1
Q
Why can two cells with identical DNA function differently?
A. They contain different genes
B. They undergo different mutations
C. They express different genes
D. They have different chromosomes
A
c
2
Q
Differential gene expression depends mainly on:
A. RNA polymerase I
B. Ribosomes
C. Transcription factors
D. DNA replication enzymes
A
c
3
Q
A gene will NOT be expressed if:
A. RNA polymerase II is present
B. The gene is located on chromosome 1
C. The correct transcription factors are absent
D. The gene is methylated at all times
A
c
4
Q
In eye cells, Gene 3 is expressed in both aerial and aquatic cells because:
A. It has no promoter
B. It is required in all eye cells
C. It codes for a transcription factor
D. It is always methylated
A
b
5
Q
Which term best describes cells becoming specialised?
A. Replication
B. Translation
C. Differentiation
D. Mutation
A
c
6
Q
Which statement is TRUE?
A. All genes are expressed in all cells
B. Transcription factors are identical in all cells
C. Gene expression patterns vary between cell types
D. DNA sequence changes during differentiation
A
c
7
Q
Which molecule directly determines whether a specific gene is transcribed?
A. Ribosomal RNA
B. Transfer RNA
C. Transcription factor
D. Amino acid
A
c
8
Q
Epigenetics refers to changes that:
A. Alter DNA base sequence
B. Affect RNA sequence only
C. Change gene expression without altering DNA sequence
D. Are always permanent
A
c
9
Q
Which modification is most commonly associated with transcriptional repression?
A. Histone acetylation
B. DNA methylation
C. Histone phosphorylation
D. RNA splicing
A
b
10
Q
Acetylation of histone proteins results in:
A. More compact chromatin
B. Reduced transcription
C. Looser chromatin structure
D. DNA degradation
A
c
11
Q
CpG islands are usually found:
A. In introns
B. In exons only
C. Near gene promoters
D. In mitochondrial DNA
A
c
12
Q
X-inactivation is an example of:
A. Mutation
B. Transcriptional control
C. Epigenetic regulation
D. Alternative splicing
A
c
13
Q
Which molecule is methylated in eukaryotic DNA methylation?
A. Adenine
B. Thymine
C. Guanine
D. Cytosine
A
d
14
Q
Differences between monozygotic twins are often due to:
A. DNA mutations
B. Chromosome loss
C. Epigenetic changes
D. Different genes
A
c
15
Q
Transcription factors are best described as:
A. RNA molecules that bind mRNA
B. Proteins that bind DNA to regulate transcription
C. Enzymes that degrade proteins
D. Structural chromatin proteins
A
b
16
Q
Which RNA polymerase transcribes protein-coding genes?
A. RNA polymerase I
B. RNA polymerase II
C. RNA polymerase III
D. DNA polymerase
A
b
17
Q
Activator transcription factors primarily:
A. Condense chromatin
B. Block RNA polymerase
C. Promote transcription initiation
D. Degrade mRNA
A
c
18
Q
Repressor transcription factors:
A. Increase transcription rate
B. Prevent transcription initiation
C. Promote histone acetylation
D. Act only in prokaryotes
A
b
19
Q
Which transcription factor is important for muscle cell differentiation?
A. p53
B. MyoD
C. Sxl
D. Tra
A
b
20
Q
Expression of the p21 gene causes:
A. DNA replication
B. Cell cycle arrest
C. Increased mitosis
D. Apoptosis
A
b
21
Q
A single transcription factor regulating many genes is an example of:
A. Alternative splicing
B. RNA interference
C. Coordinated gene expression
D. DNA methylation
A
c
22
Q
Alternative splicing occurs at which stage?
A. DNA replication
B. Transcription initiation
C. mRNA processing
D. Translation
A
c
23
Q
Alternative splicing allows a single gene to:
A. Produce one protein only
B. Be permanently silenced
C. Produce multiple proteins
D. Change its DNA sequence
A
c
24
Q
In Drosophila, the absence of Sxl protein results in:
A. Female-specific development
B. Nonfunctional Tra protein
C. Functional Tra protein
D. DNA methylation
A
b
25
The dsx gene produces male- or female-specific proteins due to:
A. Mutation
B. DNA methylation
C. Alternative splicing
D. Translation inhibition
c
26
Processing control acts:
A. Before transcription
B. During DNA replication
C. After transcription
D. After protein degradation
c
27
Which molecule is directly altered during alternative splicing?
