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DNA, RNA & Proteins Transcription Translation Chapter 3, 15 & 16.

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Presentation on theme: "DNA, RNA & Proteins Transcription Translation Chapter 3, 15 & 16."— Presentation transcript:

1 DNA, RNA & Proteins Transcription Translation Chapter 3, 15 & 16

2 Learning Outcomes Explain how DNA carries the instructions for the characteristics of individuals. Given a sequence of DNA, write the sequence of mRNA and the resulting amino acids. Explain how defects in a sequence of DNA causes a defect in proteins and causes disease.

3 Sequences of DNA code for proteins indirectly Sequence of bases in DNA is used to produced mRNA The order of the bases in mRNA determines the order of the amino acids (mRNA codes for specific amino acids) Amino acids combine to make proteins

4 Understanding the Code George Gamow predicted that each word (codon) in the genetic code —the rules that specify the relationship between a sequence of nucleotides in DNA or RNA and the sequence of amino acids in a protein—would be three nucleotides long based = minimum code length that could specify the 20 different amino acids found in proteins.

5 How Did Researchers Crack the Code? The three-nucleotide sequence coding for each amino acid. Most of the 20 amino acids have multiple codons that designate their addition to a protein.

6 Genetic Code Redundant: – More than 1 triplet can code for the same amino acid Not Ambiguous – No triplet codes for more than 1 amino acid

7 Central Dogma of Molecular Biology The DNA is copied or transcribed into RNA RNA is translated in protein Applies to ALL cells

8 Exceptions to the Central Dogma Many genes code for RNA molecules that do not function as mRNAs and are not translated into proteins. – These other RNAs perform important functions in the cell. Sometimes information flows in the opposite direction—from RNA back to DNA. – For example, some viral genes are composed of RNA and use reverse transcriptase, a viral polymerase, to synthesize a DNA version of the virus’s RNA genes. – HIV

9 Central Dogma of Molecular Biology

10 The Messenger RNA Hypothesis DNA mRNA Do mRNA molecules connect DNA to proteins? mRNA Ribosome Protein DNA is found in the nucleus Protein synthesis takes place in the cytoplasm

11 The Central Dogma of Molecular Biology The central dogma summarizes the flow of information in cells: DNA is transcribed (copied) into RNA, and RNA is translated into protein.

12 DNA Stores information long-term Allows for stable maintenance of information

13 Transcription: Making RNA from DNA DNA unzips RNA polymerase synthesizes RNA by transcribing one strand of DNA Complementary base pairing

14 Initiation: How does transcription begin? Transcription factors-proteins Promoters – sections of DNA where transcription begins RNA polymerase

15 Transcription Is the Synthesis of RNA from a DNA Template

16 Initiation Promotor- sequence of bases telling RNA Polymerase where to bind. RNA Polymerase binds to exposed DNA template

17 Elongation RNA Polymerase Moves along DNA Template mRNA continues to elongate

18 Termination Termination sequence is a sequence of bases telling RNA Polymerase to stop

19 Exons, Introns, and RNA Splicing The transcription of eukaryotic genes by RNA polymerase generates a primary transcript that contains exons and introns. Introns are removed by splicing.

20 RNA Splicing

21 Other Aspects of Transcript Processing: Caps and Tails Two additional steps of RNA processing are performed in eukaryotic cells after splicing of the primary transcript: the addition of a 5' cap and a poly (A) tail (Figure 16.7). The 5' cap serves as a recognition signal for the translation machinery, and the poly (A) tail extends the life of an mRNA by protecting it from degradation.

22 Transcription Produces mRNA – Messenger RNA which is code for a protein carried from nucleus to the cytoplasm for translation tRNA – Transfer RNA 3-D protein transfers specific amino acids to the ribosome

23 mRNA Shuttles information from DNA to translation machinery (ribosomes) Unstable Intermediary between a sequence of DNA (gene) and proteins

24 tRNA

25 mRNA & tRNA exit nucleus

26 Amino Acid Activation



29 Translation – protein synthesis Sequence of bases in mRNA is converted to amino acid sequence Amino acid sequence = protein mRNA is decoded by ribosomes

30 Ribosomes Site of protein synthesis Consist of large and small ribosomal subunits and rRNA tRNA is adapter molecule


32 Initiation of Translation Ribosome binding site AUG start codon

33 Ribosome The A site of the ribosome is the acceptor site for an aminoacyl tRNA. The P site is where a peptide bond forms that adds an amino acid to the growing polypeptide chain. The E site is where tRNAs no longer bound to an amino acid exit the ribosome.

34 Initiation Phase

35 Termination Phase


37 © 2011 Pearson Education, Inc.

38 Post-translational modifications ER, Golgi Add sugar or lipid groups Add or remove phosphates Insulin – Proinsulin active hormone – C-peptide (remaining portion of proinsulin)

39 © 2011 Pearson Education, Inc.

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