Structure Of Proteins Flashcards
What are peptides
Polymers made up of amino acid molecules (the monomers)
What do proteins consist of
One or more polypeptides arranged as complex macromolecules and they have specific biological functions
What do all proteins contain
Carbon, hydrogen, oxygen and nitrogen
Amino acid structure
All amino acids have same basic structure. Different R-groups(variable groups)result in different amino acids. Twenty different amino acids are commonly found in cells. Five of these are said to be non-essential as our bodies are able to make them from other amino acids. Nine are essential and can only be obtained from what we eat. A further six are said to be conditionally essential as they are only needed by infants and growing children.
How do amino acids join
When the anime and carboxylic acid groups connected to the central carbon atoms react. The R-groups are not involved at this point. The hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid. A peptide bond is formed between the amino acids and water is produced (condensation reaction) the resulting compound is a dipeptide.
What is a polypeptide
When many amino acids are joined together by peptide bonds a polypeptide is formed. This reaction is catalysed by the enzyme peptidyl transferase present in ribosomes, the sites of protein synthesis.
The different R-groups of the amino acids making up a protein are able to interact with each other (R-group interaction) forming different types of bonds. These bonds lead to the long chains of amino acids (polypeptides) folding into complex structures (proteins). The presence of different sequences of amino acid leads to different structures with different shapes being produced. The very specific shapes of proteins are vital for the many functions proteins have within living organisms.
What is the primary structure
The SEQUENCE in which the amino acids are joined. It is directed by information carried within the DNA. The particular amino acids in the sequence will influence how the polypeptide folds to give the proteins final shape. This in turn determines its function. The only bonds involved in the primary structure of a protein are peptide bonds.
What is the secondary structure
The oxygen, hydrogen and nitrogen atoms of the basic, repeating structure of the amino acids (the variable groups are not involved at this stage) interact. Hydrogen bonds may form within the amino acid chain, pulling it into a coil shape called an alpha helix.
Polypeptide chains can also lie parallel to one another joined by hydrogen bonds, forming sheet-like structures. The pattern formed by the individual amino acids causes the structure to appear pleated, hence the name beta pleated sheet.
Secondary structure is the result of hydrogen bonds and forms at regions along long protein molecules depending on the amino sequences.
What is the tertiary structure
The folding of a protein into its final shape. It often includes sections of secondary structure. The coiling or folding of sections of proteins into their secondary structures brings R-groups of different amino acids closer together so they are close enough to interact and further folding of these sections will occur.
Interactions between R-groups in tertiary structure
-hydrophobic and hydrophilic interactions-weak interactions between polar and non-polar R-groups
-hydrogen bonds-these are the weakest of the bonds formed.
This produces a variety of complex-shaped proteins , with specialised characteristics and functions.
-ionic bonds-these are stronger than hydrogen bonds and form between oppositely charged R-groups.
-disulphide bonds(also known as disulphide bridges)-these are covalent and the strongest of the bonds but only form between R-groups that contain sulfur atoms.
Quaternary structure
This results from the association of two or more individual proteins called subunits. The interactions between the subunits are the same as in the tertiary structure except that they are between different protein molecules rather than within one molecule.
The protein subunits can be identical or different. Enzymes often consist of two identical subunits whereas insulin (a hormone) has two different subunits. Haemoglobin, a protein required for oxygen transport in the blood, has four subunits, made up of two sets of two identical subunits.
Hydrophobic and hydrophilic interactions
Proteins are assembled in the aqueous environment of the cytoplasm. So the way in which a protein folds will also depend on whether the R-groups are hydrophilic or hydrophobic. Hydrophilic groups are outside of the protein while hydrophobic groups are on the inside of the molecule shielded from the water in the cytoplasm.
Breakdown of peptides
Peptides are created by amino acids linking together in condensation reactions to form peptide bonds. Proteases are enzymes that catalyse the reverse reaction- turning peptides back into their constituent amino acids. A water molecule is used to break the peptide bond in a hydrolysis reaction, reforming the amine and carboxylic acid groups.
Buiret test
Tests for proteins- peptide bonds form violet coloured complexes with copper ions in alkaline solutions. Therefore goes violet if peptide bonds present.
