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gene expression Flashcards

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1
Q

What is gene expression?

A

The process by which DNA directs protein synthesis (transcription and translation).

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2
Q

What is the central dogma of molecular biology?

A

DNA → RNA → Protein.

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3
Q

What are the roles of transcription and translation?

A

: Transcription: DNA → mRNA. Translation: mRNA → Polypeptide (protein).

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4
Q

What is a codon?

A

A codon is a triplet of nucleotides in mRNA that codes for a specific amino acid or a stop signal.

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4
Q

What is the start codon and what amino acid does it code for?

A

AUG; it codes for methionine (Met).

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5
Q

What is the difference in transcription/translation between prokaryotes and eukaryotes?

A

In prokaryotes, they are coupled; in eukaryotes, they are separated by the nuclear membrane.

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6
Q

How many codons are there and what do they code for?

A

64 total codons: 61 code for amino acids; 3 are stop codons (UAA, UGA, UAG).

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7
Q

What makes the genetic code redundant but not ambiguous?

A

Multiple codons can code for the same amino acid, but each codon codes for only one amino acid.

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8
Q

What are the three stages of transcription?

A

: Initiation, Elongation, Termination

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9
Q

What enzyme carries out transcription?

A

RNA Polymerase

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10
Q

What is the promoter, and what key sequence is often found there in eukaryotes?

A

The DNA region RNA polymerase binds to; the TATA box is a key eukaryotic promoter element.

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10
Q

What is the template strand?

A

The DNA strand used by RNA polymerase to make complementary RNA.

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11
Q

: In which direction is RNA synthesized?

A

5′ → 3′ direction.

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12
Q

What are transcription factors?

A

Proteins that help RNA polymerase bind to DNA and initiate transcription.

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13
Q

What is the transcription initiation complex?

A

RNA polymerase + transcription factors bound to promoter.

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14
Q

What modifications occur to pre-mRNA?

A

5′ cap (modified guanine), 3′ poly-A tail, and splicing of introns.

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15
Q

What is the purpose of the 5′ cap and poly-A tail?

A

Protect mRNA, aid in export from nucleus, and help ribosome binding.

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16
Q

What are introns and exons?

A

: Introns are non-coding regions removed during splicing; exons are coding regions retained in mRNA.

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17
Q

What catalyzes RNA splicing?

A

Spliceosomes made of snRNPs and snRNAs

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18
Q

What is alternative RNA splicing?

A

Process by which different mRNAs (and thus proteins) are produced from the same gene.

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18
Q

What are ribozymes?

A

Catalytic RNAs that can splice RNA (discovered by Altman & Cech).

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19
Q

What is wobble base pairing?

A

Flexibility in pairing between the 3rd base of mRNA codon and tRNA anticodon

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19
Q

What is the role of tRNA in translation?

A

It brings amino acids to the ribosome and matches them to mRNA codons using its anticodon.

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20
Q

What enzyme charges tRNA with amino acids?

A

Aminoacyl-tRNA synthetase.

