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Y1 - MCD > Nucleic acids 5-7 > Flashcards

Nucleic acids 5-7 Flashcards

1
Q

What is non-coding DNA?

A

Any RNA molecule that is not translated into a protein. Does not include mRNA.

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2
Q

How much of non-coding DNA has a function?

A

20%

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3
Q

How much of non-coding DNA has no known function as of yet?

A

60%

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4
Q

What are the four main types of non-coding DNA with known functions?

A

1) microRNA
2) siRNA (RNAi)
3) piRNA
4) long ncRNA

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5
Q

What does microRNA do?

A

Controls translation of roughly 30% of all genes.

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6
Q

What does siRNA do?

A

Involved in viral defence.

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7
Q

What does piRNA do?

A

Germ cell proliferation.

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8
Q

What does long ncRNA do?

A

Important for X chromosome inactivation.

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9
Q

What is X-chromosome inactivation?

A

Also known as lyonization. When one X chromosome in females is inactivated due to a special conformation (heterochromatin) preventing translation.

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10
Q

How long are microRNA strands typically?

A

18-26 nucleotides. Precursors are between 60 and 80 nucleotides long before exonuclease activity cleaves off the final microRNA strand.

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11
Q

How do microRNA work?

A

Can inhibit mRNA through incomplete base-pairing in certain binding sites, reducing translation of that gene. One microRNA can target several different mRNA binding sites.

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12
Q

What is DNA cloning?

A

Selectively amplifying certain DNA sequences to generate homologous DNA populations. Cell-based or cell-free (PCR).

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13
Q

What do restriction endonuclease do?

A

Cleave DNA at specific recognition sequences (normally 6-8bp palindromic sequences)

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14
Q

How is host DNA protected from restriction endonuclease activity?

A

RE sites are methylated (by methylase) and REs will only cleave unmethylated DNA from invading organisms.

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15
Q

What gels are normally used in gel electrophoresis?

A

Agarose or polyacrylamide.

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16
Q

What is nucleic acid hybridisation?

A

Form of detecting specific nucleic acid sequences, allowing single-stranded DNA or RNA to anneal to form double stranded molecules.

17
Q

How does nucleic acid hybridisation work?

A
  • Probe identifies targets
  • Target DNA is immobilised
  • Target DNA is hybridised (radioactively/fluorescently)
  • DNA is isolated

Carried out 25 degrees below melting temperature of DNA.

18
Q

What does denaturation of DNA depend on?

A
  • Strand length
  • Base composition (GC bonds take more energy to break)
  • Chemical environment (denaturants and monovalent cations)
19
Q

What enzyme is used in PCR?

A

taqDNA polymerase (thermostable)

20
Q

Where does translation occur?

21
Q

What is the start codon sequence?

22
Q

What do tRNA molecules do?

A

Transport amino acids to the ribosome during translation

23
Q

What bring the amino acid to the tRNA molecule?

A

Aminoacyl tRNA syntheses (tRNA activating enzymes)

24
Q

What takes place in the invitation stage?

A

1) Ribosomal subunits disassociate
2) Pre-initiation complex forms (initiation factors bind to 5’ cap and Met-tRNA binds to 40S subunit)
3) mRNA binds to pre-initiation complex
4) 60S subunit binds

25
Q

What takes place during the elongation stage?

A

1) tRNA molecule binds to A site
2) Catalysis of peptide bond between two amino acids
3) Translocation to P site using energy from GTP

26
Q

What takes place during the termination stage?

A

1) Recognition of stop codon

2) Release

27
Q

What does GTP do during translation?

A

Hydrolysis allows translocation of tRNA molecules along ribosome as well as providing “pauses” to allow for correct base pairing recognition.

28
Q

What are polyribosomes?

A

Multiple ribosomes working on one strand of mRNA.

29
Q

What can occur in post-translation modification?

A

Diversity of proteins:

  • Disulphide bridge formation
  • Proteolytic cleavage (hormones)
  • Glycosylation (carbohydrate)
  • Phosphorylation
  • Hydroxylation
  • Acylation and prenylation (addition of lipid groups)
30
Q

What are siRNAs and what is their function?

A

Short interfering RNAs that combine with mRNA via hybridisation to interfere with the expression of genes and prevent translation of specific mRNA strands.

31
Q

What is RISC?

A

RNA induced silencing complex - destroys the target mRNA by binding to the hybridised mRNA, causing the transcript to break and preventing translation.

32
Q

Which ribosomal subunit binds to the mRNA first?

A

Small subunit

33
Q

What are the two classes of antibiotics used to prevent translation of bacteria?

A

50S and 30S inhibitors

34
Q

How do 50S inhibitors work?

A

Physically block initiation or translocation of peptides tRNAs by inhibiting peptides transferase.

35
Q

How do 30S inhibitors work?

A

e.g. streptomycin

Bind to the 16 rRNA subunit and interfere with peptides-tRNA binding.

Y1 - MCD (38 decks)

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