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BIO 2 > GENE TO PROTEIN (LECTURE 7) > Flashcards

GENE TO PROTEIN (LECTURE 7) Flashcards

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1
Q

What goes into transcription and what can it result in? (4)

A

DNA becomes mRNA, rRNA, tRNA or snRNA.

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2
Q

What goes into translation and what results from it?

A

mRNA becomes a protein (or at least a polypeptide).

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3
Q

Where do transcription and translation occur in eukaryotes? What does this entail? (3)

A

In eukaryotes, transcription occurs in the nucleus while translation occurs in the cytosol. There is thus a conversion from pre-mRNA to mRNA.

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4
Q

Where do transcription and translation occur in prokaryotes? (3)

A

Both processes occur in the cytosol and there is no conversion from pre-mRNA to mRNA.

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5
Q

What is the main difference between eukaryotes and prokaryotes in terms of transcription and translation?

A

There is no conversion from pre-mRNA to mRNA in prokaryotes like there is in eukaryotes.

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6
Q

What are codons? (2)

A

Codons are nucleotide triplets that correspond to specific amino acids.

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7
Q

What is transcription? (mRNA)

A

It is the synthesis of mRNA from a DNA template.

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8
Q

What enzyme is involved in transcription?

A

RNA polymerase is involved in transcription.

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9
Q

What does RNA polymerase do? How does it do it?

A

RNA polymerase synthesizes mRNA from 5’ -> 3’ by catalyzing phosphodiester bond formation between ribonucleotides.

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10
Q

In what ways is RNA polymerase “superior” to DNA polymerase? (2)

A

RNA polymerase can perform it’s own helicase activity (to unwind DNA) and does not need a free 3’-OH end to begin synthesizing RNA.

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11
Q

What are the 3 steps to transcription?

A

Initiation, elongation and termination.

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12
Q

What occurs in the initiation of transcription? (3)

A

Transcription factors bind to the promoter, RNA polymerase is recruited (it too binds to the promoter) and RNA polymerase unwinds DNA.

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13
Q

What are transcription factors?

A

These are proteins that help recruit RNA polymerase to a gene.

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14
Q

What is a promoter?

A

A region of DNA that includes a start point and a TATA box.

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15
Q

Is the promotor transcribed?

A

No.

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16
Q

What nucleotide sequence characterizes the TATA box (on the coding strand)?

A

TATAAAA.

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17
Q

What nucleotide sequence characterizes the TATA box (on the template strand)?

A

ATATTTT.

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18
Q

How many base pairs are separated during RNA polymerase’s unwinding of DNA?

A

10-20 base pairs.

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19
Q

If all our cells have the same DNA, then how can we have so many different types of cells?

A

Different genes are being transcribed due to different transcription factors being active.

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20
Q

What occurs in the elongation of transcription? (2 directions)

A

RNA polymerase synthesizes mRNA from 5’ -> 3’. It reads the template strand from 3’ -> 5’.

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21
Q

Is a primer needed in the elongation phase of transcription?

A

A primer isn’t needed since RNA polymerase doesn’t need a free 3’-OH end.

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22
Q

What occurs in termination of transcription in prokaryotes? (2)

A

RNA polymerase transcribes a terminator sequence, causing it to detach from the mRNA. mRNA is then released and is immediately ready for translation.

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23
Q

What occurs in termination of transcription in eukaryotes? (2)

A

RNA polymerase reaches termination sequence on template strand: TTATTT. The complementary AAUAAA sequence is called the poly A signal sequence. Proteins are recruited to the poly A signal sequence and cut the transcript 10-35 nucleotides after the signal sequence. mRNA is released as pre-mRNA.

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24
Q

In eukaryotes, what occurs to mRNA after transcription?

A

In eukaryotes, mRNA is processed after transcription. Pre-mRNA to mature RNA.

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25
Q

What 3 modifications are made to mRNA during pre-mRNA processing?

A

5’ cap, poly A tail and RNA splicing.

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26
Q

Describe the 5’ cap modification that is made to pre-mRNA.

A

The 5’ cap is a modified guanine nucleotide that is added to the 5’ end of the mRNA.

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27
Q

What functions does the 5’ cap serve? (3)

A

It protects the mRNA against degradation, it allows for the attachment of ribosomes and facilitates the mRNA’s transport out of the nucleus.

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28
Q

Describe the poly A tail modification that is made to pre-mRNA.

A

The poly A tail is 50 - 200 adenine nucleotides that are added to the 3’ end of the mRNA.

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29
Q

What functions does the poly A tail serve? (3)

A

It protects the mRNA against degradation, it allows for the attachment of ribosomes and facilitates the mRNA’s transport out of the nucleus.

