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Genetics > RNA and Transcription > Flashcards

RNA and Transcription Flashcards

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Biology 101 flashcards
1
Q

In the 19th century, scientists were convinced DNA was everything (molecule that carried genetic instructions for every organism).

What issue did they face?

A

The DNA never left the nucleus. How could it control everything happening outside the nucleus (protein synthesis)?

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2
Q

In the early 1950s, name the key breakthrough.

A

The Pulse-Chase Experiment.
- Paul Zamecnik
- Sydney Brenner

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3
Q

What was the Pulse-Chase Experiment?

A

Paul Zamecnik and Sydney Brenner investigated how proteins were made in cells.

  1. Cells exposed to radioactive uracil.
  2. Cells made RNA.
  3. RNA moved from nucleus to cytoplasm.
  4. Proteins synthesised.
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4
Q

What was the significance of the Pulse-Chase experiment?

A

It was the first clue that RNA was a messenger (transported genetic instructions out of the nucleus and to the ribosomes).

Later known as messenger RNA (mRNA).

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5
Q

What is the central dogma?

A

The flow of genetic information within a biological system. DNA makes RNA and RNA makes proteins.

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6
Q

In 1965 what did Francois Jacob, Jacques Monod and Andre Lwoff win the Nobel Prize in Medicine for?

A

Discovery relating to genetic regulation of enzyme and virus synthesis.

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7
Q

In 1959, what did Ochoa and Kornberg win the Nobel Prize for?

A

Their work on DNA and RNA polymerases.
They discovered the enzymes responsible for synthesising DNA and RNA.

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8
Q

In 1993, what did Richard J. Roberts and Phillip A. Sharp win the Nobel Prize for?

A

Discovering ‘split genes’.

Gene consisting of introns and exons.

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9
Q

List 5 differences between DNA and RNA.

A
  • RNA is single stranded and DNA is double
    stranded.
  • RNA nucleotide has a ribose sugar (OH on
    C2) but DNA nucleotide has a
    deoxyribose sugar (H on C2).
  • In RNA the nitrogen-containing organic
    base thymine in DNA is replaced with
    uracil.
  • RNA is more chemically reactive than DNA.
  • DNA is accurate long-term storage and
    RNA is transient .

Transient = only lasts for a short time because RNA is less stable and used as mRNA for short term information transfer.

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10
Q

Why does uracil have the same base pairing properties as thymine?

A

Due to its similar structure.

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11
Q

Why is RNA more chemically reactive than DNA?

A

Ribose has 2 OH groups.

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12
Q

Describe the structure of RNA.

A

Single-stranded but often finds nucleotides that can base pair with complementary sequences found elsewhere.
Forms regions of conventional base pairs, non-conventional base pairs and unpaired bases.
Form a variety of 3D shapes.

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13
Q

What can RNA base pair with other than itself?

A

Other nucleic acids.

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14
Q

Give the role of mRNAs.

A

messenger RNAs - code for proteins.

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15
Q

Give the role of rRNAs.

A

ribosomal RNAs - form the core of ribosome’s structure and catalyse protein synthesis.

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16
Q

Give the role of miRNAs.

A

micro RNAs - regulate gene expression.

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17
Q

Give the role of tRNAs.

A

transfer RNAs - serve as adaptors between mRNA and amino acids during protein synthesis.

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18
Q

How are other non-coding RNAs used?

A

Used in RNA splicing, gene regulation, telomere maintenance (genome stability) and many other processes.

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19
Q

What is the role of the ribosome?

A

Site of protein synthesis in cytosome (portion of cell which is cytoplasmic).

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20
Q

What happens in transcription (simple terms)?

A

RNA is synthesised from a DNA template by RNA polymerase.

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21
Q

What happens to the DNA double helix after transcription?

A

It is reformed.

22
Q

What does 1 DNA strand need to be used as?

A

A template.

23
Q

Which direction is transcription?

A

5’ to 3’ (each nucleotide is added to the 3’ end of the strand).

24
Q

What is the relation of the template strand to the RNA strand?

