Biochemistry:
Proteins
STUDY WELL!
Definition: PROTEINS
§
General definition: are naturally occurring,
unbranched polymer in which the monomer units
are amino acids.
§ Structural definition: Is a peptide in which at least
40 amino acid residues are present.
Examples of
PROTEINS
Ø
Ø
Ø
Ø
Ø
HORMONES = messengers
ENZYMES = speed up reactions
CELL RECEPTORS = “antinnae”
ANTIBODIES = fight foreign invaders
MEMBRANE CHANNELS = allowing specific molecules to
enter or
leave a cell
QUESTION
What are the fundamental
components that make up
proteins?
AMINO ACID: the building block of proteins
• -amino acid- is an
amino acid in which the
amino group and the
carboxyl group are
attached to the -carbon
atom.
• Except: Proline
• has a structural feature
not found in any other
standard amino acid.
• side chain- propyl
group is bonded to
both the a-carbon
atom and the amino
nitrogen atom,giving a
cyclic side chain
CLASSIFICATION OF AMINO
ACIDS ACCORDING TO SIDE
CHAIN POLARITY
CLASSIFICATION OF
AMINO ACIDS
Nonpolar amino acid
• is an amino acid that contains one amino group, one carboxyl group, and a nonpolar side
chain. G,A,V,L,I,P,F,M,W
Polar neutral
• is an amino acid that contains one amino group, one carboxyl group, and a side chain that is
polar but neutral. S,C,N,T,Q,Y
Polar basic
• is an amino acid that contains two amino groups and one carboxyl group, the second amino
group being part of the side chain. H,K,R
Polar acidic
• is an amino acid that contains one amino group and two carboxyl groups, the second carboxyl
group being part of the side chain. D,E
NAMING AMINO
ACIDS
GIV-LAPMWF
CNS-TQY
NON POLAR AMINO ACID
POLAR NEUTRAL
HKR
POLAR BASIC
DE
POLAR ACIDIC
CLASSIFICATION OF AMINO
ACIDS :
AMINO
ACIDS
(9)
HYDROPHOBIC SIDE CHAIN
FUNCTIONAL GROUP
G
H group
A
Aliphatic R group (methyl)
V
Aliphatic R group (isopropyl)
I
Aliphatic R group
(isobutyl group)
L
P
Aliphatic R group (additional
methylene group)
Aliphatic R group (propyl)
F
Aromatic Ring (Phenyl group/
alanine w/ phenyl substituent on
the - carbon)
M
Sulfur group (thioether)
W
Aromatic Ring (indole ring -5
membered nitrogen ring fused w/
benzene ring)
CLASSIFICATION OF AMINO
ACIDS :
AMIN
O
ACIDS
(6)
Uncharged, Non-Ionic Side
Chains
C
due to SH or Thiol group
S
T
N
Q
Y
FUNCTIONAL GROUP
due to OH group
(Hydroxyl group)
due to OH group
(Hydroxyl group)
due to Amide groups
(amide w/ one methylene/
amide of aspartic acid)
due to Amide groups
(amide w/ 2 methylene)
due to OH group
(Aromatic Hydroxyl group)
CLASSIFICATION OF AMINO
ACIDS :
AMIN
O
ACIDS
(3)
Positively charged
K
(-amino group/ butyl
amine/ alanine w/
propylamine substituent
on the -carbon)
H
R
FUNCTIONAL GROUP
(imidazole ring/ 5
membered heterocyclic
ring)
(guanidino group)
CLASSIFICATION OF AMINO
ACIDS :
AMINO
ACIDS
(2)
Negatively charged
D
(4C atom/ one methylene)
E
FUNCTIONAL GROUP
5C atom/ two methylene)
IDENTIFY THE AMINO
ACID:
I
IDENTIFY THE AMINO
ACID:
T
IDENTIFY THE AMINO
ACID:
D
IDENTIFY THE AMINO
ACID:
W
IDENTIFY THE AMINO
ACID:
F
Classification of
amino acids
ESSENTIAL AMINO ACIDS
▹ is a standard amino acid needed
for protein synthesis that must be
obtained from dietary sources
because the human body cannot
synthesize it in adequate amounts
from other substances.
