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DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid Central Dogma of Biology How does the information.

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Presentation on theme: "DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid Central Dogma of Biology How does the information."— Presentation transcript:

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2 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid Central Dogma of Biology How does the information flow in biological systems?

3 DNA copy itself: Replication DNA synthesize RNA Transcription RNA synthesize protein Translation Two Main Process: Transcription and Translation

4 DNA (deoxyribonucleic acid) RNA (Ribonucleic acid) Two strands forming a double helix One strand only DeoxyriboseRibose A, C, G and TA, C, G and U H Compare the structure of RNA and DNA

5 3.5.2 DNA Transcription 1.DNA helix unzips 2.One of the 2 DNA strands acts as a template 3. RNA nucleotides line up along one strand of the DNA following the base-pairing rules. 4. No T, Instead U

6 5.RNA polymerase forms covalent bonds between nucleotides. 6.Transcription continues until one entire gene has converted to RNA. 7.The single-stranded messenger RNA separate and the DNA strands rejoin DNA Transcription

7 3.5.3The Genetic Code How do nucleotides specify 20 amino acids? 1.4 different nucleotides (A, G, C, T) 2.Possible codes: 1 letter code 4 AAs<20 2 letter code 4 x 4 = 16 AAs<20 3 letter code 4 x 4 x 4 = 64 AAs >>20 3.Three letter code with 64 possibilities for 20 amino acids suggests that the genetic code is degenerate (i.e., more than one codon specifies the same amino acid).

8 1.Triplete Code 2.Degenerated 3.Universal 3.5.3The Genetic Code

9 Nucleic Acids: RNA types There are 3 different types of RNA: 1.Messenger RNA: Transcription 1.Single strand 2.Transport nucleus – Cytoplasm 2.Ribosomal RNA 1.Structural & Functional component of Ribosomes 3.Transfer RNA: Translation 1.Bring aa to Ribosomes for protein assembly

10 3.5.4 DNA Translation: 1. The base sequence of mRNA is used as a guide for assembling the sequence of amino acids that will be a polypeptide. 2. This process of protein production using a mRNA as a guide is called TRANSLATION. T ACCGAA T GGCC ACCGAGGC UUU G MetionineAlanineTyrosine Arginine DNA mRNA Polypeptide:

11 Translation take place on cell structures called Ribosomes, using mRNA & tRNA. Ribosomes are in the cytoplasm, outside the cell nucleus DNA Translation: Transfer RNA: 1. Amino acids are carried to the ribosomes by smaller RNA molecules called transfer RNA (tRNA). 2. Single strands folded back on themselves: Clover Leaf structures 3. Role = Carry aa to the ribosomes -aminoacid attachment site -anticodon –codon attachment site

12 1. mRNA binds the small subunit of the ribosome 2. tRNA molecules are present, each one carrying the specific aa & anticodon 3. tRNA binds to the ribosome at the site where the anticodon matches the codon on the mRNA 4. Two tRNAs binds at once and the first one in transfers the growing polypeptide chain to the second one in. 5. The ribosome moves along the mRNA and the process continues until a stop codon is reached when the polypeptide is realeased DNA Translation: Process

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14 3.5.4 DNA Translation: Overview

15 3.5.5 One Gene – One Polypeptide Theory One gene is transcribed and translated to produce one polypeptide. Some protein are composed of a number of polypeptides and in this theory each polypeptide has its own gene. e.g. haemoglobin is composed of 4 polypeptides (2 of each type) and there is a gene for each type of polypeptide. This theory, like so many in biology has exceptions. 1) Some genes code for types of RNA which do not produce polypeptides. 2) Some genes control the expression of other genes.


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