Molecular basis of DNA transcription

Question 1

Definition of initiation

Answer 1

Beginning of transcription when RNA polymerase binds to promotor

Question 2

Definition of elongation

Answer 2

Addition of nucleotides on mRNA strand, RNA polymerase builds mRNA with complementary base pairs

Question 3

Definition of termination

Answer 3

Ending of transcription, when RNA polymerase crosses stop codon, mRNA strand is complete and detached from DNA

Question 4

Definition of exons

Answer 4

Regions of DNA within a gene formed in mRNA

Question 5

Definition of introns

Answer 5

Don’t code for AA in protein, region of DNA not found in mRNA

Question 6

Definition of capping

Answer 6

Formation of 7-methylguanosine can at 5’ end

Question 7

Definition of polyadenylation

Answer 7

Addition of tail to 3’ end of RNA

Question 8

Definition of methylation

Answer 8

Addition of methyl groups to cytosine bases

Question 9

Definition of acetylation

Answer 9

Addition of acetyl groups to histones

Question 10

Definition of epigenetics

Answer 10

Study of heritable changes in gene expression that occur without DNA sequence change

Question 11

Transcription of DNA

Answer 11

DNA transcribed to RNA from template strand
Uracil replaces thymine in complementary base pairing
RNA polymerase makes RNA
Adds nucleotides in 5’-3’

Question 12

Action of RNA polymerase on mRNA synthesis

Answer 12

Ribonucleoside triphosphates enter RT uptake channels
Combine in active site to form a short region of DNA/RNA
Newly synthesized RNA transcript leaves RNA polymerase

Question 13

3 main steps in RNA transcription

Answer 13

Initiation
Elongation
Termination

Question 14

Initiation in prokaryotic transcription

Answer 14

Sigma factor bound to RNA Pol
Both bind to promoter => transcription starts
Sigma factor dissociates after transcription starts
When RNA Pol detaches, rebinds to Sigma

Question 15

Elongation in prokaryotic transcription

Answer 15

Reading DNA sequence on template and synthesis of mRNA

Question 16

Termination in prokaryotic transcription

Answer 16

Reaching of transcriptional termination site, synthesis ends

Controlled by STOP sequence in DNA, GC rich

Question 17

Eukaryotic transcription, splicing of introns

Answer 17

Only fully processed mRNA exported from nucleus, made available for translation
Some hnRNA spliced in different ways, resulting in different protein product from 1 gene

Question 18

Capping of mRNA

Answer 18

Formation of 7-methylaguanosine cap at 5’ end of RNA
GTP reacts w 5’ of mRNA resulting in addition to 5’ PO4 3-
Guanine methylated at 7’

Question 19

Polyadenylation of mRNA

Answer 19

Addition of A tail to 3’ end of RNA

Question 20

Order of events in eukaryotic transcription

Answer 20

Transcription of DNA=> RNA to form heteronuclear RNA
5' capping
RNA splicing
3' polyadenylation
Translation in cytosol

Question 21

Transcriptional output and types of polymerase

Answer 21

Polymerase I
rRNA (long)

Polymerase II
mRNA
microRNA

Polymerase III
rRNA (5s)
tRNA

Question 22

Transcriptional regulations

Answer 22

All cells have same genome, different regulatory programs
Activators
Repressors
Enhancers

Question 23

Chromatin, methylation and acetylation

Answer 23

When cytosine methylated
Chromatin condenses
Deacetylation of histones, increases +ve charge
Transcription impeded

When cytosine unmethylated
Chromatin uncondensed
Acetylation of histones, decreases -ve charge
Transcription possible

Question 24

Issues with methylation

Answer 24

If DNA repair gene promotor methylated => uncontrolled proliferation

Question 25

What is epigenetic affected by

Answer 25

Age
Diet
Lifestyle

Question 26

What is the difference between
Pribnow Box
TATA Box

Answer 26

Pribnow => prokaryotic promoter

TATA => eukaryotic promoter