Transcript Structure of Macromolecules Dr. Nakhshab

Structure of
Macromolecules
…by small and simple things are
great things
brought to pass.
Macromolecules
Molecular weight exceeding 1000
Macromolecules are polymers constructed by
the formation of covalent bonds between
smaller molecules called monomers
Condensation and Hydrolysis
Monomers are joined
by condensation
reactions, which
release a molecule of
water for each bond
formed.
Hydrolysis reactions
use water to break
polymers into
monomers.
Molecular organization in the cell is
a hierarchy
4 BASIC BIOLOGICAL
MACROMOLECULES
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Proteins
Carbohydrates
Lipids
Nucleic acids
Proteins
Proteins are polymers composed of hundreds
or even thousands of amino acids linked in
series by peptide bonds.
Basic building block is the amino acid
The functions of proteins include
support, protection, catalysis,
transport, defense, regulation, and
movement.
What is amino acid?
• Amino means?
• Acid?
• There are 20 amino acids commonly
found in proteins
• peptide linkages form by condensation
reactions between the carboxyl and
amino groups of adjacent amino acids.
Amino Acids
1. Alanine
2. Arginine
3. Lysine
4. Glycine
5. Asparagine
6. Methionine
7. Isoleucine
8. Aspartic acid
9. Tryptophan
10.Leucine
11.Cysteine
12.Tyrosine
13.Phenylalanine
14. Glutamic acid
15. Threonine
16. Proline
17. Valine
18. Histidine
19. Glutamine
20. Serine
Proteins: Structure
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Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure
Proteins: Structure
Primary Structure: the sequence of amino
acids bonded by peptide linkages (Diversity
20n) (covalent bonding)
Even a slight change in the
amino acid sequence can
cause the protein to
malfunction
For example, A single amino acid substitution
in hemoglobin causes sickle cell disease
Secondary Structure
Results from hydrogen bonding between the
oxygen of one amino acid and the hydrogen of
another(non covalent interactions)
α helices and β pleated sheets (maintained by hydrogen
bonds between atoms of the amino acid residues)
The alpha helix is
a coiled
secondary
structure due to a
hydrogen bond
every fourth amino
acid
The beta pleated sheet is formed by
hydrogen bonds between parallel
parts of the protein
A single polypeptide may have
portions with both types of
secondary structure
Tertiary Structure
Generated by
bending and
folding of the
polypeptide
chain
1) Covalent
disulfide bridges,
2)Hydrophobic
interactions 3)
van der Waals
forces 4) Ionic
bonds
Quaternary structure
results from interactions among
separate polypeptide chains.
Proteins: Denaturation
A loss of three-dimensional
structure sufficient to
cause loss of function is called
denaturation. Proteins are denatured
by heat, alterations in pH, or certain
chemicals lose their tertiary and
secondary structure as well as their
biological function. Renaturation is
not often possible.
Carbohydrates
Carbohydrates are polyhydroxy
aldehydes or ketones,
or substances that yield such
compounds on hydrolysis
They act as source of energy that can be
transported
They also have structural roles
classification
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Monosaccharides
Disaccharides
Oligosaccharides (3-20)
Polysaccharides
Monosaccharides
The monosaccharides
are also called simple sugars and have the
formula (CH2O)n. Monosaccharides
cannot be broken down into smaller sugars
Ring form of sugars
• There are two forms of
the ring structure (αglucose and β-glucose),
which differ only in the
placement of the —H
and —OH attached to
carbon 1.
• The α and β forms
(called anomers)
interconvert and exist in
equilibrium when
dissolved in water.
Glycosidic
linkages
Covalently link
monosaccharides
into larger units
such as
disaccharides,
oligosaccharides,
and
polysaccharides
Digestible
Polysaccharides
The polysaccharides are sugar polymers
containing more than 20 or so
monosaccharide units; some have hundreds
or thousands of units. Some polysaccharides,
such as cellulose, are linear chains; others,
such as glycogen, are branched. For example
Cellulose: Glucose polysaccharide β Linkages
Starch: Glucose polysaccharide α Linkages
Glycogen: Glucose polysaccharide Branched
Polysaccharides
Modified Carbohydrates
Lipids
Lipids are a class of biological
molecules defined by low solubility in water
and high solubility in nonpolar solvents. As
molecules that are largely hydrocarbon in
nature, lipids represent highly reduced
forms of carbon and, upon oxidation in
metabolism, yield large amounts of energy.
Lipids are thus the molecules of choice for
metabolic energy storage.
• Water insoluble due to nonpolar covalent
bonds
• Hydrophobic molecules aggregate together
(by hydrophobic and Van der Waals force)
1) Store energy as triglycerides
2) Phospholipids form cell membranes
3) Carotenoids help plants capture light
energy
4)Steroids are hormones and vitamins
5) Animal fat is thermal insulator
6) Insulation of nerves
7) Water repellant for skin, fur and feathers
Triglycerides
Fats and oils are
triglycerides,
composed of three
fatty acids covalently
bonded to a glycerol
molecule by
ester
linkages.
