Module 33 Flashcards
Transcription and RNA Processing
Purpose of DNA Replication
Allows genetic information to be transmitted from cell to cell AND generation to generation
How is information transmitted from DNA
When the double helix separates and each parental strand serves as a template.
Central Dogma of molecular biology
The flow from DNA to RNA to proteins.
Transcription
1st step of gene expression
When RNA is synthesized from a DNA template
Where are proteins synthesized
On ribosomes
Where are ribosomes located
in the cytoplasm
Template Strand
The DNA strand that is used as the model for the synthesis of an RNA transcript
RNA polymerase
The enzyme that synthesizes new RNA molecules from DNA
It does so at the 3’ end of the RNA strand
Why does RNA need its own synthesis enzyme
Since RNA contains Uracil instead of Thymine
Growing Transcript
The 3’ end of the newly synthesized RNA molecule
Describe the RNA trancript
The reverse complement of the template strand
What causes RNA to be the reverse complement of its template
RNA grows in the opposite direction that DNA is read in (antiparallel)
The base paring rules= complementary strands
Nontemplate Strand
The DNA strand that is not used as the template for transcription
The same as the new RNA strand
-Same bases and direction
- Also a reverse complement of the template strand
Which strand can also be called the minus, antisense or noncoding strand
the template strand
Three stages of transcription
- initiation
- elongation
- termination
Initiation stage
RNA polymerase and other proteins bind to the double-stranded DNA, the strands separate, and the transcription of the template strand begins
Elongation Stage
Successive nucleotides are added in the 3’ direction of the growing RNA transcript as the RNA polymerase proceeds along the template strand
Termination
RNA polymerase encounters a sequence in the template strand that will cause the transcription to stop and the RNA transcript to be released.
Promoter
regions of a few hundred base pairs on the DNA molecule where RNA polymerase and other proteins bind to start transcription
Terminator
Sequence on DNA strand where transcription stops
How man DNA strands are transcribed per gene
Only one DNA strand is transcribed per gene
Do all genes come from the same template strand
No. Different strands can be used to transcribe different genes
What are other names for the non-template strand
Coding, sense and plus strand
In what type of cells can transcription occur at all times
House keeping genes
Why can transcription occur at all times for housekeeping genes
Since their products are needed at all times in all cells.
How is transcription regulated
It depends on whether the RNA polymerase and associated proteins are able to bind with the PROMOTER
What direction is RNA synthesized in
5’ to 3’ end
In what direction does RNA polymerase move along the DNA strand
3’ to 5’
RNA polymerization
Another name for RNA synthesis
Does RNA proof read
No.
RNA polymerase purposes
5
- Separates DNA strands from each other
- Forms RNA-DNA molecule
- Elongates transcript
- Releases the transcript
- Stores OG DNA double helix
Bond connecting one phosphate t the next
Phosphate bond
Phosphodiester Bond
Attaches the 3’ end of the growing chain to the income nucleotide
Forms the sugar-phosphate backbone
3’ -OH to the 5’ carbon of the nucleotide
Primary Transcript
The RNA transcript that comes off the template DNA strand
Messenger RNA
(mature) mRNA
The RNA molecule that combines with the ribosome to direct protein synthesis
Carries the genetic “message” from DNA to ribosome
RNA Processing
When the primary transcript undergoes a series of chemical modifications that convert it into mRNA
What kind of RNA is transcribed from DNA in prokaryotes
mRNA
In which type of cell does RNA processing not occur
Prokaryotic cells
From what end do ribosomes synthesis proteins
the 5’ end of mRNA
Why does transcription and translation occur at the same place and time in prokaryotes
They do not have a nucleus to separate the DNA from the cytoplasm
When does the primary transcript become mRNA in eukaryotes
Before exiting the nucleus
What other feature does prokaryotic RNA have that DNA doesn’t
They can often have the genetic info for more than one different protein
GTP Cap
A modified nucleotide (7-methylguanosine) attaches to the 5’ end of the primary transcript
The 5’ carbon links with the 5’ carbon of the two nucleotides
-Added with an enzyme
-Instead of a phosphodiester bond
Purpose of the GTP Cap and when is it added
Added during RNA processing
Allows the ribosome to recognize the mRNA
Why is RNA susceptible to enzymes that break them down
Their single-stranded structure
Poly(A) tails purpose
Help export the mRNA into the cytoplasam
Poly(A) tail
250 consecutive adenine nucleotides added to the 3’ end of the transcript
Exons
Regions of the transcript expressed as proteins
Introns
Regions of the transcript not expressed as proteins and are REMOVED from the primary transcript
When are introns remvoed
during RNA processing
What is it called when exons are stitched together and introns are removed
RNA splicing
Purpose of introns
Alternative splicing
Alternative Splicing
Primary transcripts from the SAME GENE are spliced in different ways to produce different mRNA’s and, therefore, DIFFERENT/MULTIPLE PROTEINS products
Allows the same transcript to be processed in diverse ways to produce mRNA molecules with different combos of exons, encoding different proteins
Ribosome RNA
(rRNA)
Noncoding RNA
It makes up most of the ribosomes and is essential for translation
Nucleolus
dense, non-membrane-bound spherical structure within the nucleus
Houses the genes and transcripts for rRNA
nucleolus
Transfer RNA
(tRNA)
Carries individual Amino Acids for use in translation
Most abundant types of RNA molecules in mammals w/ percents
rRNA (80%) of RNA
tRNA (10%) of RNA
