1.4 Proteins Flashcards
What are proteins made up from?
Monomers called amino acids
What elements do proteins contain?
C,H,O,N and S
What is the structure of an amino acid?
R
|
H2N— C —-COOH
|
H
What is the COOH group called?
Carboxyl group
What is the H2N group called?
Amino group
What does the R mean in an amino acid?
-Any possible number of chains
- it’s a side chain
What is the simplest amino acid and what is its structure?
Glycine
H H O
| | || H—N—C—C—OH
|
H
What forms a peptide bond?
A condensation reaction between two amino acids
What forms from a condensation reaction between two amino acids?
A peptide bond
How are dipeptides formed?
Formed by the condensation of two amino acids.
How are polypeptides formed?
Formed by the condensation of many amino acids.
What may a functional protein contain?
One or more polypeptides.
What 4 levels does protein structure occur at?
-Primary Structure
-Secondary structure
-Tertiary structure
-Quaternary structure
What is primary structure?
The number and sequence of amino acids in a polypeptide chain
What is secondary structure?
The secondary structure is made when hydrogen bonds form between some of the atoms in the polypeptide chain, this pulls the chain into a shape, there are two shapes that are generally made - alpha helix or beta pleated sheets
What is tertiary structure?
The folding of the polypeptide chain into a 3D shape, this is held in place by hydrogen bonds and disulfide bridges
What is quaternary structure?
One or more polypeptide chains joined together to make a fully functional protein. Often there are prosthetic groups with quaternary structure. In haemoglobin the prosthetic group is iron
What is the test for proteins?
The Biuret Test - Which detects peptide bonds
What is the method of the Biuret test?
-Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
-Add a few drops of very dilute copper sulfate solution and mix gently
-A purple colouration indicates the presence of peptide bonds and hence a protein. If no protein is present, the solution remains blue
How many amino acids are there and how do they differ from one another?
20
differ only by side ‘R’ group
What is 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
What is the structure and function of fibrous proteins?
• can form long chains or fibres
• insoluble in water
• useful for structure and support
How could chromatography be used to identify the amino acids in a mixture?
- use a capillary tube to spot mixture onto pencil origin line and 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 and solubility in solvent
- use revealing agent to see spots
- Calculate Rf values and match to database
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 and easily broken
