Proteins - Biological Molecules Flashcards
What is the general structure of an amino acid?
-COOH carboxyl/ carboxylic acid group
-R variable side group consists of carbon chain & may include other functional groups e.g. benzene ring or -OH (alcohol)
-NH2 amine/ amino group
check picture on google
Describe how to test for proteins in a sample.
Biuret test confirms presence of peptide bond
1. Add equal volume of sodium hydroxide to sample at room temperature.
2. Add drops of dilute copper (II) sulfate solution. Swirl to mix. (steps 1 & 2 make Biuret reagent)
3. Positive result: colour changes from blue to purple
Negative result: solution remains blue.
How many amino acids are there and how do they differ from one another?
20
differ only by side ‘R’ group
How do dipeptides and polypeptides form?
● Condensation reaction forms peptide bond (-CONH-) & eliminates molecule of water
● Dipeptide: 2 amino acids
● Polypeptide: 3 or more
amino acids
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How many levels of protein structure are there?
4
Define ‘primary structure’ of a protein.
● Sequence, number & type of amino acids in the polypeptide.
● Determined by sequence of codons on mRNA.
Define ‘secondary structure’ of a protein.
Secondary structure refers to the specific 3D shape that the protein takes due to hydrogen bonding between the amino acids. This structure is crucial for the protein’s function
Hydrogen bonds form between O 𝛿- (slightly negative) attached to ‒C=O & H 𝛿+ (slightly positive) attached to ‒NH.
Describe the 2 types of secondary protein structure.
α-helix:
● all N-H bonds on same side of protein chain
● spiral shape
● H-bonds parallel to helical axis
β-pleated sheet:
● N-H & C=O groups alternate from one side to the other
Define ‘tertiary structure’ of a protein. Name the bonds present.
3D structure formed by further folding of polypeptide
● disulfide bridges
● ionic bonds
● hydrogen bonds
Describe each type of bond in the tertiary structure of proteins.
● Disulfide bridges: strong covalent S-S bonds between molecules of the amino acid cysteine
● Ionic bonds: relatively strong bonds between charged R groups (pH changes cause these bonds to break)
● Hydrogen bonds: numerous & easily broken
Define ‘quaternary structure’ of a protein.
● Functional proteins may consist of more than one polypeptide.
● Precise 3D structure held together by the same types of bond as tertiary structure.
● May involve addition of prosthetic groups e.g metal ions or phosphate groups.
Describe the structure and function of globular proteins.
● Spherical & compact.
● Hydrophilic R groups face outwards & hydrophobic
R groups face inwards = usually water-soluble.
● Involved in metabolic processes e.g. enzymes &
haemoglobin.
Describe the structure and function of fibrous proteins.
● Can form long chains or fibres
● insoluble in water.
● Useful for structure and support e.g.
collagen in skin.
Outline how chromatography could be used to identify the amino acids in a mixture.
- Use capillary tube to spot mixture onto pencil origin line & place chromatography paper in solvent.
- Allow solvent to run until it almost touches other end of paper. Amino acids move different distances based on relative attraction to paper & solubility in solvent.
- Use revealing agent or UV light to see spots.
- Calculate Rf values & match to database.
Explain the induced fit model of enzyme action.
● Shape of active site is not directly complementary to substrate & is flexible.
● Conformational change enables ES complexes to form.
● This puts strain on substrate bonds, lowering activation energy.
