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Genetics > Lecture 13 > Flashcards

Lecture 13 Flashcards

Transcription and RNA processing

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1
Q

Gene transcription –

A

RNA is synthesized or
“transcribed” from the DNA template

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2
Q

Translation

A

mRNA is translated into a protein product

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3
Q

“The central dogma”

A

DNA -> RNA -> Protein

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4
Q

DNA is localized in the __ in eukaryotic organisms

A

nucleus

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5
Q

Protein synthesis takes place in the :

A

cytoplasm

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6
Q

The messenger molecule that carries the information of a gene to the cytoplasm for translation into protein is an:

A

RNA called messenger RNA or MRNA

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7
Q

RNA – ribonucleic acid, is similar to DNA
There are three major differences:

A
  1. The sugar-phosphate backbone is composed of
    ribose sugars NOT deoxyribose sugars
  2. RNA contains the pyrimidine base URACIL
    instead of thymine.
  3. RNA is typically single stranded (there are
    some double stranded RNA
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8
Q

Ribosomal RNA, rRNA –

A

is part of the translation complex

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9
Q

Transfer RNA, tRNA

A

– participates in translation. It carries
specific amino acids to be
incorporated into the new proteins

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10
Q

Messenger RNA – mRNA –

A

protein encoding transcript
of a gene.

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11
Q

The RNA product has the same sequence as ___, but it has __

A

The RNA product has the same sequence as the upper coding strand of DNA except it has U in place of T’s

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12
Q

The lower strand of DNA is:

A

the physical template for RNA synthesis

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13
Q

template strand =

A

noncoding = nonsense= antisense

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14
Q

nontemplate strand

A

coding = sense

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15
Q

RNA is synthesized, or transcribed, in the

A

5’ to 3’ direction

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16
Q

Chromosomes have different genes in different orientations, but all
genes transcribed in the same direction are

A

on the same strand;

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17
Q

genes transcribed in the other direction are on

A

the other strand.

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18
Q

The bases in RNA are added in a sequence that is complementary
to the DNA sequence

A

G opposite C’s
C opposite G’s
U opposite A’s
A opposite T’s

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19
Q

The bottom strand is

A

the physical template for RNA synthesis.

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20
Q

mRNA is :

A

a copy of the top strand of DNA, except uricil occurs in place of thymidines, and RNA has a ribose sugar backbone.

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21
Q

primase:

A

makes the primers for the
Okazaki fragments of the lagging strand during DNA replication

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22
Q

RNA polymerase I

A

produces rRNA

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23
Q

RNA polymerase II

A

makes copies of genes -mRNA

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24
Q

RNA polymerase III

A

produces tRNAs

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25
Q

Genes have characteristic regulatory sequences that are
upstream of the beginning of transcription.
These are referred to as

A

promoters and promoter elements

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26
Q

The bacterial -10 sequence is sometimes called a:

A

TATA box, or a
Pribnow box

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27
Q

RNA transcription starts at:

A

promoters

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28
Q

RNA transcription ends at :

A

terminators

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29
Q

One transcript encodes

A

several genes (which are typically functionally related)

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30
Q

the arrangement in which related genes are co transcribed into a single mRNA is termed:

A

an operon

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31
Q

A single transcript can encode up to:

A

several different proteins.

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32
Q

Eukaryotic mRNAs generally encode

A

a single polypeptide

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33
Q

Eukaryotic mRNAs are said to have:

A

a single open reading frame

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34
Q

eukaryotic genes have a larger, and more complicated :

A

promoters than bacteria

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35
Q

TATA in eukaryotic geners boxes are usually in the:

A

-30 region

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36
Q

In eukaryotic genes, there is a CAAtT box :

A

in the minus 50 base pair region

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37
Q

__ are spliced out before the mRNA is exported to the cytoplasm

A

introns

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38
Q

The removal of introns and the splicing together of the exons is performed by:

A

a complex of proteins and RNA molecules called a spliceosome

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39
Q

many human genes have:

A

alternate splicing patterns (several different related proteins can be produced by one gene)

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40
Q

The eukaryotic introns have very conserved boarder sequences: introns begin with __ and end with__

A

introns begin with GU and end with AG

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41
Q

Once the mRNA is transcribed (and processed in the case of
eukaryotic messages), it is used to code for the production of
proteins. This is the process of

A

translation

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42
Q

In the case of transcription, the nucleotide information in the
DNA is transferred to

A

Nucleotide information in the mRNA.
The transfer is 1:1, each DNA nucleotide represents 1 RNA
nucleotide.

