Subjects

Biology

The control of gene expression (a-level only)

Gene technologies allow the study and alteration of gene function allowing a better understanding of organism function and the design of new industrial and medical processes (a-level only)

Les cellules souches et l'expression des gènes en Module 8 de biologie

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Les cellules souches et l'expression des gènes en Module 8 de biologie

Biology

Revision note

Stem cells and gene expression control are crucial topics in biology. This guide explores the nature of stem cells, their differentiation process, and various applications in both animals and plants. It also delves into the mechanisms of gene expression control, including epigenetics and gene mutations, and their role in cancer development.

Stem cells are unspecialized cells with the potential to form different cell types
Gene expression control involves activating or inhibiting genes
Epigenetics refers to heritable changes in gene function without altering DNA sequence
Gene mutations can lead to cancer through uncontrolled cell division

07/05/2023

Gene Mutations and Cancer

Gene mutations are changes in the base sequence of DNA. There are two main types:

Substitution: Replacing one base with another
Insertion/Deletion: Adding or removing a base

Example: A substitution mutation can be silent (no change in amino acid), mis-sense (different amino acid), or non-sense (premature stop codon).

Cancer is the formation of a malignant tumor due to uncontrolled cell division (mitosis). Malignant tumors differ from benign tumors in several ways:

Rapid growth
Unspecialized cells
Ability to spread (metastasis)
Systemic effects
Require aggressive treatment (surgery, chemotherapy, radiotherapy)

Highlight: Cell division is normally controlled by two genes: proto-oncogenes and tumor-suppressor genes.

Proto-oncogenes stimulate cell division by producing growth factors and receptor proteins, while tumor-suppressor genes inhibit cell division. Mutations in these genes can lead to cancer development.

Vocabulary: Metastasis is the spread of cancer cells from the primary tumor to other parts of the body.

Module 8 (Genes) Revision Notes
What is a Stem Cell?
a unspecialised/undifferentiated cell
potential to form different types of cells
How do

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What are Stem Cells and How Do They Differentiate?

Stem cells are unspecialized cells with the potential to form different types of cells. They become specialized through a process called differentiation, which involves changes in cell shape, number of organelles, and new content. This occurs by controlling gene expression, where some genes are activated while others are inhibited.

Definition: Differentiation is the process by which stem cells become specialized cells with specific functions.

In animals and humans, stem cells are classified based on their potential:

Totipotent: Zygote
Pluripotent: Embryonic stem cells
Multipotent: Bone marrow stem cells
Unipotent: Tissue-specific stem cells

Vocabulary: Induced pluripotent stem cells (iPS cells) are created by turning unipotent body cells into pluripotent cells, similar to embryonic stem cells.

Stem cell therapy in humans has two main uses:

Producing tissues or organs for transplant
Treating irreversible diseases by injecting stem cells at the site of the disorder

In plants, stem cells are found in the embryo (zygote/embryonic stem cells) and in adult plants (meristem cells in stem, shoot, and root).

Example: Plant stem cells are used in tissue culture (micro propagation) for large-scale production of genetically identical plants.

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Controlling Gene Expression and Epigenetics

Controlling gene expression involves either activating or inhibiting genes. Activation leads to protein production, while inhibition prevents it.

Example: Oestrogen can activate genes by binding to receptors on transcription factors, causing them to enter the nucleus and bind to DNA promoters.

Gene inhibition can be achieved using siRNA (small interfering RNA), which binds to complementary sections on mRNA and prevents translation.

Highlight: Epigenetics refers to heritable changes in gene function without altering the DNA base sequence.

The epigenome, a chemical layer surrounding chromatin (DNA-histone complex), can cause chromatin to become more condensed or loose, affecting gene activation or inactivation.