8: Gene Mutations & Expression for A-Level Biology (Edexcel)

During DNA replication, what type of mutation occurs when a single base in the DNA sequence is replaced by another?

substitution

Only one base pair is swapped. May or may not change the amino acid due to the degeneracy of the genetic code.

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What mutation occurs when one or more bases are inserted into a DNA sequence during replication?

Addition

Also called insertion; may cause a frameshift if not in multiples of three bases.

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What type of mutation results when one or more bases are removed from a DNA sequence?

Deletion

Often causes a frameshift, altering all downstream triplets.

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What mutation occurs when a section of DNA is copied and repeated within the gene?

Duplication

Produces extra copies of a DNA segment within the same gene.

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What mutation occurs when a segment of DNA is reversed within the sequence?

Inversion

A section of bases flips orientation within the DNA molecule.

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What mutation involves a segment of DNA breaking off and attaching to a different chromosome or different location?

Translocation

More commonly discussed as a chromosomal mutation but can disrupt gene sequences.

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True or False:

A mutation that changes a single DNA triplet always changes the amino acid coded for in the polypeptide.

False

Because the genetic code is degenerate, multiple codons can code for the same amino acid.

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When a mutation changes the reading frame of a gene so that all downstream triplets are altered, what type of mutation has occurred?

Frameshift

Usually caused by addition or deletion of bases not in multiples of three.

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Fill in the blank:

The genetic code is described as ______ because more than one codon can specify the same amino acid.

degenerate

This property means some base substitutions do not change the amino acid sequence.

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What process during the cell cycle most commonly gives rise to spontaneous gene mutations?

DNA replication

Errors in copying DNA can introduce changes to the base sequence.

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True or False:

Mutagenic agents increase the probability that mutations will occur in DNA.

True

Examples include radiation, certain chemicals and some viruses.

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Why can a frameshift mutation have a larger effect on a protein than a single base substitution?

It alters the reading frame, changing every downstream codon and often resulting in a different polypeptide.

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What general outcome may occur if a mutation alters the sequence of bases in a gene?

different amino acid sequence

This can alter the structure and function of the encoded protein or even shorten the protein prematurely.

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Fill in the blank:

Mutations that arise without exposure to mutagenic agents are described as ______ mutations.

spontaneous

These often result from errors during DNA replication.

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During early mammalian development, what type of cells can divide and produce any type of body cell?

Totipotent cells

Present in very early embryos; capable of forming all body cell types and extra-embryonic tissues.

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Why do cells become specialised during development even though they contain the same DNA?

Only part of the DNA is translated.

Different genes are expressed in different cells, producing different proteins and structures.

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True or False:

Totipotent cells remain present throughout the entire life of a mammal.

False

Totipotent cells exist only for a short period in early embryonic development.

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What name is given to stem cells that can divide indefinitely and differentiate into almost any body cell type?

Pluripotent stem cells

They cannot form extra-embryonic tissues but can generate most body cell types.

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Fill in the blank:

Stem cells that can produce a limited range of specialised cells within a particular tissue are called ______ stem cells.

Multipotent

Example: stem cells in bone marrow producing different blood cells.

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What type of stem cell can divide to produce only one specialised cell type?

Unipotent cells

They still retain the ability to self-renew through mitosis.

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Which specialised heart muscle cells are an example of unipotent cells?

Cardiomyocytes

They mainly produce more of the same cell type within cardiac tissue.

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True or False:

Pluripotent stem cells can divide many times and are being investigated for treating human disorders.

True

Their ability to differentiate into many cell types makes them useful in regenerative medicine.

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What type of cells are created by reprogramming adult somatic cells using specific transcription factors?

Induced pluripotent stem cells

Often abbreviated as iPS cells.

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Fill in the blank:

Induced pluripotent stem cells are produced from ______ cells using transcription factors.

Study These Flashcards

adult somatic

Reprogramming activates genes associated with pluripotency.

What property of **stem cells** allows them to divide repeatedly while maintaining an **undifferentiated state**?

Self-renewal ## Footnote Essential for maintaining stem cell populations.

# True or False: **Cell specialisation** occurs because different cells possess **different DNA sequences**.

False ## Footnote Most cells contain the same genome; differences arise from gene expression.

Why are **pluripotent stem cells** considered valuable in **medical treatments**?

They can differentiate into many cell types. ## Footnote This allows potential replacement of damaged or diseased tissues.

In mammalian development, why is most **DNA** not translated in any given **cell**?

Only specific genes are expressed. ## Footnote Gene regulation ensures cells produce proteins appropriate for their function.

A **lipid-soluble hormone** diffuses through the cell membrane, binds to a receptor, and the complex moves into the **nucleus** to activate transcription of specific genes. Which hormone is a classic example used to illustrate this mechanism?

Oestrogen ## Footnote The hormone–receptor complex acts as a transcription factor that binds to DNA and stimulates transcription of target genes.

What type of **regulatory protein** moves from the cytoplasm into the nucleus and either stimulates or inhibits transcription of specific genes?

Transcription factor ## Footnote Transcription factors bind to regulatory DNA sequences and influence whether RNA polymerase initiates transcription.

After binding to its intracellular receptor, where must the **hormone–receptor complex** travel to influence **gene expression**?

Nucleus ## Footnote The complex binds to specific DNA sequences, promoting transcription of particular genes.

What general term describes **heritable changes in gene function** that occur without altering the **DNA base sequence**?

