Proteins Building blocks, structure and function
Proteins
Building blocks, structure and function
Learning outcomes• The basic structure of an amino acid
(structure of specific amino acids is not required).
• The formation of polypeptides and proteins (as amino acid monomers linked by peptide bonds in condensation reactions)
• The significance of the proteins primary structure in determining its 3-d structure and properties (globular and fibrous proteins and types of bond involved in 3-d structure)
Homework – learning objectives
• Compare and contrast the structures and functions of globular and fibrous proteins. Use examples of different types of proteins to illustrate your answer.
• Minimum 500 words
• Reference your work. Include at least three different references, at least one must be a book or journal.
ProteinsChemical nature• Contain the elements C, H, O, N (S, P sometimes)
• Monomer: Amino Acid• They all have the same basic structure• Apart from a variable group ‘R’ JOBS of Proteins• Structural components• Membrane carriers• Enzymes• Hormones• Antibodies
Enzymes – amylase, sucrase, pectinase Hormones – insulin, glucagon Oxygen transporters - haemoglobin Cell membrane transport – sodium channels Cell surface receptors – beta receptors Structural – hair, skin Cytoskeleton – spindle fibres cell division Antibodies - immunoglobulins Pigments - melanin
1000s different proteins different functions
All proteins are made from amino acids
Acid or carboxyl group Amino Group
The simplest Amino Acid
Joining amino acids togehter
2 amino acids molecules bond together
via a
condensation reaction
to form
a peptide bond
to make
a dipeptide
A Condensation Reaction
© Pearson Education Ltd 2008This document may have been altered from the original
The same condensation reaction occurs over and over again to join many amino
acids together to make a polypeptide
Breaking a peptide bond - Hydrolysis
Proteins from amino acids – Protein Synthesis
• Site of manufacture: Ribosome
• Uses m-RNA to put amino acids in the right order
• A specific polypeptide is made
PRIMARY Structure
The sequence of an amino acids linked together in a polypeptide chain
val
lys
phe
gly ar
g
cys
val
gly
PRIMARY STRUCTURE sequence of amino acids in the
polypeptide chain
Held together by STRONG peptide bonds
Definition of secondary structure
• A regular repeating pattern of shape in a polypeptide chain, for example an alpha- helix or beta pleated sheet
SECONDARY STRUCTUREPolypeptide chain folds forming
α-HELIX or β-SHEETStructure held by HYDROGEN
BONDS
α-HELIX
β-SHEET
Hydrogen bonds
Polypeptide Chain
β-SHEETα-HELIX
How is the shape maintained?
• By hydrogen bonds between different amino acids in chain.
• Although weak there are many of them
• So great stability given
Tertiary Structure
• The overall 3-D shape of a protein molecule.
What holds the shape in place?
..Different types of bond and interaction.
• Disulphide bridges• Ionic bonds• Hydrogen bonds• Hydophobic and
hydrophillic interactions
What is the role of the tertiary structure?
Vital to the protein’s function
• Many molecules must have a specific shape in order to do a job:
• Examples –
hormones to fit into the receptor site on a membrane
an enzymes’s active site must have a complementary shape to its substrate
Types of ProteinThe 3-D shape of proteins fall into two main
categories
• Globular – e.g. haemoglobin
compact and globe shaped
water soluble
• Fibrous- e.g. collagen
regular repeating sequences, fibres, insoluble
P103 OCR text book has a good table
What happens when there is a change of a single amino acid in
the sequence its primary structure?
The places in which the different types of bonds can form are determined by the amino acid sequence.
Change this and there is a change on the tertiary structure – its 3-D shape
And therefore the proteins ability to carry out is function
Quaternary Structure
• Where protein structure consists of more than one polypeptide chain – the overall 3-D structure of the molecule.
Haemoglobin• Job – to transport oxygen around body
• Globular protein
• Soluble in water
• Wide range of amino acids in primary structure
• Contains prosthetic group (a non-protein part) called haem
• Much of moleclue would into an alpha-helix
Collagen• Job – provide mechanical strength
arteries, bones tendons and cartilage
• Fibrous protein
• Insoluble
• 35% of amino acids are glycine
• No prosthetic group
Collagen