Chapter 5: Proteins, Structure, And Synthesis Flashcards
What is a protein?
A macromolecule in biological systems made up of a combination of the 20 different amino acids. They are essential in several cellular tasks in the body.
What are the two main types of protein and what are their roles?
Enzymes: proteins that catalyse and control metabolic reactions.
Transporters: proteins that transport molecules through otherwise impermeable membranes.
What reaction links two amino acids?
Condensation reaction
Describe the structure of an amino acid and how it condenses to an amino acid chain
Left: amino acids as non-ionised, separate molecules
Right: amino acids as ionised chain
Are amino acids connected to each other rigidly (can movement occur)?
No, the central carbon in each amino acid is a point of rotation so the orientation of them can be defined by dedihedral angles.
Describe the primary structure of a protein
The initial form of a protein; a singular polypeptide chain made up of a series of amino acids. This structure determines the ultimate shape, hence function, of the protein.
Describe the secondary structure of a protein
‘Folding’ of the the primary structure into local motifs, the α-helix and the β-sheet. The number, types of and extent of these motifs determines the secondary structure.
What determines if the secondary structure is an α-helix or β-sheet?
The characteristic set of dihedral angles for the peptide bond of the molecules.
What bond forms the α-helix and the β-sheet?
Hydrogen bonds between the -NH group and -C=O group (but in different places).
Where do bonds form to produce an α-helix?
Between the two helical pitches.
Where do bonds form to produce a β-sheet?
Between parallel strands of amino acids.
Describe the tertiary structure of a protein
Further ‘twisting’ of secondary structure proteins into more complex shapes meaning that they have a 3D globular configuration.
Give 3 examples of bonds that maintain the tertiary structure
- Disulphide bridges
- Ionic bonds
- Hydrogen bonds
Describe the quaternary structure of a protein
The subunits of a molecular complex. Multiple quaternary structure proteins are combined together with non-protein prosthetic groups to produce large structures e.g. haemoglobin.
Define the Ramachandran plot
A plot of the dihedral angle combination, φ and ψ, for all the peptide bonds in a protein. The density of these plots determines how many α-helices and β-sheets there are in a protein.
What are the dihedral angles for an α-helix?
For an α-helix: φ = -57º; ψ = -47º
What are the dihedral angles for a β-sheet?
For a β-sheet: φ = -100º; ψ = 140º
What are the 6 important interactions that can impact a proteins structure?
• Disulphide bonds between cysteine (amino acid) residues in polypeptides.
• Covalent bonds between two sulphur atoms.
• Electrostatic interactions, known as salt bridges, between the charge residue of two amino acids.
• Cation π interactions between the amino acids tryptophan, arginine, and/or lysine.
• Hydrophobic interactions are mainly responsible for initial protein folding.
• Hydrogen bonds provide stabilisation.
What percentage of chemical groups form hydrogen bonds in proteins given that they are able to? (EXTRA: what is the result of this?)
90%
EXTRA: even though the bond is weak, in large numbers the overall impact is great.
What are the two stages of protein synthesis?
Transcription and translation.
Where is translation performed?
In the ribosome (found in the cytoplasm of a cell).
What is a ribosome?
A complex catalytic molecule consisting of over 50 proteins and several rRNA, ribosomal RNA, molecules. These components form two subunits in the ribosome. There are 10 ribosomes in the typical cell.
