Proteins - 1.6 Flashcards
What are amino acids?
The basic monomer units which combine to make up a polymer called a polypeptide.
What can polypeptides be combined to form?
Proteins
What evidence do amino acids provide for evolution?
The fact that the same 20 amino acids occur naturally in all living organisms provide indirect evidence for evolution.
What is the central atom of every amino acids?
Carbon
What four chemical groups attach to the central carbon atom of an amino acid?
- Amino group (-NH2)
- Carboxyl group (-COOH)
- Hydrogen atom (-H)
- R (side) group
What is the amino group of an amino acid?
A basic group from which the amino part of the name amino acid is derived.
What is the carboxyl group of an amino acid?
An acidic group which gives the amino acid the acid part of its name.
What is the R (side) group of an amino acid?
A variety of different chemical groups. Each amino acid has a different R group. These 20 naturally occurring amino acids differ only in their R (side) group.
What can two amino acids combine to form?
A dipeptide.
In what reaction are dipeptides and polypeptides formed?
Condensation reaction.
How is the water produced in the condensation reaction of two amino acids?
By combining an -OH group from the carboxyl group of one amino acid with an -H from the amino group of another amino acid.
What bond is formed when two amino acids are joined?
Peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.
How can a peptide bond be broken?
Hydrolysis.
In what process are many amino acid monomers joined together?
Polymerisation.
What is a chain of hundreds of amino acids called?
Polypeptide.
What does the sequence of amino acids in a polypeptide form?
The primary structure of any protein.
How is the primary structure of a protein (amino acid sequence) determined?
By DNA
Why is there an almost limitless of number of possible types of primary protein structure?
Polypeptides have many (usually hundreds) of the 20 naturally occurring amino acids joined in different sequences, so it follows that there is an almost limitless number of possible combinations, and therefore types, of primary protein structure.
What does the primary structure of a protein determine?
The proteins shape and hence its function.
What can a change in a single amino acid in a proteins primary structure lead to?
A change in the shape of the protein, so it may stop carrying out its function.
What is the secondary structure of a protein?
when hydrogen bonds cause the long polypeptide chain to be twisted into 3D shape, such as alpha-helix or Beta pleated sheets.
How are the hydrogen bonds formed in the secondary structure of a protein?
The linked amino acids that make up a polypeptide possess both -NH and -C=O groups on either side of every peptide bond. The hydrogen of the -NH group has an overall positive charge while the O of the -C=O group has an overall negative charge. These two groups therefore readily form weak bonds, called hydrogen bonds.
What is the tertiary structure of proteins?
The alpha-helices of the secondary protein structure can be twisted and folded even more to give the complex, and often specific, 3D structure of each protein.
How its the tertiary structure of a protein maintained?
By a number of bonds, such as disulphide bridges, ionic bonds and hydrogen bonds.
What bonds are important in the tertiary structure of a protein?
- Disulphide bridges - which are fairly strong and therefore not easily broken.
- Ionic bonds - Which are formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They are weaker than disulphide bond and are easily broken by changes in pH.
- Hydrogen bonds - which are numerous but easily broken.
Why is the 3D structure of a protein important?
It is important when it comes to how it functions. It makes each protein distinctive and allows it to recognise, and be recognised by, other molecules. It can interact with them in a very specific way.
What is the quaternary structure of a protein?
When large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. There may also be non-protein (prosthetic) groups associated with the molecules, such as the iron-containing haem group in haemoglobin.
What is the test for proteins called?
The Biuret test
What does the Biuret test detect?
Peptide bonds
How is the Biuret test conducted?
- Place a sample of the sodium 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 (0.05%) copper (II) sulphate 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.
What are the two basic types of molecular shapes of proteins?
- Fibrous proteins, such as collagen.
- Globular proteins, such as enzyme and haemoglobin.
What function do fibrous proteins have?
Structural functions.
What function do globular proteins have?
Metabolic functions.
What is the molecular structure of fibrous proteins?
Primary - unbranched polypeptide chains.
Secondary - the polypeptide chain is very tightly wound. Lots of the amino acid glycine helps close packing.
Tertiary - The chain is twisted into a second helix.
Quaternary - made up of three such polypeptide chains wound together in the same way as individual fibre are wound together in a rope.
Where is collagen found?
In tendons, which join muscles to bones. When a muscle contracts, the bone is pulled in the direction of the contraction.
How are individual collagen polypeptide chains in the fibres held together?
By bonds between amino acids of adjacent chains.
The points where one collagen molecules ends and the next begins are spread throughout the fibre rather than all being in the same position along it.
