3. Transcription and RNA Processing

Question 1

Function rRNA

Answer 1

Most abundant type. Structural component of ribosome

Question 2

Function tRNA

Answer 2

Second most abundant type. Carry amino acids to ribosome.

Question 3

Function mRNA

Answer 3

Specifies amino acid sequence

Question 4

Heterogenous nuclear RNA (hnRNA, pre-mRNA)

Answer 4

Only in nucleus, precursor of mRNA

Question 5

Small nuclear RNA (snRNA)

Answer 5

Participates in splicing (removal of introns) of mRNA

Question 6

Ribozymes have..

Answer 6

Enzymatic activity

Question 7

Prokaryotic RNA polymerase (2)

Answer 7

• Synthesizes all types of RNA

- Core: alfa2,betabeta’.

Question 8

Sigma factor

Answer 8

Required for initiation of transcription in prokaryotes (helps RNA polymerase to recognize promotor region), released immediately after initiation

Question 9

Rho factor

Answer 9

Sometimes needed to terminate transcription in prokaryotes

Question 10

Rifampin

Answer 10

Inhibits prokaryotic RNA polymerase

Question 11

Actinomycin D

Answer 11

Binds to DNA, prevents transcription (pro- and eukaryotes)

Question 12

Three eukaryotic RNA polymerases + function

Answer 12

• RNAP I: nucleolus, 28S, 18S and 5.8S rRNAs
• RNAP II: nucleoplasm, hnRNA/mRNA, some snRNA
• RNAP III: nucleoplasm, tRNA, soms snRNA, 5S rRNA

Question 13

Transcription factor IID

Answer 13

RNA polymerase II

Question 14

Alfa-amanitin

Answer 14

• Toxin from certain mushrooms

- Inhibits RNA polymerase II

Question 15

Binding site for RNA polymerases

Answer 15

Promotor region

Question 16

First base transcribed as RNA

Answer 16

+1 base

Question 17

DNA coding strand is identical to..

Answer 17

mRNA

Question 18

DNA template strand is..

Answer 18

Used for transcription

Question 19

Bacterial/prokaryotic promotor contains two consensus sequences..

Answer 19

1. Pribnow box (TATA box)

2. -35 sequence

Question 20

Rho-independent termination

Answer 20

GC-rich hairpin (=stem + loop) + 6-8 U residues (in newly formed RNA)

Question 21

Rho-dependent termination

Answer 21

Rho binds to newly formed RNA and displaces RNA polymerase from 3’ end of RNA. Also stem and loop (G-C rich hairpin)

Question 22

In bacteria translation and transcription..

Answer 22

Can occur simultaneously (no processing of mRNA, no introns)

Question 23

Prokaryotic ribosomes bind to..

Answer 23

Shine Dalgarno sequences in 5’ UTR

Question 24

Startcodon

Answer 24

AUG

Question 25

Protein in synthesized from.. to..

Answer 25

Amino terminus (5') to carboxyl terminus (3')

Question 26

Monocistronic

Answer 26

One gene

Question 27

Polycistronic

Answer 27

Related genes groups together are transcribed as one unit (eg lactose operon) Only in bacteria

Question 28

Eukaryotic promotor contains two consensus sequences..

Answer 28

1. TATA box (-25, Hogness) | 2. CAAT box (-70)

Question 29

Posttranscriptional processing of mRNA in eukaryotes (2)

Answer 29

1. 7-methylguanosine cap to 5' end | 2. Poly-A-tail to 3' end

Question 30

7-methylguanosine cap

Answer 30

While still being synthesized: ribosome binding site + protection from degradation

Question 31

Poly-A-tail

Answer 31

- Poly-A addition signal is AAUAAA, cut by endonuclease - Poly-A-polymerase adds poly-A tail (200 As) - Protects from degradation and aids in transport

Question 32

Splicing

Answer 32

Removes introns, lariat structure is degraded

Question 33

Spliceosomes

Answer 33

Complexes of snRNA and protein (snRNP, snurp)

Question 34

Example alternative splicing (2)

Answer 34

- Tropomyosin and troponin T | - Immunoglobulins (membrane-bound or secreted)

Question 35

How can alternative splicing be detected?

Answer 35

By Northern Blot

Question 36

Eukaryotic ribosomes

Answer 36

- 40S and 60S -> 80S ribosome - RNAPI (45S -> 28S, 18S, 5.8S) - RNAPIII (5S)

Question 37

Prokaryotic ribosomes

Answer 37

- 50S and 30S -> 70S ribosome - 50S = 5S and 23S - 30S = 16S

Question 38

Shiga toxin and Verotoxin (ETEC)

Answer 38

Inactivate 28S rRNA in 60S subunit. RNA glycosylases remove single adenine residue from 28S, prevents aminoacyl-tRNA binding to ribosome.

Question 39

RNA editing + give example

Answer 39

Insertion, deletion, base alterations | - Cytosine to uracil deamination of apoprotein B gene (B100 in liver, B48 in intestines due to stop codon)