DNA transcription

Question 1

enzyme required for prokaryotic transcription

Answer 1

RNA pol holoenzymes

Question 2

parts of RNA pol holoenzymes

Answer 2

1. sigma σ sub-unit or factor: They are responsible for determining the specificity of promoter DNA binding and control how efficiently RNA synthesis (transcription) is initiated.
2. core enzyme: responsible for the polymerization.

Question 3

parts of core enzymes of RNA pol holoenzyme.

Answer 3

1. (2α)
2. one beta (β)
3. one beta prime (β’).
4. one omega (ω).

Question 4

what is promotor region

Answer 4

is a sequence of DNA to which proteins bind to initiate transcription of a single RNA transcript from the DNA downstream of the promoter.

Question 5

what are the enzymes used in eukaryotic DNA transcription.

Answer 5

RNA pol I: give rRNA
RNA pol II: give mRNA
RNA pol III: give tRNA

RNA pol II and III give also snRNA
RNA pol I and III give also rRNA

Question 6

what is gene regulation

Answer 6

a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).

Question 7

what is

What is Enhancer

Question 8

What is Enhancer

Answer 8

An enhancer is a short piece or sequence of DNA that works to enhance or speed up the rate of genetic transcription.

Question 9

what is silencers

Answer 9

a silencer is a DNA sequence capable of binding transcription regulation factors, called repressors.

Question 10

what is a repressors

Answer 10

a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers.

Question 11

Steps of Transcription

Answer 11

1. initiation: Identification of the Promoter region and initiate the transcription.
2. elongation: is the stage of transcription in which the RNA pol a complementary strand of mRNA.
3. termination: the process where a nascent RNA is released from its complex with RNA polymerase and the DNA template.

Question 12

prokaryotic transcription initiation.

i. promoters
ii. enzymes

Answer 12

i. 1. -1o region
2. -35 region
3. + 1 region
ii. RNA pol holoenzymes

Question 13

initiation step in eukaryotic transcription

i. promoters
ii. enzymes

Answer 13

i. 1. TATA box
2. CAAT box
3. GC box

ii. 1. RNA pol I, II, and III
2. General transcription factors ( GTFs)

Question 14

is elongation step of transcription same in both prokaryotic and Eukaryotic cells

Answer 14

yes

Question 15

elongation step of transcription

Answer 15

1. Basically, elongation is the stage when the RNA strand gets longer, thanks to the addition of new nucleotides. During elongation, RNA polymerase “walks” along one strand of DNA, known as the template ( antisense strand ) strand, in the 3’ to 5’ direction.
2. synthesize 5’-3’ strands.

Question 16

role of RNA pol enzymes in the transcription process

Answer 16

1. opens up DNA for transcription
2. hold opened DNA strands from winding again.
3. read antisense strand from 3’ to 5’
4. synthesize RNA strand from 5’ to 3’

Question 17

termination step in transcription

Answer 17

the final step of gene expression, which plays an important role in making an end of RNA without affecting unnecessary gene expression from downstream genes.

Question 18

termination step in prokaryotic cells use main two ways:

Answer 18

1. Rho-dependent termination

2. Rho-independent termination

Question 19

Rho-dependent termination

Answer 19

the rho-protein locates and binds the signal sequence in the mRNA and signals for cleavage.

Question 20

Rho-independent termination

Answer 20

intrinsic termination does not require a special protein to signal for termination and is controlled by the specific sequences of RNA. When the termination process begins, the transcribed mRNA forms a stable secondary structure hairpin loop, also known as a Stem-loop.

Question 21

Eukaryotic termination

Answer 21

1. use poly-adenylation sign AAUAAA to activate enzymes that cleavage RNA to DNA

Question 22

what is post-transcription modifications

Answer 22

are processes that facilitate the generation of mature, functional RNA.

Question 23

three major steps that significantly modify the chemical structure of the RNA molecule:

Answer 23

1. 5’ processing, capping
2. 3’ processing, tailing ( Cleavage and polyadenylation )
3. Introns Splicing

Question 24

5’ processing capping

Answer 24

1. Capping of the pre-mRNA involves the addition of 7-methylguanosine (m7G) to the 5’ end. To achieve this, the terminal 5’ phosphate requires removal, which is done with the aid of a phosphatase enzyme. ( removal of phosphate from 5’ end )
2. The enzyme guanosyl transferase then catalyses the reaction, which produces the diphosphate 5’ end. The diphosphate 5’ end then attacks the alpha phosphorus atom of a GTP molecule in order to add the guanine residue in a 5’5’ triphosphate link. ( addition of GTP molecules )

The enzyme (guanine-N7-)-methyltransferase (“cap MTase”) transfers a methyl group from S-adenosyl methionine to the guanine ring.[4] This type of cap, with just the (m7G) in position is called a cap 0 structure. ( addition of methyl group )

Question 25

To achieve this, the terminal 5’ phosphate requires removal, which is done with the aid of a ……………

Answer 25

phosphatase enzyme

Question 26

………………………………… then catalyzes the reaction, which produces the diphosphate 5’ end. The diphosphate 5’ end then attacks the alpha phosphorus atom of a GTP molecule in order to add the guanine residue in a 5’5’ triphosphate link. ( addition of GTP molecules to 5’ end )

Answer 26

The enzyme guanosyl transferase

Question 27

the enzyme …………………………………..transfers a methyl group from S-adenosyl methionine to the guanine ring.[4] This type of cap, with just the (m7G) in position, is called a cap 0 structure. ( addition of methyl group )

Answer 27

methyltransferase (“cap MTase”)

Question 28

what is the role of capping

Answer 28

1. help to initiate the translation.

2. help to prevent the degradation of the mRNA

Question 29

3’ processing ( Cleavage and polyadenylation ), tailing

Answer 29

1. identification of adenylation end

2. add adenine nucleatide on the end to make poly-A-tail

Question 30

what enzyme is used to identify poly-adenylation end and add adenine nucleatide tail

Answer 30

poly-A-polymerase

Question 31

role of poly-A-tail

Answer 31

1. initiate translation

2. prevent degradation of RNA

Question 32

intron splicing

Answer 32

1. RNA splicing is the process by which introns, regions of RNA that do not code for proteins, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule.
2. Exons are sections of mRNA which become “expressed” or translated into a protein. They are the coding portions of a mRNA molecule. Although most RNA splicing occurs after the complete synthesis and end-capping of the pre-mRNA, transcripts with many exons can be spliced co-transcriptionally.
3. The splicing reaction is catalyzed by a large protein complex called the spliceosome assembled from proteins and small nuclear RNA molecules that recognize splice sites in the pre-mRNA sequence. Many pre-mRNAs, including those encoding antibodies, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences. This process is known as alternative splicing, and allows production of a large variety of proteins from a limited amount of DNA.

Question 33

The splicing reaction is catalyzed by a large protein complex called ……………………….. assembled from ……………………., and …………that recognizes splice sites in the pre-mRNA sequence.

Answer 33

1. the spliceosome
2. proteins
3. small nuclear RNA molecules

Question 34

Alternative splicing, or alternative RNA splicing, or differential splicing

Answer 34

Is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins.