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Winter 2023 - Biology > Cycle 7: Transcription & Translation > Flashcards

Cycle 7: Transcription & Translation Flashcards

1
Q

What does tRNA do?

A

bring amino acids to the ribosome for assembly into the polypeptide chain

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2
Q

What is the start codon/amino acid?

A

AUG

Methionine (Met)

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3
Q

What are the stop codons?

A

UAA
UAG
UGA

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4
Q

What happens when a stop codon is reached?

A

polypeptide synthesis stops and the new polypeptide chain is released from the ribosome

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5
Q

Why is it important to remain in the correct reading frame?

A

insertion/deletion causes all bases to shift changing all codons –> amino acids which can change the translated protein

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6
Q

What are the two parts of a gene? What are their functions?

A
  1. promotor: control sequence for TRANSCRIPTION
  2. transcription unit: section of gene that is COPIED into an RNA molecule
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7
Q

What is pre-mRNA?

A

first transcript of a eukaryotic protein-coding gene, which is processed in the nucleus to form TRANSLATABLE mRNA

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8
Q

Where is mature mRNA translated?

A

ribosomes in cytoplasm (after leaving nucleus from processing)

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9
Q

What is the purpose of the 5’ cap?

A
  • protects single stranded mRNA from degradation

-the site where ribosomes attach at the start of translation instead of SD box

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10
Q

When is the 5’ cap added?

A

soon after transcription begins

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11
Q

How is transcription terminated in eukaryotes?

A

near the 3’ end of the gene is a DNA sequences that is transcribed into the pre-mRNA called the POLYADENYLATION SIGNAL

protein bind to the signal in the RNA and cleave it just downstream

this signals RNA polymerase to stop transcription

poly(A) polymerase adds a chain of adenine nucleotides

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12
Q

Do the 5’ cap and poly A tail need complementary base pairing?

A

NO! guanine 5’ cap and poly A tail are just added

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13
Q

What is the poly A tail purpose?

A

enables mRNA to be translated efficiently and protects it from attack by RNA-digesting enzymes in the cytoplasm

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14
Q

What are introns?

What are exons?

A

intervening sequences that interrupt the protein-coding sequences and are spliced out only in eukaryotes!

introns are trasncribed into pre-mRNA but are removed from pre-mRNA

exons - AA coding sequence present in pre-mRNA translated to proceed a polypeptide

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15
Q

What is mRNA splicing?

A

remove introns and join exons in pre-mRNA in nucleus

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16
Q

What is a spliceosome?

A

a complex formed between the premRNA and small ribonucleoprotein (snRNA and protein = snRNP) particles

cleaves pre-mRNA to released intron

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17
Q

What does the snRNPs do?

A

bind to an intron pre-mRNA and form active spliceosome

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18
Q

How is the reading frame intact during splicing?

A

complementary base pairing region of snRNA and mRNA

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19
Q

What is alternative splicing?

A

mechanism that joins exons in different combinations to produce different mRNAs from a single gene which is evolved and not random

same gene -> diff mRNA -> diff protein

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20
Q

Why is alternative splicing beneficial?

A

increases variety of proteins without increasing genome size

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21
Q

What is translation?

A

assembly of amino acids into polypeptides on ribosomes

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22
Q

Where does translation occur in prokaryotes? eukaryotes? What does this mean?

A

prokaryotes: throughout cell - mRNA immediately available for translation

eukaryotes: cytoplasm (specialized genes are transcribed and translated in mitochondria or chloroplast) - must exit nucleus and is them translated

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23
Q

How is mRNA read? How is the polypeptide assembled?

A

5’ to 3’

N-terminal end to C-terminal end

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24
Q

How is mRNA read? How is the polypeptide assembled?

A

5’ to 3’

N-terminal end to C-terminal end

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25
Q

What does tRNA structure look like?

A

cloverleaf pattern with anticodon - base pairs with codon in mRNA

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26
Q

Where do ribosomes function in prokaryotes? eukaryotes?

A

prokaryotes: throughout cell

eukaryotes: only in cytoplasm - freely suspended or attached ER membranes

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27
Q

What are the 3 steps of translation?

A
  1. initiation - translation components assemble on the start codon of the mRNA
  2. elongation - assembled complex reads the string of codons in the nRMA one at a time while joining the specified AA into the polypeptide
  3. termination - complex disassembles after the last AA of the polypeptide is added
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28
Q

How is prokaryotic translation different?

A

rather than scanning from 5’ end of mRNA, the initiator Met-tRNA and GTP bind directly to the region of the mRNA with the AUG start codon

initiation complex is guided by ribosome binding site (instead of the start codon on mRNA) that base-pairs with a complementary sequence of rRNA in the small ribosomal unit

large ribosomal subunit then binds to the small subunit to complete the ribosome

GTP hydrolysis begins translation

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29
Q

How does termination occur?

A

release/termination factor binds to A site and causes ribosome to disassemble into its subunits

  • this is a protein (not tRNA) so it can’t base pair with stop codon
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30
Q

What is a polysome?

A

multiple ribosomes attached to mRNA which increases the rate of polypeptide synthesis

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31
Q

Why is transcription and translation couple in prokaryotic cells? What does this mean?

A

no nuclear envelope

as soon as 5’ end of new mRNA emerges from RNA poly, ribosomal subunits attach to initiate translation

– much faster than eukaryotes!

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32
Q

What is alternative processing?

A

when ribosomes release polypeptide chains, they are inactive and new do have AA & organic groups removed and folding into final 3D shapes

removing different AA sequences increases the number of proteins encoded by a single gene

33
Q

Missense mutation?

A

change sense codon to a sense codon for a different amino acid

34
Q

Nonsense mutation?