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30
Q

Describe the RNA splicing modifications that are made to pre-mRNA.

A

RNA splicing entails the removal of nucleotides (introns) from pre-mRNA and the remaining exons are stuck together.

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31
Q

What are exons?

A

Exons are coding sequences of nucleotides in mRNA.

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32
Q

What are introns?

A

Introns are non-coding sequences of nucleotides found in pre-mRNA.

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33
Q

What carries out RNA splicing?

A

The spliceosome.

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34
Q

What does the spliceosome consist of?

A

It is a complex of proteins and RNA (snRNA).

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35
Q

What type of RNA is found in the spliceosome?

A

snRNA

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36
Q

What does the spliceosome do?

A

It removes introns and links exons.

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37
Q

The RNA component of a spliceosome acts as a what?

A

The RNA component acts as an enzyme.

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38
Q

RNA that has enzymatic activity is called a what?

A

A ribozyme.

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39
Q

Do bacteria have snRNA? Why or why not?

A

No! No pre-mRNA processing occurs in prokaryotes, thus there are no introns to cut out and no spliceosome and thus no snRNA.

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40
Q

List all 4 intron functions.

A

(1) Control of gene expression (2) Regulating transport of RNA out of the nucleus (3) Alternative splicing (4) Evolution of new proteins.

41
Q

Introns are involved in alternative splicing - what is alternative splicing?

A

Alternative splicing occurs when a single gene can result in more than one type of polypeptide, depending on how it is spliced.

42
Q

Due to alternative splicing, how many genes code for how many proteins in the human body?

A

20 000 genes code for 75 000 proteins.

43
Q

Describe how introns are involved in the evolution of new proteins.

A

Introns participate in the evolution of new proteins via exon shuffling - introns are involved in crossover events between alleles of the same gene (or different genes). Crossing over can occur anywhere in the introns and not affect the coding region - increased chance that a recombinant protein will be functional.

44
Q

Describe the final mRNA structure that is ready for translation.

A

5’ cap - leader sequence (5’ UTR) - Coding sequence (start to stop codon) - Trailer (3’ UTR) - poly A tail.

45
Q

What does UTR stand for (in the final mRNA structure)?

A

Untranslated region.

46
Q

Is the TATA box part of the final mature mRNA?

A

No, the promoter is never transcribed in the first place.

47
Q

What is translation?

A

The synthesis of polypeptide from mRNA transcript.

48
Q

What are the 3 steps to translation?

A

(1) Initiation (2) Elongation (3) Termination

49
Q

What is required for all steps in translation? (2)

A

All steps require protein factors and energy.

50
Q

Describe the role of the AUG codon.

A

Start and Met - establishes the reading frame.

51
Q

List all stop codons. What do they do?

A

The 3 stops codons tell the ribosome where to stop translation (UAA, UAG, UGA).

52
Q

Explain the redundancy in the genetic code (translation) and explain why this is a good thing.

A

Several codons may code for the same amino acids - this redundancy acts as a buffer for mutations by decreasing the chances that a mutation will change the amino acid.

53
Q

What are the 3 types of RNA involved in translation?

A

Ribosomal RNA (rRNA), transfer RNA (tRNA) and messenger RNA (mRNA).

54
Q

What are ribosomes composed of? (2)

A

Ribosomes are formed from rRNA and ribosomal proteins.

55
Q

Describe the structure of a ribosome.

A

Ribosomes consist of 2 subunits (small subunit and large subunit).

56
Q

What binding sites are there on the small subunit of a ribosome?

A

Only the mRNA binding site.

57
Q

What binding sites are there on the large subunit of a ribosome?

A

The E-site (exit site), the P-site (peptidyl-tRNA binding site) and the A-site (aminoacyl-tRNA binding site).

58
Q

In what direction do ribosomes read mRNA?

A

They read mRNA in the 5’ –> 3’ direction.

59
Q

How long is the tRNA?

A

Approximately 90 nt long.

60
Q

What is there at the 3’-end of a tRNA?

A

The amino attachment site is at the 3’-end, where specific amino acids attach to the tRNA.

61
Q

What is the Anti codon?

A

It is a sequence of 3 bases on the tRNA that are complementary to a codon on the mRNA strand.

62
Q

What is Aminoacyl-tRNA synthetase?

A

An enzyme that catalyzes the attachment of amino acids to tRNA.

63
Q

Is there only 1 type of aminoacyl-tRNA synthetase?

A

No, each amino acid has a specific aminoacyl-tRNA synthetase.

64
Q

How many aminoacyl-tRNA synthetases are there?

A

20 - one per amino acid.