A. DNA
B. Protein
C. pre-mRNA
D. Ribosome
c
28
Alternative splicing increases:
A. DNA length
B. Chromosome number
C. Protein diversity
D. Mutation rate
c
29
Proteins targeted for degradation are first bound to:
A. RNA polymerase
B. Proteasome
C. Ubiquitin
D. miRNA
c
30
The proteasome is best described as:
A. A transcription factor
B. A protein-digesting complex
C. A DNA repair enzyme
D. A ribosome
b
31
Degradation of cyclins results in:
A. Increased CDK activity
B. Decreased CDK activity
C. DNA replication
D. Translation inhibition
b
32
p53 normally functions to:
A. Promote cell division
B. Degrade DNA
C. Halt the cell cycle when DNA is damaged
D. Activate ribosomes
c
33
HPV promotes cancer development by:
A. Increasing histone acetylation
B. Mutating DNA polymerase
C. Targeting p53 for degradation
D. Blocking transcription factors
c
34
Regulation of protein longevity acts at which level?
A. Chromatin modification
B. Transcription
C. mRNA processing
D. Post-translational
d
35
Which statement is TRUE?
A. All proteins are permanent
B. Protein degradation is random
C. Ubiquitin tags proteins for destruction
D. Proteasomes synthesize proteins
c
36
RNA interference regulates gene expression by:
A. Altering DNA sequence
B. Modifying histones
C. Degrading mRNA or inhibiting translation
D. Increasing transcription
c
37
Approximately what percentage of the human genome codes for proteins?
A. 50%
B. 30%
C. 10%
D. < 5%
d
38
Mature miRNAs are approximately how long?
A. 10 bases
B. 22 bases
C. 100 bases
D. 1000 bases
b
39
Why can one miRNA regulate many different mRNAs?
A. It is very long
B. It binds DNA
C. Base pairing does not need to be perfect
D. It changes DNA sequence
c
40
Which small RNA usually shows near-perfect base pairing with its target?
A. miRNA
B. tRNA
C. rRNA
D. siRNA
d
41
RNA interference primarily affects gene expression at which level?
A. Chromatin modification
B. Transcription initiation
C. Post-transcriptional
D. Protein degradation
c
42
RNA silencing regulates approximately what fraction of human genes?
A. 5%
B. 10%
C. 30%
D. 90%
c
43
Which level of regulation occurs before transcription begins?
A. mRNA degradation
B. Alternative splicing
C. Chromatin structure modification
D. Protein degradation
E. Translation initiation
c
44
Which enzyme adds acetyl groups to histone proteins?
A. DNA polymerase
B. Histone acetyltransferase
C. RNA polymerase II
D. DNA methyltransferase
E. Proteasome
b
45
A single microRNA can regulate:
A. Only one gene
B. Two genes
C. Dozens of genes
D. Thousands of chromosomes
E. Only mitochondrial genes
c
46
The ubiquitin–proteasome system primarily regulates:
A. DNA replication
B. Protein longevity
C. Transcription initiation
D. RNA splicing
E. Chromatin methylation
b
47
The protein p53 is known as:
A. the transcription machine
B. the guardian of the genome
C. the ribosome activator
D. the chromatin stabilizer
E. the spliceosome regulator
b
48
Which statement best summarizes eukaryotic gene regulation?
A. Regulation occurs only during transcription
B. Regulation occurs only during translation
C. Regulation occurs at multiple stages of gene expression
D. Regulation occurs only after protein synthesis
E. Regulation occurs only through DNA mutation
c
49
How do specific and general transcription factors regulate transcription rate?
General transcription factors
Bind to the core promoter (e.g., TATA box).
Recruit and position RNA polymerase II.
Required for transcription of all protein-coding genes.
Specific transcription factors
Bind regulatory DNA sequences (enhancers/silencers).
Increase or decrease transcription rate.
Interact with mediator proteins and chromatin modifiers.
👉 Result: control how often RNA polymerase initiates transcription.
50
2. How do transcription factors recognize specific DNA sequences?
They contain DNA-binding domains.
These recognize specific base patterns in the major groove of DNA.
Recognition depends on:
hydrogen bonding
shape complementarity
charge interactions.
51
How can more than one gene show the same regulation in eukaryotes?
