Chemical Basis of Inheritance: Genes to Proteins

Chemical Basis of Inheritance: Genes to Proteins.

Flow of Genetic Information. Image result for genes to proteins.

Chromosome. This series of diagrams and transmission electron micrographs depicts a current model for the progressive levels of DNA coiling and folding. The illustration zooms out from a single molecule of DNA to a metaphase chromosome. which is large enough to be seen with a light microscope. helix (2 nm in Histones Nuckoscyne (10 nm in Histone tail.

Chromosome. C hrotnatid (7(X) run) 3CD-nm fit— 30-nm fiber The next level of l»cking results from.

Learning Outcome for this Module. What is the chemical basis of inheritance? DNA Replication is the process through which DNA makes two identical copies of itself. Central Dogma of Molecular Biology : DNA directs the synthesis of RNA and RNA directs the synthesis of Protein Transcription is the process of making mRNA from the information stored in DNA. Translation is the process of making proteins from the information carried by mRNA. Mutation is the permanent change in the DNA sequence..

DNA Replication. Image result for dna replication.

Simplistic Picture of DNA Replication. Origin of replication Double-stranded DNA molecule Bubble Eukaryotic chromosome Parental (template) strand Daughter (new) strand Replication fork Two daughter DNA molecules.

Detailed picture of start of DNA Replication. Topoisomerase breaks, swivels, and rejoins the parental DNA ahead of the replication fork, relieving the strain caused by unwinding. 5' 3' Helicase unwinds and separates the parental DNA strands. Primase synthesizes RNA primers, using the parental DNA as a template. 5' 3' Replication fork Single-strand binding proteins stabilize the un- wound parental strands. 3' RNA primer 5'.

- Replication occurs at the rate of ~50 nucleotides per second. - The rate of mutation is approx. 1 per 100 million nucleotides. (Talk about efficiency!!).

Template Strands as a result of Replication. (a) The parental molecule has two complemen- tary strands Of DNA. Each base is paired by with its sgx•cific partner. A with T and G with C. (b) First. the two DNA strands are separate•d. Each parental strand can now serve as a template for a new. complementary strand. (c) Nudeotides complementary to the parental (dark blue) strand are connected to form the sugar-phosphate tmex)nes Of the rrw •daughter • (light blue) strands..

Questions to ask… How does the information in DNA result into traits of an individual such as albinism, brown hair, joined ears etc … DNA inherited by an individual leads to specific traits by dictating the synthesis of proteins and of RNA molecules..

Transcription: Process by which the RNA is synthesized using information present in DNA The RNA which is synthesized through transcription carries the information for protein synthesis and hence, is known as messenger RNA ( m RNA).

Pictorial representation of the ‘Central Dogma’. apndedÅ10d ewosoq!Y VN'dl_u VN81-U-OJd VNQ edopnue JeapnN NOIIVISNVHI nsV1dOLO sn-31)nN 9NlSS3)OHd VNU N011dlH)SNVH1.

There are only 4 nucleotides but 20 amino acids which means certainly 1 nucleotide can’t encode for 1 amino acid..

Genetic code: m RNA Codons. mRNA base UUU phe UUC UUA Leu I-JUG CUU CUC Leu CUA COG A1-JIJ AUC Ile AUG start GUIJ GUC Val GUA GUG Second UCU UCC UCA IJCG CCU ccc pro CCA CCG ACU ACC Thr ACA ACG GCU GCC Ala UAU UAC UAA I-JAG CAU CAC CAA CAG AAU AAC AAG GAU GAC GAA GAG Stop Stop His Gln Asn Asp Glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG Cys Stop Trp Arg Ser Arg Gly GCA GCG.

Prof. Har Gobind Khorana Prof. Robert Holley. Cracking the code.

Triplet Codon and transfer of information. abstract.

mRNA code 5’- CUACCAAGGGGUAACCGA -3’. Polypeptide Sequence: Leu-Pro- Arg - Gly-Asn-Arg.

Evolution of Genetic Code. (a) Tobacco plant expressing a firefly gene. The yellow glow is produced by a chemical reaction catalyzed by the protein product of the firefly gene. (b) Pig expressing a jellyfish gene. Researchers injected a jellyfish gene for a fluorescent protein into fertilized pig eggs. One developed into this fluorescent pig..

Transcription. Transcription - Servier Medical Art.

Transcription: An overview. Promoter 5' 3' Transcription unit DNA 3' 5' Start pint RNA polymerase O Initiation. After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand..

Rewound DNA 5' 5' RNA transcript @ Elongation. The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5' —i 3'. In the wake of transcription, the DNA strands re-form a double helix. 3' 5'.

Initiation Step: A Closer Look. RNA polymerase II 5' 5' Transcription factors 3' 5' RNA transcript Transcription initiation complex.

Elongation Step. RNA nucleotides 3' 5' 5' Nontemplate strand of DNA RNA polymerase T C CA 3' end Direction of transcription 5' 3' Template strand of DNA Newly made RNA.

Termination Step. RNA Polymerase transcribes a DNA sequence of – AAUAAA- which acts as a signal. This sequence is known as ‘ Poly-Adenylation ’ or ‘ Poly-A ’. The moment this sequence is transcribed, some proteins are recruited which cleaves the pre- m RNA from the polymerase some 10-35 nucleotides downstream..

Translation. mRNA directed synthesis of polypeptides (eventually proteins)!!.

Translation: An Overview. Translation is the mRNA directed synthesis of a polypeptide chain..

