Cell Reproduction

Types of Cell Reproduction Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Mitosis & binary fission are examples of asexual reproduction Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells

Cell Division in Prokaryotes

Cell Division in Prokaryotes Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission Single chromosome makes a copy of itself Cell wall forms between the chromosomes dividing the cell Parent cell Chromosome doubles Cell splits 2 identical daughter cells

Prokaryotic Cell Undergoing Binary Fission

Animation of Binary Fission

Asexual Reproduction in Eukaryotes Three main types: all result in genetically identical offspring. Budding Fragmentation Vegetative Reproduction

What makes us so different, but still the same. Cell Differentiation What makes us so different, but still the same.

What is cell differentiation? cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type.

Why differentiate cells? Because the various cells of each plant and animals need to perform different functions! Differentiation dramatically changes a cell's size, shape, membrane potential, metabolic activity, and responsiveness to signals. Once an egg cell is fertilized and becomes a zygote, mitosis produces MORE cells and differentiation produces DIFFERENT cells that eventually becomes tissues, organs, etc.

How do cells differentiate? Cellular differentiation almost never involves a change in the DNA sequence itself. Thus, different cells can have very different physical characteristics despite having the same genome These changes are largely due to highly controlled modifications in gene expression: this means that different cells use different genes.

Muscle cells Muscle cells are designed to contract and relax allowing for movement.

Nerve cells Nerve cells are designed to receive and transmit impulses from one area to another.

It also patrols the body as part of the defense system. Blood Blood is responsible for transporting various materials to and from the cells. It also patrols the body as part of the defense system.

Introducing….stem cells! This slide is designed to be interactive. Start with a question like “What do you think of when someone mentions stem cells?” and allow the students to suggest key words. At the click of a mouse in will come key words associated with stem cell research. 15

What are stem cells? the body is made up of about 200 different kinds of specialised cells such as muscle cells, nerve cells, fat cells and skin cells all cells in the body come from stem cells a stem cell is a cell that is not yet specialised the process of specialisation is called differentiation once the differentiation pathway of a stem cell has been decided, it can no longer become another type of cell on its own This slide introduces some basic terms and concepts about stem cells. 16

Why are stem cells special? Stem cells can: self-renew to make more stem cells differentiate into a specialised cell type Embryonic stem cells (pluripotent) Stem cells that can become many types of cells in the body are called pluripotent Tissue stem cells (multipotent) Stem cells that can become only a few types of cells are called multipotent This slide explains the basic properties of stem cells and introduces the concept of classification based on potency.

Tissue stem cells often known as adult stem cells also includes stem cells isolated from fetal and cord blood reside in most tissues of the body where they are involved in repair and replacement Bone marrow Kidney Lung This slide provides key information about tissue stem cells. Other points you may wish to raise are: tissue stem cells are multipotent, meaning they only give rise to a limited number of different tissues under the right conditions tissue stem cells can be grown in the laboratory tissue stem cell are widely use in research treatments based on tissue stem cells are limited to blood cancers like leukeamia and auto-immune diseases (and have been for over 50 years). These treatments involve stem cells obtained from bone marrow and umbilical cord blood there are many other therapeutic applications of tissue stem cells currently being evaluated but these are not yet clinically proven and widely accepted. For example, clinical trials are underway to use adult stem cells to treat long bone fractures, kidney failure, heart failure, arthritis and cartilage regeneration, just to name a few possible future applications the use of tissue stem cells in research and in the clinic attracts less controversy than other types of stem cells (eg ES cells) but still require ethics approval to create and use in the laboratory and the clinic. generally very difficult to isolate already used to treat patients (haematological malignancies, diseases of the immune system) 18

Where do embryonic stem cells come from? Donated excess IVF embryos Inner cell mass egg fertilised egg 2-cell 8-cell blastocyst This slide provides an overview of embryo development during IVF. To understand where embryonic stem cells come from it is helpful to introduce how embryos are made. Other points you may wish to raise are: At the completion of their infertility treatment, IVF couples must decide what happens to any embryos they may still have frozen. Not all couples will have excess embryos. Their options are to discard the embryo (disposed of in biological waste), donate the embryo to research, or donate their embryo/s to another couple. Couples decide what to do and are not forced to donate their embryos if they don’t want to Concept of early cell division from fertilised egg (PN visible in D1 image) through to formation of blastocyst approximately one week after fertilisation Blastocyst has two different cell types – inner cell mass and trophectoderm (ICM highlighted by red oval). These cell types has different function with ICM generating all the cells of the body ES cells are made by isolating the ICM and growing it in the laboratory It has been legal to use human embryos in research in Australia since 2002 when specific legislation was passed Research Involving Human Embryos Act 2002. Any researcher wanting to use embryos in their research must obtain a licence from the government specifically for their project Human embryos have been used in research to improve infertility treatment and to make embryonic stem cells. Day 0 Day 1 Day 2 Day 3 Day 6 Images from www.advancedfertility.com 19

human embryonic stem cells derived from donated IVF embryos can be grown indefinitely in the laboratory in an unspecialised state retain ability to specialise into many different tissue types – know as pluripotent can restore function in animal models following transplantation human embryonic stem cells This slide introduces key facts about embryonic stem cells. The first image is of a blastocyst (100-200 cells but very small – 10 can fit on the head of a pin). Embryonic stem (ES) cells are isolated from the inner cell mass of the blastocyst. The red oval highlights the inner cell mass (ICM) Other points you may wish to raise are: differentiation is controlled/manipulated in culture and ES cells can differentiate into many different types of cells such as: nerves including motor neurons blood (haematopoietic) stem cells insulin producing cells liver cells (hepatocytes) bone forming cells Embryonic stem cells may provide a new way of studying diseases by making patient - or disease - specific stem cell lines. These can then be used to test drugs and treatments Potentially, embryonic stem cells can be used to replace or restore damaged tissue, as with the proposed Geron trial in patients with acute spinal cord injury in the USA, however there remains significant hurdles to clinical translation such as the potential to form tumours and what stage of a cells differentiation is the most appropriate to deliver to a patient. Human embryonic stem cells can become any cell in the body including these beating heart cells