Proteins: Polymers of Amino Acids

1
Proteins Polymers of Amino Acids

• 20 different amino acids many combinations
• Proteins are made in the RIBOSOME

2
Amino Acid Chemistry
3
Amino Acid Chemistry
The free amino and carboxylic acid groups have
pKas
4
Amino Acid Chemistry
Also titratable groups in side chain
Note the axes
5
Amino Acids with Aliphatic R-Groups
pKas

6
Amino Acids with Polar R-Groups
7
Acidic Amino Acids and Amide Conjugates
8
Basic Amino Acids
9
Aromatic Amino Acids and Proline
10
Hierarchy of Protein Structure
Tertiary/Quaternary Structure
Overall structure of the chain(s) in full 3D
11
Binding Classification of Proteins

• Structural- other structural proteins
• Receptors- regulatory proteins, transmitters
• Toxins- receptors
• Transport- O2/CO2, cholesterol, metals, sugars
• Storage- metals, amino acids,
• Enzymes- substrates, inhibitors, co-factors
• Cell function- proteins, RNA, DNA, metals, ions
• Immune response- foreign matter (antigens)

12
Classification

• Essential amino acids
• There are amino acids that cannot be synthesized
  in the body.
• They must be taken in diet.
• Their deficiency affects growth , health and
  proteins synthesis.

13
(No Transcript)
14
(No Transcript)
15
Half essential amino acids

• These amino acids are synthesized in the body in
  amount enough for adults , but not for growing
  children.
• Arginine
• Histidine

16
Arginine is very popular among athletes and
bodybuilders because it is required in muscle
metabolism maintaining the nitrogen balance,
and helping with weight control since it
facilitates the increase of muscle mass, while
reducing body fat.
17
(No Transcript)
18
Non essential amino acids

• These are the rest of amino acids which are
  synthesized in the body , mostly from
  carbohydrates, in amount enough for adults and
  growing children.

19
Metabolic classification

• Ketogenic amino acids which gives both ketone
  ketones bodies. Leucine is the only ketogenic
  amino acids.

20
People with liver and kidney problems can also
benefit form L-Leucine supplementation because it
can enhance liver protein synthesis and improve
breathing ability and quality of sleep for those
with kidney disorders. Finally, L-Leucine may
lower blood sugar levels and normalize and
control insulin release and insulin function.
Because of this, diabetics may find L-Leucine a
helpful addition to their disease management
program.
21
Glucogenic and ketogenic amino acids

• Which give both ketone bodies and glucose are
• Phenylalanine
• Tyrosine
• Tryptopohan
• Lysine
• Isoleucine

22
Functions of amino acids

• Body peptides and proteins E.g plasma proteins
  , tissue proteins, enzymes etc
• Hormones Some hormones are amino acids
  derivatives. E.g thyrosine and catecholamines.
• Amines Some amino acids give corresponding
  amines by decarboxylation e.g histidine gives
  histamine which is vasodilator.

23
Cont.

• Neurotransmitters Some amino acids, glutamate
  acts as neurotransmitters.
• Detoxification Some amino acids are used
  detoxification reaction e.g glycine
• Health and growth Essential amino acids support
  growth in infants and maintain health in adults.

24
physical properties

• Solubility Soluble in water, dilute acids ,
  alkalies and ethanol.
• Optical activity Optically active because they
  contain asymetric carbon.
• Melting point High ionic forces. Tm 200C.

25
Chemical properties

• Peptide bond formation.
• Properties of R group.

26
Proteins

• Proteins are molecules having a very high
  molecular weight ,ranging from 5,000 to several
  million.
• The term protein is applied to describe molecules
  greater than 100 a.a
• Molecules contain less than 100 a.a are termed
  larger polypeptides.

27
Functions

• Enzymes all enzymes are proteins
• Transport of small molecules and ions e.g
• 1. Hemoglobin is a carrier for oxygen.
• 2. lipoproteins , are carriers of lipids.

28
Structural proteins

• Cell membrane Glycoproteins
• Skin and bones e.g collagen

29
Hormonal regulation

• Some hormones are protein in nature e.g insulin.
• Cellular receptors that recognise hormones are
  proteins.

30
Defence mechanism

• Antibodies (immunoglobulins) are proteins in
  nature.
• Keratin found in skin and tissues is proteins
  that act against mechanical and chemical injuries.

31
Cont.

• Blood clotting coagulation factor
• Storage Ferritin ,which is a storage form of
  iron.
• Control of genetic expression activator
  receptors and many regulators of genes are
  protein in nature.

32
Conformation of proteins

• Every protein in its native state has a
  3-dimensional structure.(primary, secondary, and
  tertiary),which is known as conformation .
  Conformation is essential for the function of
  each protein. Any change in conformation may lead
  to disease.

