Transcription

Theme 6

Genes. Structure and function of genes.

1. Learn Basic Anatomy of a Gene

• Promoter - Region of DNA where RNA polymerase attaches and initiates transcription
• Gene - area of DNA which codes mRNA

Transcription

• RNA polymerase binds to promoter region and pries the two strands of DNA apart
• RNA polymerase can only bind to one of the strands of DNA at the 3' end (so that the transcribed mRNA will be constructed 5' to 3')
• The stretch of DNA that will be transcribed is known as the transcription unit
• The promoter includes the transcription start point (AUG) and typically extends several dozen bases "upstream"
• RNA polymerase binds to DNA and begins to synthesize mRNA
• In prokaryotes, RNA polymerase specifically recognizes the promoter and binds
• In eukaryotes, RNA polymerase binding is mediated by one or many proteins called transcription factors
• These transcription factors must be completely bound to the promoter in order for RNA polymerase to bind
• The TATA box is a region about 25 bp's up from the start point which is recognized by the transcription factors
• The completed assembly of transcription factors and RNA polymerase bound to the promoter is known as the transcription initiation complex
• When RNA polymerase is finished, mRNA leaves and is either modified or immediately used to form protein
• Transcription in prokaryotes terminates immediately after the stop sequence is transcribed
• In eukaryotes, transcription usually proceeds at least 30 bp's after the RNA stop signal.
• There is usually a AAUAAA sequence transcribed in the mRNA (TTATTT on the DNA).
• Termination of transcription occurs shortly thereafter

2. Learn the Genetic Code

• universal - with very few exceptions, all organisms use the same code in the formation of protein
• mRNA bases read as triplets (codons). The codons are non-overlapping
• The genetic code is redundant (64 combinations, only 20 aa's)

o Example: CCC, CCU, CCA, CCG all code for Proline

3.Write the corresponding amino acids

AUG	UAU	CAU	UAC	GGA	UAA	AUG	CCU	UAA	UAU	UAA
		o	o	o	o	o	o	o	o	o

4. Learn the structure of tRNA and draw a diagram of the structure of tRNA

tRNA is the interpreter of the codons contained in a mRNA The function of tRNA is to transfer amino acids from teh cytoplasm's amino acid pool to a ribosome The Cell keeps its cytoplasm well stocked with all 20 amino acids, either by synthesizing them or by taking them up from the surrounding solution A charged tRNA is one which has a specific amino acid bound to the acceptor arm Each tRNA has a three-base sequence called the anticodon which binds to a complementary triplet on the mRNA according to the base-pairign rules

5. Learn Lac operon - set of inducible genes involved in digestion of lactose.

Дата добавления: 2015-08-10