▹ R*,H,M,I,L,K,W,T,F,V
NON-ESSENTIAL AMINO
ACIDS
▹ Synthesized
by the body
▹ C,A,N,D,E,Y,S,
Q,G,P,
USES, FUNCTIONS AND
DEFICIENCY OF PROTEINS
KWASHIORKOR
MARASMUS
Inability to grow or gain
weight
Weight loss
Edema or swelling of
the hands and feet
Dehydration
Stomach bulging
Stomach shrinkage
occurs in people who
have a severe protein
deficiency. Children who
develop kwashiorkor are
often older than
children who develop
marasmus.
occurs more often in
young children and
babies. It leads to
dehydration and weight
loss. Starvation is a
form of this disorder
USES, FUNCTIONS AND
DEFICIENCY OF AMINO ACIDS
AMINO
ACIDS
USES/ FUNCTIONS
DEFICIENCY
Trp
§ Necessary for the synthesis of neurotransmitter serotonin (5hydroxytryptamine). A natural relaxant, helps alleviate insomnia by
inducing normal sleep; reduces anxiety and depression.
§ Can be metabolized to niacin if needed
§ Used to synthesized melatonin (5-methoxy-N-acetyltryptamine)
Pellagra,
Tyr
§ Precursor of dopamine, norepinephrine, epinephrine
§ Promotes healthy thyroid functioning
Hypothyroidism
Val,
I l e ,
Leu
§ enhance energy, increase endurance, and aid in muscle tissue recovery and
repair.
§ lowers elevated blood sugar levels and increases growth hormone
production.
MSUD (maple
syrup urine
disease)
Lys
§ precursor for L-carathine which is essential for healthy nervous system
function.
§ for adequate absorption of calcium and bone development in children
R e t a r d e d
growth
USES, FUNCTIONS AND
DEFICIENCY OF AMINO ACIDS
AMINO
ACIDS
USES/ FUNCTIONS
Met
§ Is antioxidant. It helps in breakdown of fats and aids in reducing muscle
degeneration. Helps lower cholesterol levels by increasing the liver's
production of lecithin; reduces liver fat and protects the kidneys.
§ principle supplier of sulfur, which inactivates free radicals. Is a natural
chelating agent for heavy metals and helps detoxify the body of these
metals.
§ Adequate methionine prevents disorders of the hair, skin and nails;
Phe
§ Beneficial for healthy nervous system. It may be useful against depression
and suppressing appetite.
§ Used to produce dopamine and norepinephrine, chemicals that promote
alertness, elevate mood, decrease pain, aid in memory and learning, and
reduce hunger and appetite.
§ D-phenylalanine - natural form. May improve rigidity, walking disabilities,
speech difficulties and depression associated with Parkinson’s disease.
§ L-phenylalanine can be converted into L-tyrosine, which is in turn
converted into L-DOPA. L-DOPA is a precursor for dopamine,
norepinephrine (noradrenalin), and epinephrine (adrenaline)
§ DL-phenylalanine
DEFICIENCY
L i v e
Deterioration
r
USES, FUNCTIONS AND
DEFICIENCY OF AMINO ACIDS
AMINO
ACIDS
Ala
Cys
Gln
Gly
His
Thr
USES/ FUNCTIONS
§ Removes toxic substances released from breakdown of muscle protein during
intensive exercise
§ antioxidant (free radical scavenger), and has synergetic effect when taken with
other antioxidants such as vitamin E and selenium.
§ Promotes healthy brain function. It is also necessary for the synthesis of RNA and
DNA molecules.
§ Component of skin and is beneficial for wound healing. It acts as neurotransmitter
§ Important for the synthesis of red and white blood cells.
§ It is a precursor for histamine which is good for sexual arousal. Improve blood
flow.
§ It helps promote equilibrium in the central nervous system—aids in balancing
state of emotion.
USES, FUNCTIONS AND
DEFICIENCY OF AMINO ACIDS
AMINO
ACIDS
Asp
Pro
Arg
USES/ FUNCTIONS
§ Enhances stamina, aids in removal of toxins and ammonia from the body, and
beneficial in the synthesis of proteins involved in the immune system.
§ plays role in intracellular signaling.
§ plays role in blood vessel relaxation, stimulating and maintaining erection in men,
production of ejaculate, and removal of excess ammonia from the body.
