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medical genetics > Gene Expression > Flashcards

Gene Expression Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What is a codon?

A

Codons are triplets of nucleotides in mRNA that encode the information for a specific amino acid in a protein

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2
Q

What is a stop codon?

A

Stop codons are codons in mRNA that signal the end of translation (end of protein synthesis)

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3
Q

Identify 3 stop codons

A
  • UAA
  • UAG
  • UGA
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4
Q

What is a start codon (AUG)?

A

A start codon is always the first codon in a gene, present in mRNA to signal the location for translation to begin.

AUG = methionine

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5
Q

How is genetic code written?

A

Genetic code is written as it appears in an RNA copy of the DNA template

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6
Q

What is transcription?

A

Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase.

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7
Q

Identify the 3 stages in transcription

A
  • Initiation
  • Elongation
  • Termination
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8
Q

Describe initiation in transcription

A

Initiation: RNA polymerase binds to a specific nucleotide sequence (called a promoter) that marks the beginning of a gene.

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9
Q

Describe elongation in transcription

A

- Elongation: DNA strands unwind, and RNA polymerase reads the nucleotide sequence of the template strand.

  • As it moves along, it inserts and pre-mRNA molecule.
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10
Q

Describe termination in transcription

A
  • Termination: RNA polymerase reaches the end of the gene, marked by nucleotides called a 3’ termination sequence
  • RNA-polymerase stops adding nucleotides to pre-mRNA which falls off the DNA template strand and is released
  • DNA strands re-form a double helix
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11
Q

What is an intron?

A

An intron is a sequence in the pre-mRNA molecule that is not transcribed

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12
Q

What is an exon?

A

An exon is a sequence in a pre-mRNA molecule that is transcribed

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13
Q

Outline the process of RNA splicing

A
  • RNA splicing is when pre-mRNAs are processed in the nucleus to remove introns which occur between exons
  • As introns are removed, the exons are spliced together to form mature mRNA molecules
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14
Q

How are mRNA molecules processed?

A

Ends of the mRNA are modified:

  • A nucleotide cap is attached to the 5’ end of eukaryotic mRNA
  • A poly-A tail is added at the 3´ end (aids in export of the mRNA from nucleus)
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15
Q

How is the mature mRNA molecule released?

A

The final product, mature mRNA is exported from the nucleus into the cytoplasm, where translation takes place

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16
Q

What is translation?

A

Translation is the process in which ribosomes in the cytoplasm/rER produce polypeptides from information in mRNA

17
Q

What is the structure and function of ribosomes?

A
  • Structure: cytoplasmic organelles with a large and a small subunit
  • Function: site of polypeptide synthesis
18
Q

What kind of ribosomes are there?

A
  • Free ribosomes: float in the cytoplasm
  • Bound ribosomes: attached to the outer membrane of the rough endoplasmic reticulum
19
Q

Explain the role of ribosomes in translation

A

The large subunit contains ribosomal RNA (rRNA) which acts as an enzyme, linking amino acids together to form a polypeptide during translation

20
Q

What is tRNA?

A

Transfer RNA (tRNA) molecules bring amino acids to the mRNA ribosome complex during translation.

21
Q

Each tRNA molecule has two attachment sites. Identify and describe them

A
  • An anticodon that pairs with a complementary codon sequence in mRNA
  • A site for attachment of the amino acid specified by the mRNA codon
22
Q

Identify the three steps in translation

A
  • Initiation
  • Elongation
  • Termination
23
Q

Describe initiation in translation

A
  • Initiation: mRNA binds to a small ribosomal subunit and the anticodon of the initiator
  • tRNA carrying the amino acid methionine pairs with the AUG codon of mRNA.
24
Q

Describe elongation in translation

A
  • Elongation: amino acids are added to the growing polypeptide chain
  • The rRNA of the large subunit forms peptide bond between amino acids
25
Q

Describe termination in translation

A
  • Termination occurs when the ribosome reaches a stop codon (UAA, UAG, and UGA)
  • Proteins called release factors bind to stop codons
  • Polypeptide, mRNA, and tRNA are released from the ribosome
26
Q

What is a gene?

A

Gene: a unit of inheritance which is transferred from a parent to offspring and is held to determine some characteristic of the offspring

27
Q

Distinguish between DNA replication, transcripion and translation in terms of its overall function

A

- DNA Replication: making DNA

- DNA Transcription: making RNA

- DNA Translation: making a polypeptide

28
Q

Distinguish between DNA replication, transcription and translation in terms of the enzymes involved

A

- DNA Replication: DNA polymerase

- DNA Transcription: RNA polymerase

- DNA Translation: rRNA

29
Q

Distinguish between DNA replication, transcription and translation in terms of the activated substrates used

A

- DNA Replication: dNTPs

- DNA Transcription: NTPs

- DNA Translation: amino acids

30
Q

Distinguish between DNA replication, transcription and translation in terms of the template needed

A

- DNA Replication: DNA

- DNA Transcription: DNA

- DNA Translation: mRNA

31
Q

Compare and contrast the ribosomes of prokaryotes and eukaryotes in terms of:

  • Size
  • Subunits
  • rRNAs
  • Proteins
A
32
Q

Identify 5 factors which characterise protein synthesis in bacteria.

A
  • Simple promoters
  • Single RNA polymerase
  • No post-transcriptional processing
  • Short-lived mRNAs
  • Simpler ribosomes

medical genetics (12 decks)

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