bio final

Which scenario represents positive control of gene expression?

a) A repressor binding DNA and blocking transcription

b) An activator enhancing RNA polymerase binding

c) mRNA degradation preventing translation

d) Protein modification after translation

b) An activator enhancing RNA polymerase binding

• Positive control = activator helps transcription

• Activators (like CAP) increase transcription

A mutation prevents the repressor from binding the operator. What is the result?

a) Genes are never transcribed

b) Genes are only transcribed when inducer is present

c) Genes are always transcribed

d) RNA polymerase cannot bind

c) Genes are always transcribed

• If repressor can’t bind, nothing blocks RNA polymerase

• ➜ Genes stay ON all the time

Why does glucose reduce lac operon activity even when lactose is present?

a) It destroys lactose

b) It prevents RNA polymerase synthesis

c) It reduces cAMP levels, preventing CAP activation

d) It blocks transcription factors entirely

c) It reduces cAMP levels, preventing CAP activation

• High glucose → low cAMP

• No CAP binding → low transcription

• ➜ Lac operon stays mostly OFF

Which level of regulation allows the fastest response to environmental change? a) Transcriptional

b) Translational

c) Post-translational

d) DNA replication

c) Post-translational

• Protein already made → just activate/deactivate

• ➜ Fastest response

Which condition results in the HIGHEST gene expression?

a) Closed chromatin with activators

b) Open chromatin with no transcription factors

c) Open chromatin with activators and mediator

d) Methylated DNA with RNA polymerase

c) Open chromatin with activators and mediator

• Open chromatin = DNA accessible

• Activators + mediator = recruit RNA polymerase

Alternative splicing results in:

a) DNA replication

b) Multiple proteins from one gene

c) Increased transcription

d) Protein degradation

b) Multiple proteins from one gene

A protein tagged with ubiquitin will:

a) Be translated

b) Activate transcription

c) Be degraded

d) Bind DNA

c) Be degraded

• Ubiquitin = “destroy this protein” signal

Why do different cell types express different genes?

a) They have different DNA
b) DNA is mutated in each cell
c) Differential gene expression
d) RNA polymerase is absent

c) Differential gene expression

Which condition turns a gene OFF in eukaryotes?

a) Open chromatin
b) Histone acetylation
c) DNA methylation
d) Enhancer binding

c) DNA methylation

What is the role of histone acetylation?

a) Tightens DNA
b) Loosens chromatin
c) Degrades DNA
d) Blocks RNA polymerase

b) Loosens chromatin

Which structure must RNA polymerase bind to start transcription in eukaryotes?

a) Enhancer
b) TATA box
c) Introns
d) Ribosome

b) TATA box

What do enhancers do?

a) Block transcription
b) Destroy mRNA
c) Increase transcription
d) Remove introns

c) Increase transcription

What is required for transcription in eukaryotes?

a) RNA polymerase alone
b) Ribosomes
c) Transcription factors
d) DNA replication

c) Transcription factors

Alternative splicing allows:

a) Faster transcription
b) DNA repair
c) Multiple proteins from one gene
d) RNA degradation

c) Multiple proteins from one gene

What does RNA interference do?

a) Enhances translation
b) Destroys or blocks mRNA
c) Activates DNA replication
d) Produces proteins

b) Destroys or blocks mRNA

Which is the FASTEST form of regulation?

a) Transcriptional
b) Translational
c) Post-translational
d) Chromatin remodeling

c) Post-translational

What is the function of ubiquitin?

a) Activates transcription
b) Signals protein degradation
c) Stabilizes mRNA
d) Opens chromatin

b) Signals protein degradation

In bacteria, what is the MOST energy-efficient level of control?

a) Translational
b) Post-translational
c) Transcriptional
d) DNA replication

c) Transcriptional

What is an operon?

a) Single gene
b) Group of genes controlled together
c) Protein complex
d) RNA molecule

b) Group of genes controlled together

What happens in the lac operon when lactose is ABSENT?

a) Genes ON
b) Repressor removed
c) Genes OFF
d) CAP activated

c) Genes OFF

What does lactose do in the lac operon?

a) Activates the repressor
b) Removes the repressor from DNA
c) Blocks RNA polymerase
d) Decreases cAMP

b) Removes the repressor from DNA

What happens when glucose is HIGH?

a) cAMP increases
b) CAP binds DNA
c) Transcription increases
d) cAMP decreases

d) cAMP decreases

Which condition gives MAX lac operon expression?

a) High glucose + lactose
b) Low glucose + lactose
c) High glucose only
d) No lactose

b) Low glucose + lactose

What is the function of CAP?