GLUCOGENIC- glycine, alanine, serine,
aspartic acid, asparagine, glutamic acid,
glutamine, proline, valine, methionine,
cysteine, histidine and arginine
KETOGENIC-lysine and leucine
BOTH-tryptophan, phenylalanine,
tyrosine, isoleucine and threonine
Acid-base
properties
Zwitterion = means double ion Is a molecule that has a positive charge on
one atom and a negative charge on another atom but which has no net charge.
§ Basic solution - NH3+ of the zwitterion loses a proton and
negatively charged species is formed.
§ Acidic solution - the zwitterion accepts a proton (H+) to form a
positively charged ion.
Guidelines for amino acid form
as function of solution pH
follows:
§ Low pH:
§ High pH:
All acid groups are protonated (-COOH).
All amino groups are protonated (NH3 +)
All acid groups are deprotonated (COO-).
All amino groups are deprotonated (-NH2).
§ Neutral pH:
All acid groups are deprotonated (COO-).
All amino groups are protonated (NH3+).
ISOELECTRIC POINT
§ the pH at which an amino acid exists primarily
in its zwitterion form. At the isoelectric point,
almost all amino acid molecules in a solution
(more than 99%) are present in their zwitterion
form.
PEPTIDE
FORMATION
Peptide bond
§ a covalent bond (amide bond)
between the carboxyl group of one
amino acid and the amino group
of another amino acid.
is an unbranched chain of
amino acids, each joined to the next by
a peptide bond.
TYPES OF PEPTIDE:
§ dipeptide – a compound containing
two amino acids.
§ Tripeptide – three amino acids joined
together in a chain.
§ Oligopeptide – refer to peptides with
10 to 20 amino acid residues.
§ Polypeptide – long unbranched chain
of amino acids, each joined to the next
by a peptide bond.
R
H2N
C
H
C
O
N
O
C
R
C
H
N
R
C
C
O
N – terminal end (left)
C – terminal end (right)
Backbone (peptide bond
& a-carbon –CH group)
R- substituent
PEPTIDE BOND
Peptide
Nomenclature
IUPAC Rule:
1. The C-terminal amino acid residue keeps its full amino acid
name.
2. All of the other amino acid residues have names that end in –yl.
The –yl suffix replaces the –ine or ic acid ending of the amino
acid name, except for tryptophan (tryptophyl), cysteine
(cysteinyl), glutamine (glutaminyl), and asparagine (asparaginyl).
3. The amino acid naming sequence begins at the N-terminal
amino acid residue.
Biochemically
important small
peptides
• Hormones both produced
by the pituitary gland:
1. Oxytocin
▹ regulates uterine contraction and lactation, plays a role in
stimulating the flow of milk in a nursing mother.
2.Vasopressin (ADH)
▹ regulates the excretion of
water by the kidneys;
▹ Enhances reabsorption of free
water
▹ also affects blood pressure.
Biochemically important small peptides
▹ Neurotransmitters:
Enkephalins – pain killers
(pentapeptide):neurotransmitters or
neuromodulators at many locations in
the brain and spinal cord and are involv
ed with pain perception, movement,
mood, behavior, and neuroendocrine
regulation; they are also found in
nerve plexuses and exocrine glands
of the gastrointestinal tract.
■Met-enkephalins
= Tyr – Gly – Gly – Phe –
Met
■Leu- enkephalins
= Tyr – Gly – Gly – Phe –
Leu
Biochemically important small peptides
▹ Antioxidants:
Glutathione
- regulator of oxidationreduction reaction
- antioxidant, protecting
cellular contents from
oxidizing agents such as
peroxides and superoxides
(highly reactive forms of
oxygen often generated within
the cell in response to
bacterial invasion) with
unusual features.
Glutathione - (Glu – Cys - Gly)
(tripeptide)
Unusual features.
The amino acid Glu, an acidic amino
acid,
is bonded to Cys, through the sidechain carboxyl
group rather than through its acarbon carboxyl group.
Bonding in proteins
1. Peptide bond – the strongest bond
2. Disulfide bond - is a covalent bond
between two sulfur. Results from the
oxidation of the –SH (sulfhydryl) groups
of two cysteine molecules to form
“cystine”
3. Hydrogen Bond - result from the
attraction of electronegative atoms in
the protein molecule. Weaker than the
peptide and disulfide bonds.
