Amino Acids Flashcards
What are proteins and polypeptides composed of?
What is the generic structure of a single unit?
What is its shape?
Proteins and polypeptides are polymers of amino acids (joined by peptide bonds)
Generic structure of an amino acid:
Central Alpha-carbon bonded to:
- Hydrogen atom: H
- Basic amino group: NH2
- Acidic carboxyl group: COOH (C=O;OH)
- Side chain: R-group
Tetrahedral in shape
What is glycine?
Glycine is the simplest amino acid, where the R-group is a hydrogen atom
What are stereoisomers?
What form do amino acids take?
Stereoisomers are molecules that are chiral: mirror images of one another
Amino acids exist as stereoisomers (except Glycine)
In proteins they are ALL in the L-configuration
What determines an amino acid’s properties?
What are the different types of amino acids that result?
The side chain (R-group) determines the amino acid’s properties:
- It’s structure
- It’s function
- It’s overall charge
The different types of amino acids are:
- Acidic: negatively charged at physiological pH/hydrophilic
- Basic: positively charged at physiological pH/hydrophilic
- Polar: uncharged/hydrophilic
- Non-polar: hydrophobic
Describe the properties of a water molecule
What makes a molecule hydrophobic or hydrophilic?
How does the hydrophilic interaction occur?
Water is
- a polar molecule: it has a dipole (both hydrogens partial positive charge, oxygen partial negative charge)
- It is tetrahedral in shape but is bent (bc of the nonbonding electron pairs)
Molecules that are polar are hydrophilic (SOLUBLE in water e.g. ethanol)
Molecules that are non-polar are hydrophobic (INSOLUBLE in water e.g. hydrocarbons)
Hydrophilic interactions of polar or charged molecules with water occurs via hydrogen bonding
How does hydrogen bonding happen?
Describe its property
Hydrogen has partial positive charge (δ+), Oxygen has partial negative charge (δ-).
The interaction of a hydrogen and oxygen (from different water molecules/between polar molecules) is called a hydrogen bond
Property:
Individually much weaker than covalent bonds, but can be strong collectively
What determines protein structure?
Interactions between R-groups dictate protein structure
What are the main types of interactions between R groups?
- Hydrogen bonds
- Hydrophobic interactions
- Disulfide bonds
- Salt bridges (ionic interactions)
What does amphoteric mean?
Which biomolecule is amphoteric?
A substance that can act both as an acid and a base, depending on the conditions they’re in
Amino acids are amphoteric (basic amino group/acidic carboxyl group)
What is a zwitterion?
An amphoteric molecule in which both the acidic and basic groups are ionised
Therefore holds NO overall charge
What is an acid/base?
What determines their strength?
Acid: molecule which donates a proton (becomes -vely charged)
Base: molecule which accepts a proton (becomes +vely charged)
How readily they do so determines their strength
What is a buffer?
Which biomolecule acts as an important buffer?
Why are buffers important?
Buffers are substances that minimize changes in the CONCENTRATION of H+ (i.e. pH)
Proteins and amino acids act as buffers. Inorganic molecules can also act as buffers (e.g. bicarbonate, phosphate)
Buffers are important because MAINTENANCE of pH is VITAL to SURVIVAL
What is the name of the bond between amino acids?
Describe the bond and its properties
Peptide bond: NCC - peptide bond - NCC
The carboxyl group of one amino acid bonds with the amino group of another = dipeptide
A condensation reaction (produces water) whicih produces a covalent bond (strong)
What is the primary structure of polypeptides/proteins?
The sequence of amino acids in a protein from the N terminal (NH2) to the C terminal (COOH) is called the primary structure