Multiple genes share:
the same regulatory DNA sequences (response elements).
A single transcription factor can therefore activate many genes at once.
52
4. Difference from coordinated regulation in prokaryotes
Prokaryotes
Genes organized in operons.
One promoter → one polycistronic mRNA → many proteins.
Eukaryotes
Genes scattered across chromosomes.
Coordinated by shared regulatory elements and transcription factors.
53
5. Advantages of the nucleus as a compartment
Separates transcription from translation.
Allows:
RNA processing (splicing, capping, poly-A tail)
quality control of mRNA
complex gene regulation
protection of DNA.
54
6. CpG islands — definition and role
CpG islands
DNA regions rich in C–G dinucleotides.
Usually near gene promoters.
Typically unmethylated in active genes.
Role
Methylation → gene silencing.
Unmethylated → transcription allowed.
55
7. How histone acetylation affects transcription
Acetyl groups added to histone lysines.
Neutralizes positive charge.
DNA binds histones less tightly.
Chromatin becomes open (euchromatin).
✅ Increased transcription.
56
8. Environmental effects on epigenetics (example)
Diet or stress altering DNA methylation patterns.
57
9. X chromosome inactivation — how and why?
Where: early embryonic cells in females (XX).
How:
One X expresses Xist RNA.
Xist coats that chromosome.
Histone modification + DNA methylation silence it.
Forms Barr body.
Why:
Dosage compensation → equal X-linked gene expression between XX females and XY males.
58
10. Are CpG cytosines more mutation-prone?
eason:
Methylated cytosine → can spontaneously deaminate → thymine.
Harder to repair → higher mutation rate.
59
11. How histone modifications affect transcription
They change chromatin accessibility:
Modification Effect
Acetylation activates
Methylation activate or repress (context dependent)
60
12. Evidence epigenetics affects behavior
Example:
Maternal care in rats alters methylation of stress-response genes.
Offspring show lifelong behavioral differences.
61
✅ Cancer & Epigenetic Silencing 13. How to test mutation vs epigenetic silencing in colorectal cancer
Sequence DNA
Detect promoter/coding mutations.
Check methylation
Bisulfite sequencing or methylation assays.
Demethylation treatment
If gene reactivates → epigenetic cause.
62
14. Why proteins > number of genes?
Because of:
Alternative splicing
RNA editing
Post-translational modification.
63
15. Three ways mRNA and protein levels differ
Different mRNA stability.
Translation efficiency differences.
Protein degradation rates.
64
16. How miRNAs and siRNAs reduce protein levels
They:
bind complementary mRNA.
cause:
mRNA degradation OR
translation inhibition.
(Post-transcriptional regulation.)
65
17. Protein resistant to ubiquitination — prediction
✅ Persists longer.
Because ubiquitin tags proteins for degradation.
66
18. Function of the proteasome
Protein degradation complex.
Recognizes ubiquitinated proteins.
Breaks them into peptides.
67
✅ Alternative Splicing Questions
19. Four introns (→ five exons)
First and last must remain.
Middle 3 exons optional.
Each exon:
included or skipped →
2
3
=
8
2
3
=8
✅ 8 possible proteins.
68
20. miRNA & siRNA regulation (summary)
Guide RISC complex to target mRNA.
Silence gene expression post-transcriptionally.
69
21. How mRNA 3D structure regulates expression
Secondary structures can:
block ribosome binding,
hide splice sites,
affect stability.
70
22. Why genome has fewer genes than expected
mRNA processing:
alternative splicing → many proteins from one gene.
71
23. How miRNA drugs might treat cancer
They could:
silence oncogenes,
restore tumor suppressor regulation.
72
24. Can epigenetic changes be manipulated?
Yes:
HDAC inhibitors
DNA methylation inhibitors
used in cancer therapy.
73
25. Why some cytosines are never methylated
Lack CpG context.
Bound by protective proteins.
Essential promoters kept unmethylated.
74
26. Why CpG methylation is inherited
After replication:
maintenance methyltransferases methylate new strand using old strand as template.
75
28. Four-exon gene (first & last fixed)
Middle 2 exons optional:
2 squared
=4
✅ 4 possible proteins
76
29. Why protein level low despite high mRNA?
inefficient translation,
rapid protein degradation,
miRNA repression.
