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Topic 3.5 Transcription and Translation What is the function of DNA? DNA controls the cell, but how? DNA controls the cell by determining which proteins.

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Presentation on theme: "Topic 3.5 Transcription and Translation What is the function of DNA? DNA controls the cell, but how? DNA controls the cell by determining which proteins."— Presentation transcript:

1 Topic 3.5 Transcription and Translation What is the function of DNA? DNA controls the cell, but how? DNA controls the cell by determining which proteins are made.

2 All enzymes are proteins, so DNA controls which enzymes are made. What do enzymes do? Speed up chemical reactions so they can occur at body temperature.

3 Every chemical reaction in a living organism is controlled by a specific enzyme. http://www.wellesley.edu/Biology/Concepts/Images/enzyme.htm_txt_catalase.gif http://people.hsc.edu/faculty-staff/edevlin/edsweb01/enzyme3.jpg http://nerds.unl.edu/pages/preser/sec/skills/images/enzyme2.gif

4 In order to make protein enzymes, DNA needs to work with RNA.

5 The section of DNA that codes for a polypeptide is called a _______ gene.

6 There are three types of RNA: mRNA (messenger RNA) tRNA (transfer RNA) rRNA (ribosomal RNA) http://www.biologycorner.com/resources/mRNA-colored.gif http://www.juniata.edu/faculty/keeney/trna.gif http://www.biochem.umd.edu/biochem/kahn/bchm465-01/ribosome/16SrRNA.gif

7 DNA is confined to the nucleus. mRNA carries the message from the nucleus to the cytoplasm where the protein will be made http://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/MRNA-interaction.png/300px-MRNA-interaction.png

8 Transcription: step 1 RNA polymerase binds to the promoter (beginning of the gene) and starts to unwind the DNA molecule. http://universe-review.ca/I11-21-mRNA1.jpg

9 Transcription: step 2 http://universe-review.ca/I11-21-mRNA1.jpg RNA polymerase matches free RNA nucleotides to the DNA template strand. Adenines match to uracil, Guanine to cytocine

10 Transcription: step 3 http://universe-review.ca/I11-21-mRNA1.jpg RNA polymerase continues matching RNA nucleotides until it reaches the termination site.

11 The initiation site is preceded by a sequence of A’s and T’s. The initiation site is always TAC so the first three bases of an mRNA are always _____ AUG The termination site is always one of three sets of three nucleotides.

12 Once mRNA is transcribed, it moves out of the nucleus to the ribosome where a protein is made.

13 The sequence of the DNA nucleotides determines the sequence of RNA nucleotides in the mRNA The sequence of RNA nucleotides in mRNA determines the sequence of amino acids in the protein. Next stop: Translation

14 Translation: step 1 The mRNA molecule attaches to the ribosome at the first two codons. A ribosome is made of rRNA and proteins A codon is a set of three nucleotides that code for one amino acid. http://bioweb.uwlax.edu/GenWeb/Molecular/Theory/Translation/ribosome.jpg

15 Translation: step 2 A tRNA matches its anticodon to the mRNA codon. Each tRNA has an specific amino acid attached to its opposite end. http://bioweb.uwlax.edu/GenWeb/Molecular/Theory/Translation/ribosome.jpg

16 A second tRNA anti codon bonds to the next codon The two amino acids are now close enough to bond. An enzyme catalyzes this condensation reaction. http://www.scq.ubc.ca/wp-content/uploads/2006/08/protein-synthesis.gif

17 The bond between the first tRNA and its amino acid is broken, the tRNA floats away to find another of the same kind of amino acid. http://media-2.web.britannica.com/eb-media/80/780-004-BB3E8762.gif

18 Another tRNA (with another amino acid) hydrogen bonds to the next mRNA codon. The ribosome moves down one codon on the mRNA.

19 The next two amino acids bond in a _______________ reaction condensation

20 This continues until the ribosome hits a stop codon. ( UAA,UAG, UGA) The tRNAs that bond to the stop codons do not have an amino acid attached so the protein is released.

21 One gene/one polypeptide “theory” Because each gene codes for a single mRNA and each mRNA codes for a single protein, scientists determined that each gene coded for one protein. 20,000 to 25,000 genes How many genes do humans have? http://www.life.uiuc.edu/ib/494/images/genome.jpg

22 http://www.umiacs.umd.edu/labs/CLIP/BIP/BIPASS/images/WhyAS_clip_image002.jpg Text Scientist have recently discovered that each mRNA can be modified before it reaches the ribosome and the modifications determine which protein will be made.

23 Summarize Animation

24 http://www.youtube.com/w atch?v=lpb5s2F1pyM

25 Homework: Make a chart comparing DNA and RNA (mRNA, tRNA and rRNA), including the structure (type of sugars, phospates and bases), size, shape, types of nucleotides, location and functions.

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