1A - Proteins Flashcards
Are proteins usually large or small molecules?
Large
What are the basic monomers of proteins?
Amino acids.
What is the polymer formed when you combine amino acids?
Polypeptide.
What is formed when you combine many polypeptides?
Proteins.
How many amino acids have been identified?
About 100.
How many naturally occurring proteins are there?
20
What does the fact that the same 20 amino acids occur in all living organisms provide indirect evidence for?
Evolution
What does every amino acid have?
A central carbon atom to which are attached four different chemical groups: Amino group (-NH2) Carboxyl group (-COOH) Hydrogen atom (-H) R (side) group
What is the amino group?
-NH2
A basic group from 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 its name.
What is the R (side) group and what is special about them?
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 do 2 amino acids combine to form?
A dipeptide.
From where is a water molecule removed in the condensation reaction of 2 amino acids?
-OH from the carboxyl group form one amino acid and -H from the amino group of another amino acid.
What bond is formed between 2 amino acids following a condensation reaction?
A peptide bond.
Through what process can many amino acids monomers be joined together?
Polymerisation.
Up to how many levels of structure can proteins have?
4
What is a chain of hundreds of amino acids called?
A polypeptide.
What is the primary structure of proteins?
The sequence of amino acids in the polypeptide chain.
What is the sequence of amino acids in the primary structure caused by?
DNA
What does the primary structure determine?
The ultimate shape and functionality of the protein.
A change in just a single amino acid in the primary sequence can lead to a change in the shape of the protein and may stop it carrying out its function.
What is the secondary structure of a protein?
The polypeptide chain doesn’t remain flat or straight. Hydrogen bonds form between the amino acids in the chain ( the + charged hydrogen of the -NH group and the - charged oxygen of the -C=O group). This causes the chain to automatically coil into alpha helix or fold into a beta pleated sheet. (3D shape).
What do the hydrogen bonds in the secondary structure of a protein cause?
Causes the chain to automatically coil into alpha helix or fold into a beta pleated sheet.
Are the hydrogen bonds in the secondary structure of proteins strong or weak?
Weak which causes the chain to twist.
What happens in the tertiary structure of proteins?
The coiled or folded chain of amino acid is often coiled and folded further giving a more complex and specific 3D structure.
More bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds.
For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.
What 3 bonds are formed in the tertiary structure?
Disulfide bridges - form whenever 2 molecules of the amino acid cysteine come close together (the sulfur atom in one cysteine bonds to the sulfur atom in the other). These bridges are fairly strong as so are not easily broken.
Ionic bonds - (attractions between negative and positive charges on different parts of the molecule). Formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They are weaker than disulfide bonds and are easily broken by changes in pH.
Hydrogen bonds - Which are numerous but easily broken.
What is the quaternary structure in proteins?
The way the polypeptide chains are assembled together as some proteins are made out of several different polypeptide chains held together by bonds.
For proteins made from more than one polypeptide chain (e.g. haemoglobin, insulin, collagen), the quaternary structure is the protein’s final 3D structure.
What is the test for proteins?
Biuret test
What does the Biuret test detect?
Peptide bonds
How is the Biuret test carried out?
- Place a sample of the solution 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) sulfate 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 is a positive result of the Biuret test?
A purple colouration.
Remaining blue indicates that no protein is present.
What are the 2 basic types of proteins?
Fibrous
Globular
What are fibrous proteins?
Such as collagen, have structural functions.
What are globular proteins?
Such as enzymes and haemoglobin, carry out metabolic functions.
What is the structure of fibrous proteins?
Form long chains which run parallel to one another. These chains are linked by cross-bridges and so form very stable molecules.
Primary - unbranched polypeptide chain.
Secondary - polypeptide chain very tightly wound. Lots of amino acid, glycine helps close packing.
Tertiary - chain is twisted into a second helix.
Quaternary - 3 such polypeptide chains wound together in the same way as individual fibres are wound together in a rope.
Where is collagen found?
In the tendons.
What are enzymes?
Globular proteins that act as catalysts lowering activation energy.
