized form at any pH.
All amino acids have a carboxyl group with a pKa around 2 and an amino group with a pKa between 8 and 10.
One group is significantly more acidic and one is more basic.
To have an un-ionized amino acid, the hydrogen would have to be on the carboxyl group and have vacated the amino group. Given that the carboxyl group is the stronger acid, this would never happen.
What is the effect of thyroxine on metabolism?
Thyroxine is a hormone that controls overall metabolic rate. Both humans and animals sometimes suffer from low levels of thyroxine, causing lack of energy and tiredness.
Is a random coil a primary, secondary, tertiary, or quaternary structure?
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