Biology 205 Protein Synthesis: Transcription Chapter 11.

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I. Transcription vs translation

• Distinguish between transcription and translation.
• List the main types of RNA. See page 228
• Give the basic function of the following types of RNA:
  • mRNA
  • tRNA
  • rRNA
  • snRNA
• Tell the function of RNA polymerase.
• Distinguish between the template strand and the non template strand.
• Compare the synthesis of RNA during transcription to DNA synthesis.
• Note the directionality of RNA synthesis- similar to DNA. Bases added to 3' end See fig 11.1 and 11.2

II. Structure of genes

• List the three parts of a prokaryotic gene and tell what each does:
• Promoter
  • Define consensus sequence(-10 Box or Pribnow Box)
  • See figure 11.3
• RNA coding sequence
• Terminator

III. Main events in transcription

A. Describe the main events in each of the main steps of transcription in prokaryotes:

• Initiation
  • Explain the role of RNA polymerase, sigma factor and -35 and -10 boxes. See figure 11.4
• Elongation
• Explain what happens to the sigma factor after a small number of RNA nucleotides have been linked together.
• Give the rate of transcription in prokaryotes.
• Termination: RNA polymerase recognizes certain terminator sequences often in conjunction with certain proteins called rho. See p 231

Comment: Transcription in eukaryotes is a bit more complex.

1. There are three RNA polymerases:

• RNA polymerase I transcribes ribosomal RNA genes
• RNA polymerase II transcribes mRNA and some snRNA genes
• RNA polymerase III transcribes some rRNA and tRNA and some snRNA genes

2. As in prokaryotes initiation involves special sequences in the promoter region. See figure 11.5

The TATA box about at position -25 is the best known.

Initiation in eukaryote protein coding genes involves the following steps:

1. Assembly of a set of small proteins called basal transcription factors which bind to one of the boxes such as TATA forming the initial committed complex

2. Attachment of RNA polymerase and other protein factors to the initial complex. Eukaryote RNA polymerases do not recognize the promoter regions directly. The result is the minimal initiation complex.. Other protein factors bind to this complex to form a preinitiation complex. Capable of low rate of transcription

3. Binding of activator proteins at an enhancer site upstream from the TATA box and also to the preinitiation complex.

IV. mRNA production

A. List the main regions common to both prokaryote and Eukaryote mRNA's

• Diagram the general structure of mRNA shown in fig 11.6.
  • Note that the mRNA shown in this figure would result from transcription of the RNA coding sequence shown in figure 11.3
• 5' leader sequence (5' UTR);
• Protein coding sequence
• 3' trailer sequence

B. Eukaryotes: introns and exons

• Explain the role of the following in eukaryote RNA processing:
  • Small nuclear ribonucleoprotein particles (snRNP's) See p 236- 238.
  • Splicosome and the Lariat structure
  • Ligase
• Note other forms of RNA editing see. p 238

V. Other RNA's:

A. Discuss the basic structure of ribosome's

• Compare the size of prokaryote and eukaryote ribosome's. See figure 11.13 and 11.14
  • Comment: the protein components of the ribosome are synthesized in the cytoplasm, imported into the nucleus where they interacted with the rRNA's to form the ribosomal subunits. The subunits then are exported to the cytoplasm (in eukaryotes through the nuclear pores).

B. Explain what is meant by self splicing and ribozymes. See p 242-243

C. Transfer RNA

• Diagram the general shape and parts of a typical tRNA See fig 5.21
• Anticodon Vs codon
• Amino acid at the 3' end. See figure 5.21 - 5.22

Study:

Q11.1 and Q11.2

and under Questions and Problems:

11.1, 11.2, 11.4, 11.17, 11.21

pgd 10/03/02 revised 10/16/04