Proteins Flashcards
Describe the structure of an amino acid
Alpha carbon, carboxyl group, amino group, R group and H atom.
Describe the properties of amino acids in a polypeptide based on their R groups
Charge, hydrogen-bonding capacity, chemical reactivity, size and shape
Describe the formation of a peptide bond
OH from COOH and H from NH2 are removed as one water molecule. By condensation, peptide bond formed.
Distinguish between charged R groups and polar R groups
Charged R groups have an imbalance of COOH or NH2 groups.
Polar R groups can form H bonds with water (Electronegativity).
Identify the correct sequence of amino acids base on their terminuses
C-terminus = End
Define the terms zwitterion and amphoteric
Zwitterion is an ion with both positive and negative charges (dipolar).
Amphoteric means exhibiting both acidic and alkaline properties.
Can donate and accept pH: allows them to act as buffers
Define the terms primary, secondary, tertiary and quaternary protein
Primary: sequence, number and type of amino acids held together by peptide bonds. Sequence of R groups will determine uniqueness and specific 3D conformation they are folded into
Secondary: specific coiling of pleating of single polypeptide chain held together by H bonds formed between CO and NH groups Of polypeptide backbone. R groups not involved
Tertiary: more extensively folded polypeptides by HIHIS between R grps, has a globular structure
Quaternary: more than one polypeptide chain, held together by HIHIS.
Describe the types of bonds that hold the secondary, tertiary and quaternary protein in shape
Hydrogen bonds between polar R groups (electronegativity)
Ionic bonds formed between oppositely-charged R groups
Hydrophobic Interactions between non-polar, hydrophobic R groups (tend to point inwards)
Disulfide bridges between cysteine amino acids, strong cov bond that increases stability
To heat denaturation
State the 2 types of secondary structure and describe their structures
Alpha-helices are coiled, helical structures. 3.6 amino acid residues per turn. H bonds form
between CO groups of one turn and NH groups of the next turn, at every 4th peptide bond
Beta-helices formed when two or more regions of single polypeptide chain lying side by side,
Linked by hydrogen bonds between CO of one region and NH group of adjacent. Chains may
Run parallel or anti-parallel, forming a flat sheet.
Explain the significance of the R group of different amino acids to protein structure.
Affects the type of bond formed at the location of the amino acid, consequently affects folding pattern of polypeptide and its specific 3D conformation.
Describe the structure of haemoglobin and its functions
Haemoglobin is a protein in quaternary structure, composed of four subunits, 2 alpha globin and
2 beta globin. Each subunit is made of a prosthetic haem group which has a porphyrin ring and
A Fe2+ ion which binds reversibly to oxygen to form oxyhaemoglobin.
Soluble in water: Hphilic on exterior, Hphobic interior.
Haemoglobin does not have any disulfide bridges so that subunits can move with respect to
each other in a way that influences its affinity to oxygen
For cooperative binding of oxygen:
When one oxygen binds to one of the subunits, the other subunits change conformation to be
More complementary to oxygen which speeds up occupation of the other four active sites.
Describe the structure of collagen and its functions
Collagen is made up of three polypeptide chains loosely coiled around each other in a triple helix
Repeating tripeptide unit of X-Y-glycine, almost every third R group is glycine which is the smallest
Amino acid and fits into tight junctions.
X and Y are frequently hydroxyproline and proline, which are bulky, inflexible and confer rigidity.
Most OH groups are involved in hydrogen bonding between residues
Cross-linking of chains, covalent bonds between lysine residues which increases tensile strength
So it is insoluble.
Staggered arrangement minimises weak points. Many tropocollagen molecules unite to form
a fibre. Bundling effect
Compare between the structures of fibrous and globular protein
Shape: long and straight vs spherical
Solubility: insoluble vs soluble (polar R grps exposed to water)
Variety: Less variety of AAs, more regular structure vs More
Length: May vary slightly vs Must be identical to function
Function: Structural vs Metabolic roles
Explain the effects of temperature on protein structure
When temperature is too high, KE increases, intramolecular vibrations increase,
breaks hydrogen bonds that keep in 3D confm.
Explain the effects of pH on protein structure
Affects ionisation of R groups and disrupts ionic bonds