43
Q

In the case of translation, the nucleic acid information is
transferred into:

A

an entirely different type of polymer, a protein, made up of amino acids rather than nucleotides.

44
Q

3 RNA nucleotides specify

A

1 amino acid

45
Q

Analysis of the arrangement of amino acids in the sequence of
proteins showed that

A

the code was non-overlapping

46
Q

RNA is degraded by

A

deadenylase
an exonuclease
and by removal of the 7-methyl guanine cap
by a decapping enzyme, followed by exonuclease digestion

47
Q

RNA polymerase, a DNA dependent enzyme

A

synthesizes RNA from the DNA template

48
Q

Correct transcription of the genetic material is dependent on

A

base complementarity of RNA to DNA (like the complementarity between the two DNA strands)

49
Q

In E coli, the RNA polymerase has four different protein subunits:

A

ß, ß’, a, a, s (beta, beta’, alpha, alpha, sigma).

50
Q

transcription of a gene: initiation:

A

Transcription factors bind to promoter region -35 and -10 to a “consensus sequence” i.e. a similar sequence is found in many genes. This sequence is similar in different genes, though it is not identical in all cases.

51
Q

transcription of a gene: elongation

A

synthesis of RNA proceeds in a 5’ to 3’ direction

52
Q

transcription of a gene: termination

A

a) GC rich sequence that has self-complementary. The region can form a hairpin loop based on the self-complementarity, it is normally followed by a stretch of A’s
b) Rho factor interacting with Rut site on RNA

53
Q

An mRNA is translated in continuous triplets called:

A

codons

54
Q

codons do not __

A

overlap

55
Q

there is no space or any extra nucleotides between:

A

codons

56
Q

standard start signal:

A

AUG

57
Q

A set of stop signals

A

UAG, UAA or UGA

58
Q

the genetic code is:

A

non-overlapping, and consecutive with no gaps

59
Q

What do we mean by the genetic code is also degenerate in terms of the amino acid?

A

several codons may represent the same amino acid

60
Q

In a random DNA sequence, we expect a stop codon:

A

once every 21 codons

61
Q

A mature eukaryotic mRNA has:

A

-5’ cap structure
-5’untranslated region (5’UTR)
-AUG start codon (in DNA: ATG)
-Long open reading frame (ORF) - a long stretch of codons encoding amino acids with no stop codons
-Stop codon - UAG or UAA or UGA
- 3’ untranslated region (3’UTR followed by poly A’s)

62
Q

In eukaryotic organisms, one mRNA encodes:

A

a single protein

63
Q

In prokaryptes: one mRNA typicalle encodes:

A

several proteins

64
Q

Bacteria have polycistonic mRNAs, in which:

A

adjacent genes are transcribes in one message (this collection of cotranscribed genes represents an operon)

65
Q

In prokaryotes, there is no:

A

5’ cap and no poly A tails
if they are added, they are signals for degradation of the message, whereas in eukaryotes, they stabilize the message

66
Q

initiation of translation in prokaryotes: a key requirement for initiation of translation is:

A

to put the N-formyl methionine charged initiator tRNA at the P site, in association with the mRNA

67
Q

What happens subsequently after initiation of translation in prokaryotes

A

subsequently, a large ribosomal subunit joins to the complex and a second charged tRNA enters at the A site. As it moves to the P site as it releases its amino acid to link it to the growing polypeptide chain, the uncharged tRNA exits at the E site of the ribosome

68
Q

What is a shine dalgarno sequence?

A

Prokaryotic organisms have a sequence in the 5’ UTR region of their mRNAs called a Shine delgarno sequence that binds to the small subunit of the ribosome

69
Q

Do eukaryotic organisms have an upstream shine dalgarno sequence?

