BioChem Quiz 10: Transcription & Regulation of Gene Expression

How is RNA synthesized?

5 to 3 direction (same as DNA replication)

Where does energy to drive bond formation come from?

hydrolysis of high-energy bond of incoming nucleotide

What are the substrates for both DNA and RNA?

4 nucleotide triphosphates (3 of the same, one diff)

How does DNA transcription and Replication use enzymes?

use enzymes to select the appropriate nucleoside triphosphate in a template-directed manner following base-pairing rules

What must occur to the DNA helix to gain access to the genetic info?

2 strands of the DNA helix must be transiently separated

What are the linkages formed between RNA and DNA nucleotides?

3'-5' bonds with chain growth occurring in a 5' to 3' direction

How many strands in DNA?

two strands

sense strand and template strand

How many strands in RNA? What is it identical to?

one

RNA is identical to sense strand of DNA template except U replaces T and ribose replaces deoxyribose

What is true as the RNA chain is synthesized? (difference between replication and transcription)

it does not remain hydrogen-bonded to the DNA template

What is mRNA? What is its role and what % is it of the total RNA?

messenger RNA

DNA transcript, 3%

What is rRNA? What is its role and what % is it of the total RNA?

ribosomal RNA

functions in translations, 80% or more

What is tRNA? What is its role and what % is it of the total RNA?

transfer RNA

deciphers code in mRNA, 15%

Describe the size and shape of RNA molecules in transcription

discrete in size, defined by transcriptional start and stop sites

Which direction does transcription occur along a DNA molecule?

either direction

How many copies does replication make of a genome?

one

How many copies does transcription make of a RNA?

many

Describe the initiation step of transcription

RNA polymerase binds at the DNA start site, known as the promoter, and forms the first bond of the RNA chain

most regulated step

Describe the elongation step of transcription

nucleotides are sequentially added to 3'- end of growing chain in template-directed manner

Describe the termination step of transcription

both the RNA product and RNA polymerase are released from the DNA

What are promoters?

the DNA sequences that the RNA polymerase binds to and initiates transcription

What is the rate at which RNA polymerase utilizes the promoter sequence regulated? What does it determine?

highly regulated

largely determines the rate of transcription and often controls gene expression

What is a repressor?

proteins that bind to DNA that overlaps with the promoter, blocking RNA Polymerase binding and inhibiting transcription

What is an activator?

proteins can bind to DNA and promote RNA Polymerase binding, increasing transcription

Describe strong promoters

have strong (high affinity) interactions with RNA polymerase through the formation of many bonds

more likely to initiate transcription and lead to mRNA synthesis

Describe weak promoters

have weaker interactions with RNA polymerase through the formation of fewer bonds

weaker bonds and fall off the DNA

What represents the strongest affinity site possible for binding?

high conserved consensus sequence --> TATA box

How has evolution tailored each promotor?

tailored each promoter to provide the appropriate amount of RNA and protein for the corresponding gene

Which gene has the stronger promoter?

Gene A

Gene B has a weaker promoter bc less copies

When are promoters in prokaryotes expressed? (no nucleus in prokaryotes)

in the presence of lactose and the absence of glucose

What does DNA Replication use?

DNA polymerase & 4 dNTPs (A, C, G, T)

What does RNA Transcription use?

RNA polymerase & 4 NTPs (A, C, G, U)

How many copies of the genome does DNA Replication make?

one

How many copies of the genome does Transcription make?

many

Does DNA Replication copy one strand or both?

both

Does Transcription copy one strand or both?

one - template strand

What happens to the product in DNA Replication?

stays bound to template

What happens to the product in Transcription?

released from template

What is the error rate of DNA Replication?

low error rate, proofreading

What is the error rate of Transcription?

higher error rate, no proofreading

Describe promoters in prokaryotes

Situation: body is creating proteins to break down lactose because glucose is low

1. central dogma is carried out and active repressor is blocking the area that RNA polymerase needs to bind so no protein to break down lactose is being made

2. lactose in the body binds to repressor to remove it from its site so that RNA can bind

3. meanwhile glucose activates CAP with cAMP to induce transcription and active CAP can bind to CAP site

4. CAP is bound to site and RNA polymerase can bind and transcribe and lactase is made

**if we have high glucose, this process is not needed

Describe promoters in eukaryotes

connect enhancers or repressors to promoter to stop or start the process

Describe promoters & mRNA processing in eukaryotes

exons exit nucleus

introns stay in nucleus

mature transcript is left with all exons