A

change sense codon to a stop codon

35
Q

Silent mutation?

A

changes sense codon to another codon for a same amino acid

36
Q

Frameshift mutation?

A

insertion or deletion

37
Q

Why can’t eukaryotic cells have transcription and translation occurring concurrently?

A

nuclear envelope separates the processes

eukaryotes, have pre-mRNA which then gets translated

38
Q

Where can you find tRNA?

A
  • nucleus when transcribed
  • mitochondria, chloroplast
  • cytoplasm
39
Q

Where can you find RNA polymerase?

A
  • synthesized in cytoplasm
  • mito, chloro
  • nucleus for transcription
40
Q

What does the RNA transcript look like?

A

coding, sense, non-template strand

41
Q

What is non coding RNA? coding RNA?

A

non coding: tRNA, rRNA, snRNA (does NOT get translated)

coding: mRNA

42
Q

Which end of RNA is released first in transcription?

A

5’ end! (3’ to 5’ template)

43
Q

Which ribosome is oldest?

A

closest to the 3’ end because translation occurs 5’ to 3’

44
Q

What the the 5’ and 3’ UTR?

A

untranslated region present in DNA and mRNA that regulate translation but they are transcribed

45
Q

What is the TATA box? What is -35 -10 region?

A

both section of promotor that are conserved

TATA box - recognized by transcription factors when determine specialization which causes RNA poly to bind

-35 -10: -10 is start sequence

46
Q

What is the Open Reading Frame?

A

part of reading frame that has the ability to be translated containing start and stop codon

47
Q

What is the SD box?

A

sequence in prokaryotic mRNA which rRNA is ribosome recognizes so ribosome aligns with mRNA for translation

48
Q

What is the 3’ splice site sequence? What recognizes it?

A

N C A G G - recognized by snRNP (snRNP coupled with protein) to create spliceosome

must used comp base pair bc

49
Q

Where does snRNA bind?

A

only to mRNA! it is the only one that does translated with introns

50
Q

Where does prokaryotic transcription occur? eukaryotic?

A

prokaryotic: cytoplasm

eukaryotic: nucleus

51
Q

What does RNA polymerase recognize in prokaryote? eukaryote?

A

prokaryotic: -35 and -10 regions in promotor to initiate transcription

eukaryotic: transcription factors that are bound to TATA box in the promotor to initiate transcription

52
Q

How is prokaryotic transcription initiated?

A

RNA polymerase recognizes -35 -10 region in promotor

53
Q

How does RNA polymerase recognize to begin transcription in prokaryotes? eukaryotes?

A

prokaryotic: recognizes sequence directly on promotor

eukaryotic: can’t recognize actual TATA sequence, only recognizes transcription factor

54
Q

What are additional regulation regions in eukaryotes not in prokaryotes?

A

enhancer regions and promotor proximal regions
and transcription factors

55
Q

How does the promotor compare in prokaryotes and eukaryotes?

A

not transcribed in both and recognized as DNA and not present in mRNA and premRNA

56
Q

How is transcription terminated in prokaryotes?

A

terminator - sequence is inverted repeat that forms hairpin loop)

57
Q

How does termination of transcription occur in eukaryotes?

A

cleavage site just after 3’UTE that is cut by site specific RNase

58
Q

How care introns recognized by snRNPs?

A

RNA not DNA

59
Q

Where is the poly A signal? How is it recognized?

A

within 3’ UTR
recognized by Poly A polymerase as RNA

60
Q

Where does prokaryotic translation occur?

A

cytoplasm at the same time as transcription

61
Q

Where does eukaryotic translation occur?

A

cytoplasm, ER, mitochondria, chloroplast

62
Q

How is translation initiated in prokaryote?

A

ribosome recognizes SD box and its rRNA component comp base pairs with mRNA and then initiates translation at the start codon

63
Q

How is translation initiated in eukaryotes?

A

ribosome recognizes 5’ cap and scans the 5’ UTR of the mRNA until it reaches AUG start codon

64
Q

What does DNA base pair with?

A

self, DNA in rep, mRNA, tRNA, snRNA, rRNA (all during transcription)

65
Q

What does mRNA base pair with?

A

self, DNA(transcription), snRNA(splicing pre-mRNA), rRNA (SD box), tRNA (translation)

66
Q

What does rRNA base pair with?

A

DNA(transcription), rRNA, mRNA (SD box)

67
Q

What does tRNA base pair with?

A

tRNA, DNA (transcription), mRNA (translation)

68
Q

What does snRMA base pair with?

A

snRNA, mRNA in splicing, DNA (transcription_

69
Q

What does proteins base pair with?

A

nothing

70
Q

What is -10/-35 understood as and by?

A

DNA by RNA polymerase

71
Q

What is TATA box understood as and by?

A

DNA by transcription factors

72
Q

What is ATG & TAG/TGA/TAA/TGA understood as and by?

A

mRNA by tRNA with its anticodon and release factor

73
Q

What is the terminator understood as and by?

A

RNA (mRNA - hairpin loop) by RNA polymerase

74
Q

What is polyA signal understood as and by?

A

pre-mRNA polyA polymerase

75
Q

What is the cleavage site understood as and by?

A

pre-mRNA by RNase

76
Q

What is intronic splice sites understood as and by?

A

pre-mRNA by snRNPs

77
Q

What is SD box understood as and by?

A

RNA (mRNA) by rRNA in ribosome – not found in tRNA or rRNA or snRNA bc no translation

78
Q

What is exons understood as and by?

A

RNA by tRNA

79
Q

What is a polyribosome?

A

ribosome complex with peptide chain

Winter 2023 - Biology (11 decks)

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