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Lecture 3

BIOLOGY 1A03 Lecture 3: Bio 1A03 Theme 2 Module 1 Trascription


Department
Biology
Course Code
BIOLOGY 1A03
Professor
Dr.Da Silva
Lecture
3

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Saturday, February 4, 2017
Theme 2 Module 1; Transcription
Unit 1; Reading The Blueprint
-DNA acts as a “Blueprint”
Same subunits of DNA are found in both prokaryotes and eukaryotes
Each DNA molecule will contain 1000s of genes that code for proteins, or RNA
molecules that have various functions in the cell
In DNA info is stored
-Interpreted and transmitted for important cellular process
Genes are segments of DNA molecule that is then transcribed into RNA molecules
RNA is either functional alone or is then coded to become proteins
-The Central Dogma
Genes code for specific proteins
Process of copying and interpreting genes into proteins is known as the central
dogma
Proposed by Francis crick in 1950s
Info in DNA acts as blueprint as it specifies sequence in RNA which then specifies
sequence of Amino acids to form proteins
DNA can be copied multiple times into mRNA
Process of going from DNA to mRNA to Protein is gene expression
Unit 2; Transcription in Prokaryotes
-DNA is transcribed from a template strand
Genetic info that codes for RNA is contained within genes on chromosome
RNA consists of Single strand not double strand like DNA
During transcription, DNA is utilized as template to generate complementary and
anti-parallel strand
!1
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Saturday, February 4, 2017
Only one DNA strand will be transcribed
Sequence of RNA is same of the contemplate strand of DNA as it is coding the
template strand of DNA except that uracil replaces thymine
- DNA transcription has a start and end site
Transcription is initiated at a promoter sequence and ends at a terminator
sequence
Transcript is synthesized in a 5’-to-3’ directed
Both DNA strands serve as templates for transcription fro different RNA strands
For RNA to be transcribed from DNA, RNA polymerase (enzyme) attaches to
specific promoter regions of the DNA
Promoter regions indicate starting regions for RNA transcription
RNA polymerase will bind to promoter and once transcription is initiated will move
along DNA in 3’ to 5’ direction
-Will start moving in 3’ to 5’ end on DNA synthesizing RNA from 5’ end to 3’ end
RNA polymerase will keep moving along template strand in 3’-to-5’ direction until
nucleotide sequence on template strand known as terminator will stir transcription
and lead to release of RNA
Terminator is end of specific gene
Once transcription is ended, all transcription machinery included RNA polymerase
is disassembled
- Transcription Initiation
Prokaryotic DNA sits on non-membrane bound nucleoid
prokaryotic gene expression has served as model to understand how gene
expression is turned on and off
In prokaryotes, consensus nucleoid sequence of TATAAT is positioned about 10
base pairs upstream (5’ direction) of start position and serves as part of promoter
region
Consensus sequence represents nucleotide sequence in DNA that is found at this
site rather than the only variation and is derived by comparing particular region of
sequence is many different promoters and finding common elements (nucleotides)
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Saturday, February 4, 2017
Many prokaryotic genes have additional consensus sequences
- TTGCCA sequence, approximately 35 nucleotides upstream of transcription start
cite
These additional sequences enhance rate of transcription
ALL prokaryotes utilize single type of RNA polymerase
Transcription process also requires additional proteins known as sigma factors,
which facilitate binding to promoter region of DNA
To initiate transcription, prokaryotic RNA polymerase is able to recruit different
types of sigma factors as a way to initiate transcription of different types of genes
Initiation of transcription will occur when RNA polymerase binds to sigma subunit
to create hollow enzyme that is capable of binding to and unwinding the double
strand of DNA to allow transcription to occur
Various sigma factors are able to identify promoters for RNA polymerase and assist
with turning genes on and off
- Transcription Occurs Within RNA Polymerase
Process of transcription occurs within RNA polymerase enzyme
Once RNA polymerase binds to promoter region, it separates the double helix
strand into template and non template strand in transcription bubble
When RNA starts the process of transcription, it forms the RNA-DNA duplex
- RNA Polymerase is a Molecular Machine
Once bound to template strand of gene, RNA polymerase engages in open
confirmation and functions as molecular machine
Transcription occurs through the length of gene and RNA nucleotides are added
one nucleotide at a time
Structure of RNA polymerase separates the 2 strands of helix to form transcription
bubble
As transcription continues, RNA polymerase continues to pass the DNA through
channel, transcribe template into complementary RNA, and then threads same
DNA template out through another channel
RNA polymerase restores the DNA double helix after it has been transcribed
!3
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