Structure of Structure of MacromoleculMacromolecul

eses

…by small and simple things are great things

brought to pass.

Macromolecules

Macromolecules are polymers constructed by the formation of covalent bonds between

smaller molecules called monomers

Molecular weight exceeding 1000

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

• 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 Acids1. 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

• 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

Generated by bending and folding of the polypeptide chain

1) Covalent disulfide bridges, 2)Hydrophobic interactions 3) van der Waals forces 4) Ionic bonds

Tertiary Structure

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

• Monosaccharides

• Disaccharides

• Oligosaccharides (3-20)

• Polysaccharides

Monosaccharides

The monosaccharidesare also called simple sugars and have the formula (CH2O)n. Monosaccharidescannot be broken down into smaller sugars

Ring form of sugars• There are two forms of

the ring structure (α-glucose 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

PolysaccharidesThe 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 LinkagesGlycogen: 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

Fats and oils are triglycerides, composed of three fatty acids covalently bonded to a glycerol molecule by ester linkages.

Triglycerides

Lipids: Saturated and unsaturatedSaturated 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 phosphate-containing 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 groupsare 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 (nitrogen-containing) 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 three-dimensional 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 double-stranded 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 . Thesecatalytic RNAs are called ribozymes.

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