Proteins 1 Flashcards
What occurs during protein synthesis?
- DNA transcribed to RNA
- RNA translated to protein
Codon
Chain of three bases which code for an amino acid
What is a codon defined by?
The initial nucleotide from which translation starts
What is the basic structure of an amino acid?
Central carbon with 4 bonds:
- amino group
- variable side chain
- carboxylic acid group
- hydrogen
What are the different types of amino acids?
Aliphatic Aromatic Sulphur containing Basic Uncharged polar Acidic Other
What is a peptide bond?
Covalent bond between a carboxylic acid and amine group
Where does the formation of peptide bonds occur?
Within a ribosome in during translation
What is a polypeptide chain?
A chain of two or more amino acids covalently bonded
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide chain
What is the source of versatility in a proteins structure and function?
The primary structure
What is the secondary structure of a protein?
The spatial arrangement of amino acid residues that are near each other in linear sequence
What two structures are involved in secondary structure?
Alpha Helix
B Pleated Sheet
How is the alpha helix structure held in place?
By hydrogen bonds between every N-H group and the O2 of the C=O group in the next turn of the helix
How is the beta pleated sheet structure held in place?
Held together by hydrogen bonds between the amide groups of linear polypeptide chains
What is the tertiary structure of a protein?
The spatial arrangement of amino acid residues that are far apart in a linear sequence
What forces are involved in the tertiary structure of a protein?
Van der Waals Ionic interactions Hydrogen bonds Disulphide bridges Hydrophobic interactions
When do ionic interactions occur?
Between 2 close, oppositely charged R groups
What are Van der Waals?
- Non-specific, weak attractions between atoms 0.3-0.4 nm apart
- They are individually weak but in a folded protein structure, a large number exist- thereby stabilising the structure
What are hydrogen bonds?
- Similar to Van der Waals but are stronger and permanent
- Occur when H is bonded to either O, N or F and a lone pair of electrons are present
Name 2 substances that hydrogen bonding takes place in?
Water
Ammonia
What are hydrophobic interactions?
Intra-polypeptide interactions which occur in an environment within proteins from which water is excluded
Where are the hydrophobic R groups in globular water-soluble proteins?
Inside of the protein
What makes a protein water soluble?
Hydrophilic R groups on the outside hydrogen bonding to water
What are disulphide bridges?
- Strong covalent bonds between two cysteine residues.
- Common in extra-cellular proteins
- Can occur between as well as within a polypeptide
What is the quaternary structure of a protein?
Refers to the spatial arrangement of individual polypeptide chains in a multi-subunit protein
What does the denaturation of proteins involve?
The disruption and possible destruction of both secondary and tertiary structures
Why does the primary structure remain the same after denaturation?
Denaturation reactions are not strong enough to break the peptide bonds
What can cause denaturation?
- Acids
- Heat
- Solvents (ethanol, methanol)
- Cross linking reagents (formaldehyde)
- Chaotropic agents (urea)
- Disulphide bond reducers (2 mercaptoethanol)
What are the effects of denaturation?
- Decreased solubility
- Altered water binding capacity
- Loss of biological activity
- Improved digestibility
What are peptidases responsible for?
Cleavage of peptide bonds
What are endopeptidases responsible for?
Cleavage of internal bonds
What are exopeptidases responsible for?
Cleavage of one amino acid at a time
What are carboxypeptidases responsible for?
Cleavage at -COOH terminal
What are aminopeptidases responsible for?
Cleavage at -NH2 terminal
