Cell differentiation and gene expression

Question 1

What are totipotent stem cells?

Answer 1

Totipotent stem cells can differentiate into all cell types: including specialised cells of the organism and extraembryonic cells.

Question 2

What are pluripotent cells?

Answer 2

Pluripotent stem cells can differentiate into all specialised cells in an organism except extraembryonic cells.

Question 3

When do totipotent stem cells become pluripotent?

Answer 3

After the first few embryotic divisions.

Question 4

How does differential gene expression result in specialisiation?

Answer 4

Depending on certain conditions, some stem cell genes are activated and others are deactivated. mRNA is only translated from active genes, so only certain proteins are formed. The produced proteins determine cell structure and cell processes including further gene activation, which prodcues yet more proteins.

Question 5

What are the two types of transcription factors and how do they affect gene expression?

Answer 5

1. Activators - help RNA Polymerase bind to the DNA and promote transcription.
2. Repressors - prevent binding and transcription.

Question 6

What is an operon?

Answer 6

An operon is a DNA section of a prokaryote that contains: a cluster of structural genes (code for useful proteins), control elements (promoter DNA sequence for RNA P to bind to and an operator DNA sequence for TFs to bind to), and sometimes a regulatory gene (codes for an activator or repressor).

Question 7

Describe the lac operon in E.coli

Answer 7

E.coli can respire using glucose or lactose.
The lac operon contains 3 structural genes which produce proteins that help the bacteria digest lactose e.g lactose permease.

Question 8

What process takes place in the lac operon when no lactose is present?

Answer 8

Regulatory gene produces the lac repressor, a TF that binds to the operator site, preventing RNA P from binding to the promoter.

Question 9

What process takes place in the lac operon when lactose is present?

Answer 9

Lactose binds to the lac repressor, changing the shape of its active site so it can no longer bind to the operator.
RNA P begins transcription of the structural genes.

Question 10

What are the two sources of stem cells?

Answer 10

1. Adult stem cells

2. Embryonic stem cells

Question 11

How are adult stem cells obtained and what is their limitation?

Answer 11

1. A needle is inserted into the bone marrow of a donor and a small quantity is removed.
2. Adult stem cells are multipotent and thus less flexible than embryonic stem cells. There is also a risk of rejection.

Question 12

How are embryonic stem cells obtained?

Answer 12

From early embryos, created using IVF. At 4-5 days, stem cells are removed and the rest of the embryo is destroyed.

Question 13

What are three roles of regulatory authorities?

Answer 13

1. Produce guidelines and codes of practice - scientists will use similar methods, results can be compared
2. Licensing and monitoring centres - prevent unregulated research
3. Providing info and advice to the public - helps to promote the benefits of embryo research

Question 14

What type of variation do monogenic charcs. tend to show?

Answer 14

Discontinuous variation

Question 15

What type of variation do polygenic charcs. tend to show?

Answer 15

Continuous variation

Question 16

Give an example of how a monogenic and a polygenic charc. can be affected by environmental factors

Answer 16

1. MAOA (monogenic) - low levels have been linked to mental health issues, smoking tobacco can reduce levels further.
2. Height (polygenic) - affected by nutritition

Question 17

What are two examples of epigenetic changes to gene expression?

Answer 17

1. Methylation of DNA - increased methylation (methyl groups binding to CpG sites) can change DNA structure, resulting in gene repression or inactivation.
2. Histone modification - how condensed the chromatin is, this can cause expression (less condensed) or repression (more condensed).

Question 18

How does histone modification work?

Answer 18

Histones are acetylated - chromatin is less condensed - gene expression occurs.
Histones are not acetylated - chromatin is more condensed - gene expression is repressed.

Question 19

What is a benefit of epigenetic changes being passed on to daughter cells?

Answer 19

If the epigenetic changes occurred in response to a change in the env., the daughter cells will be equipped to deal with the env. just as the original cell was.