molecular basis of inheritance, class 12, cbse notes

Molecular Basis of Inheritance

DNA (Polynucleotide)

DNA

NITROGENOUS

BASE

A DEOXYRIBOSE

PENTOSE

SUGAR

A PHOSPHATE

GROUP

PURINE PYRIMIDINE

CYTOSINE

THYMINE

ADENINE

GUANINE

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DNA

Nitrogenous base is linked to pentose sugar through a n-glycosidic linkage to form a nucleoside.

Phosphate group attached to5’-OH of a nucleoside through phospho-ester linkage, and a nucleotide is formed.

Two nucleotides are linked through 3’-5’ phosphodiester linkage to form a dinucleotide, and in this manner many nucleotides are linked forming polynucleotide.

A polynucleotide has a free sugar at its5’ end and a free phosphate at its 3’ end.

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Double helix model of DNA

( Watson and Crick model)

DNA is made of 2 polynucleotides.

Backbone is formed by sugar and phosphate.

Nitrogen bases project inside.

Hydrogen bonds between nitrogen bases hold the chain together.

Adenine pairs with thymine through 2 hydrogen bonds and guanine with cytosine with 3 bonds.

Two chains have antiparallel polarity.

Two chains are coiled in a right handed fashion. And pitch of each helix is3.4nm, and 10 base pairs in each turn.

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A NUCLEOSOME

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Griffith’s experiment on transformation

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DNA is the genetic material

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Characteristics of genetic material

Able to generate its replica.

Chemically and structurally stable.

Provide the scope for mutation necessary for

evolution.

Able to express itself in the form of Mendalian

character.

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RNA (Polynucleotide)

RNA

NITROGENOUS

BASE

A

PENTOSE

SUGAR

A PHOSPHATE

GROUP

PURINE PYRIMIDINE

CYTOSINE

URACIL

ADENINE

GUANINE

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TYPES OF RNA

RNA

MESSENGER

mRNA

TRANSFER/

SOLUBLE

tRNA

RIBOSOMAL

rRNA

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A tRNA MOLECULE

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Semiconservative replication of DNA

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Meselson- Stahl experiment

(semiconservative replication)

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Replication of DNA

(schematic representation)

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A TRANSCRIPTION UNIT

A promoter

Structural genes

A terminator

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Transcription

A TRANSCRIPTION UNIT

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TRANSCRIPTION IN PROKARYOTES

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GENETIC CODE

Codons are triplets

61 codons code for 20 amino acids.

Unambigous – each coden codes for only one/ particular amino acid.

Degenerate – some amino acids are coded by more than one codon.

Commaless –codons are read in continuous manner in a 5’ to 3’ direction without punctuation

Universal –codes for same amino acid in any organism.

AUG- initiation codon and codes for methionine.

UAA, UAG and UGA are stop codons..

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MUTATION

MUATION

POINT FRAME SHIFT SILENT

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TRANSLATION

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TRANSLATION

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TRANSLATION

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COMPONENTS OF OPERON

Structural gene

Promoter gene

Operator

Regulator gene

Inducer

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LAC OPERON IN E.COLI

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LAC OPERON IN E.COLI

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GOALS OF HUMAN GENOME PROJECT (HGP)

Identification of all genes

Determination of the sequence of the 3 billion base pairs in human DNA.

To store the information in data base.

Improvement of the tools for data analysis

Transfer of the technology to other sectors (industries)

To address the ethical, legal and social issues (ELSI) that may arise from this project.

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METHODOLOGIES OF HGP

Expressed sequence tags (ESTs)- identifying all genes

that expressed as RNA.

Sequence annotation- sequence the whole sequence of

genome, that included all coding and noncoding

sequences and later assigning function to different

regions in the sequence.

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SALIENT FEATURES OF HUMAN GENOME

Contains3164.7 million nucleotides.

Size of genes varies, average size contains 3000 bases, the largest

gene dystrophin contains 2.4 million bases.

Total no. genes about 30000 and99.9 % of the nucleotides are

same in all humans.

Function of 50% genes are not known.

2% of the genome codes for protein.

Repetitive sequence make up large portion of genome which throw

light on structure, dynamics and evolution though they do not have

coding function.

In 1.4 million locations DNA differs in single base. http://schools.aglasem.com

USES OF HGP

To diagnose, treat and prevent a number of disease or

disorder that affects human beings.

Provides clues to the understanding of human biology.

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THE PROCESS OF DNA FINGER PRINTING

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STEPS OF DNA FINGERPRINTING

Extraction

Amplification

Restriction digestion

Separation of DNA sequence/ restriction fragments

Southern blotting

Hybridisation

Autoradiography

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USES OF DNA FINGERPRINTING

To identify criminals

To determine the true biological mother or father in

case of disputes

To verify an immigrant, really a close relative of a

resident

To identify racial groups to rewrite the biological

evolution.

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PRESENTATION BROUGHT TO YOU BY:

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