77
30. Lysine → arginine mutation increases stability — why?
Both positively charged, but:
arginine forms stronger hydrogen bonds.
may prevent ubiquitination site formation.
improves folding stability.
78
✅ 1. Outline the main control points of gene regulation in eukaryotes.
(4–5 marks — VERY LIKELY)
Gene expression in eukaryotes is regulated at several stages:
Chromatin modification — DNA methylation and histone modification alter DNA accessibility.
Transcriptional control — transcription factors regulate RNA polymerase binding.
RNA processing — alternative splicing produces different mRNAs.
Post-transcriptional regulation — miRNAs and siRNAs affect mRNA stability or translation.
Protein regulation — proteins are degraded via ubiquitin–proteasome pathways.
79
2. Explain how transcription factors drive cell-type–specific gene expression.
(HIGH PROBABILITY)
Different cell types contain different transcription factors. These proteins bind specific DNA regulatory sequences and activate or repress particular genes. Because each cell expresses a unique combination of transcription factors, different sets of genes are expressed, allowing cells with identical DNA to perform specialized functions.
80
3. How can two cells with the same genome function differently?
(Lecture diagram question)
high probability
Cells differ because they express different genes. The presence or absence of specific transcription factors determines which genes are transcribed. This differential gene expression produces different proteins, leading to specialized cell functions.
81
Describe how histone acetylation affects transcription.
(Very common epigenetics question)
Histone acetylation adds acetyl groups to lysine residues in histone proteins, reducing their positive charge. This weakens DNA–histone interactions, loosening chromatin structure and making DNA more accessible to transcription machinery, thereby increasing transcription.
82
Explain how DNA methylation regulates gene expression.
DNA methylation involves adding methyl groups to cytosine bases, usually at CpG sites. Methylation condenses chromatin and prevents transcription factor binding, leading to repression of gene transcription.
83
✅ 6. Define CpG islands and explain their role in gene regulation. high field question
CpG islands are DNA regions rich in cytosine–guanine dinucleotides located near gene promoters. They are typically unmethylated in active genes, allowing transcription. Methylation of CpG islands silences gene expression.
84
Describe X-chromosome inactivation and explain why it occurs.
(VERY HIGH YIELD)
In female mammals, one X chromosome is randomly inactivated early in embryonic development. The Xist RNA coats the chromosome, triggering DNA methylation and histone modifications that silence gene expression, forming a Barr body. This ensures equal expression of X-linked genes between males and females (dosage compensation).
85
✅ 8. Explain how alternative splicing increases protein diversity. high field question
Alternative splicing allows different combinations of exons from the same pre-mRNA to be joined together. This produces multiple mRNA variants from one gene, resulting in different proteins with distinct functions.
86
✅ 9. Describe how miRNAs and siRNAs regulate gene expression. high field question
miRNAs and siRNAs are small RNA molecules that bind complementary sequences on target mRNAs. They recruit protein complexes that either degrade the mRNA or inhibit translation, reducing protein production. This process is called RNA interference.
87
10. Describe how proteins are targeted for degradation in eukaryotic cells.
(ALMOST CERTAIN EXAM QUESTION)
Proteins destined for degradation are tagged with ubiquitin molecules. The ubiquitin tag directs the protein to the proteasome, a large protein complex that unfolds and degrades the protein into peptides.
88
Predict what would happen to a protein that cannot be ubiquitinated. high chance coming on exam
The protein would not be efficiently targeted to the proteasome and would therefore persist longer in the cell, increasing its stability and abundance.
89
✅ 12. Explain how environmental factors can cause epigenetic changes.
high field question
Environmental factors such as diet, stress, or early life experiences can alter DNA methylation or histone modification patterns. These changes affect gene expression without altering DNA sequence and can sometimes be inherited through cell divisions.
90
✅ 13. Explain why the number of proteins in humans greatly exceeds the number of genes.
high field
A single gene can produce multiple proteins through alternative splicing, RNA processing, and post-translational modifications, greatly increasing protein diversity.
Cells And Organelles
flashcards
Decks in class (13)
# Cards
-
Plasma Membrane84
-
Cell and Organelles48
-
DNA structure35
-
DNA replication51
-
transcription and translation69
-
mendelian inheritance65
-
recombination and gene mapping66
-
population genetics and hardy Weinberg equilibrium66
-
bacteria119
-
Viruses101
-
gene regulation90
-
cell cycle83
-
microscope definition19
