Transcription RNA, Processing, and Translation

Bio exam 2 chapter 17

What is Gene expression?

the control of which genomic information is used

What do RNA polymerases do?

synthesize an RNA version of the instructions stored in DNA

What are RNA polymerases?

An enzyme that catalyzes the transcription process

Do DNA polymerases require a primer to begin transcription?

yes

Do RNA polymerases require a primer to begin transcription?

no

How many RNA polymerase do bacteria have?

One

What does RNA polymerase use to make RNA molecules?

Ribonucleoside triphosphates (NTPs)

How many RNA polymerase do Eukaryotes have?

at least three distinct types (RNA polymerases I, II, III)

What does RNA polymerase II synthesize?

mRNA and other RNAs

What do RNA polymerase do similar to DNA polymerase?

preform template-directed synthesis in the 5’ → 3’ direction

What do RNA polymerase do that is NOT similar to DNA polymerase?

RNA polymerases do not require a primer to begin transcription

What are the three steps of transcription?

Initiation, elongation, termination

What is the first phase of transcription?

Initiation

Can RNA polymerase initiate transcription on its own?

no, a sigma protein must bind to it first (in bacteria)

What gets formed when RNA polymerase and sigma bind?

a holoenzyme

What are sigma proteins responsible for?

recognizing sites called promoters where transcription occurs

What is a core enzyme

A minimal set of subunits required for the catalytic activity of an enzyme

what is RNA polymerase responsible for

transcribing genes

What are bacterial promoters

a DNA sequence about 40-50 base pairs long that contains two sites that are recognized by the sigma protein as promoters

what are the two sequences recognized by the sigma protein?

The -10 box and -35 box

What is the -10 box

a sequence ~10 bases “upstream” of the transcription start site

What does “upstream” vs “downstream” mean

“downstream” - the same direction that RNA polymerase moves

“upstream” - the opposite direction that RNA polymerase moves

What is the -35 box sequence

a sequence ~35 bases “upstream” of the transcription start site

What do bacteria do in order to recognize the -10 and -35 boxes

make several sigma proteins which will recognize the -10 box and -35 box with different affinity

How does transcription begin

when the sigma part of the holoenzyme complex binds to the -35 and -10 boxes

How many orientations can the sigma protein bind in

only one

What does promoter orientation do?

determines which DNA strand will be used as the template and determines direction RNA polymerase will move

How is a transcription bubble formed?

When RNA polymerase opens the DNA double helix

How does polymerization begin?

When complementary NTPs pair with complementary DNA bases

How do NTPs enter the active site?

incoming NTPs enter a channel in the enzyme and diffuse into the active site

what is polymerization?

When many monomers come together to form polymers

What is the second phase of transcription?

elongation

What is the third phase of transcription?

termination

what happens during elongation?

RNA polymerase reads the DNA template and nucleotides are added to the 3’ end of the RNA

when does termination occur

when RNA polymerase transcribes a transcription-termination signal

what is a transcription-termination signal

a code for RNA that forms a hairpin structure, causes the RNA polymerase to separate from the RNA transcript

How many polymerases are formed with eukaryotic transcription?

three RNA polymerases

What is the general difference between eukaryotic and bacteria transcription

overall message is increased complexity, increased gene expression regulation

what is the Poly-A signal sequence?

a signal that is transcribed rather than a hairpin, and the RNA downstream is cut

Where does transcription occur in eukaryotic cells?

in the nucleus

Where does translation occur in eukaryotic cells?

in the cytoplasm

what is the difference in the result of transcription between bacteria and eukaryotes?

In bacteria, transcription produces fully functional RNAs. In eukaryotes, the initial product of transcription is an immature primary transcript or pre-mRNA

what has to happen to the primary transcript/pre-mRNA before it can be translated

must undergo RNA processing

what do primary RNA transcripts contain

exons and introns

what are exons and introns

exons are coding sequences that are retained in mature mRNA. introns are non-coding intervening sequences.

How are introns removed?

splicing

How is splicing catalyzed?

small nuclear ribonucleoproteins (snRNPs)

What is a spliceosome

a complex formed by small nuclear RNAs (snRNAs) and protein

what does splicing do?

allows different mRNAs and proteins to be produced form a single gene

How many steps are there to splicing?

Four steps

What is the first step of splicing?

snRNPs bind to the 5’ exon-intron and 3’ intron-exon boundaries and to an A near the end of the intron

What is the second step of splicing?

other snRNPs join complex to form a spliceosome

what is the third step of splicing?

The intron forms a single-stranded stem plus a loop (lariat) with A as its connecting point

what is the fourth step of splicing?

The lariat is cut out and the two exons are linked. The intron is degraded