A

Antiparallel.

25
Q

What does RNA polymerase 2 transcribe?

A

mRNAs

25
Q

What does RNA polymerase 1 transcribe?

A

rRNAs

26
Q

What does RNA polymerase 3 transcribe?

A

tRNAs

27
Q

Transcription continues until a stop signal is reached.
What happens next?

A

This is where the gene has finished and mRNA leaves DNA strand.

28
Q

How is pre-mRNA formed?

A

Incoming ribonucleoside triphosphates go to RNA polymerase active site through the ribonucleoside triphosphate uptake channel.

Complementary base pairing occurs.

Newly synthesised bases form phosphodiester bonds and pyrophosphate (2 phosphates) is lost.

29
Q

What are rNTPs, list them for RNA.

A

ribonucleoside triphosphates = monomeric building blocks consumed in the synthesis of an RNA chain.

ATP, CTP, GTP, UTP (uridine)

30
Q

When is energy released as RNA is formed?

A

The breakage of the phosphoanhydride bond of NTP releases energy.

30
Q

Why is it essential to process the ends of mRNA?

A

For stability.

30
Q

When is mRNA processed?

A

as mRNA is transcribed

31
Q

What happens to eukaryotic mRNA before it leaves the nucleus?

A

It’s processed from pre-mRNA to mature mRNA.

32
Q

Give 3 ways pre-mRNA is processed to mature mRNA.

A

5’ end of mRNA ‘capped’ with an atypical nucleotide.

3’ end of mRNA gets a tail of poly-A-nucleotides (long chain of adenine nucleotides).

Introns (non-coding sequences) have to be removed from the RNA.

33
Q

Name the 3 parts of an intron.

A

5’ splice site
Branch point
3’ splice site

34
Q

Why is the intron divided into these parts?

A

They help in the removal of the intron.

35
Q

What is splicing primarily (mainly) performed by?

A

snRNAs - small nuclear RNA molecules.

36
Q

What do snRNAs do?

A

Bind to proteins to form snRNPs (small nuclear ribonucleoprotein particles) that form the core of the spliceosome.

Spliceosome = removes introns.

37
Q

What is a ribonucleoprotein?

A

A complex of ribonucleic acid and RNA-binding protein.

38
Q

Give the process of intron removal.

A
  1. RNA portion of U1 and U2 snRNP base
    pairs with sequences that signal splicing.
  2. U6 replaces U1.
  3. Active site of spliceosome created by U2
    and U6.
  4. Splicing occurs, U2 and U6 take intron.
  5. Exon junction complex joins exons to give
    the portion of spliced mRNA.
39
Q

What does alternative splicing allow?

A

More than one protein to be expressed from a single gene.

AND

Different cell types can form different proteins using the same mRNA.

40
Q

In humans the transcripts of 95% of genes exhibit…

A

Alternative splicing.

41
Q

What does alternative splicing lead to in terms of proteins?

A

Multiple different protein isoforms from a single gene.

Protein isoforms = two/more functionally similar proteins that have similar but not identical amino acid sequences.

42
Q

How are protein isoforms made?

A

RNA transcripts from the same gene have had different exons removed.

43
Q

What happens to mature mRNA?

A

Its selectively exported from the nucleus.

44
Q

What marks a mature and intact mRNA for export from the nucleus?

A

RNA binding proteins (cap-binding and poly-A-binding proteins).

45
Q

Why are only a small fraction of mRNAs exported?

A

Incorrectly synthesised mRNAs are broken down and the nucleotides are reused.

46
Q

What is the purpose of nuclear pore complexes?

A

Act as checks.

47
Q

What happens to the protein cap before translation occurs?

A

It is exchanged for initiation factors for protein synthesis.

48
Q

What does the stability of an mRNA determine?

A

How much protein is translated in the cell (because mRNAs can be translated many times).

49
Q

What does the sequence of mRNA affect in terms of stability?

A

Its half-life.

(some lifetimes > 10 hours and some < 30 minutes)

Genetics (10 decks)

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