Proteins Flashcards
(15 cards)
Describe proteins
All contain C, H, O, N. And some very strong ones contain sulphur
They’re often large molecules and the principal material in skin, muscles, tendons, hair, blood, nerves, enzymes, antibodies and hormones
They’re chemical polypeptides made up of chains of amino acid monomer units
Describe amino acids
Contain an amine group, carboxylate group, and a carbon-containing variable side chain.
There’s 20 commonly occurring amino acids but animals don’t synthesise all of them so some must be consumed (essential amino acids).
They’re small soluble molecules which can ionize and a mixture of different amino acids can be separated by electrophoresis/chromatography.
In chromatography amino acids have different densities and in electrophoresis they have different densities and charges
What is electrophoresis
Separation of charged molecules by migration through a matrix due to application of an electric field, with net movement towards electrodes of opposite charge. The rate of movement depends on the field strength and number of charges. Biomolecules such as proteins process surface charge due to the presence of acidic and basic amino acids.
Describe dipeptide formation
2 amino acids join in a condensation reaction to form a dipeptide and releasing water, and forming a peptide bond. The dipeptide will be hydrolysed by adding water across the peptide bond to produce 2 amino acids.
A H atom from the amine group of one amino acids joins with the OH from the carboxyl group of a second amino acid to produce H2O which is released forming a peptide bond
Describe polypeptides
-many amino acids join in condensation reactions to form polypeptides
-the 2 ends will always be different (either a N-terminal or a C-terminal)
-a functional protein may contain one or more polypeptide chains
- several polypeptides coil together to form a protein and sometimes contain non-amino acid molecules called prosthetic groups
Describe the shape of polypeptides
- the chains of amino acids that make up polypeptides often take up a specific 3 dimensional shape which is important in the functioning of the protein
- the 3D shape is due to 3 types of intramolecular bond and 1 type of interactive force:
->disulphide bonds
->ionic bonds
-> H bonds
As well as hydrophobic and hydrophilic interactions.
Describe disulphide bonds
Occur between sulphur containing groups in amino acids, they are very strong covalent bonds
Describe ionic bonds
Free amino and carboxylic acid groups can ionize and then opposite electrostatic charges attract
Describe H bonds
Occur between the amine and COOH groups with unequal sharing of electrons, the O2 pulls e- in a covalent bond so its slightly negatively charged and as H atoms lose, they’re positive. The H bond is the electrostatic attraction between these partial charges - its a weak bond
Describe the primary structure of proteins
-the sequence/order of amino acids in the polypeptide chain.
-this determines its shape and so function
-a slight change in primary structure e.g. substitution of a base caused by mutation in DNA can lead to a protein with different properties
Describe the secondary structure of proteins
-describes the coiling of the polypeptide chain with H bonds alone between these partial charges amine of one and carboxyl of another.
-these form either an a-helix or b-pleated sheet.0
Describe the Tertiary structure of proteins
-describes the shape of the polypeptide chain with H, ionic and disulphide bonds between the R groups
-its often the 3D shape of the protein that is so important in how it functions e.g. enzymes complementary to the shape of a specific substrate
Describe the quaternary structure of a protein
-describes the shape of the molecule when more than one polypeptide chains are wound around each other
-often there may be a non-amino acid part called a prosthetic group e.g. haemoglobin has a quaternary structure and is made up of 4 polypeptide chains wound around each other with 4 haem groups called iron.
-proteins with prosthetic groups are called complex and those without are simple
Describe the test for proeins
-add biuret reagent / copper sulphate and sodium hydroxide
-purple = positive
-blue = negative
How is the structure of proteins linked to their function
The roles of proteins depends on their molecular shape, there are 2 main ones:
- Fibrous
-collagen and keratin
-structural function
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