Block B Part 1: Proteins and Enzyme Catalysts Flashcards
State 5 functions of proteins.
Catalysts
Transport Molecules
Storage Molecules
Mechanical Support
Immune protection
Movement
Transmission of nerve impulses
Growth and differentiation
(Lecture 1, Slide 3)
How are amino acids chiral?
As 4 different groups are bonded to the tetrahedral α (alpha) carbon
(Lecture 1, Slide 5)
What are the two mirror image isomers of amino acids?
L isomer and D isomer
(Lecture 1, Slide 5)
Which isomer of amino acids is the only one found in proteins?
The L isomer (remember L for Life)
(Lecture 1, Slide 5)
Why do amino acids exist as dipolar ions at neutral pH?
As the amino group (NH3+) and the carboxyl group (COO-) are charged
(Lecture 1, Slide 6)
What changes the ionisation state of the amino acids?
The pH in solution
(Lecture 1, Slide 6)
What is the reaction that forms a peptide bond between amino acids and what does it release?
It is a condensation reaction which releases water
(Lecture 1, Slide 8)
What is the primary structure of a protein?
The sequence of the amino acids
(Lecture 1, Slide 9)
What termninal is taken as the beginning of a polypeptide chain?
The amino terminal end
(Lecture 1, Slide 10)
Why does the backbone of a polypeptide have hydrogen bonding potential?
Because of the carbonyl groups and the hydrogen atoms that are bonded to the nitrogen of the amine group (NHR1R2)
(Lecture 1, Slide 10)
What is a disulphide bridge?
A way to connect 2 proteins using 2 sulphur atoms from 2 cysteines
(Lecture 1, Slide 11)
How are disulphide bridges formed?
By the oxidation of 2 cysteines
(Lecture 1, Slide 11)
What are the cross-linked cysteines in a disulphide bridge called?
Cystine
(Lecture 1, Slide 11)
How is the peptide bond essentially planar?
As six atoms lie in a plane
(Lecture 1, Slide 12)
What is a plane in biochemistry?
A plane refers to a flat surface or geometrical arrangement
(Lecture 1, Slide 12)
How does the peptide bond have partial double bond character?
Due to resonance
(Lecture 1, Slide 12)
What does the partial double bond character of a peptide bond result in?
Prevention of rotation around the bond
(Lecture 1, Slide 12)
Why is the trans peptide bond strongly favoured over the cis peptide bond?
As steric (spatial) clashes that arise in the cis form between the R groups
(Lecture 1, Slide 12)
Why is rotation allowed around the phi and psi bonds despite rotation around the whole peptide bond not being allowed?
As these involve single bonds in the protein backbone and don’t have resonance
(Lecture 1, Slide 13)
What do the phi (Φ) and psi (ψ) bonds and angles refer to?
Phi refers to the N-Cα bond whereas psi refers to the Cα-Carbonyl bond
(Lecture 1, Slide 13)
What does rotation around the phi and psi angles allow?
Proteins to fold in many ways
(Lecture 1, Slide 13)
What 2 things makes protein folding possible?
Restrictions by the rigidity of the peptide bond due to resonance
A restricted set of allowed phi and psi angles due to steric hinderance
(Lecture 1, Slide 13)
What is the secondary structure of a protein?
The 3D structure formed by hydrogen bonds between NH and CO groups of amino acids near each other in the primary structure
(Lecture 1, Slide 15)
What 3 things are prominent examples of secondary protein structure?
α-helices
ß-strands
turns
(Lecture 1, Slide 15)
What is an α-helix in secondary structure of a protein?
A tightly-coiled rod-like structure with the R groups sticking out from the axis of the helix
(Lecture 1, Slide 16)
Which of the backbone CO and NH groups form hydrogen bonds in an α-helix?
All of them, except those at the end of the helix
(Lecture 1, Slide 16)
What is the α-helix stabilised by?
Intrachain (same chain) hydrogen bonds
(Lecture 1, Slide 16)
Are α-helices primarily right or left handed?
Right handed
(Lecture 1, Slide 16)
What are ß-sheets formed by?
Adjacent ß-strands
(Lecture 1, Slide 17)
What is a ß-strand?
A linear, or nearly linear stretch of a polypeptide that is stretched out and extended
(Lecture 1, Slide 17)
How are ß-sheets stabilised?
Hydrogen bonds between strands
(Lecture 1, Slide 18)
Are the strands of a ß-sheet parallel or antiparallel?
They can be parallel, antiparallel or mixed
(Lecture 1, Slide 18)
What 2 conformations can ß-sheets have?
Flat or twisted
(Lecture 1, Slide 18)
What 2 ways can proteins change directions?
ß-turns (hairpin turns) and Omega (Ω) loops
(Lecture 1, Slide 19)
What does the tertiary structure of a protein refer to?
The spatial arrangement of amino acids that are far apart in the primary structure, and the pattern of disulphide bridges
(Lecture 1, Slide 20)
What is the location of polar and non-polar (hydrophobic) amino acids in globular proteins ?
The interior contains mainly non-polar amino acids whereas the exterior contain mainly polar amino acids
(Lecture 1, Slide 21)
What is the location of polar and non-polar (hydrophobic) amino acids in membrane proteins?
The interior contains mainly polar amino acids whereas the interior contains mainly non-polar amino acids
(Lecture 1, Slide 22)
What are motifs (supersecondary structures)?
Combinations of secondary structures that are found in many proteins
(Lecture 1, Slide 23)
What do some proteins have that can be called (modular) domains?
Two or more similar or identical compact structures
(Lecture 1, Slide 23)
What is the role of ß-mercaptoethanol?
It reduces disulphide bonds and is itself oxidised forming dimers
(Lecture 1, Slide 25)
What proteins are said to display quaternary structure?
Proteins composed of multiple polypeptide chains (known as subunits)
(Lecture 1, Slide 26)
What determines the folding of a protein into its 3D structure?
The amino acid sequence
(Lecture 1, Slide 28)
What is post-translational modification in a protein?
After synthesis (translation), many proteins undergo further modification determining their fate in the cell
(Lecture 1, Slide 31)
What are 2 types of post-translational modification?
Converting a proprotein (precursor protein) into a mature protein by proteolytic cleavage
Addition of various chemical groups modifying either the N-terminal amino group, the C-terminal carboxyl group or the side chains of the amino acids throughout the length of the protein
(Lecture 1, Slide 31)
What can lack of appropriate post-translational protein modification lead to?
Pathological conditions
(Lecture 1, Slide 31)
What does a catalyst do to the activation energy of a reaction?
It lowers it
(Lecture 2, Slide 5)
What does a catalyst do to the rate of a reaction?
It increases it
(Lecture 2, Slide 5)
Is a catalyst consumed in a reaction?
No, it remains chemically unchanged
(Lecture 2, Slide 5)
Do catalysts affect the equilibrium?
No
(Lecture 2, Slide 5)
How is an enzymes active site formed?
Folding of a protein brings side-chains of various amino acids that may be far apart in the primary sequence into close proximity, forming an active site
(Lecture 2, Slide 6)