Transcription!

Question 1

Basic features of RNA

Answer 1

Contains the base uracil in place of thiamine
Has a ribose sugar bearing a hydroxyl group on it to prime carbon
Has tertiary structure
Can interact as functional units quaternary structure like in the ribosomes
Various structures of RNA resemble proteins

Question 2

Why is RNA less stable than DNA?

Answer 2

The presence of the hydroxyl group on the two prime carbon on the sugar ribose causes it to react, intramolecularly with the three prime OH site, resulting in a phosphate bond breakage

Question 3

Why use unstable RNA?

Answer 3

RNA evolved first
RNA can form many tertiary structures, allowing it to have different confirmations for different functions. Where has DNA generally only double stranded.
It offers a way of controlling it’s gene level, shutting off expression

Question 4

Types of RNA

Answer 4

mRNA
And non-coding RNA (housekeeping and regulatory)

Question 5

Housekeeping nc RNA

Answer 5

tRNA and rRNA

Question 6

Transcription

Answer 6

Synthesis of RNA from DNA templates
all cellular RNAs are synthesized from DNA templateS
Exhibited as Christmas tree structure

Question 7

What direction is RNA transcribed in? Which direction template is the template strand?

Answer 7

RNA synthesized in the five prime to three prime direction
The template strand is there for the three prime to five prime
RNA synthesis is complementary and anti-parallel to the DNA template strand
New nucleotides are added to the three prime OH group of the growing RNA

Question 8

Which strand is utilized for transcription?

Answer 8

Oh, jeans can be located on either DNA strand
Transcription can utilize either DNA strand as the 3 to 5 template, but transcription always occurs in the five prime to three prime direction

Question 9

Components needed for transcription

Answer 9

1. DNA template
2. 4 ribonucleotide triphosphates (rNTPs)
3. DNA dependent polymerase

Question 10

Differences btw rna and dna synthesis

Answer 10

Similar to DNA synthesis except:
the precursors RRNTs
Only one strand of DNA is used as a template
RNA chain can be initiated without a primer
RNA synthesis is catalyzed by RNA polymerase, and always proceeds in the five prime to three prime direction

Question 11

What does DiNova mean?

Answer 11

Means no primer is required

Question 12

What are the components of the RNA polymerase holoenzyme?

Answer 12

There’s only one RNA polymerase in prokaryotes, called the hollow enzyme
It contains
Alpha
Beta
Better prime
Omega
And sigma

Question 13

Alpha function

Answer 13

Subunit of the holoenzyme
assembly of the tetrameric core

Question 14

Function of beta

Answer 14

rNTP binding site

Question 15

Function of beta prime

Answer 15

DNA template binding region

Question 16

Function of omega

Answer 16

Helps to stabilize the tetrameric core

Question 17

Function of sigma

Answer 17

Binds to the tetrameric core,
Many types of sigma factors allow for specificity
Recognizes and binds to the -35 and -10 consensus sequence in the promoter region
Positions RNA polymerase to begin transcription
Leaves once transcription starts at position this one

Question 18

Initiation in prokaryotes

Answer 18

Once the hollow enzyme is attached to the promoter tightly
RNA polymerase is placed over the transcription start site add position +1
It unwinds DNA to produce a single strand a template
Joins the first two nucleotides

Question 19

Does RNA synthesis/transcription require a primer?

Answer 19

No

Question 20

Elongation in transcription in prokaryotes

Answer 20

Elongation occurs when the sigma factor is released, and RNA polymerase begins to move along the template strand
An rNTP complementary to the dna base of template +1 is the first nucleotide in the RNA mlc
Two phosphate groups are cleaved from each subsequent RNTP
Creates an RNA nucleotide that is added to the 3’ end of the growing RNA mlc

Question 21

Termination

Answer 21

Transcription stops when rna polymerase reaches the terminator region of the gene
This is upstream of where the actual termination takes place
Two types in prokaryotes rho dependent and rho independent

Question 22

How many polymerases do eukaryotes have

Answer 22

Most eukaryotes have at least 3

Question 23

Promoter in eukaryotes

Answer 23

In eukaryotes, there are specific promoter sequences for genes transcribed by rna polymerase 1, 2 and 3
Accessory proteins recognize each of these specific types of promoters (through interaction with their dna sequence)
Pol I, Pol II and Pol III are only recruited to their promoter specific accessory proteins

Question 24

Eukaryotic promoters

Answer 24

More complex than those in prokaryotes
Contain:
A regulatory promoter and a core promoter with
- TFIIB recognition element
- TATA box
- initiator element (transcription start site)
- downstream core promoter element

Question 25

Initiation in eukaryotes

Answer 25

Involves stepwise assembly of general transcription factors of pol II
(TFII A, B, D, E, F and H)
TFIID complex contains the TATA binding protein and is first to assemble at the TATA box, followed by the remaining general transcription factors and Pol II
Forms the pre initiation complex or PIC that is sufficient to initiate basal levels of transcription

Question 26

Mediator

Answer 26

Regulates transcription
Multi subunit complex