Assistant Professor Agril Botany DBCA Sulcorna Quepem Goa DON BOSCO COLLEGE OF AGRICULTURE SULCORNA QUEPEM GOA Affiliated to Goa University BSc Hons Agriculture ID: 911168
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Prepared byDR. PRASHANT PRAMOD PATILAssistant Professor (Agril. Botany)D.B.C.A., Sulcorna, Quepem, Goa
DON BOSCO COLLEGE OF AGRICULTURE, SULCORNA, QUEPEM, GOA
(Affiliated to Goa University)
B.Sc. (
Hons
) Agriculture
Fundamentals of Genetics (2+1=3)
GPB 121
Slide2Genetic Code - CodonGamov :- Ist suggested Triplete genetic code. Nucleotide – ATGC in DNA & AUGC in RNA Three adjacent nucleotide called as Codon.Amino Acids :- 20 different Amino acids required to synthesis protein. Each type of protein determined by sequence of amino acids. Generally one codon required to specify one amino acid.Codon :- A set of nucleotide bases constitute of codon. Each codon specifies a single A.A. eg. AUG – methionine
Slide3Protein :- A polymer of Amino acids.Genetic Code :- Definition… In brief the relation ship between 4 letter language of nucleotides and 20 letters language of amino acids is known as Genetic code.eg. DNA transcribes m-RNA and various base sequences of RNA code for 20 amino acids. So, Triplet of RNA bases i.e. 43 = 64 combinations are sufficient to code 20 Amino acids.
Slide4Properties of Genetic codeThe genetic code is…..TripletUniversalComma lessNon-overlapping Non- ambiguous Redundant Has polarity
Slide5Properties of Genetic codeTriplet :- Code codons… Singlet : 41 = 4 Insufficient to code for 20 Amino Doublet : 42 = 16 acids….Triplet : 43 = 64 (sufficient to code , start and stop for synthesis of protein. Triplet code i.e. 3 RNA bases codes for 1 Amino acid.)
Slide6Properties of Genetic codeUniversal :- The specific codon associated with specific A.A. and same for start and stop signals = applied and valid for all organisms in the Universe i.e. plants, animals and micro-organisms….
Slide7Properties of Genetic codeComma less :- the codons are continuous and there are no demarcation lines between codons, deletion of single base in comma less code changes the entire sequences of Amino acids.
Slide8Properties of Genetic code4. Non-Overlapping :- In non-overlapping code, one base or letter is read only once and six bases are code for Two amino acids. In mutation, one base into another leads in alteration of one amino acid only, it indicates that the codes are non-overlapping.
Slide9Properties of Genetic codeNon- ambiguous :- out of 64 codons of genetic code 61 codons codes for 20 different amino acids, each codons code for only one amino acid. This indicates that codes are Non- ambiguous.
Slide10Properties of Genetic codeRedundant :- Several codons codes for one amino acid. This multiple system of coding is k/as Degenerate or Redundant code system. Such system provides protection against many harmful Mutations.
Slide11Properties of Genetic codeHas polarity :- The codes has definite direction for reading of message, which is referred as Polarity. The message in m-RNA is read in 5’ – 3’ direction, this
Slide12CodonDefinition :- The Triplet sequence of RNA bases which codes for particular amino acid k/as Codon.i.e. 64 triplet codon constitutes genetic code.Types of codon :-Sense codonSignal codon a. Start codon b. Stop codon
Slide13Types of codon :-Sense codon :- codon that codes for Amino acids k/as Sense codon.eg. 61 codons in genetic code which codes for 20 amino acidsCodon
Slide14B. Signal codon :- (Total 4 codons) Those codons that codes for signals during protein synthesis are k/as Signal codon.Types :- a. Start codon/ Initiation codon. Codon initiates synthesis of polypeptide chain k/as Start codon.eg. AUG – (it also codes for Methionine)
Slide15b. Stop codon/ Termination codon/Non Sense codon Those codons which provides signal for termination of polypeptide chain eg. 3 stop codons – UAA, UAG & UGA They do not codes any amino acids. So, called as Non-sense codon.
Slide16Anti codons : Definition : The base sequence of t-RNA which pairs with codons of m-RNA during Translation is called as Anticodons. Anticodons usually written as 3’ - 5’ direction. The nos of t-RNA molecule much lesser than codons. Hence, the anticodon of some t-RNA molecules have to pair with more than one codon.
Slide17ParticularsCodonsAnticodonsAUG (m-RNA)UAC (t-RNA)No. in code64<64Amino acids coded One by one codonSome pair with >1 codonPolarity5’ – 3’ direction3’ - 5’ directionBase no. 1 2 3 3 2 1 Difference Between Codons and Anticodons
Slide18Transcription Translation genetic code and Outline of Protein synthesisGeneral Dogma of molecular biology, transcription unit and translation in eukaryotes and prokaryotes.The process of transcription
Genetic code codon characteristics of genetic code
Process of Translation
Protein synthesis – Process, initiation, elongation and termination.
Slide19TranscriptionDefn : The process of synthesis of m-RNA from DNA template in presence of enzyme RNA polymerase is k/as Transcription Or RNA polymerasem-RNADNA
RNA polymerase
Transcription
Slide20Synthesis : m-RNA synthesized from DNA template i.e. single strand of DNA molecule in nucleus Template strand – DNA strand used for m-RNA synthesis
Coding strand
– DNA strand which does not take part in RNA synthesis.
