B20 - Gene expression

Question 1

What is a mutation?

Answer 1

Change to the quantity or the base sequence of DNA

Question 2

When do mutations tend to arise?

Answer 2

During DNA replication

Question 3

What is a point mutation?

Answer 3

A nucleotide in the DNA is replaced by another, changing the triplet code

Question 4

What is a nonsense mutation?

Answer 4

Formation of a stop codon from mutation, resulting in premature polypeptide production

Question 5

What is a missense mutation?

Answer 5

Formation of a different codon, leading to a different amino acid in the polypeptide

Question 6

What is a silent mutation?

Answer 6

A different codon leads to the same amino acid due to the degeneracy of the genetic code

Question 7

What is a frameshift mutation?

Answer 7

Loss or addition of bases that alters the reading frame of the DNA sequence

Question 8

What happens if three bases are added to a DNA sequence?

Answer 8

No frameshift occurs, but the resulting protein will still be different

Question 9

What is a duplication of bases?

Answer 9

One or more bases are repeated, resulting in a frameshift mutation

Question 10

What is an inversion of bases?

Answer 10

A group of bases is separated and reinserted in inverse order

Question 11

What is translocation of bases?

Answer 11

A DNA sequence from one chromosome is removed and inserted into another chromosome

Question 12

What are factors that cause mutations?

Answer 12

• Spontaneous mutations - naturally occurring random events
• Basic mutation rate can be increased by outside factors called mutagenic agents
• High energy ionising radiation
• X-rays
• UV radiation
• Nitrogen dioxide (nitrous acid)
• Benzopyrene

Question 13

What are stem cells?

Answer 13

Undifferentiated dividing cells that can differentiate into specialized structures suited for a particular role

Question 14

What are totipotent cells?

Answer 14

Cells that can develop into any type of cell, such as a fertilized egg. Develop into pluripotent cells

Question 15

What are pluripotent cells?

Answer 15

Found in embryos, can differentiate into almost any type of cells, e.g. embryonic stem cells and fetal stem cells

Question 16

What are multipotent stem cells?

Answer 16

Cells that differentiate into a limited number of cells, such as adult stem cells

Question 17

What are unipotent stem cells?

Answer 17

Cells that can only differentiate into one type of cell, made in adult tissue

Question 18

What are induced pluripotent stem cells (iPSCs)?

Answer 18

Unipotent cells genetically altered to express other genes, resembling embryonic stem cells

Question 19

How do plants differ in terms of stem cells compared to animals?

Answer 19

Plants retain totipotent cells in adulthood that can develop into any type of cell

Question 20

What is the role of transcription factors in gene expression?

Answer 20

They bind to promoter regions to enable RNA polymerase attachment

Question 21

How do steroid hormones like oestrogen affect gene expression?

Answer 21

They bind to transcription factors, activating them to stimulate transcription

Question 22

What is siRNA?

Answer 22

Small interfering RNA involved in post-transcriptional gene silencing

Question 23

What is the epigenome?

Answer 23

The DNA-histone complex and chemical tags covering it

Question 24

What is acetylation?

Answer 24

Transfer of an acetyl group to histone proteins, the attraction between the DNA and histone weakens. Transcription of gene is possible as the DNA unwinds

Question 25

What is methylation?

Answer 25

Addition of a methyl group to cytosine, preventing transcription factor binding as DNA-histone complex condenses even more

Question 26

What is a tumor?

Answer 26

A group of cells that divide rapidly and uncontrollably, when it has metastasised it becomes a cancer

Question 27

What is the difference between benign and malignant tumors?

Answer 27

Benign tumors are localized, while malignant tumors can spread (metastasis)

Question 28

What are proto-oncogenes?

Answer 28

Genes that code for growth factors controlling cell division

Question 29

What happens when a proto-oncogene becomes an oncogene?

Answer 29

It stimulates cells to divide too quickly

Question 30

What is the role of tumor suppressor genes?

Answer 30

They slow cell division, repair DNA, and promote apoptosis

Question 31

What is the effect of increased methylation on tumor suppressor genes?

Answer 31

Inactivates the gene, potentially leading to cancer

Question 32

What do genome projects do?

Answer 32

Determine the DNA sequence of genes and map their locations on chromosomes

Question 33

What is whole-genome shotgun sequencing (WGS)?

Answer 33

A method to sequence DNA by cutting it into small chunks and aligning overlapping fragments

Question 34

What are single nucleotide polymorphisms (SNPs)?

Answer 34

Single base variations within genes associated with diseases

Question 35

What is the human proteome project?

Answer 35

An effort to identify all proteins produced by human cells

Question 36

What is a significant challenge in sequencing complex eukaryotic organisms?

Answer 36

They have non-coding sequences, making genome sequencing more complex

Question 37

What is a promoter region?

Answer 37

They are not part of the gene but are found just before the coding region. When a protein binds to it (transcription factor) it enables RNA polymerase to attach to the coding region

Question 38

How does post-transcriptional gene silencing work?

Answer 38

1. Enzyme cuts large dsRNA (double stranded) into smaller sections, called siRNA (small interfering) 2. One of the strands combines with another enzyme 3. siRNA guides the enzyme to the mRNA. Complementary bases allow pairing between siRNA and mRNA 4. Enzyme cuts mRNA into sections and so it can not be translated into a polypeptide. Parts complementary to siRNA are removed 5. Gene expression is blocked

Question 39

What is the definition of epigenetics?

Answer 39

Epigenetics involves heritable changes in gene function without changes to the DNA sequence