H-bond: can occur
between amino acids
with polar R groups.
functional groups:
-OH
-NH2
-COOH
-CONH2
1. Ionic bond or salt bridges - formed
between groups which are positively
and negatively charge.
2. Hydrophobic bond - formed by amino
acids like leucine, valine,
phenylalanine, tryptophan, and proline
which adhere each other forming a
“micelle” and which do not mix well
with water
- result when two nonpolar
side chains are close to
each other.
CLASSIFICATION
OF PROTEINS
47
CLASSIFICATION OF
PROTEINS
Based on the:
I. number of peptide chain
II. chemical composition
III. level of structural organization
IV. gross structure
V. Function
48
I. Based on the
number of peptide
chain
1. monomeric protein
- is a protein in which
only one peptide
chain is present.
▹ Example: myoglobin
2. multimeric protein
- is a protein in which more
than one peptide chain is
present.
▹ The peptide chains
present in multimeric
proteins are called protein
subunits.
▹ Example: insulin
49
II. Based on chemical
composition
I.
A.
Simple protein is a protein in which only amino
acid residues are present.
1.
2.
Albumins
a.
b.
c.
a.
b.
Examples:
Serum albumin (blood)
Lactalbumin (milk)
Ovalbumin (eggwhite)
Properties:
Soluble in water and dilute neutral salt solution
Coagulated by heat and precipitated by full saturation with
(NH4)2SO4 but not w/ NaCl except with the presence of acid.
50
II. Based on chemical
composition
B. Globulins
1. Examples:
a. Ovoglobulin (eggwhite)
b. Edestin (hempseed)
c. Legumin (peas)
d. Myosinogen (muscles)
e. Serum globulin (blood)
2. Properties:
a. Soluble in neutral dilute salt solutions but not in water. (Neutral salts refers
refer to salts of strong acids and bases as NaCl, MgSO4 and (NH4)2SO4.)
b. Coagulated by heat and can be precipitated from their solutions by half
saturation with (NH4)2SO4 and complete saturation with NaCl.
51
II. Based on chemical
composition
C.
Glutelins
1. Examples:
a. Glutenin (wheat)
b. Oryzenin (rice)
2. Properties:
a. Soluble in dilute
acids and alkalies
but insoluble in
neutral solvents.
C.
Prolamines
1.
Examples:
a. Gliadin (wheat)
b. Zein (corn)
c. Hordein (barley)
2. Properties:
a. Insoluble in ordinary solvent
(water, dilute salt solutions,
dilute acid and alkalies) but
soluble in 70% alcohol at about
neutral point.
b. Not coagulable by heat.
52
II. Based on chemical
composition
E.
Histones
1. Examples:
a. Globin (hemoglobin)
b. Thymus histones
c. Scobrone of Mackerel
2. Properties:
a. Soluble in water, dilute acids
and alkalies but not in
ammonia.
b. Not readily coagulated by heat
c. Strongly basic and occur in the
tissues in the form of salt
combinations with acid
substances like the heme of
the hemoglobin
E.
Protamines
1.
2.
Examples:
a. Salmin (salmon sperm)
Properties:
a. Contain smaller number
of amino acids
b. S o l u b l e i n w a t e r a n d
dilute acids and alkalies
c. Not coagulated by heat
53
II. Based on chemical
composition
G.
Scleroproteins (Albuminoids)
1. Examples:
a. Keratin (epidermal tissues)
b. Elastins (Ligaments)
c. Collagen (hides, bones and cartillage)
2. Properties:
a. Insoluble in water and neutral solvents
54
II. Based on chemical composition
II. Conjugated protein is a protein that has one or more non-amino acid
entities present in its structure in addition to one or more peptide chains.
• prosthetic group is a non-amino acid group present in a conjugated protein.
These non-amino acid components, which may be organic or inorganic.
55
II. Based on chemical composition
Nucleoprotein
A.
Examples:
1.
a.
b.
c.
d.
e.
Ribosomes (site for protein synthesis in cells)
Viruses (self-replicating, infectious complex)
Chromatin
Products from glandular tissues
Germ of grains
Properties:
2.
a.
b.
c.
d.
Prosthetic group: Nucleic acids
Combination of histones and protamins with nucleic acids
Soluble in dilute solutions of NaCl
Precipitated by acidification
56
Based on chemical composition
B. Glycoproteins (more proteins less
carbohydrates)
Examples:
1.
a.
b.
c.
d.
e.
f.
