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IMS- Strand 2 > From Genes to Proteins > Flashcards

From Genes to Proteins Flashcards

1
Q

What is Transcription?

A

The synthesis of messenger RNA (mRNA) using DNA as a template. RNA polymerase uses DNA as a template to produce pre-mRNA

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2
Q

What is translation?

A

The production of proteins from mature mRNA, builds the protein encoded by the original gene

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3
Q

What are promoter elements in eukaryotes?

A

TATA BOX

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4
Q

How is transcription started?

A

The short run of T & A bases can vary slightly from gene to gene and is probably the best characterised promoter element (TATA box)

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5
Q

Why are T & As used?

A

they form the lowest energy base pairs so are easiest to unwind

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6
Q

What is the first step in transcription?

A

INITIATION

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7
Q

Where does RNA polymerase bind?

A

Binds to DNA upstream (5’) of the gene at a promoter sequence

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8
Q

What Co factors does RNA polymerase use and why?

A

cofactors= general transcription factors
TFIID recognises the TATA box and ensures that the correct start site is used

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9
Q

What does alteration of promoter strength cause?

A

Can have deleterious effects upon a cell, often resulting in disease

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10
Q

What is the second step in transcription?

A

ELONGATION

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11
Q

What happens during elongation?

A

The DNA double helix unwinds, RNA polymerase reads template strand and adds complementary nucleotides

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12
Q

What is the final step in transcription?

A

TERMINATION

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13
Q

What stops transcription?

A

Terminator sequences are found close to the ends of noncoding sequences

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14
Q

What stops transcription in Pol I genes

A
  • termination factor
  • through a mechanism similar to rho-dependent termination in bacteria (rRNA)
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15
Q

What stops transcription in pol II genes?

A

can continue for hundreds of or thousands of nucelotides beyond the end of the noncoding sequence (mRNA)

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16
Q

What stops transcription of Pol III genes

A

ends after transcribing a termination sequence that includes a polyuracil stretch (tRNA)

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17
Q

What is splicing?

A

removal of intronic sequences from the pre-mRNA. Coding regions (Exonic sequences) are spliced together. Num of exons varies. forms mature mRNA

18
Q

How does splicing occur?

A

2 transesterification reactions

19
Q

What are the steps in splicing?

A
  • 1st reaction is the free 2’- hydroxy group
  • the 3’ hydroxy group of the 5’ exon attacks and cleaves the phosphodiester linkage at the 3’ splice site
  • The products are spliced mRNA product and excised intron
20
Q

What is the excised intron called?

A

lariat product

21
Q

What is self splicing?

A

The intron itself folds into a specific conformation without the involvement of other RNA or protein

22
Q

What is alternative splicing?

A

the process by which a given gene is spliced into more than one type of mRNA molecule

23
Q

Why is splicing important

A
  • Fundamental role in cellular metabolism
  • Protein diversity
  • Regulation of gene and protein content
  • Evolution of new and improved proteins
  • Key to cancer pathology
24
Q

How is protein diversity brought about?

A

Changes in the number & sequence of exons and introns present in the RNA sequence

25
Q

What is a frameshift mutation?

A

The addition (insertion) or loss (deletion) of a base would result in a change of reading frame and proteins with altered function

26
Q

What can frameshift mutation cause?

A

Array of diseases

27
Q

Where does translation occur?

A

RIBOSOME

28
Q

What is a ribosome comprised of?

A

2 subunits, large and small, each subunit exists separated in the cytoplasm, but join together on the mRNA molecule

29
Q

What are tRNA molecules

A

Adaptor molecules, one end can read the triplet code on mRNA via complementary base pairing & the other attaches to a specific amino acid

30
Q

What does rRNA do?

A

catalyses the attachment of each new amino acid to the growing chain
forms the ribosome

31
Q

What is the first step in translation?

A

Initiation
- Translation begins with formation of a complex on the mRNA
Three initiation factor proteins bind to small subunit of the ribosome
The preinitiation complex and a methionine carrying tRNA then bind to mRNA forming an initiation complex

32
Q

What are the 3 initiation factor proteins?

A

IF1, IF2, IF3

33
Q

What is the second step in translation?

A

ELONGATION
- Ribosome moves along mRNA in a 5-3 direction, elongation factor G is required for TRANSLOCATION
- Methionine- carrying tRNA starts out in the middle slot of the ribosome

34
Q

What acts as the energy source for translation?

A

Guanosine triphosphate acts as energy source
On binding of the tRNA- amino acid complex
GTP= guanosine diphosphate

35
Q

How are peptide bonds formed between amino acids?

A

peptidyl transferase activity

36
Q

What is the 3rd step in translation?

A

TERMINATION
- Three stop codons UAA, UAG, UGA

37
Q

How are stop codons recognised?

A

By release factors which fit into the P site
When a ribosome reaches the stop codon it dissociates and protein is released

38
Q

What is the genetic code?

A

64 triplets called codons
Each codon except 3 codes for one of the 20 amino acids
Some aa encoded for by more than one codon

39
Q

What is a triplet?

A

Sequence of three nucleotides found on a strand of DNA or RNA to code for a specific amino acid

40
Q

What are the 3 stop codons?

A

UAA (U ARE ANNOYING)
UGA (U GO AWAY)
UAG (U ARE GONE)

41
Q

What is the Methionine codon (Met)

A

AUG (A universal go)

42
Q

What is the wobble hypthesis?

A

Suggests that specificity for the base at the 3’ end of the condon is not always observed
explains why multiple codons can code for one amino acid

IMS- Strand 2 (4 decks)

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