1. Protein Shape & Function
DNA and the Genome
Key Area 3e
Protein Shape & Function

2. Protein shape and structure
Learning Intentions
Protein shape and structure
Describe the overall shape of protein molecules
Describe what can happen to polypeptide chains as they are transformed into protein
Identify the position and function of peptide bonds and hydrogen bonds in protein
Explain how proteins determine the phenotype

3. Protein Structure and Function

4. Protein Structure

5. Amino Acids
All proteins are made up of Carbon (C), Hydrogen (H), Oxygen (O) and Nitrogen (N) arranged into amino acids which are the structural building blocks (monomers) of proteins
There are twenty different kinds of amino acids used to make up proteins.
Amino acids are characterized by a central carbon with 4 bonds coming off of it:
a amino group (NH2)
a carboxylic group (COOH)
a hydrogen
a characteristic side chain (R Group) that gives the amino acid its unique properties

6. Basic Amino Acid Structure

7. Peptide Bonds
Amino acids are linked together by peptide bonds during a condensation (dehydration) reaction to form polypeptides.
These bonds are very strong and link the carboxylic group of one amino acid to amino group the of the next amino acid
Water is produced as a result of this reaction

8. Peptide bonding H C N O R H C N O R
Carboxylic group
Amino group

9. Peptide bonding H C N O R H C N O R
Carboxylic group
Amino group

10. Peptide bonding R R O O H H N C C N C C H O H H H H H O

11. Peptide bonding C H N O R
water
Peptide bond
A condensation reaction

12. Protein Structures
As you know, the shape of a protein is essential for its function.
Polypeptide chains fold to form the three-dimensional shape of a protein. This shape is held together by hydrogen bonds and other interactions between individual amino acids
Primary Structure sequence of amino acids
Secondary Structure α-helix and β-pleated sheets
Tertiary Structure bonds between R groups

13. Primary Structure
The primary structure of a protein is determined by the sequence of bases on the DNA. This determines the sequence of bases on the mRNA which then determines the amino acid sequence
The sequence of amino acids is referred to as the proteins primary structure and the amino acid chain is a polypeptide

14. Secondary Structure
Hydrogen bonds form between the carboxylic (–COOH) and the amino group (-NH2) of adjacent amino acids
This results in the chains folding into 2 types of structure:
α-helix
β-pleated sheet

15. α-helix
This is the more common secondary structure where the polypeptide chain is twisted into a helix shape
Weak hydrogen bonds form between the carboxyl group of one amino acid on with the amino group of the amino acid 4 residues away. This causes the polypeptide chain to twist into a helix
One example of this is keratin

16. β-pleated sheet
This secondary structure is not as common as α-helix and is a result of hydrogen bonds forming between carboxyl and amino groups in different regions of the polypeptide.
When chains of polypeptides lie adjacent to one another, β sheets form between the chains forming a flat sheet.
These sheets are very strong and form the likes of silk

17. Tertiary Structure
The tertiary folding of a polypeptide can result from several types of bonding between R groups and gives the protein its final 3D shape:

18. Functional variety of proteins

19. 3 Types of Protein
Proteins have a large variety of shapes which determine their function:
Fibrous Proteins
Globular Proteins
Conjugated Proteins

20. 7 Uses of Proteins Structural – eg. tendons, cartilage, hair, nails
Contractile – eg. Muscles
3. Transport – eg. haemoglobin, myoglobin
4. Storage – eg. milk, nuts, seeds
Hormonal - eg. Growth hormone, insulin
6. Enzymes - eg. catalyze reactions in cells
7. Protection – eg. antibodies used in immune response

21. Fibrous Proteins
Several spiral shaped polypeptide molecules linked together in parallel, which creates a strong, rope-like regular structure.
Some examples are:
Elastin – provides flexible support in the wall of large arteries
Collagen – structural/support, found in bones, tendons & ligaments
Keratin – strong, inelastic, provides protection in hair
Actin & Mysosin – allow contractile movement in muscles

22. Globular Proteins
Globular proteins are vital parts of all living cells.
Globular proteins are made of several polypeptide chains folded together roughly into a spherical shape like a tangled ball of string.
Globular protein have several vital roles:
Enzymes
Structural protein
Hormones
Antibodies

23. Globular Proteins: Enzymes
Enzymes are essential for life as they control many biochemical processes
All enzymes are made of globular proteins. The particular folding that occurs within an enzyme, leaves a very specific active site shape exposed which can then combine with its specific substrate.
Image source: scholar.hw.ac.uk

24. Globular Proteins: Structural
Globular protein is one of the two components of cell membranes. It is also an essential part of intercellular membranes such as the nuclear membrane.
Phospholipid bilayer
Proteins
Image source:

25. Globular Proteins: Hormones
Hormones are chemical messengers carried in the blood. Some hormones are made of globular proteins and regulate an animals growth and metabolism.
Insulin is a hormone, produced in the pancreas, that converts glucose to glycogen. Diabetics are unable to produce enough insulin and many inject insulin to control their blood sugar levels.
Image source:

26. Globular Proteins: Antibodies
Image source:
Antibodies are also globular proteins, but are Y-shaped instead of spherical.
Antibodies are made by lymphocytes (a type of white blood cell) and specific antibodies defend the body against specific antigens.

27. Conjugated Proteins
Conjugated proteins are made of a globular protein with a non-protein chemical.
Glycoproteins – protein with a carbohydrate attached e.g. mucus
Haemoglobin – the oxygen transporting pigment in blood. It contains the globular protein globin and haem, a non-protein part containing iron. It associates and dissociates from oxygen depending on its environment
Cytochrome – a conjugated protein containing iron, part of the aerobic respiratory pathway.

28. Environmental Effect
The phenotype of an organism is determined by the proteins produced as a result of gene expression. However, environmental factors can also influence the phenotype of an organism… Effect of climate (sunlight, Uv exposure, chance to exercise) Diet Access to quality food/hygene…