Mucin aka mucoproteins – more carbs less proteins
(saliva, mucous secretion of the nose)
Tendomucoid (tendons)
Osseomucoid (bones)
gamma globulin (antibody)
Interferon (antiviral protection)
Simple proteins like globulins and albumins
Properties:
2.
a.
b.
c.
Prosthetic group: carbohydrates
Use: Utilize for lubricating purposes in view of their
slimy nature
Use: Help in protecting the membranes of the GIT
against digestion since they are not digested by the
enzymes of GIT.
C. Phosphoproteins
1.
2.
a.
b.
a.
Examples:
Casein (milk)
Vitellin (egg
yolk)
Properties:
Prosthetic
group: H3PO4
57
Based on chemical composition
D. Chromoproteins/ Hemoproteins
1.
Examples:
a.
b.
c.
d.
2.
Hemoglobin (blood carrier of O2 in blood )
Myoglobin (oxygen
binder in muscles)
Cytochromes
Rhodopsin
Properties:
a.
Prosthetic group:
hematin or heme unit
E. Lipoproteins
1.
a.
b.
c.
d.
2.
a.
b.
Examples:
Lecithin
Cephalin
low-density lipoprotein (LDL) –
lipid carrier
high-density lipoprotein (HDL) –
lipid carrier
Properties:
Prosthetic group: Lipids/ fatty
substance
Occurrence: Blood serum, brain
tissues, cell nuclei, egg yolk and
milk
58
Based on chemical composition
D. Metalloproteins
1.
a.
b.
2.
a.
Examples:
iron–ferritin (storage
complex for iron)
zinc–alcohol dehydrogenase
(enzyme in alcohol oxidation)
Properties:
Prosthetic group: metal ion
59
II. Based on chemical composition
iii.Derived proteins. These include substances
formed from simple conjugated proteins.
A.
1.
Primary Protein derivatives – proteins which have
undergone slight intramolecular rearrangement
through the hydrolytic action of certain physical and
chemical agents.
- synonymous w/ denatured proteins
a.
b.
Proteans
Examples:
§
§
§
Myosan from myosin
Edestan from edestin
Properties
Are insoluble substances resulting from the preliminary actions of water,
dilute acids or enzymes
60
Based on chemical composition
2. Metaproteins
a.
Examples:
§
§
b.
Acid metaproteins
(acid albuminate)
A l k a l i
metaproteins
(alkali albuminate)
Properties
§
§
§
Are product of
further hydrolysis
Soluble in weak
acids and alkalies
neutral salt
solution
Insoluble in neutral
salt solutions
3. Coagulated proteins
a.
b.
Examples:
§
§
§
Cooked egg albumin
Cooked meat
Properties
Insoluble products
res u l t in g f ro m eit her
the action of heat,
alcohol, ultraviolet rays
o r e v e n s i m p l e
mechanical shaking
61
Based on chemical composition
B. Secondary Protein derivatives
Product of more extensive hydrolysis
§ Mixtures of fragments of original proteins varying in composition
and size
§ Exhibit certain common properties such as solubility in water and
non-coagulability by heat.
§
Primary proteoses
1.
a.
Properties
§
§
Soluble in water,
precipitated by conc.HNO 3
and by half saturation with
(NH4)2SO4 or ZnSO4.
Not coagulated by heat
2. Secondary proteoses
a.
Properties
§
Precipitated only by
complete saturation
with (NH 4 ) 2 SO 4 but nit
with picric acid and
HNO3 .
62
Based on chemical composition
3. Peptones
a.
Properties
§
§
§
Soluble in water
Not coagulated by heat
Not precipitated by saturation with (NH4)2SO4 but by certain alkaloidal reagents,
such as,phosphotingstic and tannic acids.
4. Peptides
§
§
§
Are combinations of two or more amino acids, the carboxyl group of one being
united with the amino group of the other.
Present properties like peptones
Ex. di, tri,tera,penta etc.
63
III. Level of structural
organization
64
III. Level of structural
organization
65
III. Level of structural
organization:
PRIMARY
§ Sequence of amino acids in a
protein – that is, the order in
which the amino acids are
connected to each other
§ Also involves the order of
attachment of the amino acids to
each other through covalent*
peptide bonds.
