Slide 1 : APT ACADEMIC SOLUTIONS believes in people who will deliver the right solutions, and it proudly possesses them.
Home Work : Home Work Give examples in which single stranded DNA
& double stranded RNA occurs Single stranded DNA occurs in f174
Double stranded RNA occurs in Cauliflower virus
Slide 5 : Session Objectives DNA Replication
Transcription
Slide 6 : Replication of DNA Self duplication process of DNA
Semi-conservative in nature
Replication produce molecules with both old and new DNA
Each molecule consists of one old strand and one new one, hence called as semi-conservative
Slide 7 : Experimental evidence for semi-conservative replication:
Meselson and Stahl (1958) provided experimental evidence supporting semi-conservative mode of DNA replication in E. coli by DNA banding techinique
Taylor provided experimental evidence supporting semi-conservative mode of DNA replication in Vicia faba by autoradiographic technique Semi-conservative replication of DNA
DNA Replication : DNA Replication Replication occurs in replication fork or replication bubble
Prokaryotes are mono repliconic
Eukaryotes are multi-repliconic
Step 1: Unwinding of DNA chain : Step 1: Unwinding of DNA chain
Illustrative Problem : Illustrative Problem Unwinding of DNA is done by topoisomerases
exonuclease
helicase
ligase DNA is helical structure & for unwinding negative coiling has to be induced. Topoisomerase is known for inducing negative coiling or unwinding of DNA chain.
Step 2: Priming : Step 2: Priming
Step 3: Polymerization : Step 3: Polymerization DNA polymerase is the main replicating enzyme
Complimentary base pairing occurs
Chain grows in 5’ to 3’ direction
Slide 13 : Step 4: Leading & Lagging strand As a result of further opening of chain, one strand has continuous synthesis and is known as leading strand
Discontinuous synthesis on other strand & is known as lagging strand
Okazaki fragments are formed on lagging strand
Lagging strand is formed as synthess always occurs in 5’ to 3’ direction
Step 5: DNA Polymerase I : Step 5: DNA Polymerase I It act as proof reader
Removes the wrongly inserted base pair
It fills the gap formed due to removal of base pair by complimentary base pairing
Slide 15 : Step 6: DNA Ligase DNA Ligase seals the gap
It forms PDE bond
It is NAD dependent enzyme
Step 7: Topoisomerase (DNA Gyrase) : Step 7: Topoisomerase (DNA Gyrase)
DNA Replication : Prokaryote vs Eukaryote : DNA Replication : Prokaryote vs Eukaryote
Quiz : Quiz Leading & lagging strands are formed simultaneously in both strand of a replicon True / False
Central Dogma : Central Dogma Coined by Crick (1958)
It is flow of information from genetic material to protein synthesis
Involves two steps – Transcription & Translation DNA Transcription m-RNA Translation Protein
Reverse Transcription (Temins & Baltimore) : Reverse Transcription (Temins & Baltimore) Genetic material of retrovirus (like HIV)is RNA
It uses its genetic material for the formation of DNA
Process is known as reverse transcription
Enzyme used in the mechanism is reverse transcriptase m-RNA Reverse
Transcription DNA Transcripton m-RNA Protein
Transcription : Transcription Process of formation of RNA from DNA template
Involves rewriting the genetic message coded in DNA into an RNA molecule
Mechanism can be discussed in 3 steps :
Initiation
Elongation
Termination
Initiation : Initiation Sigma factor disassociate & core enzyme elongates the chain RNA poly binds at P site P site is recognized by sigma factor
Elongation : Elongation DNA chain opens at P site
Core enzyme adds complimentary bases
Chain grows in 5’ to 3’ direction
One chain act as sense strand and other as mis-sence strand
Termination : Termination Core enzyme reaches T site
Rho protein is present at T site
Entire complex is withdrawn & DNA structure is restored
Sigma factor binds with core enz releasing ‘rho’
Rho finally joins T site of DNA
Mutation : Mutation Sudden inheritable changes in genetic material is known as mutation Spontaneous mutation : Occurs randomly & naturally Induced mutation : occurs due to some artificial mutagens
Mutagens : Mutagens
Physical Mutagen : Physical Mutagen Rise in temperature breaks hydrogen bond between the two strands of DNA
High energy radiations like X-rays, a, b, g - rays breaks the PDE bond
UV rays result in the formation of Thymine dimer
Chemical Mutagen : Chemical Mutagen Nitrous acid is deaminating which changes
Chemical Mutagen : Chemical Mutagen Alkylating agents like Nitrogen mustard, diethyl sulphate, dimethyl nitsoamine etc causes methylation or ethylation of nitrogenous bases. The later fails to pair normally & also prevents separation of DNA strand Base analogous are structurally similar but functionally dissimilar to the normal bases. It disturbs in replication and translation. Acridines enter DNA chain in between two base pairs & cause deletion or addition of few bases. It results in frame shift mutation or gibberish mutation
Mechanism of Mutation : Mechanism of Mutation
Inversion : Inversion Mutagen can change the base sequence of cistron in the reverse order
The new sequence will have different codons
It will code for different amino acids GCC TAT TTG GTT TAT CCG
Substitution : Substitution Transition : Purine is replaced by another purine (adenine by guanine)
Pyrimidine is replaced by another pyrimidine ( cytocine by thymine) Transversion : Purine is replaced or subsituted by a pyrimidine basa
and vice versa
Frame-shift Mutation : Frame-shift Mutation Reading of the frame of base sequence shifts laterally either in forward direction due to insertion of base or in backward direction due to deletion of base. Insertion ACC TAT TTG AAC CTA TTT G
Deletion : Deletion Deletion ACC TAT TTG CCT ATT TG One or more segment of DNA is lost
Nonsense Mutation : Nonsense Mutation It stops polypeptide synthesis due to the formation of a terminating codon (UAA, UAG & UGA) Mis-sense Mutation It involves changes in codon resulting into production of non-functional amino acid. Same-sense Mutation
Next Class : Next Class Genetic Code
Translation Join me after reading the topics from CBSE book