Animal Cell Culture Lecture 6

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Questions and Answers

What is the Hayflick limit in human cells?

75 divisions

25-40 divisions

52 divisions (correct)

100 divisions

What happens to telomeres with each cell division?

They are replicated with high fidelity

They remain unchanged

They shorten until they are consumed (correct)

They lengthen, improving cell lifespan

Which statement about replicative cell senescence is true?

It is a phenomenon exclusive to unicellular organisms

All normal cells can divide indefinitely

Senescence has no impact on cell longevity

Senescence occurs after cell proliferation slows down (correct)

What role do telomeres play in cellular function?

They protect chromosome ends from deterioration Signup and view all the answers

In which type of cells is replicative cell senescence most commonly observed?

Normal human fibroblasts Signup and view all the answers

What is the primary role of oncogenes in cancer cells?

To promote uncontrolled cell division Signup and view all the answers

Which of the following methods can artificially induce cell immortalization?

Chemical mutagens Signup and view all the answers

SV40 T antigen primarily interacts with which tumor suppressor proteins?

p53 and Rb Signup and view all the answers

What is the effect of introducing viral genes into somatic cells related to cancer?

Partial deregulation of the cell cycle Signup and view all the answers

In normal cells, what is the general status of tumor suppressor genes?

Active Signup and view all the answers

What happens to telomeres each time a cell divides?

Some telomere length is lost. Signup and view all the answers

At what average length do human telomeres decline by the time of old age?

4 kilobases Signup and view all the answers

When does a chromosome become unable to replicate?

When it reaches a critical length. Signup and view all the answers

What type of enzyme is telomerase?

Reverse transcriptase Signup and view all the answers

In which of the following cell types is telomerase expressed?

Cancerous cells Signup and view all the answers

What defines the process of transformation in cultured cells?

Permanent alteration in DNA leading to genetic instability. Signup and view all the answers

What phenomenon is described as the acquisition of an infinite lifespan in cells?

Immortalization Signup and view all the answers

What is a significant consequence of transformed cell lines when injected into animals with a non-functional immune system?

Development of invasive tumors Signup and view all the answers

What is a primary advantage of using cancer/immortalized cell lines in research?

They can be grown indefinitely in culture. Signup and view all the answers

Which cell line is derived from a cervical cancer patient?

HeLa cells Signup and view all the answers

What is a significant limitation of cancer/immortalized cell lines?

They may exhibit genome instability. Signup and view all the answers

What process represents the ability of stem cells to generate specialized cell types?

Differentiation Signup and view all the answers

Which of the following cell types is derived from human fetal cells?

HEK 293 cells Signup and view all the answers

What role do stem cells serve in the body?

They produce specialized cells and aid in tissue repair. Signup and view all the answers

Which cell line is known for being derived from a lung tumor?

A549 cells Signup and view all the answers

What is a key characteristic of stem cells that distinguishes them from other cell types?

Capability for self-renewal and differentiation. Signup and view all the answers

What primary systems does the mesoderm develop into?

Musculoskeletal, circulatory, and excretory systems Signup and view all the answers

Which layer develops into the epithelia linings of the digestive and respiratory tracts?

Endoderm Signup and view all the answers

What term describes the range of different cell types a cell can develop into?

Potency Signup and view all the answers

What type of cells are formed from the zygote during early development?

Totipotent cells Signup and view all the answers

What primary role do stem cells have in research?

Self-renewal and differentiation Signup and view all the answers

What is a common application of stem cell therapy?

Transplantation to regenerate diseased tissues Signup and view all the answers

What hypothesis suggests that cancers are maintained by tumor-initiating cells?

The Stem Cell Hypothesis Signup and view all the answers

Which of the following is NOT a function of stem cells?

Homeostasis maintenance Signup and view all the answers

What hypothesis suggests that a subset of tumor cells, the cancer stem cells, drive the development of tumors?

