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Genetics chapter 8: Gene Expression: The Flow of Information from DNA to RNA to Protein > 8.2 Transcription: From DNA to RNA > Flashcards

8.2 Transcription: From DNA to RNA Flashcards

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1
Q

What catalyses transcription?

A

RNA polymerase

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2
Q

What are promoters?

A

They are DNA sequences that signal RNA polymerase to start transcription

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3
Q

Which of the two DNA strands serves as the template strand for transcription?

A

The 3’-5’ direction strand

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4
Q

In which direct does RNA polymerase add nucleotides ?

A

5’-3’ direction

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5
Q

What provides energy for transcription?

A

Hydrolysis of bonds in NTPs

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6
Q

What are terminators?

A

They are RNA sequences that signal RNA polymerase to stop transciption

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7
Q

Briefly explain Initiation (in prokaryotes)

A

RNA polymerase binds to the promoter sequence located near the beginning of the gene. Sigma factor binds to RNA polymerase. Region of DNA is unwound to form open promoter complex. Phosphodiester bonds formed between first two nucleotides

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8
Q

Briefly explain elongation(contructing RNA copy of the gene)

A

sigma factor separates from RNA polymerase (core enzyme). Core RNA polymerase loses affinity to promoter, moves in 3’-5’ direction on template strand. Within transcription bubble, NTPs added to 3’ end of nascent mRNA.

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9
Q

Briefly explain termination (The end of transcription in prokaryotes)

A

There are two kinds of terminators in bacteria:
1. Extrinsic: require rho factor
2. Intrinsic: do not require rho factor
Terminators usually form hairpin loops (intramolecular H-bonding)

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10
Q

How does the initiation of eukaryotes differ from that of prokaryotes

A

Eukaryotic genes often have enhancers:
1. Can be thousands of base pairs away from the promoter
2. Require for efficient transcription

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11
Q

How do the products of transcription differ between prokaryotes and eukaryotes

A

Prokaryotes: The primary trnascript is mRNA
Eukaryotes: The primary transcript is processed to make an mRNA in the following ways:
1. 5’ methylated cap
2. 3’ poly-A-tail (poly-A polymerase)
3. Introns removed by RNA splicing

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12
Q

Define exon

A

A coding region of a gene that remains in the final mRNA and is translated into protein.

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13
Q

Define intron

A

A non-coding region of a gene that is removed during RNA splicing and does not appear in the final mRNA.

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14
Q

Splicing removes _______ and joins adjacent ______-

A

introns, exons

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15
Q

What three short sequences in the primary transcript determine where splicing occurs?

A
  1. Splice donor
  2. Branch site
  3. Splice acceptor
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16
Q

How many sequential cuts remove an intron

A

2

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17
Q

What catalyses RNA splicing

A

the spliceosome

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18
Q

Translation takes place on _________ that coordinate movements of tRNA carrying specific amino acids

A

ribosomes

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19
Q

What is tRNA

A

they are short single-stranded RNAs of 74-95 nt

20
Q

Each tRNA has an _________ that is complementary to an mRNA codon

A

anticodon

21
Q

What is a charged tRNA

A

A specific tRNA that is covalently coupled to a specific amino acid

22
Q

How many levels of tRNA structure?

A

three

23
Q

Explain the primary structure of tRNA

A

it is the nucleotide sequence

24
Q

Explain the secondary structure of tRNA

A

(cloverleaf shape) is formed because of complementary sequences within the tRNA

25
Q

Explain the tertiary structure of tRNA

A

(L shape) is formed by 3D folding

26
Q

What enzymes catalyse attachment of tRNAs to specific amino acids

A

Aminoacyl-tRNA synthetases

27
Q

How do Aminoacyl-tRNA synthetases perform their function

A

By recognizing a specific amino acif and the structural features of its corresponding tRNA

28
Q

The tRNA anticodon base pairs with ________

A

the mRNA codon

29
Q

What did Wobble discover?

A

Some tRNAs recognise moe than one codon coding for the same amino acid

30
Q

How many subunits does a ribosome have

A

2

31
Q

Prokaryotic vs eukaryotic ribosomal subunits

A

P(70S): large =50S
small = 30S
E (80S): large= 60S
small= 40S

32
Q

true or false: different parts of a ribosome have different functions

A

true

33
Q

Where does the small subunit of a ribosome bind?

A

it binds to the mRNA

34
Q

Wqhat is the function of the large subunit of a ribosome

A

It has peptiyl transferase activity

35
Q

What are the 3 distinct tRNA binding areas

A
  1. Aminoacyl (A) site
  2. Peptidyl (P) site
  3. Exit (E) site
36
Q

In bacteria, initiator tRNA has___________

A

formylated methionine (fMet)

37
Q

Briefly explain initiation of translation in prokaryotes

A

Ribosomes bind to a shine-Dalgarno box and an AUG.
Three sequential steps:
1. small ribosomal subunit binds to mRNA
2. fMet-tRNA is positioned in P site
3. Large subunit binds

38
Q

Briefly explain initiation of translation in Eukaryotes

A

Small ribosomal subunit binds to 5’ methylated cap, then migrates to the first AUG. Initiator tRNA carries Met and not fMet

39
Q

Explain Elongation of translation

A

Addition of amino acids to the C-terminus of the growing polypeptide chain. (Charged tRNAs ushered into A site by elongation factors)

40
Q

What direction do ribosomes move along the mRNA

A

5’-3’ direction

41
Q

Explain termination of translation

A

No normal tRNAs carry anticodons for the stop codons. Release factors bind to the stop codons. Release of ribosomal subunits, mmRNA, and polypeptide

42
Q

What consists of several ribosomes translating the same mRNA, thus causing simultaneous synthesis of many copies of a polypeptide from a single mRNA

A

polyribosomes

43
Q

What are the two types of posttranslational processing?

A
  1. Enzymatic cleavage
  2. Addition of chemical constituents
44
Q

Explain enzymatic cleavage

A

It may remove an amino acid (eg N-terminal Met removal), split a polyprotein(into multiple smaller polypeptides), or activate a zymogen

45
Q

Explain what addition of chemical constituents do

A

They may alter protein structure, activity, or cellular location

46
Q

Name the 4 processes that add chemical constituents

A
  1. Phosphorylation
  2. Glycosylation
  3. Lipidation
  4. Ubiquitination

Genetics chapter 8: Gene Expression: The Flow of Information from DNA to RNA to Protein (4 decks)

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