Molecular Component-I: Transfer RNA ( t RNA). 5' Hydrogen bonds Anticodon Amino acid attachment site 3' Anticodon.

Molecular Component-II: Ribosomes. P site (Peptidyl-tRNA binding site) E site (Exit site) mRNA binding site Exit tunnel A site tRNA binding site) subunit — Small subunit.

Stages of Translation: Initiation. 3' 5' Met Initiator tRNA mRNA 5' Start mRNA binding site 5' 3' GTP 3' Small ribosomal subunit P site Met Tjtl 5' Large ribosomal subunit 3' O A small ribosomal subunit binds to a molecule of mRNA. In a bacterial cell, the mRNA binding site on this subunit recognizes a specific nucleotide sequence on the mRNA just upstream of the start codon. An initiator tRNA, with the anticodon UAC, base-pairs with the start codon, AUG. This tRNA carries the amino acid methionine (Met). Translation initiation complex The arrival of a large ribosomal subunit completes the initiation complex. Proteins called initiation factors (not shown) are required to bring all the translation components together. Hydrolysis of GTP provides the energy for the assembly. The initiator tRNA is in the P site; the A site is available to the tRNA bearing the next amino acid..

Stages of Translation: Elongation. Ritx»sorne ready fcy rvxt aminoacyl t RNA O Translocation. The ribosome translocates the tRNA in the A site to the p site. At the same time, the empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its tX)und tRNAs, bringing the next codon to translated into the A site. Amiro Of plypeptide GDP + GTP site site GDP O Codon The anticcxion of an incoming aminoacyl tRNA base. pairs with the complementary mRNA codon in the A site Hydrolysis Of GTP increases the accuracy and efficiency Of this step, Although not shown, many different aminoacyl tRNAs are present. but only the one with the appropriate anticodon Will bind and allow the cycle to progress. Peptide bond formation. n rRNA molecule of the large ribosomal subunit catalyzes the formation of a peptide bond between the amino group Of the new amino acid in the A site and the cartx»xyl end of the growing polypeptide in the P site. This step removes the polyg»ptide from the tRNA in the P site and attaches it to the amino acid on the tRNA in the A site..

Stages of Translation: Termination. 5' factor Stop codcn (UAG. UAA. UGA) 5' 2 GDP + 21)' O Whel a riboscxne reaches a stcp codon on mRNA ttw A site of the ribosome a -release factor. a protein shaped like a tRNA instead of an aminoacyl tRNA. The rekase prcmotes hydroysis Of the bond between typ tRNA in the P site and tip last amirx) acid Of the polypeptide. thus freeing the from ritx»scme. O Tip two ribcmmal subunits tre other ccmporpnts of ttp assernuy åssociate..

Computational Model of Translation. DNA "bosome TRANSLATION Polypeptide Growing polypeptide tRNA molecules Exit tunnel Large subunit Small subunit 5' mRNA 3'.

Summary of Central Dogma. DNA RNA Protein Transcription factor Promoter Transcribed region Gene 1 Gene 2.

Mutation. A permanent change in the DNA sequence is known as ‘ Mutation ’. Mutations can change the phenotype (observable features) of an organism. If the mutations occur in germ cells, they can be passed on from generation to generation. Most of the mutations are neutral , some are beneficial while others have adverse effect . In case of adverse effect, it is called as genetic disorder or hereditary disease. Mutations are ultimate source of variation on which natural selection works during evolution and leads to the birth of new species. Mutations are purely random in nature..

Types of small scale mutations: Single nucleotide pair substitution - Silent Mutation - Missense mutation - Nonsense mutation (2) Nucleotide pair insertions and deletions.

Substitution: Silent mutation. Wild type DNA template strand 3' mRNA 5' Protein Amino end T A T Met G G A T A A C G A u A U A T U c G G c G G Gly G c T U A 5' A Stop Carboxyl end.

Substitution: Missense mutation. Wild type DNA template strand 3' mRNA 5' Protein Amino end A A T U c G G U Met T A Lys C G U U c G G Gly 5' c T Stop Carboxyl end.

Stark Effect of Missense mutation. Wild-type Wild-type ß-globin DNA mRNA Normal hemoglobin Sickle-cell Mutant ß-globin DNA mRNA Sickle-cell hemoglobin In the DNA, the mutant (sickle-cell) template strand (top) has an A where the wild- type template has a T. The mutant mRNA has a U instead of an A in one axion. The mutant ß-globin has a valine (Val) instead of a glutamic acid (Glu)..

Substitution: Nonsense mutation. Wild type DNA template strand 3' mRNA 5' Protein Amino end A A T U c G G U Met T A Lys C G U U c G G Gly 5' c T Stop Carboxyl end.

Nucleotide pair insertions and deletions: Insertion Mutation.

Nucleotide pair insertions and deletions: Deletion Mutation.

Deletion Mutation. Wild type DNA template strand 3' mRNA 5' Protein Amino end A A T U c G G U Met T A Lys C G U U c G G Gly 5' c T Stop Carboxyl end.

Causes of Mutations. Errors during DNA replication is a major cause. Leads to substitution, insertion or deletion of nucleotide bases. - The rate of such mutation is ~ ONE in 10 billion . Physical and chemical agents can also cause mutations. They are known as ‘ Mutagens ’. X-ray is one such physical agent. Some chemicals can interact with DNA in number of ways and hence, can be mutagenic in different ways..