Cancer stem cell model Signup and view all the answers

What evidence initially supported the cancer stem cell theory?

Transplantation studies in leukemia Signup and view all the answers

Which cancer is noted as having a very large number of tumor cells with cancer stem cell characteristics?

Melanoma Signup and view all the answers

How are cancer stem cells believed to contribute to tumor recurrence after initial treatment?

They evade detection from targeted therapies. Signup and view all the answers

According to the stochastic model, how do tumor cells operate in a cancerous growth environment?

Each cell has equal potential for tumor growth. Signup and view all the answers

What event is proposed to initiate the formation of cancer stem cells?

Mutation in a stem cell Signup and view all the answers

In which type of cancer might cancer stem cells be particularly rare?

Colon cancer Signup and view all the answers

What is a key characteristic of cancer stem cells identified in leukemia research?

Only a small subset can initiate cancer upon transplantation. Signup and view all the answers

Study Notes

Animal Cell and Tissue Culture Lecture 6

SIO2004 is the course code for Animal Cell and Tissue Culture, taught by Dr. Nuradilla Mohamad Fauzi at Universiti Malaya. Lecture 6 is part of the Biotechnology Program.

Can Normal Cells Divide Forever?

Most normal cells have a finite lifespan in culture.
They will eventually stop dividing.

Replicative Cell Senescence

Multicellular organisms replace worn-out cells through cell division.
Proliferation slows in many cells until division eventually halts, entering a non-dividing state called senescence.
In humans, this typically occurs after an average of 52 divisions, known as the Hayflick limit.
Primary cells in culture have a limited lifespan.
Cells stop dividing due to telomere shortening. Telomeres are protective DNA sequences at chromosome ends.

Telomeres

Telomeres are repetitive nucleotide sequences at the ends of chromosomes.
They protect chromosomes from deterioration or fusion with neighbouring chromosomes.
They act as disposable buffers, preventing the truncation of the genes when replicating.
In vertebrates, the telomere sequence is TTAGGG.

Telomeres and Cellular Aging

Each cell division results in some telomere loss (typically 25-200 base pairs).
In humans, average telomere length decreases from around 11 kilobases at birth to less than 4 kilobases in old age.
DNA replication enzymes cannot replicate the entire chromosome, causing shortening in each duplication cycle.
Short telomeres result in a "critical length" – the cell can no longer replicate, entering a senescence or apoptosis state.

Telomerase

Telomerase is a reverse transcriptase enzyme that adds telomere repeats to DNA strands.
It prevents chromosomal end degradation after multiple replication rounds.
Active in fetal tissues, adult germ cells, and stem cells, but usually deficient in most post-natal somatic cells

Cells that Express Telomerase

Fetal tissues, adult germ cells, stem cells, and cancer/transformed cells express telomerase.
Telomerase expression allows senescent cells, that otherwise become post-mitotic and undergo apoptosis, to exceed the Hayflick limit and become potentially immortal (transformation).

Activation of Telomere Extension

Telomere shortening, senescence, and apoptosis occur when telomeres are too short.
Inactivation of DNA checkpoints, accumulation of mutations, and cancerous transformation lead to cellular immortality.

Transformation

Transformation is a spontaneous or induced permanent phenotypic change in cultured cells.
This is due to a heritable change in DNA and gene expression, contributing to genetic instability.
Immortalization, loss of contact inhibition, aberrant growth control, density limitation, malignancy are characteristics in cell lines.
Injected into animals with non-functional immune systems, transformed cell lines can cause tumors.
Immortalization versus transformation, while related, are not identical.

Transformation and Cancer

Transformed cell lines are in vitro equivalents of cancerous cells.
Cancer occurs when a somatic cell, normally unable to divide, undergoes mutations.
This deregulation leads to uncontrolled proliferation. Immortalized cell lines exhibit similar mutations, enabling a cell type not normally capable of dividing to proliferate in vitro.

