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Flashcards in Transcription_Molecules Deck (48):
1

What is the central dogma of biology for transcription?

DNA -> RNA

2

What is the central dogma of biology for translation?

RNA -> Protein

3

Where is transcription and translation taken place in prokaryotic cell?

in the same place. translation happens right after transcription

4

Where is transcription and translation taken place in prokaryotic cell?

Eukaryotic cells have a nuclear membrane,e therefore transcription and translation takes place in different compartments: transcription - nucleus; translation - cytoplasm

5

What is transcription?

When DNA of the gene is first copied into a single stranded molecule of messenger RNA

6

What is translation?

During ribosomal protein synthesis, the base sequence of mRNA is used to specify the AA sequence of a polypeptide

7

What are the properties of RNA?

1) Usually single stranded
2) Genetic material of RNA virus

8

What is the function of RNA?

1) Functional
2) Regulatory
3) Gene expression

9

What is the functional role of RNA?

e.g. Translation machinery
- rRNA (ribosomal RNA)
- tRNA (transfer RNA)

10

What is the regulatory role of RNA?

control of gene expression - microRNA (miRNA)

11

What is the gene expression role of RNA?

mRNA (messenger RNA) copy of 1 gene for translation by ribosomes

12

What happens when different parts of RNA base pair with each other?

Get double stranded RNA in a single stranded molecule. The double stranded section will be 5' -> 3'

13

What is RNA transcription catalysed by?

RNA polymerase (more than 1 needed)

14

What are the requirements for RNA transcription

1) Requires a template
2) Does not require a primer
3) Ribonucleoside triphosphates
4) Need to open chromatin

15

What are the precursor molecules of RNA synthesis?

ATP
GTP
CTP
Uridine triphosphate (UTP)

16

RNA is synthesised in what direction?

5' -> 3' direction

17

What is the template strand of the DNA?

Antiparallel and complementary to RNA

18

What is the coding strand?

Opposite DNA strand, which has the same polarity and base sequence as the RNA transcript (T replacing U)

19

Does RNA polymerase have proofreading nuclease activity?

No but it can be tolerate because the damage caused by a single faulty RNA molecule is not nearly as great as a faulty DNA

20

When does transcription stop?

Until the RNA polymerase runs into a terminator sequence which contains a palindrome

21

What happens when the terminator sequence is transcribed?

RNA transcript forms a hair pin loop by internal base pairing causing RNA polymerase to dissociate form the DNA template and release the RNA

22

Before starting transcription what needs to happen?

RNA polymerase has to bind to a promoter

23

What is a promoter?

A sequence of about 60 base pairs at the start of the gene.

24

What does a promoter do?

It recognises the sigma subunit which binds to the promoter and position the core enzyme over the transcriptional start site

25

What is determined at the promoter?

The orientation in which it binds

26

Describe the process of transcription

1) initiation
a) At promoters
b) Controlled by transcription factors
c) "Gene expression"
2) Termination
3) Processing of the transcript (Eukaryotes)
a) e.g. remove introns, add stuff to ends, modify bases
b)Produce final product e.g. mature mRNA

27

Where does the RNA polymerase separate the DNA double helix?

Conserved A - T rich sequence about 10 base pairs upstream of the transcriptional start site.

28

What makes the transition from the initiation phase to the elongation phase of transcription?

The sigma subunit separates form the core enzyme after the formation of the first 5 to 15 phosphodiester bonds

29

What does the rate of transcriptional initiation depend on?

Base sequence of promoter. The more the promoter resembles the consensus sequence, the higher is the rate of transcription

30

What prevents DNA knotting?

DNA topo-isomerases acts to unknot DNA

31

What does the transcription bubble do?

Moves along gene

32

What inhibits transcription?

1) Rifampicin - antibiotic that targets bacterial RNA polymerase
2) Actinoymcin D - Wilm's tumour
3) Alpha Amanitin - treatment is possible but it has to be quick
4) Amanita phalloides - fungi

33

What is post transcriptional processing?

chemical modification of RNA after its synthesis by RNA polymerase

34

Of the three major RNA types, what is rarely processed in prokaryotes?

mRNA, translated as soon as it is synthesised.

35

In bacterial mRNA what happens?

Ribosomes attach to the 5' end of bacterial mRNA and start translation long before the synthesis of the mRNA has been completed.

36

Is ribosomal RNA modified post transcriptionally?

Yes in both prokaryotes and eukaryotes

37

What does bacterial rRNA contain?

Methylated bases

38

What does eukaryotic rRNA contain?

Methylated ribose residues

39

What does the bacterial gene structure look like?

1) Simple promoter close to start of transcript
2) Gene transcribed as one piece of mRNA
3) Transcription terminates once terminator signal reaches
4) Ready to translate (have coding region and untranslated regions)

40

What does the eukaryotic gene structure look like?

1) Very complicated promoters e.g. human: 2000 TF, spread over 10s of kb, several kb from coding region
2) Pieces of mRNA removed before translation - introns

41

When is the pieces of mRNA removed before translation?

Before the mRNA is moved out of the nucleus, it leaves behind exons

42

Which is bigger: introns or exons?

Introns

43

What happens during eukaryotic gene processing?

1) Remove introns by splicing
2) Add 5' cap
3) Cleavage of 3' end of mRNA at polyAsite
4) Add 3' polyA tail

44

What are alternative transcripts?

1) Alternative poly A sites
2) Alternative splicing - alternative exons
3) Alternative promoters (found in liver and pancreas could be different -> impt. in metabolism)

45

What is the central dogma of RNA genome?

DNA -> RNA -> protein

46

What happens in an RNA virus such as HIV?

RNA -> DNA due to reverse transcriptase
- make DNA copy of RNA forming a double strand and integrating it to the host genome

47

Which type of RNA have 5' cap?

mRNA only (tRNA and rRNA don't have)

48

When does post transcriptional processing of mRNA take place?

while RNA polymerase II is synthesising the mRNA.