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Biology 107 > Genetic Expression > Flashcards

Genetic Expression Flashcards

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1
Q

Define/Explain the steps of Central Dogma

A

Flow of information in the cell

DNA->transcription->mRNA->translation->protein

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2
Q

What is the promotor

A

DNA sequence that directs/regulates transciption
site of RNA polymerase
-35 to -10

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3
Q

What direction do you read the template strand

A

3’ -> 5’

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4
Q

How many nucleotides form a protein

A

three

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5
Q

DNA is read (transcription occurs) in the _’ to _’ end

A

3’ to 5’ (making RNA 5’ to 3’)

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6
Q

What direction does the template run away from the promotor

A

3’ to 5’

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7
Q

Transcription changes _____ into ______

A

DNA into RNA

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8
Q

What is RNA polymerase

A

Enzyme of transcription

  • binds double stranded DNA at promotor
  • unwinds double helix, create transcription bubble
  • initiate transcription at +1
  • aligns first two ribonucleotides (5’ end of new mRNA)
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9
Q

How is the template strand chosen

A

Based on direction of promotor

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10
Q

What happens at termination of transcription

A

RNA sequence that signal the end (terminators), RNA polymerase dissociates (falls off)

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11
Q

Where does transcription happen, where does translation happen (in eukaryotes)

A

transcription: in nucleus
translation: in cytoplasm

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12
Q

Post-transcriptional processing only happens in _________ because ________________________.

A
  1. eukaryotes
  2. transcription occurs in the nucleus, translation occurs in cytoplasm (time btw end of transcription and start of translation)
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13
Q

What modifications occur in post-transcriptional processing? Why?

A
  1. Addition of methyl guanosine cap at 5’ end: “hides” the 5’ end from exonuclease digestion
  2. Addition of 100-200 adenosines to 3’ end (poly-A tail): prevent and delay exonuclease digestion, aids in translation initiation
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14
Q

What is RNA splicing

A

removal of introns

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15
Q

What are introns and exons

A

Introns (remove): non amino acid coding regions (intervening sequences) found on genes DNA but not mature RNA
Exons (leave): amino acid coding regions

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16
Q

What is the spliceosome

A

Enzyme, complex of snRNPs, recognize sequence at intron/exon boundaries

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17
Q

Steps of RNA splicing

A

1) SnRNPs bind intron/exon boundaries and loop out the intron
2) intron cut out by cutting at 5’ end of intron
3) excised intron in lariat shape (created by 5’-2’ linkage of RNA)
4) exons ligated together

18
Q

Why splice?

A

remove interrupting sequences, alternative splicing (mix and match of exons makes similar but not identical proteins from same gene. Ex. neuron vs muscular protein)

19
Q

Translation changes _____ into ______.

A

RNA into protein

20
Q

What signals start and stop of translation

A

start and stop codons

21
Q

mRNA vs tRNA

A

mRNA: codon
tRNA: anticodon (antiparallel and complementary to mRNA)

22
Q

Function of tRNA

A

carry appropriate amino acid to ribosome

23
Q

Function of Aminoacyl tRNA synthetases

A

“the translator”

pairs correct amino acid based on anticodon sequence, covalently links amino acid to tRNA in sequence dependent manner

24
Q

proteins are synthesized in what direction

A

N->C by reading mRNA 5’->3’

25
Q

Large vs small ribosomal subunits in prokaryote vs eukaryotes

A

Prokaryotes: 70s=30s(small)+50s(large)
Eukaryotes: 80s=40s(small)+60s(large)

26
Q

The large ribosomal subunit contains _____ and its function is ______. The small ribosomal subunit contains _______ and is involved in _________________.

A

rRNA, catalytic, rRNA, recognition of mRNA

27
Q

The three sites of the large subunit

A

A:approach
P:polymerization
E:exit

28
Q

What is the ribosomal binding site

A

small ribosomal subunit in prokaryotes, sequence in mRNA that is recognized by base pairing with rRNA

29
Q

What are the three steps in translation (in prokaryotes)

A

Initiation, elongation, termination

30
Q

Briefly explain initiation phase in translation

A

ribosomal binding site positions the small subunit such that AUG sits in P-site, the large subunit then associates such that F-met tRNA sits in P-site
“harmburger”

31
Q

Briefly explain elongation phase

A

BIND-BOND-SHIFT

1) Bind: tRNA a.a. approaches the A site and binds to mRNA (codon-anticodon)
2) Bond: peptide bond forms btw first and second tRNA and the growing a.a. chain moves to tRNA in A-site
3) Shift: 5’ ribosome shifts down mRNA (towards 3’) in a one codon step. tRNA in E-site dissociates

32
Q

Briefly explain Termination phase

A

Stop codons (UAA, UAG, UGA) stalls ribosome unless a release factor enters. Ribosome components dismantle and are recycled. Amino acid chain dissociates from tRNA in P-site.

33
Q

When do transcription and translation occur together

A

In prokaryotes! Ribosomes read mRNA as its being transcribed

34
Q

What direction do ribosomes move in

A

towards 3’ end

35
Q

How many RNA polymerase can be active on one gene

A

Multiple! You can make many copies of mRNA from one copy of DNA

36
Q

What is a silent mutation?

A

Base pair substitution, but it works out and leads to the same amino acid (different codons can code the same protein)

37
Q

What is a missense mutation?

A

Base pair substitution that leads to the coding of a different amino acid

38
Q

What is a nonsense mutation?

A

Base pair substitution leads to coding pre mature stop codon.

39
Q

What is a frameshift mutation?

A
  1. Base addition (or insertion) leads to premature stop

2. Base deletion results in every amino acid after being affected

40
Q

When does a mutation not affect the reading frame

A

Deletion of multiples of three

41
Q

What causes sickle cell anemia

A

Single base pair substitution (MISSENSE), misshapes red blood cells so they do not carry oxygen well

42
Q

Explain how mutations can be spontaneous or induced

A

Spontaneous: errors in DNA replication (1x10^10 copied during replication result in mutation)
Induced: x-rays, gamma-rays, oxidizing agents, base analogs

Mutagens also cause cancer (carcinogens)

Biology 107 (10 decks)

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