§ These bonds are formed between
the carboxyl group of one amino
acid with the amino group of
another.
“peptide bond planarity” is the
zigzag arrangement
66
Level of structural
organization:
PRIMARY
MYOGLOBIN
The primary structure of
human myoglobin. This
diagram gives only the
sequence of the amino acids
present and conveys no
information about the actual
three dimensional shape of the
protein.
67
Level of structural
organization:
PRIMARY
Primary Structure of Bovine Insulin
(51 AA)
First protein to be fully sequenced (by
Fred Sanger in 1953). For this, he won his first Nobel Prize
(his second was for the Sanger deoxy method of DNA
sequencing
68
III. Level of structural
organization: SECONDARY
§ Is the arrangement in space adopted
by the backbone portion of a protein.
§ I s a r e s u l t o f hy drogen b o nd i ng
between carbonyl oxygen atom of a
peptide linkage and the hydrogen
atom of an amino group of another
peptide linkage farther along the
backbone.
Common types of secondary structure
1.
2.
Alpha helix (-helix)
Beta pleated sheet (-pleated sheet).
69
Level of structural
organization: SECONDARY
ALPHA HELIX
§ is a protein secondary structure in
which a single protein chain
adopts a shape that resembles a
coiled spring (helix), with the coil
configuration maintained by
hydrogen bonds.
70
Level of structural
organization:
SECONDARY
§ is a protein secondary structure in
which two fully extended protein
chain segments in the same or
different molecules are held
together by hydrogen bonds.
§ Hydrogen bonds form between oxygen
and hydrogen peptide linkage atoms
§ different parts of a single chain that
folds back on itself (intrachain
bonds)
§ Or between atom s in different
peptide chains in those proteins
that contain more than one chain
(interchain bonds).
71
Level of structural
organization:
SECONDARY
l
l
l
Core of many proteins is
the  sheet
Form rigid structures
with the H-bond
Can be of 2 types
l
l
Anti-parallel – run in an
opposite direction of its
neighbor (A)
Parallel – run in the same
direction with longer
looping sections between
them (B)
72
Level of structural
organization:
TERTIARY
§ The overall three-dimensional
shape of a protein that results
from the interactions between
amino acids side chains (R
groups) that are widely
separated from each other
within a peptide chain.
Four types of stabilizing
interactions contribute to the
tertiary structure of a
protein:
1. covalent disulfide bonds
2. electrostatic attractions (salt
bridges)
3. Hydrogen bonds
4. hydrophobic attractions
73
Level of structural
organization:
TERTIARY
74
Level of structural
organization:
QUATERNARY
§ Is the organization among the various
peptide chains in a multimeric protein.
§ The three-dimensional shape of a protein
consisting of two or more independent
peptide chains, which results from
noncovalent interactions between R
groups
§ For example, the hum a n hem oglobin
molecule is a tetramer made up of two
alpha and two beta polypeptide chains.
§ This is also when the protein associates
with non-proteic groups. For example,
carbohydrates can be added to form a
glycoprotein.
Bonds:
§Electrostatic
§H-bond
§Hydrophobic
75
IV. GROSS
STRUCTURE:
▹ FIBROUS
▹ GLOBULAR
▹ MEMBRANEOUS
76
GROSS STRUCTURE:
Fibrous
Protein whose molecules have
an elongated shape with one
dimension much longer than
the others.
Properties:
§Tend to have simple, regular
and linear structures.
§Largely insoluble in ordinary
aqueous media
§Molecular weights are high
§Functions is for structural and
support
Fibrous
Proteins
(insoluble)
Occurrence and
Functions
Keratins
found in wool,
feathers, hooves, silk,
and fingernails
Collagen f o u n d i n t e n d o n s ,
s
bone, and other
connective tissue
Elastins
found in blood vessels
and ligaments
Myosins
found in muscle tissue
Fibrin
found in blood clots
77
GROSS STRUCTURE:
§ Protein whose molecules have
peptide chains that are folded into
spherical or globular shapes.
§ The folding in such that most of
amino acids with hydrophobic side
chains (nonpolar R groups) are in
the interior of the molecules and
most of the hydrophilic side chains
(polar) are on the outside of the
molecule.