a) Enhances transcription when bound to cAMP
b) Blocks RNA polymerase
c) Degrades lactose
d) Prevents repressor binding

a) Enhances transcription when bound to cAMP

What type of control is the lac operon?

a) Repressible
b) Inducible
c) Constitutive
d) Post-translational

b) Inducible

The trp operon is turned OFF when:

a) Tryptophan is low
b) Lactose is present
c) Glucose is absent
d) Tryptophan is high

d) Tryptophan is high

The trp operon is an example of:

a) Negative feedback regulation
b) Inducible system
c) Positive control
d) RNA interference

a) Negative feedback regulation

What is the normal role of the p53?

stop the cell cycle and initiate DNA repair or apoptosis

Which mechanism directly increase transcription initiation?

Activator proteins binding enhancers

Which situation best explains why transcriptional control is energy efficient?

mRNA is not produced unless needed

Which features BEST defines an enhancer

A DNA sequence that increases transcription when activators bind

In the presence of high tryptophan, the trp operon will be

off

What is the function of the lacl gene?

It produces the repressor protein

What is transcriptional control?

Regulation of whether a gene is transcribed into mRNA

In the absence of lactose, what happens to the lac operon?

Repressor binds operator and blocks trascription

Which regulatory step is MOSt energy efficient?

Regulating transcription before mRNA is made

Which process correctly describes transcription?

DNA→RNA

Which statement best explains how genotype leads to phenotype?

DNA is transcribed and translated to produce proteins that determine phenotype

Why does the laggin strand from Okazaki fragments?

DNA polymerase can only ad nucleotides in one direction

A DNA sequence reads ATGCCAT. What is the complementary strands?

TACGGTA

Which mutation involves replacing one nucleotide with another ?

substation

If trancription is reduced, what is the MOST likely downstream effect?

Decreased protein production

Which would MOST likely prevent a protein from being produced?

a) Silent mutation
b) Mutation in promoter
c) Redundant codon change
d) Substitution in third base

Mutation in promoter

What ensures correct amino acid placement?

a) Ribosome size
b) tRNA anticodon pairing
c) DNA replication
d) Hydrogen bonding in DN

tRNA anticodon pairing

A mutation that shifts all downstream codons is:

a) Substitution
b) Silent mutation
c) Frameshift
d) Duplication

Frameshift

Which is TRUE about the genetic code?

a) Each codon codes for multiple amino acids
b) Each amino acid has only one codon
c) Multiple codons can code for the same amino acid
d) Codons are made of two bases

Multiple codons can code for the same amino acid

Which base pairs correctly?

a) A–C
b) G–T
c) A–T
d) C–A

A–T

What is the main function of PCR?

a) Edit DNA
b) Break DNA
c) Copy DNA quickly
d) Repair DNA

Copy DNA quickly

What is required before DNA replication begins?

a) Chromosomes condense
b) Hydrogen bonds break
c) RNA is destroyed
d) Proteins stop working

Hydrogen bonds break

What enzyme builds new DNA strands?

a) RNA polymerase
b) DNA ligase
c) DNA polymerase
d) Helicase

DNA polymerase

What is the role of CRISPR-Cas9?

a) Replicate DNA
b) Cut specific DNA sequences
c) Translate RNA
d) Repair proteins

Cut specific DNA sequences

What is produced directly after transcription?

a) DNA
b) Protein
c) mRNA
d) Amino acids

mRNA

Which RNA carries amino acids to the ribosome?

a) mRNA
b) rRNA
c) tRNA
d) siRNA

tRNA

What happens at a stop codon?

a) Protein synthesis begins
b) RNA is destroyed
c) Translation stops
d) DNA replicates

Translation stops

Which mutation type may NOT change the protein?

a) Frameshift
b) Deletion
c) Silent mutation
d) Insertion

Deletion

What is the role of the ribosome?

a) Copy DNA
b) Build proteins
c) Store genes
d) Break RNA

Store genes

wjhat does negfative control do ?

Regulatory protein—repressor—binds to DNA and shuts down transcription

what does positive control do ?

