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Molecular Genetics > Week 2 > Flashcards

Week 2 Flashcards

Transcription and Translation

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1
Q

List three of the types of RNA found in a cell

A

mRNA (messenger RNA)

rRNA (ribosomal RNA)

tRNA (transfer RNA)

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2
Q

What is the basic definition given to transcription?

A

The “language” of DNA is transcribed into the “language” of RNA.

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3
Q

Draw the basic structures of both DNA and RNA and comment on the main difference

A
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4
Q

What are the three steps involved in Transcription?

A
  1. Initiation
  2. Elongation
  3. Termination
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5
Q

What is the Consensus sequence for transcription, and what are the two regions it contains?

A

The Consensus sequence is the binding site for the RNA polymerase enzyme, and it contains a -10 region (TATAAT) and a -35 region (TTGACA).

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6
Q

What is the other common name given to the non-template strand?

A

The Sense Strand

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7
Q

For transcription in prokaryotic cells, explain what is meant by the term Holoenzyme?

A

The term Holoenzyme is reffering to the RNA polymerase complex having both the Core Enzyme and the Sigma Factor present.

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8
Q

Are there any types of RNA molecules that are found only in eukaryotic cells? If so name and Distinguish them from prokaryotic cells

A

Eukaryotic cells contain:

RNA polymerase I (Large rRNA)

RNA Pol II* (mRNA, snRNA…)

RNA Pol III (Small rRNA, tRNA…)

Prokaryotic cells only contain RNA polymerase as the process is less complex

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9
Q

Where are the promotor sequences located on prokaryotic cells? and what are the two examples of the prokaryotic sequences?

A

In prokaryotes, the promotor consists of two short sequences at -10 and -35 positions upstream from the transcription start site.

  • sequence at -10 is called the Pribnow box (TATAAT)
  • The other sequence is at -35 (TTGACA)
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10
Q

Where are the promotor sequences located on Eukaryotic cells? List 3 Common promotor sequences

A

The most common promotor sequence is located -35 positions upstream from the transcription site.

  • The TATA box (Goldberg-Hogness) (TATAAA) at -35
  • The CAAT Box (GGCCAATCT) at -80
  • The GC Box (GGGCGG) -100 to -150
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11
Q

True or false: DNA Polymerase and RNA Polymerase are similar in that their newly synthesized nucleotide sequence is produced in a 5’ to 3’ direction?

A

True

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12
Q

True or false: DNA Polymerase and RNA Polymerase are different in that one requires a primer and one does not?

A

True, DNA polymerase requires a primer whereas RNA polymerase does not.

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13
Q

What does the term editing in relation to transcription mean?

A

Alters or changes some of the nucleotides in mRNA.

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14
Q

What does the term elongation mean in relation to transcription?

A

The addition of nucleotides to the growing mRNA strand.

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15
Q

what does the term exon mean?

A

Protein coding region of a gene or mRNA.

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16
Q

what does the term Initiation mean in relation to transcription?

A

The beginning of transcription; occurs when RNA polymerase binds to the promoter of a gene.

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17
Q

What does the term Intron mean?

A

Non-coding or non-regulatory region of a gene or mRNA; removed prior to translation.

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18
Q

what does the term polyadenylation mean in relation to transcription?

A

Adds a polyA (adenine bases) tail to the mRNA; signals the end of mRNA.

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19
Q

what does the term promoter mean in relation to transctiption?

A

Region of a gene where a RNA polymerase binds to initiate transcription of the gene.

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20
Q

what is RNA polymerase?

A

Enzyme that transcribes DNA, making mRNA.

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21
Q

What is meant by the term splicing?

A

The removal of introns from mRNA.

22
Q

What is meant by the term Termination in relation to transcription?

A

The ending of transcription; occurs when RNA polymerase crosses a stop (termination) sequence in the gene.

23
Q

What is the basic definition given to Transcription?

A

Process in which genetic instructions in DNA are copied to form a complementary strand of mRNA.

24
Q

What are the three modifications that need to be made for pre-mRNA to become mRNA?

A
  • 5’ cap
  • Intron splicing
  • Poly(A) tail
25
Q

What is the 5’ Cap?

A

The 5’ cap is a G ribonucleotide added backwards to the 5’ end of the pre-mRNA. Stabilises the mRNA / necessary for correct initiation of translation

26
Q

What is the basic definition given to Translation?

A

Process where the base sequence of the nucleic acid is decoded into the amino acid sequence of a protein

27
Q

What is the genetic code?

A

The genetic code are the DNA and RNA sequences that determine the amino acids for protiens that are responsible for carrying out specific roles.

28
Q

What “shape” does the tRNA demonstrate?

A

the clover leaf

29
Q

What enzyme is responsible for attaching amino acids to the tRNA?

A

aminoacyl-tRNA synthetases

30
Q

What molecule is removed when two amino acids are joined together to form a polypeptide?

A

H2O

31
Q

What are the 4 steps of polypeptide synthesis? breifly explain each one

A
  • tRNA charging – When aa are added onto their tRNAs
  • Initiation – When all the components come together on the mRNA – AUG (Starting codon), RBS (Ribosome Binding Site)
  • Elongation – During which aa are joined to make a polypeptide
  • Termination – Translation stops
32
Q

In more detail, What happens during tRNA charging?

