7.3 Transcription in prokaryotes

1. 7.3 Transcription in prokaryotes

2. 7.3.1. State that transcription is carried out in a 5’→ 3’ direction. Nucleotides are added in the form of ribonucleoside triphosphates

3. 7.3.2. Distinguish between the sense and antisense strands of DNA.

6. A section of DNA on the antisense strand has the sequence ATT TAG GCG CTA TGC TAG What is the complementary DNA sequence? What is the sequence on the codons of mRNA? What is the sequence on the anti-codons of t-RNA What is the sequence of amino acids?

7. 7.3.3: Explain the process of transcription in prokaryotes, including the role of thepromoter region, RNA polymerase, nucleoside triphosphates and the terminator.

9. Promoter and Terminator

11. DNA in the nucleus of a eukaryotic cell or DNA of the nucleoid region of a prokaryotic cell 5’ 3’ 5’ 3’

13. Transcription: Going from the DNA code to the code of mRNA RNA polymerase has two functions The promoter is a region of the DNA of a specific sequence that signals the RNA polymerase where to start transcription

15. RNA polymerase unwinds the DNA and breaks the hydrogen bonds between the complementary bases

17. Free floating nucleotides are added in a 5’ to 3’ direction. They are also added as ribonucleoside triphosphate (not show in the drawing)

21. RNA nucleotides are added forming a mRNA transcript

23. RNA polymerase also adds complementary RNA nucleotides to the antisense strand of DNA. Nucleotides are added in a 5’ to 3’ direction.

25. The terminator is a region of DNA that signals to the RNA polymerase where to stop transcription

27. At the terminator the RNA polymerase falls off and a mRNA transcript has been formed

28. IB Question: Explain the process of transcription in eukaryotes. [8] N08/4/BIOLO/HP2/ENG/TZ0/XX+

29. IB Question: Explain the process of transcription in eukaryotes. [8] N08/4/BIOLO/HP2/ENG/TZ0/XX+ DNA (sequence) is copied to (m)RNA; DNA separated; RNA polymerases separate the strands; only one strand is copied/transcribed / antisense strand is transcribed; RNA polymerase binds to promoter/initiation region (of template strand); ATP provides energy for attachment; nucleotides exist as nucleotide triphosphates; removal of phosphates (2) from nucleotide triphosphates provides energy for linkage; RNA polymerase catalyses the formation of the polymer / helps the nucleotides join; (m)RNA lengthens in 5' to 3' direction; RNA polymerase reaches terminator on DNA to stop transcription process; mRNA is separated from DNA; [8 max]

30. IB Question: Explain the process of transcription leading to the formation of mRNA. [8] N10/4/BIOLO/HP2/ENG/TZ0/XX

31. IB Question: Explain the process of transcription leading to the formation of mRNA. [8] N10/4/BIOLO/HP2/ENG/TZ0/XX RNA polymerase; (polymerase number is not required) binds to a promoter on the DNA; unwinding the DNA strands; binding nucleoside triphosphates; to the antisense strand of DNA; as it moves along in a 5'→3' direction; using complementary pairing/A-U and C-G; losing two phosphates to gain the required energy; until a terminator signal is reached (in prokaryotes); RNA detaches from the template and DNA rewinds; RNA polymerase detaches from the DNA; many RNA polymerases can follow each other; introns have to be removed in eukaryotes to form mature mRNA; [8 max]

33. One gene may code for multiple polypeptides due to alternative splicing

34. 7.3.4: State that eukaryotic RNA needs the removal of introns to form mature mRNA.

35. How many different mRNA codons can we make with adenine (A), uracil (U), guanine (G) and cytosine (C)? AAA AAU …. …. mRNA codon table

36. Three mRNA codons are stop codons (UAA, UAG and UGA) , so they do not code for any amino acid. So how many mRNA codons code for an amino acid?

37. 7.4 : Translation tRNA molecule about to fold

39. tRNA molecule Once in the cytoplasm, mRNA is translated from the nucleic acid language to the protein language by transfer RNA (tRNA) which acts as an interpreter. Transfer RNA does two things: 1) it recognizes the appropriate codons in mRNA and 2) it picks up the appropriate amino acids.

40. In the process of translation the mRNA codons bind to the anti-codons of tRNA molecules.

41. There are twenty amino acids.

42. There is a specific tRNA activating enzyme for each amino acid. So there are 20 different tRNA activating enzymes.

43. Each tRNA activating enzyme recognizes all the different anti- codons on tRNA molecules for a particular amino acid and will attach the correct amino acid to the tRNA molecule. For example the tRNA activating enzyme for phenylalanine will recognize both the anticodons on the tRNA molecules for phenylalanine

44. 7.4.1: Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy. t-RNA activating enzyme 20 different t-RNA activating enzymes; one for each of the 20 amino acids

45. The type of amino acid which can attach to a tRNA molecule depends on the sequence of the anticodon. A tRNA activating enzyme recognizes the anticodon and uses ATP to bind the appropriate amino acid to the 3' end. Each amino acid has a specific tRNA activating enzyme, and some amino acids have more than one tRNA.

46. 7.4.2: Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites.

48. IB Question: Outline the structure of a ribosome. [4] M10/4/BIOLO/HP2/ENG/TZ2/XX+

49. IB Question: Outline the structure of a ribosome. [4] M10/4/BIOLO/HP2/ENG/TZ2/XX+ small subunit and large subunit; mRNA binding site on small subunit; three tRNA binding sites / A, P and E tRNA binding sites; protein and RNA composition (in both subunits);

50. IB Question: Outline the structure of ribosomes. [6]