33
Primary proteins

• It is a order (arrangement) of amino acids in the
  polypeptide chain.(chains).
• Covalent bond.
• Free NH3 and CooH terminals.
• The arrangement of amino acids in each protein is
  determined by the genetic information present in
  DNA.

34
Secondary proteins

• Hydrogen bonds
• Two forms alpha and beta form.

35
a Helix
Right-hand a helix
Left-hand a helix
36
Tertiary structure

• Two types
• Fibrous which is an extended form e.g keratin
  ,collagen and elastin.
• Globular proteins which is a compact form and
  folding of polypeptide chain e.g myoglobin.

37
Quaternary structure

• Many proteins are composed of several polypeptide
  chain .Each polypeptide chain is called subunits.
• E.g insulin 2 subunits
• Lactate dehydrogenase enzyme 4 subunits
• Globin of haemoglobin4 subunits.

38
Denaturation of proteins

• Def protein denaturation mean unfolding and
  loss of secondary ,tertiary and quaternary
  structure.
• 1.denaturation does not affect primary structure
  i.e not accompained by hydrolysis of peptide
  bonds.
• 2. denaturation may be reversible( in rare cases)

39
Effect of protein denaturation

• Loss of biological activity insulin looses its
  activity after denaturaion.
• Denaturation proteins are often insoluble.
• Denaturation protein are easily precipitated.

40
Denaturation factor

• Heat
• Organic solvents
• Detergent
• Mechanical mixing
• Strong acids and bases
• Heavy metals.
• Enzymes
• Repeated freezing and thawing

41
Classification of proteins

• Simple proteins On hydrolysis they give only
  amino acids.
• Conjugated proteins give amino acids and non
  proteins (prosthetic group).
• Derived proteins
• 1. primary derived proteins denatured protein
• 2.secondary derived proteins product of
  hydrolysis of simple and conjugated proteins.

42
Simple proteins

• Albumin and globulin
• Scleroproteins include keratin ,collagen
  ,elastin,reticulin.

43
Alpha keratin

• Found in hair ,nail , enamel of teeth ,and outer
  layer of skin.
• Rich in cysteine
• Insoluble due to high content of hydrophobic
  amino acids

44
collagen

• Present in skin ,bones , tendons, and blood
  vessels.
• Collagen may be present as a gel e.g in
  extracellular matrix or in vitreous humor of the
  eye.

45
collagen diseases

• Scurvy it is due to deficiency in a ascorbic
  acids (vitamin c).
• Ascorbic acids acts as coenzyme in hydroxylation
  reaction of proline and lysine.
• Symptoms abnormal bone development ,bleeding ,
  loosing of teeth and swollen gums.

46
Cont.

• Osteogenesis imperfecta
• 1. It is a genetic disorders lead to weak bones
  and skeletal deformities.
• 2. It is due to mutation in the gene that code
  for a chain for collagen.
• Ehlers-Danlos syndrome
• Genetic disorder lead to connective tissues
  disease
• Symptoms stretchy skin and loosed joints.

47
Elastin

• It is a connective tissue proteins.
• Rubber like, stretched several times
• Present in lungs , the walls of large blood
  vessels and elastic ligaments.

48
Conjugated proteins

• On hydrolysis ,they give protein part
  (apoproteins) and nonproteins part(prosthetic
  group)

49
phosphoproteins

• These are protein conjugated with phosphate
  group.
• Phosphate group is attached to OH group of
  serine (phosphoserine) or threonine(phosphothreoni
  ne) present in protein part. E.g
• Caseine one of the milk protein
• Vitellin present in egg yolk.
• Phosphoenzyme phoephorylation and
  dephosphorylation.

50
lippoproteins

• These are proteins conjugated with lipids
• Plasma proteins and cell membrane.
• Helps water insoluble lipids to transport in
  blood
• Helps water insoluble substance to pass through
  cell membrane .

51
Glycoproteins and proteoglycans

• These are proteins conjugated with carbohydrates
  in varying amount .i.e 2 to 15 sugar units.e.g
  blood group, enzyme and mucin
• Proteoglycans contain long unbranched chains of
  sugar units more than 50 units. E.g cell membrane

52
nucleoproteins

• These are proteins conjugated with nucleic acid
  (DNA or RNA ).
• 1. chromosomes proteins conjugated with DNA .
• 2. Ribosomes proteins conjugated with RNA.

53
Metalloproteins

• Proteins conjugated with metals
• Mettaloproteins containing iron The iron may be
  in the form of heme or nonheme iron.
• Ferritin is the storage form of iron ,present
  in liver ,spleen, bone marrow and intestinal
  cells.
• Transferrin. Is the iron carrier protein in the
  plasma.
• Hemosiderin iron toxicity (over dosage) as in
  case of repeated blood transfusion.