Transformation Methods

Natural/spontaneous (mutations in tumor/cancer cells, random spontaneous mutations in culture)
Artificial expression of key proteins required for immortality (e.g., oncogenes, telomerase)
Artificial inactivation of tumor suppressor genes (e.g., p53, Rb)
Chemical mutagens (treatment of primary or non-transformed cell lines with chemical carcinogens, DNA methylation inhibitors)
Introduction of viral genes (inserting viral genes that partially deregulate the cell cycle, such as SV40 T antigen, HPV-16 E6/7 gene)
Tumor suppressor genes (ON in normal cells, OFF in cancer cells)
Oncogenes (OFF in normal cells, ON in cancer cells; examples include telomerase)

Tumor Suppressor oncogenes

Tumor suppressor - ON in normal cells, OFF in cancer cells
Oncogene - OFF in normal cells, ON in cancer cells

SV40 T Antigen example

The SV40 LT gene is used to induce immortalization.
Its product, T antigen, binds Rb and p53, restricting DNA surveillance.
This allows an increased chance of genomic instability, and subsequent mutations leading to immortalization (e.g. the upregulation of telomerase or the downregulation of a telomerase inhibitor).
This process allows an extended proliferative life span.

Examples of Immortal/Cancer Cell Lines

HeLa cells (cervical cancer)
3T3 cells (mouse fibroblast)
A549 cells (lung cancer)
Jurkat cells (leukemia)
Vero cells (monkey kidney)
F11 cells (neurons from rats)
HEK 293 cells (human fetal cells)

Advantages of Cancer/Immortalized Cell Lines

Cells can be grown indefinitely in culture.
Inexhaustible supply of cells for research projects.
No need to re-establish fresh primary cultures.
Easy culture (no complex medium or additives).
In vitro model for cancer.

Limitations of Cancer/Immortalized Cell Lines

Genome instability (abnormal chromosomes change genetically over multiple passages). This leads to accumulation of mutations & variability.
Poor model of normal tissues (even though often originating from a normal tissue type, mutations can alter cell biology and analysis needed)

Definition of Stem Cells

Stem cells are capable of self-renewal (multiple division cycles maintaining undifferentiated state) and differentiation (capacity to mature into specialized cell types).

Importance of stem cells in vivo

Stem cells are the body's raw material for generating other cells with specialized functions.
They are essential for cell renewal (producing new cells to replace dead ones, normal wear & tear).
They play a crucial role in the body's development & repairing damaged or diseased tissue

Importance of stem cells in research

Stem cells provide valuable tools for cellular studies.
They are used to increase understanding of disease processes.
Stem cell therapy's regenerative medicine and transplantation are used to repair damaged tissue.

Cancer Stem Cells

The "cancer stem cell" (CSC) hypothesis proposes that cancers are perpetuated by a small population of cancer stem cell-like cells.
Researchers now believe cancer stem cells may trigger cancer growth and reproduction.
These cells may survive treatment, which could lead to tumor relapse.

Evidence for Cancer Stem Cells

No definitive proof for either theory, but there is increasing evidence suggesting the cancer stem cell theory holds true in some cases.
Leukemia research showed only a subset of leukemia cells can cause further leukemia in a healthy body.
Various cell types, like breast, brain, skin, prostate, and colonic cancers, have been found to contain stem-like cell characteristics.

Potential, Cell, Source Summary

Totipotent: zygote, can differentiate into any tissue, from the zygote
Pluripotent: embryonic stem cells, can differentiate into all three germ layers
Multiopotent: Adult stem cells, differentiate into several tissue types
Oligopotent: differentiate into a few tissue types
Unipotent: differentiate into one cell type (e.g. fibroblasts)

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Description

This quiz covers Lecture 6 of the Animal Cell and Tissue Culture course, focusing on normal cell division, replicative cell senescence, and the role of telomeres. Explore the mechanisms behind cell lifespan and the Hayflick limit, crucial for understanding biotechnology applications in cellular biology.