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Genes and Protein Synthesis

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Presentation on theme: "Genes and Protein Synthesis"— Presentation transcript:

1 Genes and Protein Synthesis
Chapter 7 Genes and Protein Synthesis

2 One Gene-One Polypeptide Hypothesis
DNA contains all of our hereditary information Genes are located in our DNA ~25,000 genes in our DNA (46 chromosomes) Each Gene codes for a specific polypeptide

3 Main Idea Central Dogma Francis Crick (1956)

4 Overall Process Transcription Translation DNA to RNA
Gene 1 Gene 3 DNA molecule Transcription DNA to RNA Translation Assembly of amino acids into polypeptide Using RNA Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid

5 Key Terms RNA transcription TATA box Introns, Exons mRNA, tRNA, rRNA
Initiation, Elongation, Termination TATA box Introns, Exons mRNA, tRNA, rRNA Translation Ribosome Codon Amino Acids Polypeptide

6 Adenine pairs with Thymine Adenine pairs with Uracil
DNA RNA Double stranded Single stranded Adenine pairs with Thymine Adenine pairs with Uracil Guanine pairs with Cytosine Deoxyribose sugar Ribose sugar

7 DNA to Protein Protein is made of amino acid sequences 20 amino acids
How does DNA code for amino acid?

8 Genetic COde Codon AA are represented by more than one codon
Three letter code 5’ to 3’ order Start codon Stop codon AA are represented by more than one codon 61 codons that specify AA

9 Amino acids Abbreviated Three letters

10 Transcription DNA to RNA Occurs in nucleus Three process Initiation
RNA polymerase Transcription DNA of gene Promoter DNA Terminator DNA DNA to RNA Occurs in nucleus Three process Initiation Elongation Termination Initiation Elongation Termination Growing RNA Completed RNA RNA polymerase

11 initiation RNA polymerase binds to DNA Binds at promoter region
TATA box RNA polymerase unwinds DNA Transcription unit Part of gene that is transcribed

12 Elongation RNA molecule is built Primer not needed 5’ to 3’
RNA polymerase Primer not needed 5’ to 3’ 3’ to 5’ DNA is template strand Coding strand DNA strand that is not copied Produces mRNA Messenger RNA DNA double helix reforms

13 Termination RNA polymerase recognizes a termination sequence – AAAAAAA
Nuclear proteins bind to string of UUUUUU on RNA mRNA molecule releases from template strand

14

15 Post-transcriptional modifications
Pre-mRNA undergoes modifications before it leaves the nucleus Poly(A) tail Poly-A polymerase Protects from RNA digesting enzymes in cytosol 5’ cap 7 G’s Initial attachment site for mRNA’s to ribosomes Removal of introns

16 Splicing the pre-MRNa DNA comprised of Spliceosome
Exons – sequence of DNA or RNA that codes for a gene Introns – non-coding sequence of DNA or RNA Spliceosome Enzyme that removes introns from mRNA

17 Splicing Process Spliceosome contains a handful of small ribonucleoproteins snRNP’s (snurps) snRNP’s bind to specific regions on introns

18 Alternative Splicing Increases number and variety of proteins encoded by a single gene ~25,000 genes produce ~100,000 proteins

19 Translation mRNA to protein Ribosomes read codons
tRNA assists ribosome to assemble amino acids into polypeptide chain Takes place in cytoplasm

20 tRNA Contains Are there 61 tRNA’s to read 61 codons? triplet anticodon
amino acid attachment site Are there 61 tRNA’s to read 61 codons?

21 TRNa: Wobble Hypothesis
First two nucleotides of codon for a specific AA is always precise Flexibility with third nucleotide Aminoacylation – process of adding an AA to a tRNA Forming aminoacyl-tRNA molecule Catalyzed by 20 different aminoacyl-tRNA synthetase enzymes

22 Ribosomes Translate mRNA chains into amino acids
Made up of two different sized parts Ribosomal subunits (rRNA) Ribosomes bring together mRNA with aminoacyl-tRNAs Three sites A site - aminoacyl P site – peptidyl E site - exit

23 Translation process Three stages Initiation Elongation Termination
Amino acid Translation process Polypeptide A site P site Anticodon mRNA Three stages Initiation Elongation Termination 1 Codon recognition mRNA movement Stop codon New peptide bond 2 Peptide bond formation 3 Translocation

24 Initiation Reading frame is established to correctly read codons
Ribosomal subunits associate with mRNA Met-tRNA (methionine) Forms complex with ribosomal subunits Complex binds to 5’cap and scans for start codon (AUG) – known as scanning Large ribosomal subunit binds to complete ribosome Met-tRNA is in P-site Reading frame is established to correctly read codons

25 Elongation Amino acids are added to grow a polypeptide chain
A, P, and E sites operate 4 Steps

26 Termination A site arrives at a stop codon on mRNA
UAA, UAG, UGA Protein release factor binds to A site releasing polypeptide chain Ribosomal subunits, tRNA release and detach from mRNA

27 polysome a b What molecules are present in this photo? Red object = ?

28 Prokaryotic RNA transcription/Translation
Throughout cell Single type of RNA polymerase transcribes all types of genes No introns mRNA ready to be translated into protein mRNA is translated by ribosomes in the cytosol as it is being transcribed


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