Regulatory protein—activator—binds to DNA and triggers transcription

what si a repessopr of lacz and lacy

lacl

what are two mechanism for how glucose prevent lac operon expression

Catabolite activator protein (CAP) & Control by inducer exclusion both are positive control

can ecoil mutants produce lactose

no it can not metabolize lactose. they hope to find regulator of lactose metabolism

lac Z can not what

they can not cleave lactose bc they lack functional beta galactosidase

lac y can not

it lacks galactoside permease

what is sos response

it shoots out all it got hoping it will do somthing

what does histone acetyltransferases do

Add acetyl groups to histones, decondensing the chromatin

what does histone deacetylase do

Remove histones, leading to chromatin condensation

what does RNA interference do

controls the life span of many mRNA

What does cancer involve

uncontrolled cell division

what mutations lead to cancer

when they stop or slow cell cycle and trigger cell growth and division by initiating specific phases in cell cycle

what is p53

its is a tumor suppressor when it finds it, it arrest cell cycle and repairs DNA damage. if its to far gone it triggers apoptosis ( cell death)

A mutation disables DNA ligase during replication. What is the most likely result?
a) DNA strands separate permanently
b) Okazaki fragments cannot be joined together
c) Hydrogen bonds cannot form
d) RNA primers cannot be synthesized

Why are Okazaki fragments necessary?
a) DNA polymerase synthesizes DNA only in the 5' → 3' direction
b) DNA is double stranded
c) Helicase blocks replication
d) RNA polymerase interrupts synthesis

Which mutation would MOST likely drastically alter protein structure?
a) Silent mutation
b) Mutation in a noncoding region
c) Frameshift mutation near the start of the gene
d) Third-base substitution

A mutation prevents a ribosome from recognizing stop codons. What is the MOST likely result?
a) Proteins become shorter
b) Translation never begins
c) Proteins become abnormally long
d) mRNA cannot leave the nucleus

Which molecule physically carries amino acids to the ribosome?
a) mRNA
b) tRNA
c) rRNA
d) DNA polymerase

A mutation changes a tRNA anticodon. Which process is MOST directly affected?
a) DNA replication
b) RNA splicing
c) Translation accuracy
d) Chromatin remodeling

What is the MAIN benefit of alternative splicing?
a) Faster DNA replication
b) Increased protein diversity
c) Reduced mutation rate
d) Increased ribosome production

Two different tissues express different proteins from the same gene because:
a) Their DNA sequences differ
b) Different transcription factors and splicing patterns are present
c) Ribosomes mutate differently
d) DNA replication occurs differently

Which condition would produce the HIGHEST lac operon activity?
a) High glucose, no lactose
b) High glucose, high lactose
c) Low glucose, high lactose
d) Low glucose, no lactose

A mutation prevents tryptophan from activating the trp repressor. What is the MOST likely outcome?
a) trp operon always OFF
b) trp operon always ON
c) lac operon activated
d) Translation stops

What is the primary role of β-galactosidase?
a) Break down lactose
b) Replicate DNA
c) Produce ATP
d) Degrade RNA

Why do bacteria activate many stress-response genes simultaneously?
a) Ribosomes stop functioning
b) Coordinated regulation allows rapid adaptation
c) DNA replication increases
d) Translation becomes unnecessary

If LexA cannot be inactivated, what is MOST likely to occur?
a) DNA repair genes remain repressed
b) DNA replication speeds up
c) Protein synthesis stops
d) Ribosomes are degraded

Which condition would MOST likely produce LOW gene expression?
a) Open chromatin with activators
b) Closed chromatin with methylated DNA
c) Open chromatin with mediator present
d) Histone acetylation

How can enhancers affect genes located far away on DNA?
a) RNA carries enhancer signals
b) DNA looping brings enhancers near promoters
c) Ribosomes transport enhancers
d) Histones move the enhancer sequence

A mutation disables mediator proteins. What is the MOST likely result?
a) Translation increases
b) DNA replication stops
c) Transcription efficiency decreases
d) Chromatin condenses permanently

Which regulatory mechanism provides the FASTEST cellular response?
a) DNA methylation
b) Transcription
c) RNA processing
d) Post-translational activation

A cell contains large amounts of mRNA, but protein levels remain low. What is the MOST likely explanation?
a) DNA replication stopped
b) Translation is being inhibited
c) Chromatin is closed
d) RNA polymerase is inactive

microRNA MOST directly causes:
a) Increased transcription
b) Increased DNA replication
c) Reduced protein production
d) Histone acetylation

 A cell continues dividing despite severe DNA damage. Which protein is MOST likely defective?
a) DNA ligase
b) p53
c) RNA polymerase
d) β-galactosidase

What is the PRIMARY purpose of cell cycle checkpoints?
a) Increase mutation rate
b) Prevent damaged DNA from being passed to daughter cells
c) Speed up replication
d) Increase protein synthesis

what are the three major way to remodel chromatin

DNA methylation, histone modification, chromatin-remodeling complexes