Proteins are composed of chains of amino acids linked together by peptide bonds. There are 20 common amino acids that make up proteins. The sequence of amino acids is determined by the DNA sequence. Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Proteins serve many important functions in the body such as catalysis, muscle contraction, cytoskeleton structure, transport, cell signaling, and immunity.

1. Proteins
Proteins are larger molecules composed of one or
more chains of amino acids in a specific order
determined by the base sequence of nucleotides in
the DNA coding for the protein.
http://By,
Vigram Muneeswaran M,
180505008.

2. Properites of Proteins
Statement
1 Amino acids are linked together by condensation to form polypeptides.
2 There are 20 different amino acids in polypeptides synthesized on ribosomes.
3 Amino acids can be linked together in any sequence giving a huge range of possible
polypeptides.
4 The amino acid sequence of polypeptides is coded for by genes.
5 A protein may consist of a single polypeptide or more than one polypeptide linked together.
6 The amino acid sequence determines the three-dimensional conformation of a protein.
7 Living organisms synthesize many different proteins with a wide range of functions.
8 Rubisco, insulin, immunoglobulins, rhodopsin, collagen as examples of the wide range of protein
functions.

5. If a polypeptide contains just 7 amino acids
there can be 207 = 1,280,000,000 possible
polypeptides generated.
x
Titin is the largest known protein; its human variant
consists of 34,350 amino acids, MW of 3,906,487.6 Da.
approximately It’s empirical chemical formula is C169,719
H270,466 N45,688 O52,238.
Titin is located between the myosin thick filament.It is
a large abundant protein of striated muscle. It primary
functions are to stabilize the thick filament, prevent
overstretching of the sarcomere.

6. There are 20 common amino acids. Based on the nature of the R group, they are classified as follows ,
Amino Acids
Hydrophobic Hydrophilic
Non-polar polar
R=alkyl R=aromatic Neutral Acids Basic
Glycine Phenylalanine Tyrosine Glutamic acid Lysine
Alanine Tryptophan Serine Aspartic acid Histidine
Valine Theronine Argenine
Leucine Cysteine
Isoleucine Glutamine
Methionine Asparagine
Proline

7. 21
Amino Acids

9. Ribosomes are the molecules within
cells that facilitate the formation of
peptide bonds and hence where
polypeptides are synthesized,
peptide bond

10. A ribosome condenses two
amino acids into a dipeptide
forming a peptide bond
Example of anabolism by condensation
The bonds formed are types of covalent bonds.

11. Levels of proteins
Levels of proteins
Biochemists have distinguished four
levels of structural organization of proteins.
They are:
1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

12. (Polypeptide)
• The order / sequence of
the amino acids of which
the protein is composed
• Formed by covalent
peptide bonds between
adjacent amino acids
• Controls all subsequent
levels of structure
• The chains of amino
acids fold or turn upon
themselves
• Held together by
hydrogen bonds
between (non-
adjacent) amine (N-H)
and carboxylic (C-O)
groups
• H-bonds provide a level
of structural stability
• Fibrous proteins
• The polypeptide folds
and coils to form a
complex 3D shape
• Caused by
interactions between
R groups (H-bonds,
disulphide bridges,
ionic bonds and
hydrophilic /
hydrophobic
interactions)
• Tertiary structure
may be important for
the function (e.g.
specificity of active
site in enzymes)
• Globular proteins
• The interaction
between
multiple
polypeptides or
prosthetic
groups
• A prosthetic
group is an
inorganic
compound
involved in a
protein (e.g. the
heme group in
haemoglobin)
• Fibrous and
Globular
proteins
four levels of protein structure.

13. Fibrous proteins are found only in animals. They usually
serve as structural entities — for example, connective
tissue, tendons, and muscle fiber. They are normally
insoluble in water.
Globular proteins usually do not serve a structural
function — they act as transporters, like hemoglobin,
and are often enzymes. They are usually water-soluble
13
Fibrous proteins They usually serve as structural entities — for
example, connective tissue, tendons, and muscle fibre. They are
normally insoluble in water.
Globular proteins Usually do not serve a structural function — they
act as transporters, like haemoglobin, and are often enzymes. They are
usually water-soluble
Proteins have two major categori

14. In globular proteins the hydrophobic R groups are folded into the core
of the molecule, away from the surrounding water molecules, this makes them
soluble. In fibrous proteins the hydrophobic R groups are exposed and
therefore the molecule is insoluble.
Fibrous proteins have structural roles whereas
globular proteins are functional (active in a cell’s
metabolism).