Lipids: Saturated and unsaturated
Saturated fatty acids have a hydrocarbon chain with
no double bonds.
The hydrocarbon chains of unsaturated fatty acids
have one or more double bonds that bend the chain,
preventing close packing.
Phospholipids
Phospholipids contain fatty acids bound to
glycerol by ester linkages. In phospholipids,
however, any one of several phosphatecontaining compounds replaces one of the
fatty acids.
The phosphate functional group has a
negative electric charge, so this portion of the
molecule is hydrophilic, attracting polar water
molecules. But the two fatty acids are
hydrophobic, so they tend to aggregate away
from water.
A variety of polar
groups
are esterified to the
phosphoric acid moiety
of the molecule. The
phosphate, together
with such esterified
entities, is referred to as
a “head” group
Lipids in Aqueous Cell Environment
The interactions of the hydrophobic tails and
hydrophilic heads of phospholipids generate a
phospholipid bilayer that is two molecules thick. The
head groups are directed outward, where they
interact with the surrounding water. The tails are
packed together in the interior of the bilayer.
Lipids in Vitamins and hormones
Vitamins are small molecules that are not
synthesized by the body, but are necessary
for its normal functioning. There are four
lipid soluble vitamins- vitamin A,D,E and K.
Many hormones are also lipid in nature e.g
cortisol.
Nucleic Acids
• Nucleic acids are linear polymers of
nucleotides.
• Nucleotides have three characteristic
components: (1) a nitrogenous (nitrogencontaining) base, (2) a pentose, and (3) a
phosphate.
• Nucleotide without the phosphate group is
called a nucleoside.
Nitrogenous bases
• The nitrogenous bases are derivatives of
two parent compounds, pyrimidine and
purine.
• Both DNA and RNA contain two major
purine bases, adenine(A) and guanine(G),
and two major pyrimidines.
• In both DNA and RNA one of the
pyrimidines is cytosine(C), but the second
major pyrimidine is not the same in both:
it is thymine(T) in DNA and uracil (U) in
RNA
Purines are
double ring
bases e.g.
adenine &
guanine
Pyrimidines are
single ring
bases e.g.
cytosine,
thymine, uracil
Nucleoside
• Nucleosides are compounds formed when a
base is linked to a sugar. Nucleosides are
composed of : (1) a nitrogenous base, (2) a
pentose
• Examples :
Adenosine
Guanosine,
Cytidine,
Thymidine,
Uridine
Nucleotides
• Nucleotides have three characteristic
components: (1) a nitrogenous base, (2) a
pentose, and (3) a phosphate.
• Examples:
Adenylate (AMP)
Guanylate (GMP)
Cytidylate (CMP)
Thymidylate (TMP)
Uridylate (UMP)
Nucleic acids
• Nucleic acids are
linear polymers of
nucleotides
• Examples:
deoxyribonucleic
acid (DNA) and
ribonucleic acid
(RNA)
structure
• In both RNA and
DNA, the backbone
of the
macromolecule
consists of
alternating pentose
sugars and
phosphates (sugar—
phosphate—sugar—
phosphate). The
bases are attached
to the sugars and
project from the
chain.
• The nucleotides
are joined by
phosphodiester
linkages between
the sugar of one
nucleotide and the
phosphate of the
next .The
phosphate groups
link carbon 3 in
one pentose sugar
to carbon 5 in the
adjacent sugar.
• Most RNA
molecules consist
of only one
polynucleotide
chain. DNA,
however, is usually
double-stranded; it
has two
polynucleotide
strands held
together by
hydrogen bonding
between their
nitrogenous bases.
• The two strands of
DNA run in opposite
directions. This
antiparallel
orientation is
necessary for the
strands to fit
together in threedimensional space.
• The uniqueness of a
nucleic acid resides
in its nucleotide
sequence
Only four nitrogenous
bases—and thus only
four nucleotides—are
found in DNA:
adenine (A), cytosine
(C), guanine (G), and
thymine (T). In doublestranded DNA,
adenine and thymine
always pair (A-T), and
cytosine and guanine
always pair (C-G).
(complementary base
pairing. )
Differences between
DNA
• Double stranded
• Contains
deoxyribose
• Contains thymine
• Stores genetic
information
RNA
• single stranded
• Contains ribose
• Contains uracil
• Participates in the
expression of genetic
information stored in
the DNA
• Three types rRNA,
mRNA, tRNA
Nucleic
Acids
DNA Double Helix has Uniform Width
Information in Sequence not Shape
RNA: Genetic Material and
Enzyme
Many viruses use RNA as their hereditary material
RNAs can achieve chemical catalysis, like enzymes
e.g. in ribosome the active site is composed entirely
of RNA . These
catalytic RNAs are called ribozymes.
QUESTIONS??