Epigenetics ## Footnote Epigenetic changes alter gene expression rather than the nucleotide sequence itself.

# Fill in the blank: Increased \_\_\_\_\_\_ of **DNA** can reduce transcription by preventing transcription factors from binding to DNA.

Methylation ## Footnote DNA methylation typically occurs at cytosine bases and often silences gene expression.

# Fill in the blank: Reduced \_\_\_\_\_\_ of **histone proteins** causes DNA to become more tightly coiled, decreasing transcription.

acetylation ## Footnote Histone acetylation loosens DNA–histone interactions, allowing transcription machinery to access genes.

# True or False: Increased **acetylation of histones** generally makes DNA more accessible for transcription.

True ## Footnote Acetylation reduces positive charge on histones, weakening their interaction with negatively charged DNA.

# True or False: **Epigenetic changes** alter the base sequence of DNA.

False ## Footnote Epigenetic mechanisms modify gene expression without changing the nucleotide sequence.

What process uses **short RNA molecules** to prevent translation of specific **mRNA molecules**?

RNA interference ## Footnote RNAi molecules bind to complementary mRNA and cause its degradation or block translation.

In gene regulation, what molecule must **RNA interference** target in order to prevent **protein synthesis**?

mRNA ## Footnote By destroying or blocking mRNA, RNAi prevents ribosomes from translating the message.

What term describes the **observable characteristics** of an organism resulting from **gene expression** and environmental influence?

Phenotype ## Footnote Phenotype arises from both genetic factors and environmental influences, including epigenetic modifications.

Why can **environmental factors** influence gene expression without changing DNA sequences? Which biological mechanism explains this?

Epigenetics ## Footnote Environmental conditions can alter DNA methylation or histone modification patterns, affecting transcription.

# True or False: **Epigenetic changes** can sometimes be inherited by daughter cells after cell division.

True ## Footnote Methylation patterns and histone modifications can be passed on during cell replication.

In cancer development, abnormal patterns of **DNA methylation** can affect the expression of which category of genes that normally regulate **cell division**?

Tumour suppressor genes. ## Footnote Excessive methylation can silence genes that normally inhibit uncontrolled cell division.

Which stage of **gene expression** is directly inhibited when **RNA interference** binds to complementary mRNA molecules?

Translation ## Footnote RNAi prevents ribosomes from producing proteins from the targeted mRNA.

How do **benign tumours** differ from **malignant tumours** in their behaviour within the body?

Benign tumours remain contained; malignant tumours invade tissues and can metastasise. ## Footnote Benign tumours are enclosed within a capsule, while malignant tumours spread and may form secondary tumours.

What is the name for the process by which cancer cells spread from a **primary tumour** to other parts of the body?

Metastasis ## Footnote Cancer cells can detach, travel through blood or lymph, and establish secondary tumours elsewhere.

Which group of genes normally **slows cell division**, **repairs DNA**, or triggers cell death if damage is severe?

Tumour suppressor genes ## Footnote When these genes are inactivated, damaged cells may continue dividing uncontrollably.

Some genes can cause cells to **divide uncontrollably** if they become permanently activated. What are these genes called?

Oncogenes ## Footnote Oncogenes often arise from mutated proto-oncogenes that normally regulate cell growth.

# True or False: **Tumour suppressor genes** usually promote **cell division**.

False ## Footnote Their normal role is to slow or stop the cell cycle, repair DNA, or trigger apoptosis.

# True or False: **Oncogenes** can arise when mutations convert **proto-oncogenes** into permanently active forms.

True ## Footnote Proto-oncogenes normally regulate growth signals but mutations may lead to uncontrolled division.

# Fill in the blank: Chemical modification of **DNA** that can switch genes off without changing the DNA sequence is called \_\_\_\_\_\_.

DNA methylation ## Footnote Methyl groups added to DNA often reduce transcription of that gene.

How can **abnormal methylation** contribute to the development of **cancer**?

It can inactivate tumour suppressor genes or activate oncogenes. ## Footnote Changes in methylation patterns alter gene expression involved in cell cycle control.

# True or False: Increased **methylation of tumour suppressor genes** may reduce their expression and contribute to **tumour formation**.

True ## Footnote Silencing these protective genes removes normal control of cell division.

Why can increased **oestrogen concentration** increase the risk of some **breast cancers**?

Oestrogen stimulates cell division in breast tissue. ## Footnote Increased cell division raises the chance of mutations that may lead to cancer.

# True or False: **Environmental factors** have no role in the development of **cancer**.

False ## Footnote Cancer risk often reflects interactions between environmental exposure and genetic susceptibility.

What type of evidence helps scientists link **environmental exposures** with **cancer risk** in populations?

Correlational evidence ## Footnote For example, comparing cancer rates between exposed and non-exposed populations.

How could understanding **oncogenes** and **tumour suppressor genes** improve cancer treatment?

Targeted therapies ## Footnote Treatments can be designed to block oncogene products or restore tumour suppressor function.

How might knowledge of **genetic factors in cancer** help with **prevention strategies**?

Genetic screening ## Footnote Identifying high-risk individuals allows earlier monitoring or preventative measures.

# True or False: Understanding **gene regulation in cancer** can contribute to **prevention, treatment and potential cures**.

True ## Footnote Research into gene expression allows development of targeted drugs and improved diagnostics.

8: Gene Mutations & Expression Flashcards

Explain how mutations affect protein structure and gene regulation. (58 cards)