A
33
Q

Transcription and translation are coupled in prokaryotic cells. Transcription and translation are uncoupled in eukaryotic cells. In this context, explain what is meant by “coupled” and “uncoupled”?

A

Prokaryotic cell:

Transcription and Translation are coupled meaning that translation is beginning whilst the mRNA is still being synthesized.

Eukaryotic Cell:

Because transcription (inside nucleus) and translation( in cytoplasm) have different sites in eukatyotic cells, transcription must be completed before translation can begin.

34
Q

What is a ribosome and what is it composed of?

A

Comprises of two subunits ( 40s and 60s) that function as one to translate the mRNA into a polypeptide chain within protein synthesis. A ribosome contains an A (aminoacyl) Site, an E (exit) site, and a P (petptidyl) site that has a methionine charged tRNA.

35
Q

Describe the order in which the ribosome sub units and any other relevant molecules assemble on the mRNA during Initiation of Translation?

A

The smaller (40s) subunit is attached to IF3 (Initiating factor 3) this keeps the 40s and 60s subunits seperated. Next IF2-GTP delivers the first tRNA (tRNA-Methionine or tRNA-Met) to the P site of the ribosome. IF4 then moves this complex to the mRNA but Because Eukaryotic cells do not contain a Shine-Delgarno sequence, the whole complex is attached to the 5’ cap and slides along until it finds the start codon. The Kozac consensus sequence helps find the AUG site. AUG binding hydrolyzes IF2-GTP (locking the complex into place and dissociation of IF2), IF3 dissociates and now 60s subunit can bind to the complex on the mRNA.

36
Q

Explain the term codon and state where codons are found?

A

Codon:

  • Sequence of 3 DNA or RNA nucleotides that corresponds with a specific amino acids or stop signal during protein synthesis.
  • They are read in succesion (they do not overlap when being read)
  • Found on mRNA (where the anticodon sequence will attach)
37
Q

Explain the term anti-codon and state where anti-codons are found?

A

Anticodon:

  • Sequences of nucleotides that complementary to codons
  • Found in tRNA’s
  • Allow the tRNA’s to bring the correct amino acid in line with the mRNA during protien production
  • Attach to complementary codon site
38
Q

What is the “start codon” for most translated genes?

A

The start codon is AUG and this codes for methionine in eukaryotes.

39
Q

What is the significance of the Shine-Dalgarno sequence in relation to translation initiation?

A

The Shine-Delgarno sequence is a starting sequence for prokaryotic cells located about 8 bases upstream of the start codon. The sequence helps recruit the ribosome to the mRNA to begin protien synthesis by aligning the ribosome with the start codon.

40
Q

Explain the A-site (aminoacyl site), the P-site (peptidyl site) and the E site (exit site) as found in a ribosome and used during translation (Translation elongation) ?

A

charged tRNA binds to the A site, a peptide bond forms between the new amino acid and the one already in the P site. The ribosome moves down the mRNA in a 5’ to 3’ direction. The tRNA from the P site is shifted to the E site and then exits the ribosome. The A site is now free again and ready for the next charged tRNA to enter.

41
Q

Explain the “wobble hypothesis”?

A

Reffering to the 3rd base position of the codon to anticodon experiencing some unconventional base pairing. It basically allows an imperfect match for the 3rd base in the codon to still bind as long as the first 2 bases have bonded with their complementary bases. (The first base can also form non-standard base pairing).

42
Q

What is an operon? Are operons found in Prokaryotic cells, Eukaryotic cells, both cell types, or neither?

A

An operon is a set of genes in a prokaryotic cell under the control of a single promotor that work together to achieve a similar function. Operons allow the cell to efficiently express sets of genes whose products are needed at the same time. These operons are transcribed as plycistronic mRNA.

examples:

  • Lac operon: Contains genes that encode proteins involved in uptake and metabolism of lactose.
  • Trp Operon: encodes 5 enzymes involved in tryptophan colinear organisation
43
Q

Give an example of an eukaryotic Core Promoter and an example of an eukaryotic Regulatory sequence

A

Example:

Eukaryotic core promotor: RNA polymerase II

Eukaryotic regulatory sequence:

  • TATA (or Goldberg-Hogness) Box (TATAAA) -35
  • CAAT Box (GGCCAATCT) -80
  • GC Box (GGGCGG) -100 to -150
44
Q

What is the Kozak sequence?

A

A sequence that plays a big role in the initiation of the translation process. This Consensus sequence helps identify a start codon as unlike prokaryotic cells, eukaryotic cells do not have a Shine-Delgarno sequence to help with identification.

Kozak Sequence containing the start codon:

5’ ACCAUGG 3’

45
Q

What is the Golberg-Hogness box (TATA box)?

A

A promotor sequence that indicates where a genetic sequence can be read and decoded.

Contains the sequence:

TATAAA at -35 base pairs

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Molecular Genetics (4 decks)

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