Amino Acids Flashcards
What is chirality in amino acids?
All amino acids except glycine are chiral
Chiral molecules have non-superimposable mirror images.
What are enantiomers?
Molecules that are mirror images of each other
Enantiomers can have different biological activities.
What distinguishes L and D enantiomers?
L-amino acids rotate plane polarised light anticlockwise (-ve sense), D-amino acids rotate it clockwise (+ve sense)
All amino acids in nature are L-amino acids.
What is the Fischer projection?
A method to represent chiral molecules where horizontal bonds come out of the page and vertical bonds go into the page
Helps visualize the spatial arrangement of atoms.
What is the effect of chirality on biological function?
Chirality affects the activity of molecules, as seen in the R and S forms of thalidomide
R form is sedative, S form is teratogenic.
What are the characteristics of the R and S forms of thalidomide?
R form is less active, S form is more active
The drug was prescribed as a mixture, leading to severe side effects.
List the classifications of the 20 natural amino acids.
- Hydrophobic
- Polar
- Charged
Which amino acid is the first in any protein?
Methionine
Methionine is often abbreviated as Met.
What determines the properties of amino acids?
Defined by side chains, which lead to key functions such as protein folding and catalytic activity
Side chains also affect interactions and cellular localization.
What is the Kyte and Doolittle hydropathy scale?
A scale that classifies amino acids based on their hydropathy values
Positive values indicate hydrophobic, negative values indicate hydrophilic.
Which amino acids contain sulfur?
- Cysteine
- Methionine
What is the difference between cysteine and cystine?
Cystine is a dimer formed by two cysteine molecules linked by a disulfide bond
Cysteine is a single amino acid, while cystine refers to the oxidized form.
What are salt bridges in proteins?
Very strong hydrogen bonds between positively and negatively charged side chains
Salt bridges contribute to protein stability.
What is the role of histidine in proteins?
Acts as a pH sensor due to its pKa around 6, making it sensitive to small pH changes
Important in enzymes and biological processes.
How does the degree of ionisation depend on pH?
Ionisation varies with pH, affecting amino acid charge states
This is crucial for understanding enzyme activity.
What are common post-translational modifications?
- Phosphorylation
- Glycosylation
- Lipidation
- Ubiquitination
What is the function of phosphorylation?
Involves the addition of phosphate groups to Ser, Thr, or Tyr
Alters protein function and activity.
What is glycosylation?
Attachment of sugar molecules to proteins, typically at Ser, Thr, or Asn
Affects protein folding and stability.
What is the significance of the Green Fluorescent Protein (GFP)?
Fluoresces green under UV light due to a spontaneous modification
Used widely as a marker in biological research.
What causes sickle cell anemia?
A variation in the gene encoding the beta subunit of hemoglobin leads to chronic anemia
The mutation causes red blood cells to become rigid and sickle-shaped.
What is the effect of the mutation in sickle cell anemia?
A charged surface residue is replaced by a hydrophobic one, causing molecules to stick together
This forms long rods that distort the cell shape.
