molecular biolg

7/28/2019 Molecular Biolg

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I.Fundamental unit of Life

Life is complex phenomena and is

perhaps impossible to define

Noroman Horowitz, proposed a

useful set of criteria for living

systems : Life possesses the

properties of replication, catalysis andmutability


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I. Modern cell theory

Modern Cell theory: 4 fundamental

statements

Cells make up all living matter All cells arise from other cells

The genetic information required during the maintenance of existing

and the production of new cells passes from one generation to the next

The chemical reactions of an organism, that is its metabolism, take

place in cells


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Mitochondria

b)Mitochondria : a double membrane

organelle and is the site of energy

production. Carbohydrates, fatty acids and amino acids

are completely oxidized in the

mitochondrian.

Energy is conserved in chemical form-ATP


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Endoplasmic reticulum

c) ER: 2 types- rough ER

-smooth ER

Rough ER : studded with ribosomes

: protein synthesis

Smooth ER:devoid of ribosomes: lipid synthesis


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Golgi apparatus

d) Golgi bodies : receive products [ proteins

& lipids] from ER via transfer vesicles

which is further processed and finallyreleased via secretory vesicles

: carbohydrate and lipid

precursors are added to proteins to formglycoproteins and lipoproteins.


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Lysosome

e) lysosomes:digestive vesicles of animal

cells and contain variety of enzymes.

Can digest cellular molecules such as

proteins and nucleic acids


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Peroxisomes / microbodies

f) peroxisomes / microbodies : contain

oxidative enzymes and carry out oxidative

process, which produces H2O2[ toxicsubstances]

These H2O2 further utilized in oxidation of

other substances or degraded by the enzymecatalase


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Chloroplast

g) chloroplast : is also a double membrane

organelle of plant cell

Contains a biomolecule, chlorophyll which

captures sunlight and is involved in

photosynthesis


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Vacoules

h) Vacoules: are single membrane

structures.

Enlargement of these fluid filled organelles

is related to cell growth.

Also store solutes, water soluble plant

pigments, salts, dissolved sugars andproteins.


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Chromosome

Most bacterial genes: encoded in a single

large circular molecule of DNA, the

chromosome.

Not all bacterial genes are encoded within

the chromosome. Many bacteria contain one

or more different small circular DNAmolecules, termed plasmids


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Chromosomes [contd]

Plasmids : are small circular DNA

molecules, capable of self replicating and

encode a variety of cellular functions.

Some plasmids encode enzymes that

inactivate antibiotics or other toxic

compounds that are present in cellsenvironment.


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Chromosomes [ contd ]

Nuclear DNA in eukaryotes is organized in

complexes with proteinsas nucleoprotein

complexes called as chromatin.

The protein components of chromatin are

basic proteins called histones.


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Carbohydrates

Carbohydrates are the most abundant class

of biomolecules with a structural formula of

(C.H2O)n ,where n = or > 3.

The basic units of carbohydrates are known

as monosaccharides.


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Carbohydrates [ contd ]

Carbohydrates can be grouped into:

a) monosaccharides

b) disaccharides

c) polysaccharides


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Monosaccharides

Monosaccharides are classified according to the

chemical nature of their carbonyl group and the

number of C atoms. If the carbonyl group is an aldehyde, the sugar is

called as an aldose [ ex : glucose ]

If the carbonyl group is a ketone,, the sugar is a

ketose [ ex : fructose ]


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Monosaccharides [ contd ]

The smallest monosaccharides, those with 3

carbon atoms are called trioses.

Those with 4,5,6 and 7 C atoms arerespectively called as

tetroses,pentoses,hexoses and heptoses.


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Monosaccharides

Alcohols react with the carbonyl group of

aldehydes and ketones to form hemiacetals

and hemiketals respectively The cyclic forms of glucose and fructose

with 6and 5membered rings are known

as glucopyranose and fructofuranose


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Disaccharides

Disaccharides are made of 2

monosaccharide subunits [ ex :sucrose,

lactose and maltose] Sucrose : is the most abundant disacch. and

is made of glucose and fructose subunits

linked by alpha1,2 glycosidic bond


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Lactose : made of galactose and glucose

subunits linked by beta 1,4 glycosidic bonds

Maltose : is made of 2 glucose residues and

are linked by alpha1,4 glycosidic bond


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Polysachharides

Polysaccharides includes :

Cellulose and chitinstructural polysacch.

Starch and glycogenstorage polysacch.


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Polysaccharides [ contd ]

Cellulose : is the primary structural

component of plant cell walls.

Cellulose is a linear polymer of upto

15,000s D-glucose residues linked by beta

1,4 glycosidic bonds


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Chitin : is the principle structural

component of the exoskeletons of

invertebrates [ crustaceans,insects] and isalso present in the cell wall of fungi and

algae


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Polysaccharides [ contd]

Starch : is deposited in the cytoplasm of

plant cell as insoluble granules and is

composed of alpha amylose andamylopectin.

a) alpha amylose is a linear polymer of

several 1000s glucose residues linked byalpha 1,4 glycosidic bonds


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b) amylopectin: consists mainly of alpha 1,4

linked glucose residues but is a branched

molecule with alpha 1,6 branch points forevery 24- 30 glucose residues.


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Glycogen : is most prevalent in the skeletal

muscle and liver and occurs in the form of

cytoplasmic granules. The primary structure of glycogen

resembles that of amylopectin but, glycogen

more highly branched with branch pointsoccurring every 8-12 glucose residues.


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Lipids

Biological membranes are

organized assemblies oflipids and proteins with small

amount of carbohydrate.


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Lipids [ contd]

Lipids classification:

Fatty acids

Triacylglycerol

Glycerophospholipids

Sphingolipids

Cholesterol


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Lipids [ contd ]

Fatty acids : are carboxylic acids with longchains hydrocarbon side groups.

Fatty acids : 2 typea) Saturated fatty acids : normal constituent of

higher plant and animals [ ex: palmitic and stearicacids ]

b) Unsaturated fatty acids: are having one or moredouble bonds and are also present in plant andanimal lipids.


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Lipids [ contd ]

Triacylglycerols :are non polar, water

insoluble,fatty acid triesters of glycerols.

Triacylglycerol function as energy

reservoirs in animals and therefore the most

abundant class of lipids


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Glycerophospholipids

Glycerophospholipids are the major lipid

components of the biological membrane.

They consists of glycerol-3phosphateesterified at its C1and C2 positions to fatty

acids and C3 position attached to a

phosphoryl group.


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Lipids [ contd ]

Sphingolipids : are also major membrane

components and are derivatives of C 18

amino alcohols sphingosine,dihydrosphingosine and their C16, C17,C19

and C 20 homologs


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Lipids [ contd ]

Different types of sphingolipids:

Sphingomyelins

Cerebrosides

Glucocerebrosides

Gangliosides


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Lipids [ contd ]

Cholesterol : is a major component of

animal plasma membranes and are

derivatives ofcyclopentanoperhydrophenanthrene.

It is the metabolic precursor of steroid

hormones, which regulate physiological

functions ( sexual development andcarbohydrate metabolism

molecular biolg

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