Download - As 2 1 1 Protein Structure
-
8/10/2019 As 2 1 1 Protein Structure
1/12
Proteins from Amino Acids
Two amino acids joined together make a
dipeptide, as more and more join together by
peptide bonds, a polypeptide is formed
The amino acids in a polypeptide chain are
sometimes referred to as residues because
part of the molecule is lost in the
condensation reaction that produces the
peptide bond
-
8/10/2019 As 2 1 1 Protein Structure
2/12
Protein Synthesis
Polypeptides are made (synthesised)
inside cells on the ribosomes.
Messenger RNA (mRNA) puts the amino
acids in the right order to make a specific
polypeptide chain
-
8/10/2019 As 2 1 1 Protein Structure
3/12
Protein Synthesis
As the mRNA passesthrough the ribosome,the amino acids arejoined one at a time by a
condensation reactionforming a peptide bond
Eventually a longer andlonger chain of aminoacids is formed
The mRNA determinesthe sequence of aminoacids and therefore thetype of protein
-
8/10/2019 As 2 1 1 Protein Structure
4/12
-
8/10/2019 As 2 1 1 Protein Structure
5/12
Forming Different Proteins
We will look at a peptide chain that is 3amino acids long.
The R group of an amino acid may be any
one of the 20 available.
To calculate the total number of different
possibilities, we need to multiply the totalnumber of possibilities at each point.
In this case: 20 x 20 x 20 = 8000
This means that 8000 different sequences
of four amino acids are possible- 8000
different proteins can be made.
Given that most proteins are 100 amino
acids long, in theory the number of different
possible proteins is extremely large
-
8/10/2019 As 2 1 1 Protein Structure
6/12
Protein Structure Task
We can look at proteinsin various levels ofdetail. The first is theirprimary structure, this isfollowed by the
secondary, tertiary andquaternary structures
Task: Using CambridgeBiology p110- 113, anda two page spread in
your book, summarisethe 4 levels of proteinstructure (including thebonding involved)
-
8/10/2019 As 2 1 1 Protein Structure
7/12
Primary Structure
The sequence of amino acids that formsthe protein
-
8/10/2019 As 2 1 1 Protein Structure
8/12
Secondary Structure
The chain of amino
acids coils or folds to
form an alpha helix or
a beta pleated sheet Hydrogen bonds hold
the coils in place
weakly, but as so
many are formedthey give stability to
the protein molecule
-
8/10/2019 As 2 1 1 Protein Structure
9/12
Tertiary Structure
When the coils and pleats themselves coil or fold
Held together by:
Disulphide bonds: a covalent bond between 2 sulphuratoms
Ionic bonds: the R groups are sometimes charged (+veor ve) so they attract each other
Hydrogen bonds: +ve hydrogen atoms and ve oxygenatoms attract
Hydrophobic and hydrophilic interactions: hydrophobicamino acids will be drawn into the centre of themolecule, and hydrophilic amino acids will be found onthe outside.
-
8/10/2019 As 2 1 1 Protein Structure
10/12
-
8/10/2019 As 2 1 1 Protein Structure
11/12
-
8/10/2019 As 2 1 1 Protein Structure
12/12
Heating Proteins
Heating a protein increases the kinetic
energy in the molecule
This causes the molecule to vibrate,
breaking the bonds