Properties:
§ Soluble in aqeous media
§ Have been crystallized and have
definite molecular weights
§ Can be denatured
Globular
Proteins
(soluble)
Occurrence and
Functions
Insulin
regulatory hormone for
controlling glucose
metabolism
Myoglobin involved in oxygen
storage in muscles
Hemoglob involved in oxygen
in
transport in blood
Transferri
n
involved in iron transport
in blood
Immuno
globulins
involved in immune
system responses
78
GROSS STRUCTURE:
FIBROUS
water-insoluble
GLOBULAR
Water-soluble
usually have a single type several types of secondary
of secondary structure
structure.
generally have structural
functions that provide
support
and external protection,
involved in metabolic
c h e m i s t r y, p e r f o r m i n g
functions such as catalysis,
transport, and regulation.
Lesser in kind of proteins
Greater in kind of proteins
M o s t a b u n d a n t i n t h e Less
human body
Greater mass composition
Lesser mass composition
79
GROSS STRUCTURE:
MEMBRANEOUS
§ is a protein that is found
associated with a membrane
system of a cell.
§ Soluble in aqueous media
§ Have been crystallized and
have definite molecular
weights
§ Can be denatured
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V. BASED ON
FUNCTIONS
CATALYTIC
Proteins with the role of biochemical catalyst are called enzymes.
• Enzymes participate in almost all of the metabolic reactions that occur in cells. The
chemistry of human genetics, is very dependent on the presence of enzymes.
DEFENSE also called immunoglobulins or antibodies w/c
are central functioning of the body’s immune system
• They bind to foreign substances, such as bacteria and viruses, to help combat invasion
of the body by foreign particles.
- proteins bind to particular small biomolecules and
TRANSPORT transport them to other locations in the body and then
release the small molecules as needed at the destination
location.
• Examples:
• hemoglobin - carries oxygen from the lungs to other organs and tissues.
• Transferrin - which carries iron from the liver to the bone marrow.
• High- and low-density lipoproteins - are carriers of cholesterol in the bloodstream
81
BASED ON FUNCTIONS
transmit signals to coordinate biochemical processes between
different cells, tissues, and organs
MESSENGER
• insulin
• glucagon
• Human growth hormone
CONTRACTILE
are necessary for all forms of movement
• Actin and myosin
• Sperm can “swim” because of long flagella made up of contractile proteins.
confer stiffness and rigidity to otherwise fluid-like biochemical
STRUCTURAL systems
• Collagen - component of cartilage,
• Keratin - gives mechanical strength as well as protective covering to hair, fingernails,
feathers, hooves, and some animal shells.
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BASED ON FUNCTIONS
STORAGE
These proteins bind (and store) small molecules for future use
• During degradation of hemoglobin the iron atoms present are released and become part of
ferritin, an iron-storage protein, which saves the iron for use in the biosynthesis of new
hemoglobin molecules.
• Myoglobin - an oxygen-storage protein present in muscle; the oxygen so stored is a reserve
oxygen source for working muscle.
REGULATORY
often found “embedded” in the exterior surface of cell
membranes.
• Act as sites at which messenger molecules, including messenger proteins such as insulin,
can bind and thereby initiate the effect that the messenger “carries.”
• Are often the molecules that bind to enzymes (catalytic proteins), thereby turning them “on”
and “off” and thus controlling enzymatic action.
TRANSMEMBRANE
help control the movement of small molecules and ions
through the cell membrane
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BASED ON FUNCTIONS
NUTRIENT
These proteins are particularly important in the early
stages of life, from embryo to infant.
• Casein - milk
• Ovalbumin - found in egg white (>50% present)
BUFFER
These proteins are part of the system by which the acid-base
balance within body fluids is maintained
• Hemoglobin has a buffering role in addition to being an oxygen carrier.
• Transmembrane proteins regulate the movement of ions in and out of cells, ensuring
that ion concentrations are those needed for correct acidity/alkalinity.
FLUID BALANCE
These proteins help maintain fluid balance between
blood and surrounding tissue
• Albumin and globulin
• Found in the capillary beds of the circulatory system. When increased blood pressure generated by a pumping
heart forces water and nutrients out of the capillaries, these proteins remain behind (since they are too big to cross
cellular membranes). As their concentration increases (due to less fluid being present), osmotic pressure “forces”
draw water back into the capillaries, which is necessary for fluid balance to be maintained.
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