Proteins Flashcards
Name Globular Proteins
• Enzymes, which are biological catalysts that control biochemical reactions such as
Amylase, which catalyses the digestion of starch.
• Transport proteins such as Haemoglobin, which transports oxygen.
• Signal proteins that carry messages around the body such as insulin a hormone
involving control of glucose levels in the blood.
• Contractile proteins such as actin and myosin, which are involved in muscle
contraction.
• Defensive proteins such as antibodies which defend the body against infection.
Name Structural proteins
Structural proteins
• Keratin which is found in nails and hooves.
• Collagen which is found in tendons.
What are Proteins made up of?
Proteins are made of monomers called amino acids.
How many different types of amino acids are there?
There are about 20 different types of
amino acids, all with the same general structure.
What is known as the general structure of an amino acid?
Each amino acid contains a central carbon atom to which a nitrogen containing amine group
(H2N or N2H) and a carboxyl group (COOH) are attached. The remaining group is referred to
as the ‘R’ group and differs in different amino acids.
What do two amino acids join together by a condensation reaction form?
Two amino acids join together to form a dipeptide by a condensation reaction.
What will a peptide chain always have at each end?
A peptide chain will always have an amine group at one end and a carboxyl group at the
other end.
Name the structures of a Protein?
There are four levels of organisation of proteins – these are known as the PRIMARY
structure, the SECONDARY structure, the TERTIARY structure, and the QUATERNARY
structure.
Describe the Primary structure of a protein.
The primary structure is the number
and sequence of amino acids in a
polypeptide chain.
Proteins differ from each other
because their primary structures
are different.
Polypeptides have many (usually hundreds) of the 20 naturally occurring amino acids
joined in any sequence, therefore there is a limitless number of possible combinations
and therefore primary protein structures.
• Primary structure determines its ultimate shape and hence its function.
A change in just a single amino acid can alter its shape and may prevent it carrying out its
function.
• A proteins shape is very specific to its function.
What does a primary structure determine of a Protein?
Primary structure determines its ultimate shape and hence its function.
Describe the secondary structure of a Protein
This is the way the polypeptide chain folds or coils into alpha helixes and beta pleated-
sheets. This structure is maintained by hydrogen bonds (weak bonds) between functional groups
What bonds form between the functional groups in the secondary structure of a Protein?
This structure is maintained by hydrogen bonds (weak bonds) between functional groups.
Describe what the tertiary structure of a protein means?
The R groups on the amino acids in the polypeptide
chain determine the how the polypeptide chain folds
into its specific three dimensional shape. This shape
is held together be bonds between R groups of
different amino acids.
How is the tertiary structure of a protein maintained?
This structure is maintained by 3 different types of
bonds between R groups:
• HYDROGEN BONDS, which are weak bonds.
• IONIC BONDS, also weak bonds, which form
between oppositely charged R groups.
• DISULPHIDE BRIDGES, covalent bonds, which
form between sulphur containing R groups (amino acid cysteine)
what does the tertiary structure of a protein determine?
The tertiary structure of the protein is essential to its function. The shape of the protein
determines how it reacts with other molecules e.g. active sites in enzymes.
Why do globular proteins have a specific tertiary structure?
Globular proteins have a specific tertiary structure which gives them a specific shape which
is necessary for them to carry out their function.
what is the function of a Quaternary structure?
Some proteins consist of two or more polypeptide chains joined together. A common example
is Haemoglobin which has 4 polypeptide chains.
why is the structure and function of a protein important for its functions?
The shape of a protein is essential to its
function
• Proteins denature at high temperatures
• Increasing temperature increases the kinetic
energy of the molecules making them vibrate
breaking the weak bonds holding the structure
together
• As the bonds break the shape of the molecule
is lost – the protein is denatured.
• Denaturation can also be caused by a change in
pH which can disrupt the ionic bonds in the
tertiary structure.
What does the biuret test for proteins detect?
Peptide bonds.
Describe how to carry out the biuret test.
- Place a small amount of the extract to be tested in a labelled test tube.
- Add an equal volume of sodium hydroxide solution.
- Add a few drops of dilute copper II sulphate solution (0.05%).
- Mix gently.
what will the colour change be if a peptide bond (a protein) is present?
The colour change is blue to violet if peptide bonds i.e. a protein is present.
The colour stays blue if there is no protein present/protein is absent.
what is a Biuret reagent?
a mixture of sodium hydroxide and copper II sulphate
what is the Chromatography of amino acids used for?
This method can be used to separate amino acids within a polypeptide.
Describe the method used in the Chromotography of amino acids.
Method:
1. Draw a pencil line on the bottom of the chromatography paper as a start line.
2. Use pipette and drop several drops on same spot.
3. Allow to dry between each application.
4. Spray chromatogram with ninhydrin to visualise the amino acids.
The more soluble the amino acid the further up the chromatography paper it will travel.
Give the equation for the Rf value?
Rf= Distance travelled by compound /
Distance travelled by solvent
