Proteins Flashcards
What are the type of bonds formed between amino acids
Peptide bonds
What are proteins composed of
Carbon
Hydrogen
Oxygen
Nitrogen
Sometimes sulphur and phosphorus to
Name the different examples of proteins
- enzymes
- cell membranes
- structural protein (e.g collagen)
- hormones
- antibodies
- transport (e.g haemoglobin)
- muscle contraction (actin and myosin proteins)
What is the general structure of an amino acid
Amine group (NH2)
Central carbon and hydrogen
R group
Carboxyl group
What is an R group
It is the variable group which differs with the 20 different amino acids
How do different R groups change the properties of amino acids
- non-polar
- polar
- acidic
- bases / basics
How do peptide bonds form
A condensation reaction between 2 amino acids form a peptide bond
What forms when a condensation reaction occurs between 2 amino acids?
One water molecule
Dipeptide chain
What always forms at either end of a dipeptide/polypeptide chain?
An amine group is ALWAYS at one end and a carboxyl group is ALWAYS at the other end.
How do you test for proteins
Add a few drops of biuret reagent(1 - sodium hydroxide) and a few drops of biuret reagent(2 copper sulphate) this should look blue. When added to the test solution, if a purple/lilac colour develops, it indicates the presence of protein
What is biuret reagent p composed of?
Copper sulphate
Sodium hydroxide
Why won’t an amino acid show a positive result in the biuret test?
The biuret test - tests for peptide bonds which are not present in a single amino acid
What does a semi-quantitative test mean?
It means that with observation, you can determine that the concentration is higher or lower.
How do you make a semi-quantitative food test more accurate?
Use a colorimeter to measure colour
What is the primary structure of proteins?
The sequence of amino acids found in a proteins polypeptide chain.
What is the secondary structure of proteins
The primary structure is pulled into the secondary structure due to the hydrogen bonds forming between the double bonded oxygen and single bonded hydrogen of nearby peptide bond. This forms an Alpha helix or Beta pleated sheet
What does the secondary structure form?
Alpha helix
Beta pleated sheet
What’s the tertiary structure of protein
R group interactions pull the secondary structure into a more complex 3D shape held in place by disulphide bridges, ionic bonds, hydrogen bonds and hydrophobic/hydrophilic interactions
What is a disulphide bridge?
A bond which forms between 2 sulphur molecules in the R-group of amino acids. This causes bends/folds in the structure
What is an ionic bond in the tertiary structure?
A bond which forms between a positive and negative charge of the R-group.
This also causes folds/turns in the structure
What is the hydrogen bond in the tertiary structure?
A bond which forms between nearby peptide bonds (between O and H)
How do hydrophobic and hydrophilic interactions affect the structure of proteins?
Hydrophobic molecules fold inwards to avoid contact with water. Hydrophilic molecules push out due to the attraction with water
What is the quaternary structure of proteins?
When 2 or more polypeptide chains are bonded together. Prosthetic groups may also be present to form large, complex protein molecules.
How does the tertiary structure impact the function of a protein?
The tertiary structure aids to determine the shape of the molecule which affects its function (e.g enzymes active site)
What are the two types of proteins?
Globular
Fiborous
What function does a globular structure give proteins
It forms a :
spherical shape
Compact structure
And aids metabolic function
Name 2 globular proteins
Enzymes
Haemoglobin
What structure does haemoglobin have?
Has a quaternary structure as 4 polypeptide chains are bonded together around an iron ion
What function does a fibrous protein have?
The long strands/chains which run parallel to one another are linked by cross bridges which make them strong and stable, they are also insoluble
Name a fiborous protein
Collagen (structural function like bones)
Why are globular proteins soluble in water?
The hydrophobic R-groups flood in and cluster on the inside while the hydrophilic R-groups push towards the outside to make attractions with the water molecules
