Proteins Flashcards
What is the acidic group in amino acids?
Carboxyl group (–COOH)
What is the basic group in amino acids?
Amino group (–NH2)
What group differentiates one amino acid from another, giving it its distinctive properties such as melting point and boiling point?
R group
Do amino acids exhibit optical activity?
YES
d (lower case) isomer can rotate plane-polarized light (light in one direction only) to the right and l (lower case) isomer can rotate plane-polarized light to the left
Which amino acid enantiomer (D or L) is more predominant in nature?
L isomer
Any relationship between enantiomerism and optical activity?
NONE. You can have D, d or D, l isomers.
Why are amino acids classified as amphoteric substances?
Because they have BOTH acidic and basic groups. Thus they can serve as both acids and bases.
What would make an amino acid nonpolar?
If their sidechains are composed of hydrocarbon groups.
ex. alanine (which has a –CH3 sidechain, or tryptophan, which has a very bulky sidechain composed of only carbon and H)
What would make an amino acid polar?
Polar groups in their sidechains such –OH, –COOH or –NH2
ex. serine (has –CH2OH sidechain) or aspartic acid (has –CH2COOH sidechain)
What would make an amino acid acidic?
Carboxylic groups in their sidechains. These amino acids are NEGATIVELY CHARGED at physiological pH (pH ~7).
ex. aspartic acid (has –CH2COOH sidechain)
What would make an amino acid basic?
Amino groups in their sidechains. These amino acids are POSTIVELY CHARGED at physiological pH (pH ~7).
ex. arginine (has guanidino side chain with amino group in it)
What are essential amino acids?
Amino acids that they body cannot synthesize, therefore they must be obtained from the diet.
Mnemonic: PVT TIM HALL (phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, leucine and lysine)
What is the bond formed between 2 amino acids?
Peptide bond
Can the peptide bond rotate?
No, it has a double bond character, which makes it slightly rigid (more rigid than a single bond).
In globular proteins, which amino acids are exposed? Which are tucked away in the core of the protein?
Exposed amino acids on the surface must be able to interact with the aqueous environment, thus they must be hydrophilic, or polar. Those tucked away in the core of the protein are those that cannot interact with the aqueous environment, thus they must be the hydrophobic, or nonpolar amino acids.
What is the usual function of fibrous proteins like collagen and keratin?
Structural support
What are the 4 levels of organization in proteins?
Primary, secondary, tertiary and quaternary
What is the structure found at the pimary level of organization?
Amino acid sequence
What stabilizes the structure at the pimary level of organization?
Peptide bonds
What is the structure found at the secondary level of organization?
Alpha helixes and beta-pleated sheets
What stabilizes the structures at the secondary level of organization?
Hydrogen bonds (inter and intra)
What is the structure found at the tertiary level of organization?
3D conformation of proteins
ex. structure of myoglobin
What stabilizes the structures at the tertiary level of organization?
Disulfide bonds (bond between 2 cysteine molecules), salt bridges (between charged amino acids, example aspartic acid and histidine), hydrophobic interactions (between hydrophobic amino acids)
What is the structure found at the quaternary level of organization?
Interactions of several subunits (dimers, tetramers)
ex. structure of hemoglobin (a tetramer)
What stabilizes the structures at the tertiary level of organization?
Disulfide bonds (bond between 2 cysteine molecules), salt bridges (between charged amino acids, example aspartic acid and histidine), hydrophobic interactions (between hydrophobic amino acids)
Which provides the high rigidity of collagen?
Proline and hydroxyproline
Which amino acid occurs in every 3rd amino acid in the sequence of collagen?
Glycine
forms cross-links
What amino acids mostly make up elastin?
Glycine, alanine and lysine (few proline)
Which unusual amino acid is found in elastin?
Desmosine
What is present in alpha-keratin that makes it very tough?
Disulfide bonds
(As opposed to beta-keratin, which does not have any cysteine residues. This makes beta-keratin more soft and supple like silk.)
Between myoglobin and hemoglobin, which exhibits a hyperbolic curve, and which one exhibits a sigmoidal curve?
Myoglobin: hyperbolic
Hemoglobin: sigmoidal
Which is more ideal for transport and which is more ideal for storage?
Hemoglobin: transport
Myoglobin: storage
Hemoglobin binds O2 only at high concentrations (such as in the lungs) and releases it at low concentrations (peripheral tissues). Myoglobin releases O2 only at very very low O2 concentrations.
Sickle cell anemia is caused by a single mutation in amino acid # 6 of the beta subunit of hemoglobin. Which amino acid is it and what is it mutated to?
Glutamate to valine.
Why does it make a difference? Glutamate is POLAR, while valine is NONPOLAR. This would affect the structure because glutamate is found outside hemoglobin while valine would be found inside hemoglobin.
How does sickle cell anemia cause problems? Does the disease have any benefit?
The sickle cell structure allows for the polymerization of Hb, causing RBCs to clump together and potentially block blood vessels. The structure isn’t also ideal for O2 binding.
Yes, sickle cell anemia has benefit in malaria-infested regions. The parasite responsible for malaria spends a part of its life cycle inside the RBC. With defective Hb, however, the RBC ruptures more easily, making the parasite unable to reproduce.
