Cell Reproduction 1 Types of Cell Reproduction Asexual

Cell Reproduction 1

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

Cell Division in Prokaryotes 3

Cell Division in Prokaryotes ü Prokaryotes such as bacteria divide into 2 Parent cell identical cells by the process of binary fission Chromosome ü Single chromosome doubles makes a copy of itself ü Cell wall forms Cell splits between the chromosomes dividing the cell 2 identical daughter cells 4

Prokaryotic Cell Undergoing Binary Fission 5

Animation of Binary Fission 6

Asexual Reproduction in Eukaryotes Three main types: all result in genetically identical offspring. 1. Budding 2. Fragmentation 3. Vegetative Reproduction 7

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.

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!

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

Why are stem cells special? Stem cells can: • self-renew to make more stem cells • differentiate into a specialised cell type Stem cells that can become many types of cells in the body are called pluripotent Stem cells that can become only a few types of cells are called multipotent Embryonic stem cells (pluripotent) Tissue stem cells (multipotent)

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 • generally very difficult to isolate • already used to treat patients (haematological malignancies, diseases of the immune system)

Where do embryonic stem cells come from? • Donated excess IVF embryos egg Day 0 Inner cell mass fertilised egg 2 -cell 8 -cell blastocyst Day 1 Day 2 Day 3 Day 6 Images from www. advancedfertility. com

Embryonic stem cells 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 can become any cell in the body including these beating heart cells