What elements are proteins made of?
Carbon, hydrogen, oxygen, nitrogen and sometimes sulfur
Draw the structure of an amino acid
Go on, do it (amine group, carboxyl group and R group)
How many different R groups are there?
20
How many main amino acids are there?
20
Peptide bonds form between which groups in polypeptides?
Carboxyl and amine
What type of reaction causes polypeptides to form?
Condensation
Which two atoms does the peptide bond form between?
OH and H
What type of molecule is produced when peptide bonds are formed?
Dipeptides or polypeptides
What is released in a condensation reaction?
Water
Primary structure
- The sequence and number of amino acids in a polypeptide chain
- Determines its ultimate shape and hence its function
- A change in one amino acid can lead to a change in shape, prohibiting function
- A functional protein may consist of one polypeptide chain, but more likely multiple chains
Secondary structure
- LInked amino acids that make up a polypeptide possess both amine and carboxyl grops on either side of the peptide bond.
- The H of the NH2 is overall positive charge
- O of C=O has overall negative charge
- ALlowing for hydrogen bonding
3D shapes of a secondary structure
- Alpha helices or beta pleated sheets
- Proteins can have both in their structure
- Alpha helices is most common
Tertiary structure
Alpha helices can be further folded for a complex and often specific 3D structure of the protein.
This is maintained by multiple types of bonds, including
- Hydrogen
- Ionic
- Disulphide bridges
Between R groups
Makes a protein distinctive, allowing it to recognise/be recognised by other molecules
Disulphide bonds
The strongest of the three
Hydrogen
The most easily broken of the three
Ionic
The most extremely vulnerable to changes in pH
Quaternary Structure
Several different polupeptide chains, held together by bonds similar to those found in the tertiary structure.
Proteins made form more than one polypeptide chain have quaternary structure.
Haemoglobin
Compact, spherical, folded
4 polypeptide chains
Iron heme prosthetic (non protein) group
Carries oxygen around the body
Fibrous Proteins
Have structural functions
(eg collagen)
Globular Proteins
Have metabolic functions
(eg enzymes and haemoglobin)
Collagen Function
- Most abundant protein in the body
- Holds the whole body together, found in bones, muscles, skin and tendons (which join muscles to bones)
- When a muscle contracts, the bone is pulled in the direction of the contraction
Collagen Structure
- 3 polypeptide chains
- Triple helix
- Glycine, prolin and hydroxyprolin (and 1000 other amino acids)
- Positioned into fibrils#- Check booklet for primary-quaternary structure)
Biuret Test
- For proteins
- Blue–>purple positive result
- Sodium hydroxide and copper (II) sulfate solution