15. Function Description Key examples
Catalysis
There are thousands of different enzymes to catalyse specific
chemical reactions within the cell or outside it.
Rubisco
Muscle contraction
Actin and myosin together cause the muscle contractions used
in locomotion and transport around the body.
Actin
Cytoskeletons
Tubulin is the subunit of microtubules that give animals cells
their shape and pull on chromosomes during mitosis.
Tublin
Tensile
strengthening
Fibrous proteins give tensile strength needed in skin, tendons,
ligaments and blood vessel walls.
collagen
Blood clotting
Plasma proteins act as clotting factors that cause blood to turn
from a liquid to a gel in wounds.
Thrombin
Transport of
nutrients and gases
Proteins in blood help transport oxygen, carbon dioxide, iron
and lipids.
Haemoglobin
Usage of proteins

16. Function Description Key examples
Cell adhesion
Membrane proteins cause adjacent animal cells to stick to each
other within tissues.
Laminin
Membrane
transport
Membrane proteins are used for facilitated diffusion and active
transport, and also for electron transport during cell respiration
and photosynthesis.
Aquaporin
Hormones
Some such as insulin, FSH and LH are proteins, but hormones
are chemically very diverse.
Insulin
Receptors
Binding sites in membranes and cytoplasm for hormones,
neurotransmitters, tastes and smells, and also receptors for light
in the eye and in plants.
rhodopsin
Packing of DNA
Histones are associated with DNA in eukaryotes and help
chromosomes to condense during mitosis.
Histone
Immunity
This is the most diverse group of proteins, as cells can make
huge numbers of different antibodies.
immunoglobulins
Biotechnologically has allowed us to use proteins in industry examples are:
• enzymes for removing stains in clothing detergent
• monoclonal antibodies for pregnancy tests
• insulin for treating diabetics
• Disease treatments
Genetically modified organisms are often used as to produce
proteins. This however is still a technically difficult and
expensive process.
Usage of proteins

17. Rhodopsin
• A pigment that absorbs light
• Membrane protein of rod cells of the retina (light sensitive region at the
back of the eye)
• Rhodopsin consists of the opsin polypeptide surrounding a retinal
prosthetic group
• retinal molecule absorbs a single photon of light -> changes shape ->
change to the opsin -> the rod cell sends a nerve impulse to the brain
• Even very low light intensities can be detected.

18. • A hormone – signals many cells (e.g. liver cells) to
absorb glucose and help reduce the glucose
concentration of the blood.
• Affected cells have receptor (proteins) on their
surface to which insulin can (reversibly) bind to.
• Secreted by β cells in the pancreas and transported
by the blood.
The pancreas of type I diabetics don’t produce
sufficient insulin therefore they must periodically inject
synthetically produced insulin to correct their blood
sugar concentration.
Insulin

19. Immunoglobulins
• Also known as antibodies.
• Two antigen binding sites - one on each ‘arm’
• Binding sites vary greatly between immunoglobulins to enable them to
respond a huge range of pathogens.
• Other parts of the immunoglobulin molecule cause a response, e.g.
acting as a marker to phagocytes (which engulf the pathogen)

20. collagen
• A number of different forms
• All are rope-like proteins made of three
polypeptides wound together.
• About a quarter of all protein in the
human body is collagen
• Forms a mesh of fibres in skin and in
blood vessel walls that resists tearing.
• Gives strength to tendons, ligaments, skin
and blood vessel walls.
• Forms part of teeth and bones, helps to
prevent cracks and fractures to bones and
teeth.

21. Rubisco
• Full name ribulose bisphosphate carboxylase
• Enzyme - catalyses the reaction that fixes carbon
dioxide from the atmosphere
• Provides the source of carbon from which all carbon
compounds, required by living organisms, are
produced.
• Found in high concentrations in leaves and algal
cells

22. Thank you for your attention
The end.