Proteins Flashcards
What are Amino Acids?
The basic monomer units which combine to make up a polymer called a polypeptide, which are then combined to form proteins.
How many amino acids occur in all living organisms and what does this provide?
20 amino acids that provide indirect evidence for evolution.
What is the amino group of an amino acid?
NH2 - a basic group form which the amino part of the name amino acid is derived.
What is the carboxyl group?
COOH - an acidic group which gives the amino acid the acid part of the name.
What is the third component of an amino acid?
H - hydrogen atom.
What is the R group of an amino acid and why is it important?
The R group can be a variety of different chemical groups. Each amino acid has a different R group, and amino acids only differ on their R group.
General Structure of an Amino Acid
H
H O ---- H
N ---- C ---- C
H O
RHow is a peptide bond formed between amino acids?
Amino Acid monomers can combine to form a dipeptide, through the removal of water in a condensation reaction.
Where does the water come from in formation of a peptide bond?
Combining an - OH form the carboxyl group of one amino acid, with an - H from the amino group of another amino acid.
What is the process known as when amino acids are joined up?
Polymerisation. Amino acid molecules are joined through a series of condensation reactions.
What is a the name of a chain of many hundred amino acids?
Polypeptide
What is the primary structure of a protein?
Basic sequence of amino acids in the polypeptide chains,
How is the sequence of amino acids determined?
by the DNA.
What determines the ultimate shape and function of a protein?
The multiple combinations of a polypeptide chain determines shape and function of a protein.
Why is it significant that a protein’s shape is significant to its function?
A change in just a single amino acid in the primary sequence can change the shape of a protein and may stop it carrying out its function.
What is the secondary structure of proteins?
Hydrogen on the - NH group of an amino acid chain has an overall positive charge, whereas the - O of the carboxyl group has an overall negative charge. These chains form weak hydrogen bonds between them.
What do the weak hydrogen bonds make the secondary structure result in?
Long polypeptide chain twists into a 3-D shape, such as the coil known as the a-helix.
What is the tertiary structure of proteins?
The chains are twisted and folded even more to give a complex and specific 3-D structure to each protein which is maintained by a number of different bonds.
What are disulphide bridges in the tertiary structure?
Fairly strong bonds that are not easily broken.
What are ionic bonds in the tertiary structure?
Formed between any carboxyl and amino group that are NOT involved in the peptide bond. They are weaker than disulphide bridges and are easily overcome by changes in pH.
What are hydrogen bonds in the tertiary structure?
Numerous but easily broken.
Why is the 3-D shape of a protein important to the function?
It makes each protein distinctive and allows it to recognise and be recognised by other molecules. It can then interact with them in a very specific way.
What is the Quaternary structure of proteins?
Large proteins forming complex molecules with numbers of different polypeptide chains linked in various ways. May also be non-protein groups present, known as prosthetic groups.
Test for Proteins : Biuret Test
- Place equal volumes of sample and sodium hydroxide solution (at room temperature) in a test tube.
- Add a few drops of very dilute (0.05%) Copper II Sulphate solution and mix gently.
- Purple colouration indicates peptide bonds. If no protein is present, solution remains blue.
