BIO LEC 2025 > CHAPTER 17: Gene Expression > Flashcards

CHAPTER 17: Gene Expression Flashcards

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1
Q

what is gene expression ?

A

the process by which DNA directs protein synthesis, has 2 stages: transcription and translation

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2
Q

what is transcription?

A

it is the synthesis of RNA using information in DNA

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3
Q

what does transcription produce ?

A

messenger RNA (mRNA)

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4
Q

what is translation ?

A

it is the synthesis of a polypeptide, using information in the mRNA

genetic information flows from mRNA to protein

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5
Q

what are the sites of translation ?

A

ribosomes

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6
Q

how does translation and transcription occur in prokaryotes ?

A

translation of mRNA can begin before transcription has finished

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7
Q

how does translation and transcription occur in eukaryotes ?

A

the nuclear envelope separates transcription from translation

Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA

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8
Q

what is a primary transcript ?

A

it is the initial RNA transcript from any gene prior to processing

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9
Q

what is the triplet code?

A

a series of nonoverlapping, 3-nucleotide words that the flow of information from gene to protein is based on

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10
Q

what happens to the words of a gene ?

A

they are transcribed into triplet code of mRNA, then translated into a chain of amino acids, forming a polypeptide

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11
Q

what is the template strand ?

A

one of the 2 DNA strands.
provides a template for ordering the sequence of complementary nucleotides in an RNA transcription

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12
Q

what are codons ?

A

3 mRNA bases = 1 amino acid
occur during translation
read in the 5’ -> 3’ direction

they specifiy the amino acid at a corresponding position along a polypeptide

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13
Q

what is the coding strand ?

A

the nontemplate strand. the nucleotides are identical to codons, except that T is present in the DNA in place of U in RNA

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14
Q

how are codons suppose to be read ?

A

in the correct reading frame in order for the specified polypeptide to be produced

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15
Q

what is the first stage of gene expression ?

A

transcription

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16
Q

what is RNA polymerase ?

A

it catalyzes RNA synthesis. it pries the DNA strands apart and joins the RNA nucleotides together

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17
Q

what are the pairing rules for RNA synthesis ?

A

RNA synthesis follows the same base-pairing rules as DNA, except that uracil substitutes for thymine

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18
Q

what is the promoter ?

A

the DNA sequence where RNA polymerase attaches

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19
Q

what is the terminator ?

A

the sequence signaling the end pf transcription. in bacteria.

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20
Q

what is the transcription unit ?

A

the stretch of DNA that is transcribed

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21
Q

what is the eukaryotic transcription initiation complex ?

A

A completed assembly of transcription factors and RNA polymerase Ⅱ bound to a promoter

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21
Q

what are the 3 stages of transcription ?

A
  1. initation
  2. elongation
  3. termination
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22
Q

what are transcription factors ?

A

proteins in eukaryotic cells that help guide the biding of RNA polymerase and the initiation of transcription

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23
Q

how do the mechanisms of termination work in bacteria ?

