1.4 Flashcards
(34 cards)
What are amino acids?
The monomers from which proteins are made
Draw the general structure of an amino acid
Describe the 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
They differ only by their side R group
What bond does a condensation reaction between two amino acids form
A peptide bond
How do dipeptides form?
Dipeptides are formed by the condensation of two amino acids
How do polypeptides form?
Polly peptides are formed by the condensation of many amino acids
A functional protein may contain…
One or more polypeptides
How many levels of protein structure are there?
Four
Define primary structure of a protein
-Sequence, number and type of amino acids in the polypeptide
Define secondary structure of a protein
-The sequence of amino acids causes part of a protein molecule to bend into a-helix shapes or fold into B-pleated sheets
-The hydrogen in the -NH has a slightly positive charge while the oxygen in the -C=O has a slight negative charge
- As a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets.
Describe the two types of secondary protein structure?
a-helix:
– all N-H bonds on the same side of protein chain
– Spiral shape
– H-bonds parallel to helical axis
B-pleated sheet:
– N-H and C=O groups, alternate from one side to the other
Define tertiary structure of a protein. Name the bonds present
3-D 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 causes these bonds to break)
Hydrogen bonds:
– numerous and easily broken
Define quaternary structure of a protein
– Functional proteins may consist of more than one polypeptide.
-Precise 3-D structure held together by the same types of bond a tertiary structure.
-May involve addition of prosthetic groups, E.G metal ions of phosphate groups
Describe the structure and function of globular proteins
– Spherical and compact
– Hydrophilic, R groups face outwards and hydrophobic R groups face inwards = usually water soluble
-involved in metabolic processes, E.G enzymes and 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.
What are enzymes?
• Biological catalysts for intra & extracellular reactions.
• Specific tertiary structure determines shape of active site, complementary to a specific substrate.
• Formation of enzyme-substrate (ES) complexes lowers activation energy of metabolic reactions.
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.
How have models of enzyme action changed
– Initially lock and key model: rigid shape of active site, complimentary to only one substrate
– Currently induced fit model: also explains why binding at allosteric sites can change shape of active site
How could a student identify the activation energy of a metabolic reaction from an energy level diagram?
Difference between free energy of substrate and peak of curve
Name five factors that affect the rate of enzyme controlled reactions
– Enzyme concentration.
– substrate concentration.
– concentration of inhibitors.
– P H.
– temperature
How does substrate concentration affect rate of reaction?
Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration.
Rate levels of when maximum number of ES complexes form at any given time
