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MCAT > Central Dogma: Transcription and Translation > Flashcards

Central Dogma: Transcription and Translation Flashcards

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MCAT flashcards
1
Q

Describe the Central Dogma

A

Process which proteins are synthesized from genetic code (DNA -> RNA -> protein)

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2
Q

Describe transcription

A

DNA -> RNA: mRNA is synthesized using DNA as a template

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3
Q

What synthesizes mRNA from the DNA template?

A

RNA polymerase

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4
Q

Where does DNA transcription occur?

A

In the nucleus for eukaryotes

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5
Q

What is the difference between DNA Pol and RNA Pol?

A

RNA polymerase does not require a primer, RNA Pol cannot proofread the synthesized RNA (transcription errors are more common than replication errors)

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6
Q

What are the steps of transcription?

A
  1. Initiation: RNA Pol and factor sigma form haloenzyme to bind promoter region of DNA
  2. Elongation: RNA Pol add free floating nucleotide
  3. Termination
  4. Regulation of Transcription: through enhancers and repressors
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7
Q

Define factor sigma

A

A helper molecule that binds to the promoter region of the DNA along with RNA polymerase

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8
Q

What is the difference between prokaryotic and eukaryotic promoters

A

Prokaryotic promoters have specific sequences at -10 and -35 (upstream) which bind to RNA Pol. Eukaryotic promoters have “TATA” boxes with many T and A bases

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9
Q

Define promoter

A

A region of the DNA just upstream from the setart site that binds to RNA polymerase and factor sigma to initatie transcription

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10
Q

What direction is RNA elongated?

A

5’ to 3’

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11
Q

Describe translation

A

RNA -> protein: mRNA instructions incode polypeptide formation by ribosomes and tRNA

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12
Q

Where does DNA translation occur?

A

In the cytoplasm

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13
Q

Describe codon

A

3 nucleotides of mRNA that are complementary to the DNA template; each codon codes for a single amino acid

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14
Q

Define anticodon

A

3 nucleotides of tRNA that are complementary to the mRNA codon

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15
Q

Describe wobble pairing

A

Wobble pairing occurs when baes pairing doesn’t follow watson-crick rules (A/T/U, C/G) between codons and anticodons

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16
Q

Start codon

A

AUG (methionine)

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17
Q

Stop codon

A

UAA, UGA, UAG (u are annoying, u go away, u are gone)

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18
Q

How many total codons are there?

A

There are 64 codons total, 3 stop and remaining 61 codons for 20 AAs

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19
Q

Define the open reading fram

A

The continuous stretch of nucleotides that has the possibility of being translated as defined by start/stop codons

20
Q

Describe repressors

A

Proteins that bind to the promoter region or the silencer regions of DNA to decrease the rate of transcription

21
Q

What is the relationship between RNA Pol and the promoter?

A

The stronger the affinity between RNA pol and the promoter, the higher the transcription rate

22
Q

Describe enhancers

A

Enhancers are a region of DNA (usually distant from target gene) that activator proteins bind to to increase the rate of transcription

23
Q

Describe RNA process in eukaryotes

A

Transcription in eukaryotes produces hnRNA, a precursor to mRNA that is process in the nucleus and mature mRNA is shipped out to be translated

24
Q

Define splicing

A

Splicing occurs when a splieosome complex removes introns and joins exons

25
Q

Define introns

A

Introns are regions of a gene that are transcribed but not translated and do not encode proteins but are important to break the gene into distinct exons that contain splice sites that are recognized by the spliceosome

26
Q

Define exons

A

Exons are regions of a gene that encode the protein sequence (Exons are expressed)

27
Q

What are the components of a spliceosome?

A

snRNA (small nuclear RNA) + proteins; aka snRNPs (small nuclear ribonucleoproteins)

28
Q

Describe alternative splicing

A

Alternative splicing skips/splices some exons so that different combinations of exons can make more than 1 different mRNA from the same hnRNA

29
Q

Describe the cap and tail

A

A 5’cap (methylated guanine) and 3’ poly-A tail (multiple adenine nucelotides) is added to the 5’ and 3’ UTR of the pre-mRNA to increase the mRNA’s stability and protect it from degredation in the cytoplasm

30
Q

Define ribozymes

A

RNA enzymes found in ribosomes which catalyze translation and required for splicing

31
Q

Describe rRNA

A

rRNA makes up ribosomes which catalyze the synthesis of poly peptides

32
Q

Describe tRNA

A

tRNA contains anti-codon complementary to mRNA codons and brings the correct amino acid to the growing polypeptide chain due to this codon-anticodon-interaction

33
Q

How is the stem/loop structure in tRNA formed?

A

Intramolecular H-bonds

34
Q

What is the modified A base in tRNA?

A

Inosine - often at the wobble position of the anticodon; can pair with A, U, C

35
Q

Describe the composition of ribosome

A

Ribosomes are composed of rRNA and contain and large and small subunit

36
Q

What is the function of the large ribosomal subunit?

A

Catalyze the peptidyl transfer

37
Q

What is the function of the small ribosomal subunit?

A

Recognize and binds to the correct region of the mRNA for translation

38
Q

What are the names eukaryotic and prokaryotic sequences where the small ribosomal subunit binds for translation?

A

Eukaryotes: Kozak sequence; Prokaryotes: Shine-Dalgarno sequence

39
Q

What are the sedimentation coefficients in prokaryotic and eukaryotic ribosomes?

A

Prokaryotic (70S) = small (30S) + large (50S)

Eukaryotic (80S) = small (40S) + large (60S)

40
Q

What are the ribosome sites?

A

Regions of the large ribosomal subunit that the tRNA moves through during protein synthesis (A -> P -> E)

41
Q

Where is the growing polypeptide primarily synthesized?

A

On the P site of the large ribosomal subunit

42
Q

What direction is the polypeptide formed?

A

mRNA reads 5’ -> 3’; therefore polypeptide is made from the N-terminus to c-terminus

43
Q

What is the difference between prokaryotic and eukaryotic translation?

A

Prokaryotes have polycistronic mRNA and lack of RNA processing allows transcription and translation to occur at the same time

44
Q

How is energy provided to each step in translation?

A
  1. Initiation: initiator proteins (eIF) + small subunit associate with Kozak sequence on mRNA –> scan for start codon –> large ribosomal subunit joins
  2. Elongation: Elongation factor and GTP
  3. Termination: Release factor and GTP
45
Q

What are the energy requirements for termination of translation?

A

AA*4 = #ATP needed

46
Q

How is tRNA loading initiated?

A

tRNA and AA attachment is a non-spontaneous process which requires 2 ATP/AA (ATP–> AMP)

47
Q

What is the function of aminoacyl tRNA synthetase?

A

Aminoacyl tRNA synthetase attaches the correct AA to the correct tRNA with high specificity

MCAT (5 decks)

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