A

the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification

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23
what is the TATA box ?
the promoter element that is crucial in forming the initiation complex in eukaryotes
24
what happens when the RNA polymerase moves along the DNA
it untwists the double helix, 10-20 nucleotides at a time
25
how do the mechanisms of termination work in eukaryotes ?
RNA polymerase Ⅱ transcribes the polyadenylation signal sequence; the RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
26
what is RNA processing ?
modified pre-mRNA before the genetic messages are dispatched to the cytoplasm
27
what occurs during RNA processing ?
the genetic messages are dispatched to the cyroplasm
28
how are the ends of a pre-mRNA molecule modified ?
1. the 5' end receives a modified nucleotide, a 5' cap 2. the 3' end gets a poly-A tail
29
what are the functions of the modifications of the ends of a pre-mRNA molecule ?
1. they seem to facilitate the export of mRNA to the cytoplasm 2. they protect mRNA from hydrolytic enzymes 3. they help ribosomes attach to the 5′ end
30
what are introns ?
the noncoding segments in a gene
31
what does RNA splicing remove ?
the long nucleotides that like between coding regions that most eukaryotic genes and their RNA transcripts have.
32
what are spliceosomes ?
they remove introns and consist of a variety of proteins and several small RNAs that recognize the splice sites
33
what are ribozymes ?
catalytic RNA molecules that function as enzymes and can splice RNA
34
what are the 3 properties of RNA that enable ribozymes to function as an enzyme ?
1. it can form a three-dimensional structure because of its ability to base-pair with itself 2. some bases in RNA contain functional groups that may participate in catalysis 3. RNA may hydrogen-bond with other nucleic acid molecules
35
what is alternative RNA splicing ?
where some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing
36
what are domains ?
a modular architecture conditions of discrete regions that proteins often have
37
what is transfer RNA (tRNA)
they transfer amino acids to the growing polypeptide in a ribosome
38
what does each tRNA molecule do ?
it enables translation of a given mRNA codon into a certain amino acid 1. carries a specific amino acid at one end 2. other end has a anticodon which base-pairs with a complementary codon on mRNA
39
what is needed for accurate translation ?
2 instances of molecular recognition 1. aminoacyl-tRNA synthetsae needs to correctly match a tRNA and an amino acid 2. a correct match between the tRNA anticodon and an mRNA codon
40
what is wobble ?
a flexible pairing at the 3rd based of a codon that allows some tRNAs to bind to more than one codon
41
what do ribosomes do ?
facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
42
what are the 3 biding sites for tRNA ?
the p site, a site, and e site
43
what is the p site ?
it holds the tRNA that carries the growing polypeptide chain
44
what is the a site ?
holds the tRNA that carries the next amino acid to be added to the chain
45
what is the e site ?
is the exit site, where discharged tRNAs leave the ribosome
46
what do all 3 stages of translation require ?
protein factors that aid in the translation process some need energy
47
what happens during initiation stage of transition ?
1. the small ribosomal subunit binds with mRNA and a special initiator tRNA 2. the initiator tRNA carries the amino acid methionine 3. then the small subunit moves along the mRNA until it reaches it reaches the start codon (AUG) 4. initiation factors bring in the large subunit that completes the translation initiation complex
48
what happens during elongation ?
amino acids are added one by one to the C-terminus of the growing chain
49
what are the 3 steps of elongation has ?
1. codon recognition 2. peptide bond formation 3. translocation
50
when does elongation stop ?
until a codon in the mRNA reaches the A site
51
what is the release factor ?
it causes the additional of a water molecule instead of an amino acid, it gets accepted at the a site. it releases the polypeptide, and the translation assembly comes apart.
52
what are the 2 populations of ribosomes that are evident in cells ?
1. free ribosomes (in cytosol) 2. bound ribosomes (attached to ER)
53
what do free ribosomes do ?
they mostly synthesize proteins that function in the cytosol
54
what do bound ribosomes do ?
they make proteins of the end-membrane system and proteins that are secreted from the cell.
55
what is a signal peptide ?
a sequence of about 20 amino acids at/near the leading end of a polypeptide they're destines for the ER or for secretion
56
what a singal-recognition peptide (SRP) ?
it escorts the ribosome to a receptor protein built into the Er membrane
57
what is a polyribosome? what does it do?
when multiple ribosomes translate a single mRNA. they enable a cell to make many copies of a polypeptide very quickly
58
what are point mutations ?
changes in just one nucleotide pair of a gene ?
59
when is a condition referred to as a genetic disorder or hereditary disease ?
if a mutation has an adverse effect on the phenotype of the organism
60
what are the 2 categories point mutations within a gene can be divided into ?
1. single nucleotide-pair substitutions 2. nucleotide-pair insertions/deletions
61
what happens in a nucleotide-pair substitution ?
replaces one nucleotide and its partner with another pair of nucleotides
62
what are silent mutations ?
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
63
what are missense mutations ?
they still code for an amino acid, but not the correct amino acid
64
what are nonsense mutations
change an amino acid codon into a stop codon; most lead to a nonfunctional protein
65
what are insertions and deletions? to nucleotides ? and to outside the coding part of a gene?
1. they're additions or losses of nucleotide pairs in a gene 2. of nucleotides may alter the reading frame, producing a frameshift mutation 3. outside the coding part of a gene could affect how the gene is expressed
66
what are mutagens ?
physical or chemical agents that can cause mutations
67
what is the the central dogma ?
the concept that cells are governed by a cellular chain of command: DNA → RNA → protein
BIO LEC 2025
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