Biological molecules: Proteins Flashcards
What is the general structure of a protein?
Check biology album in photos
What is the monomer of a polypeptide?
amino acids
What do polypeptides combine to form?
Proteins
How many amino acids can occur in proteins?
20
How many different R groups can be used to make an amino acid?
20
What do 2 amino acid monomers combine to form?
What reaction is this?
Form a dipeptide in a condensation reaction
Describe how the condensation reaction occurs when two amino acids form a dipeptide
The carboxyl group (COOH) of one amino acid joins to an H from another and forms water. The two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other
What is polymerisation?
The process that joins many amino acid monomers through a series of condensation reactions
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide chain
What does the primary structure of a protein determine?
It’s shape and hence its function
What is the secondary structure of a protein?
The folding of the polypeptide chain due to hydrogen bonding
What are the 2 types of secondary structure?
Alpha helix and beta pleated sheet
How is a polypeptide chain able to fold into an alpha helix structure?
As the H of the NH group has an overall positive charge and while the O of the -C=O group has an overall negative charge and so the two groups readily form hydrogen bonds (these are weak), allowing the chain to be folded into the alpha helix shape
What is the tertiary structure of a protein?
Where the alpha helixes of the secondary structure twist and fold even more to give the more complex 3D structure of each protein
What are the bonds that maintain the tertiary structure and comment on their strength and how they form
- disulfide bridges = fairly strong bonds and so not easily broken, form between the R groups that contain sulphur
- ionic bonds = These are weaker than disulfide bonds and are easily broken by changes in pH. Form between positive and negatively charged R groups
- hydrogen bonds = numerous but easily broken, form between polar R groups through any delta minus or delta plus between hydrogen and oxygen
Why is the 3D shape of a protein important?
As it makes each protein distinctive and allows it to recognise and be recognised by other molecules and it can then interact with them in a very specific way
What is the quaternary structure of proteins?
Where more than one polypeptide chain is associated together, which are held by the same bonds as those in the tertiary structure.
What could a quaternary structure protein associate with that the structures do not? Give an example.
Prosthetic groups ( not protein groups) like the iron containing haem group in haemoglobin
How do you test for proteins? Describe how you carry it out
The biuret test as it detects peptide bonds:
- 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 coloration indicates the presence of peptide bonds and hence a protein. The solution remains blue is no protein is present
What is a fibrous protein?
A protein that is made up of long chains that run parallel to each other and are linked by strong and stable cross bridges. Fiborous proteins are insoluble and have structural functions
What is a globular protein?
A spherical, ball shaped protein that has a compact structure, is soluble and carries out metabolic functions
Give an example of a fiborous protein
Collagen found in the skin cartilage and bones
Give an example of a globular protein
Haemoglobin which transports oxygen in the red blood cells
Give 4 features of collagen’s structure
- it’s a tightly wound wound polypeptide chain that forms a secondary structure
- each chain is further linked to a second helix
- it consists of three chains wound together like a rope giving it a quaternary structure
- the cross links between adjacent chains stabilise and give strength