(Note :
Messenger RNA (m-RNA) passes on information from nucleus to cytoplasm. (mostly related to protein synthesis.
)
Slide212. Enzyme involved : Transcriptase – the RNA polymerase which catalyses the synthesis of m-RNA from DNA template k/as Transcriptase3. Genetic information coded on DNA is copied into molecule of RNA and transferred from DNA to m-RNA. 4. Direction of synthesis – as in DNA replication new RNA synthesized in 5’ – 3’ direction
.
Slide22Mechanism of Transcription Transcription process takes place during interphase and continues up to Prophase
of cell division.
Slide23Requirement of Transcription DNA templateActivated precursors (ATP, GTP, UTP & CTP)Divalent metal ions (Mg++ or Mn
++
)
RNA polymerase
Slide24Major steps of Transcription mechanism Initiation of TranscriptionElongation of RNA chainTermination of RNA chain
Slide25Initiation of Transcription:Site: begins at specific site (Promoter site) Attachment of RNA polymerase at initiation site/ Promoter site to DNA resulted in separation of DNA double helix over a short region.Synthesis of m-RNA begins on one of the two strands of DNA. The RNA chain starts with Triphosphates (PPP) and the first base is always Purines – may be Guanine (PPPG) or Adenine (PPPA).Removal of nucleotides by endo-nucleases after synthesis of terminal Triphosphates.
Slide26Elongation of RNA chainTakes place by addition of activated Ribonucleoside Triphosphates viz ATP – Adenine ribose Triphosphates
GTP – Guanine ribose Triphosphates
UTP – Uracil ribose Triphosphates
CTP – Cytosine ribose Triphosphates
All above to one strand of DNA molecule.
Slide272. The elongation of takes place with the help of core enzyme which moves along the DNA temples.3. Growth of chain tales place in 5’ – 3’ direction.4. Types of transcription based on m-RNA synthesis Symmetric transcription – when both strands of double stranded DNA transcribes for m-RNA is k/as symmetric transcription. Asymmetric transcription – when m-RNA is transcribes by one strand, it is k/as asymmetric transcription.
Slide28Termination of RNA chain (Two ways of RNA chain termination)When DNA receives termination signal or with the help of rho (ρ) factor an additional protein. Terminator gene acts as a signal to end transcription . RAN polymerase joins the nucleotide together to produce m-RAN transcript.
When m-RAN transcript is detached the DNA template strand reform the
bonds .With
its complementary strand resulting in the formation of double
helical structure.
In other words the original double helical DNA structure is restored after m-RNA synthesis
Slide29Mechanism of Translation Translation process is the formation of polypeptide chain (Protein) by using sequence of codons on m-RNA. It is actual process of protein synthesis takes place in the cytoplasmic ribosomes.Major steps of Translation :Activation of amino acids
Formation of AA-t-RNA complex
Formation of polypeptide chain
Initiation of chain
Elongation of
chain
Termination
of chain
Slide30Each step is governed by specific enzymes and cofactors. In the cytoplasm, the amino acids are activated in the presence of ATP and linked to their respective tRNAs by a process called charging of tRNA in the presence of an enzyme aminoacyl synthetase. Thus a number of tRNA molecules, pick up aminoacids freely floating in the cytoplasm and forms aminoacyl-tRNAs.
Slide31The processed mRNA enters the cytoplasm and binds to ribosomes, which serve as work benches for protein synthesis. The ribosome consists of rRNAs and different proteins. Ribosome contains two subunits; the large subunit and the small subunit. The process of translation starts when an initiating aminoacylated tRNA base pairs with an initation codon of an mRNA molecule that has been located by the small subunit of ribosome. Then the larger subunit joins. Two separate and distinct sites are available in the ribosome to which the tRNAs can bind; A (acceptor or aminoacyl attachment) site and P (peptidyl) site. An aminoacyl-tRNA first attaches to site A the kind of aminoacyl t-RNA being determined by the sequence of mRNA (codon) attached to site A. The peptide bonds are formed between the aminoacids
which is
catalysed
by the enzyme
peptidyl
transferase
. The
peptidyl
tRNA
along with the mRNA
codon
moves to the P (
peptidyl
) site making the A site available for the attachment of a new
aminoacyl-tRNA
.
Slide32Thus the translation proceeds and at the end a releasing factor binds to the stop codon terminating the translation. The ribosome releases the polypeptide and mRNA and subsequently dissociates into two subunits. Further processing of polypeptide chain into proteins and enzymes is done in the cytoplasm itself and depends upon the bonding properties of the amino acids joined in them. Most of the mRNA molecules are unstable and degraded after the release of polypeptide chain, but some mRNAs such as those coding for hemoglobin may be stable. When the cell needs large quantities of a particular enzyme or protein, more number of mRNA molecules coding for the same protein are produced to meet the demand.
Slide33Polyribosomes or polysomes: Many ribosomes read one strand of mRNA simultaneously, helping to synthesize the same protein at different spots on the mRNA.Cistron : A sub division of gene which acts as a unit of function with a gene.Muton : A sub division of gene which is the site of mutation.Recon : The smallest subunit of gene capable of undergoing recombination or a sub unit of gene which is the site of recombination.
Slide34Outline of Protein synthesis Thank You