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21
What are the three sites of a ribosome?
A site (aminoacyl), P site (peptidyl), E site (exit).
22
What is the Kozak sequence?
Eukaryotic consensus sequence around the start codon (e.g., ACCAUGG) to initiate translation.
23
What assembles first in translation initiation?
Small ribosomal subunit + mRNA + initiator tRNA (Met); then large subunit joins.
24
What are the three steps in elongation?
Codon recognition, peptide bond formation, translocation.
25
What signals termination of translation?
Stop codons (UAA, UAG, UGA); release factor binds and releases polypeptide.
26
When do proteins fold into their functional shape?
During and after translation
27
What is the role of the signal recognition particle (SRP)?
It recognizes the signal peptide and brings the ribosome to the ER.
27
What are signal peptides?
Short sequences that direct the polypeptide to specific parts of the cell.
28
What is the path for secretory proteins?
: Ribosome → ER → Golgi → Vesicles → Membrane/Exterior.
29
What is a polyribosome (polysome)?
A group of ribosomes translating a single mRNA simultaneously, enabling rapid polypeptide production.
30
: How do polyribosomes increase efficiency?
They allow multiple copies of a protein to be made from one mRNA quickly.
31
How do transcription and translation differ between bacteria and eukaryotes?
In bacteria, transcription and translation are coupled. In eukaryotes, they occur separately (transcription in nucleus, translation in cytoplasm).
32
Do both prokaryotes and eukaryotes use polyribosomes?
Yes, both use polyribosomes to translate mRNA efficiently
33
What is a mutation?
A change in the genetic material of a cell or virus.
34
How can a single nucleotide change affect a protein?
It can produce an abnormal protein, possibly leading to genetic disorders (e.g., sickle cell anemia).
35
What is a genetic disorder?
A condition caused by a mutation that adversely affects the phenotype
36
What is a point mutation?
A chemical change in just one base pair of a gene.
37
What are the two main categories of point mutations?
Substitutions and frameshift mutations (insertions or deletions)
38
What is a missense mutation?
A substitution that changes one amino acid to another (e.g., sickle cell anemia).
39
What is a silent mutation?
A substitution that has no effect due to redundancy in the genetic code.
40
What is a nonsense mutation?
A substitution that changes an amino acid codon into a stop codon, usually leading to a nonfunctional protein
41
What is an insertion mutation?
Addition of one or more nucleotide pairs in a gene.
42
What is a deletion mutation?
Loss of one or more nucleotide pairs in a gene.
43
What is the result of an insertion or deletion in coding regions?
: It may alter the reading frame, causing a frameshift mutation, which usually results in a nonfunctional protein
44
What are spontaneous mutations?
Mutations that occur naturally during DNA replication, recombination, or repair.
45
What are mutagens?
: Physical or chemical agents that cause mutations
45
How has the definition of a gene evolved?
It has been considered as: 1. A discrete unit of inheritance 2. A specific nucleotide sequence 3. A DNA sequence coding for a polypeptide
46
What is a structural gene?
A DNA region that can be expressed to produce a final functional product like a polypeptide or functional RNA (rRNA, tRNA).
47
What is a regulatory gene?
A gene that controls the expression of one or more structural genes by regulating transcription.
48
what are the three properties that make it possible for RNA to function as an enzyme?
forms a three dimensional structure, contains functional bases that can participate in catalysis, and RNA may hydrogen bond with nucleic acids
49
where is the donor splice site?
the beggining of intron
50
where is the acceptor site?
at the end of an intron
51
what are spliceosomes?
responsible for accurate cutting of introns, catalyze, consist of small nuclear ribonucleoproteins or snurps that recognize splice sites
52
what are 5 prime splice site bound by?
U1 snRNA
53
what are 3 prime splice site bound by?
U2 auxillary factor
54
what does RNA cutting and splicing do?
removes introns and joins exons creating an mRNA molecule
55
how is pre mRNA molecule modified?
its modified while still in the nucleus, 5 prime modifies nucleotide 5 prime gap, 3 prime gets a poly A tail
56
termination of transcription in bacteria?
the polymerase stops transmissionat the end of the terminator and the mRNA can be translated without further modification
57
termination of transcription in eukaryotes?
RNA polymerase 2 transcribes the polydenylation signal sequence, RNA transcript is released 10 to 35 nucleotides past this polyadenylation
58
what is a transcription factor?
a protein that binds to a DNA sequence, controls rate of transcription, regulates turns on and off gene to make sure they are expressed in the right cell at the right time
59
what is the tata box?
binds to TBP causing a bend in DNA molecule, determines starte point of transcription, present in only eukaryotes and not bacteria
60
what is the transcription rate?
40ntds/sec in eukaryotes
61
what is a gene?
a discrete unit of inheritance, a region of specific nucleotide sequence in a chromosome, a DNA sequence that codes for a specific poly peptide chain
62
is bacteria the same thing as a prokaryote in transcription and translation?
yes a prokaryotes couples transcription and translation where as in eukaryotes they are not coupled
63
process of polypeptide production?
polypeptide synthesis begins, SRP binds to a signal peptide, SRP binds to a receptor protein, SRP detaches and polypeptide synthesis resumes, signal cleabing enzyme cuts off signal peptide, completed polypeptide folds into final conformation
64
what are bound ribosomes ?
make proteins of the endomembrane system and proteins that are secreted from the cell
65
what are free ribosomes?
mostly synthesize proteins that function in the cytosol

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