Biochemistry Lecture 12

Front 1

Transcription

Back 1

The synthesis of a ssRNA copy of a segment of DNA

Front 2

Basic Process of Transcription

Back 2

1) DNA unwinds in a short region
2) RNA polymerase catalyzes the synthesis of an RNA in the 5' to 3' direction by reading 3' to 5'
Ribonucleoside triphosphates are the RNA precursor molecules used for RNA synthesis
3) RNA polymerase have ability to synthesize WITHOUT primer

Front 3

Antisense and Sense Strand

Back 3

Is the template strand of DNA that will be used for RNA synthesis. The sense strand will be the other DNA strand, and will have thee same sequence as the RNA synthesized.

Front 4

Comparision of DNA and RNA Syntehesis

Back 4

RNA:
RNA polymerase
NTPs precursor (ribonucleoside triphosphates)
no primer needed
uracil pairs with adenine

DNA:
DNA polymerase
dNTP precursor (deoxyrobonucleoside triphosphate)
primer required for initiation thymine pairs with adenine

Front 5

mRNA

Back 5

encodes the amino acid sequence of a polypeptide. They are the transcripts of a protein coding genes.

Front 6

tRNA (transfer RNA)

Back 6

Brings the amino acids to the ribosomes during the translation process

Front 7

rRNA (ribosomal RNA)

Back 7

Combines with ribosomal proteins to form the ribosome. mRNA is translated into protein at the ribosome

Front 8

snRNA (small nuclear RNA)

Back 8

Combines with certain proteins and is and is involved in RNA processing (mRNA splicing) and gene regulation

Front 9

RNA Polymerase in bacteria

Back 9

There is only only a single RNA polymerase. Associates with protein called sigma factor. Together are called holozyme, the sigma factor recognizes place where transcription starts called a promoter.
Core enzyme has helicase and polymerase activity

Front 10

RNA Polymerases in Eukaryotes

Back 10

RNA Pol1: involved in synthesizing rRNA 5.8S, 18S and 28S
RNA Pol2 2: involved in synthesizing mRNA, some snRNA and miRNA
RNA Pol 3: synthesizes tRNA and some snRNA

Front 11

Promoter and Terminator

Back 11

Located upstream of RNA coding sequence. Where rNA polymerase will bind to before starting transcription.
Termination sequence that tells RNA polymerase will to stop

Front 12

Promoter

Back 12

Prokaryote promoter are found at -35 and -10 bp from transcription site:
-10 sequence: called Pribnow box
This RNA polymerase and sigma factor bind between these two sites, allow itself to position so it starts at +1.

Front 13

Steps of Transcription

Back 13

1) RNA polymerase and sigma factor will bind between -35 and Pribnow sequence. RNA Pol has its own helicase and will begin to unwind DNA about 16 bases in the -10 region. Starts synthesis, no primer needs
2) Elongation: Syntehsizes RNA in the 5' to 3'. Will synthesize 8-9 bases initially and sigma factor disassociates from core enzyme. Sigma only needed for initial binding and synthesis.
3) Chain termination and release of RNA. Reaches termination sequence and stops and separates

Front 14

Rifampin (rifomyocin)

Back 14

-Antibiotic used in tuberculosis
-inhibits transcription
-blocks formation of the first phosphodiester bind by binding to prokaryote RNA polymerase (of eukaryotes not prokaryotes). Binds to beta subunits because of shape and fit (lock and key) -specific base
-Mutations in genes encoding for RNA polymerase can lead to drug resistance

Front 15

Eukaryotic Promoters

Back 15

GC Box: -70 to -200
TATA Box: -20 to -35
CAAT box: -80
Promoters are much more complex in eukaryotes. The positioning of these promoters are variable.

Front 16

Transcription Factors

Back 16

TATA Box binding protein, TFIID, TFIIB, TFIIH, TFIIE