A

No

70
Q

Kozak sequence:

A

In eukaryotic mRNAs, the conserved sequences near the AUG have a concensus sequence, sometimes called a kozak sequence:

The G in the +4 position and the A in the -3 position (A of AUG referred to as the +1 position)

71
Q

unlike ATP hydrolysis, which typically esrves to provide energy to reactions, GTP hydrolysis by GTPases serves to :

A

Provide directionality to a reaction, GTPases are switches, not engines

72
Q

Termination of translation of mRNA:

A

release factor (RF1,RF2, or RF3) bind to the stop codon and terminate translation

73
Q

Translation terminates when:

A

a nonsense codon appears in frame in the A site of the ribosome

74
Q

amino acids are brought to the ribosome by:

A

tRNAs

75
Q

tRNAs make the physical link between:

A

the mRNA codon and the specific amino acid corresponding to each codon

76
Q

The specific amino acid is added to its specific tRNA by:

A

amino acyl - TRNA synthetase

77
Q

Aminoacyl-tRNA synthatases are critical specificity elements in the system, its their role to :

A

connect the proper amino acid to the tRNA that has the proper anticodon recognition sequence for that amino acid in the genetic code

78
Q

The addition of an amino acid to its cognate tRNa is called:

A

charging

79
Q

where does the energy for charging come from:

A

the hydrolysis of ATP

80
Q

Wobble:

A

some tRNAs have alternate base pair matching in the third position of the codon: not classical Watson-Crick pairing
Remember: many codons code for the same amino acid

81
Q

The human genome has __ different types of tRNAs for __ codons

A

the human genome has 48 different types of tRNAs for 61 codons

82
Q

The first amino acid in bacterial translation is unusual : it is an:

A

N-formyl methionine

83
Q

In prokaryotes, the small ribosomal subunit is called the:

A

30s subunit

84
Q

In prokaryotes, the small subunit is called the :

A

40s subunit

85
Q

proteins are synthesiszed with directionality:

A

from the amino acid end to the carboxyl end

86
Q

The amino end of the protein corresponds to the

A

5’ end of the mRNA
It is called the N terminal end of the protein

87
Q

point mutations are the substitution of:

A

one nucleotide

88
Q

What are the two types of point mutations:

A

1.1 missense mutations
1.2 nonsense mutations

89
Q

In a missense mutation:

A

one amino acid is changed for another

90
Q

in a nonsense muation:

A

change amino acid to STOP codon

91
Q

frame shift muation -

A

insertion or loss of one or two nucleotides

frame shift mutations are very deleterious

92
Q

insertion or deletion:

A

of three nucleotides

93
Q

synonymous mutations are:

A

point mutations that do not cause a chanfe in amino acid sequence

94
Q

frame shift mutations can be corrected by:

A

a second mutation that corrects the frame

95
Q

transposable elements:

A

mobile elements of DNA that can change position in the genome and can insert genes and cause mutations

96
Q

which of the following is not seen in prokaryotic transcription?
a) three distinct RNA polymerases
b)1 RNA polymerase
c)TATA box at -10
d) transcription and translation happen simulataneously

A

a) Three distinct RNA polymerases

97
Q

During transcription, only one of the DNA strands is used as a template for DNA synthesis, while the other strand is not transcribed, the strand being transcribed is called:

A

template and noncoding strand

98
Q

In what cellular compartment are introns removed from pre-mrna to make mature mRNA?

A

nucleus

99
Q

In __ , there are often multiple transcription factors that work together to regulate gene expression, while in ____, a single transcription factor can regulate the expression of multiple genes

A

eukaryotes: bacteria

100
Q

How many nucleotides would be expected for the open reading frame in the mRNA from a gene coding for a protein with 300 amino acids?

A

900

101
Q

The DNA sense strand (non template strand) for a particular amino acid is 5’ -ATG- 3’.
What RNA sequence would be transcribed for this codon, what tRNA codon would recognize it, and what amino acid would be added in response to this codon?

A

RNA transcribed: 5’ - AUG - 3’

tRNA anticodon; methionine

102
Q

What would be the effect of a mutation that introduces the introduction on two additional successive nucleotides (one next to the other) into the coding sequence:

A

It would change the amino acid sequence from the point of insertion and on, in the resulting protein and likely cause a truncation of the coding sequence, i.e: shorten the open reading frame

103
Q

The A site, the P side and E site each control __ (in order) during translation

A

A: Binding incoming tRNAs
P: Retention of the peptide chain during elongation (P)
E: Exit of deaceylated tRNAs

Genetics (12 decks)

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