65
Q

The attachment of an amino acid to tRNA can be characterized as what type of reaction?

A

As an endergonic reaction (requires energy).

66
Q

What is required for the initiation of translation to occur?

A

Initiation requires initiation factors.

67
Q

What are the steps to the initiation of translation?

A

(i) Small ribosomal subunit binds to mRNA (ii) Initiator tRNA binds to mRNA (UAC anticodon binds to AUG start codon on mRNA) (iii) Large ribosomal subunit binds to small subunit (requires GTP, initiator tRNA positioned in P-site).

68
Q

What is required for the elongation of translation to occur?

A

Requires elongation factors.

69
Q

List the steps to elongation of translation.

A

(i) Codon recognition (ii) Peptide bond formation (iii) Translocation.

70
Q

Describe codon recognition of elongation of translation.

A

mRNA codon at A-site forms H-bonds with anticodon of incoming tRNA. GTP is required.

71
Q

Describe peptide bond formation of elongation of translation.

A

The growing polypeptide is transferred from tRNA in P-site to tRNA in A-site. Peptide bond is formed.

72
Q

Describe translocation of elongation of translation.

A

Growing peptide in A-site is moved to P-site. GTP is required.

73
Q

Describe termination of translation (5 steps).

A

Stop codon reaches A-site. Release factor binds to the stop codon. Bond between tRNA (in P-site) and the polypeptide chain is hydrolyzed (broken). Polypeptide is released. Ribosome dissociates and leaves mRNA.

74
Q

Where in the cell does translation occur?

A

In the cytoplasm.

75
Q

How many types of ribosomes are there?

A

2

76
Q

Name the 2 types of ribosomes and the proteins they produce.

A

Free (cytosolic proteins) and Bound to the rough endoplasmic reticulum (membrane and secreted proteins).

77
Q

The synthesis of all proteins starts where?

A

The synthesis of all proteins starts on free ribosomes.

78
Q

What directs a ribosome to the ER?

A

A signal peptide interacting with the SRP.

79
Q

What are signal peptides?

A

String of approximately 20 hydrophobic amino acids at the N-terminus of a growing polypeptide.

80
Q

What proteins have signal peptides?

A

Membrane proteins and secreted proteins have signal peptides.

81
Q

What is an SRP? What is it comprised of?

A

A signal recognition particle (SRP) is comprised of protein and RNA.

82
Q

What is an SRP receptor?

A

It is a protein complex built into the ER membrane (an integral membrane protein).

83
Q

Describe translation at the occurrence of a signal peptide.

A

Signal recognition particle (SRP) binds to signal peptide, at which point protein synthesis pauses. When SRP binds to the SRP receptor, bringing the growing polypeptide to the ER, protein synthesis continues.

84
Q

Once protein synthesis resumes following the arrival of the polypeptide to the ER, what occurs immediately after synthesis? (3)

A

Secreted proteins remain in the ER lumen, membrane proteins are embedded in the ER membrane and the signal peptide is usually removed by an enzyme.

85
Q

How many types of mutations are there?

A

2 types.

86
Q

What are the 2 types of mutations?

A

Base pair substitution (point mutation) and insertions/deletions.

87
Q

Base pair substitution is characterized by?

A

By the replacement of one nucleotide with another.

88
Q

Insertions/deletions (mutations) can be described as?

A

As an addition or loss of nucleotides.

89
Q

How many types of base pair substitutions are there?

A

4 types.

90
Q

Name the 4 types of base pair substitution.

A

(1) Silent, (2) Missense, (3) Neutral, (4) Nonsense.

91
Q

Neutral base pair substitution is also known as what?

A

As conservative missense mutation.

92
Q

In silent base pair substitutions, the…

A

amino acid does not change.

93
Q

In missense base pair substitutions, the…

A

amino acid changes.

94
Q

In neutral base pair substitutions, the…

A

amino acid changes to a similar amino acid.

95
Q

Nonsense base pair substitutions result in…

A

the introduction of a premature stop codon.

96
Q

Rank the 4 types of base pair substitutions by how likely they are to cause problems (least to most likely).

A

Silent, neutral, missense and nonsense.

97
Q

What are the 2 types of base pair insertion or deletion?

A

Frameshift mutations and no frameshift mutations.

98
Q

Describe frameshift mutations. (3)

A

These alter the reading frame of mRNA. The insertion/deletion is not a multiple of 3. All codons after mutation are changed.

99
Q

Describe no frameshift mutations. (3)

A

These do not alter the reading frame of mRNA. The insertion or deletion is a multiple of 3. Codons are either added or removed but codons before and after the mutation are unchanged.

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