Proteins Flashcards
What are amino acids?
The monomers from which proteins are made.
Describe the general structure of amino acids?
Amino acids contain an amino group (NH2), carboxylic acid group (-COOH) and a variable R group which is a carbon-containing chain.
How many types of amino acids of there?
There are 20 different amino acids, each determined by their different R groups.
How are amino acids formed?
Amino acids are joined by peptide bonds formed in condensation reactions. In this reaction a molecule of
water is formed.
What is a dipeptide?
A dipeptide contains two amino acids
What is a polypeptide?
Polypeptides contain three or more amino acids.
Describe the structure of a protein
- determined by the order and number of amino acids, bonding present and the shape of the protein:
• Primary structure of a protein is the order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will
therefore determine the protein’s function in the end.
• The secondary structure is the shape that the chain of amino acids chains – either alpha helix or beta-pleated sheet. The hydrogen in the -NH has a slight positive charge whilst 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.
• Tertiary structure of proteins is the 3D shape of the protein and is formed from further twisting and folding.
A number of different bonds maintain the structure, these are:
- Disulfide bridges - interactions between the sulfur in the R group of the amino acid cysteine are strong and not easily broken.
- Ionic bonds - form between the carboxyl and amino groups that are not involved in the peptide bond. They are easily broken by pH and are weaker than disulfide
bridges. - Hydrogen bonds - numerous and easily broken.
Proteins can be globular or fibrous.
What is a Globular protein?
Globular proteins such as enzymes are compact
What is a fibrous protein?
Long and thus can be used to form fibres. eg keratin
What test is used to find the presence of peptide bonds in a protein?
The Biuret test
How do you carry out the Biuret test?
- Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.
- Add a few drops of very dilute (0.05%) copper (II) sulfate soliton and mix gently.
- A purple colouration indicates the presence of a peptide bond and hence a protein. A negative result would mean the solution remains blue.
What are the four groups surrounding the central carbon atom in an amino acid?
- Amine group
- Carboxyl group
- Hydrogen group
- R group
The two functional groups in amino acids are:
anime group & Carboxyl group
What is the name of the structure of a protein represented by the sequence of the amino acids?
Primary structure
What bonds form between amino acids to hold the secondary structure in place?
Hydrogen bonds
The 4 Structural levels of proteins are:
Primary structure
Secondary structure
Quaternary structure
Tertiary Structure
Primary structure
Sequence of amino acids
Tertiary structure
3D structure of a polypeptide chain
Quaternary structure
The final 3D structure of a protein. This may contain multiple polypeptides
Secondary Structure
Local folding of the polypeptide chain
How many amino acids are common in all organisms
20
A sample is boiled in a test tube with ethanol. The sample is shaken and left to stand. The solution inside is then poured into a tube containing distilled water.
What would be observed if there is a lipid present in the tube
A white, milky layer
Which amino acid does not have carbon in its R group
Glycine
What molecule is released as a byproduct when the amino terminal of one amino acid reacts with the carboxyl terminal or another amino acid?
water
What colour shows a positive result in the Biuret test for protein?
Violet
What interactions are most important in protein tertiary structure?
Disulphides bridge
Ionic bonds
Protein A contains four polypeptide ma in a quaternary structure surrounding a central harm group.
What is protein A?
Haemoglobin
What is the name given to the part of the enzyme that catalysed the reaction and provides specificity?
Active site
“Increasing the temperature of an enzyme catalysed reaction will always increase the rate of reaction as there is a higher chance of a collision having the activation energy”
Is this true or false?
False
What sort of inhibitor binds to active site and has a similar structure to a normal substrate of the enzyme?
Competitive inhibitors
What causes the changes in protein structure through the three or four levels of structure?
The primary chain forms a secondary a-helix and beta-pleated sheets which fold onto each other forming the tertiary structure.
What structural level of proteins is functional? Why?
The tertiary structure is functional as it possess the geometric shape showing neccessary loops and bends
How does a chaperone work with proteins?
Chaperone assist proteins when folding
What enzyme is used to hydrolyse proteins
endopeptidases, exopeptidases and Dipeptidase
Endopeptidases
Hydrolise internal bonds
Exopeptidases
Hydrolyse bonds at the end of protein molecules.
What enzyme increases the surface area of Exopeptidse to work on?
Endopeptidases
