Human Cells Division And Differentiation Higher Human Biology Human Cells Division And Differentiation

Welcome to the class

Human Cells - Introduction This topic will look at human cells. You should be familiar with these topics from N5 Tissues, organs and systems Cell division Cell ultrastructure and function Cell division and chromosomes Base sequence and base pairing of DNA Function of proteins Enzymes Summary equation for respiration ATP and energy nat5biopl.edubuzz.org

Human Cells - Introduction You will learn: More about the division of labour in organisms More about the importance of DNA, its structure and replication More about the use of DNA technologies More about the chemistry of respiration and ATP About metabolic pathways, their importance and how they can be disrupted

Division and differentiation in human cells Somatic cells What are they? How many different ones are there in a human? What do they do? What DNA do they have? How do they make copies of themselves?

Somatic cells Specialised differentiated cells that perform a specific function within tissues or organs Over 200 different types in human body It depends on the tissues or organs they are in All of it (46 chromosomes), they are diploid By the process of mitosis

Somatic cells Skin Liver Brain Muscle Kidney Bone

Main body tissue types The main body tissue types are: epithelial connective muscle nerve tissue The body organs are formed from a variety of these tissues.

Tissue Stem Cells Tissue stem cells found in adults develop into cells to replace damaged, worn out, dead cells or to produce more tissue stem cells. These adult stem cells are limited to the type of cells they can develop into and are called multipotent. They can only produce the cells for the tissues they are from or self-renew. An example of tissue (adult) stem cells are blood (haematopoietic) stem cells in bone marrow which can produce red blood cells, platelets and the various forms of phagocytes and lymphocytes.

Haematopoietic Stem Cells

Epithelial cells Epithelial cells cover the body surface and line body cavities. These include linings of breathing system, blood vessels, lymphatic system, kidney tubules, digestive tract, uterus, mouth and obviously skin

Connective Tissue Cells Connective tissue includes blood, bone and cartilage cells.

Muscle tissue cells Muscle cells form muscle tissues. There are 3 different types of muscle: striated, smooth and heart

Nerve Tissue Cells Nerve cells form nervous tissue.

Differentiation In the beginning there was you – a zygote. You multiplied to produce a blastocyst (ball of cells). Each cell was identical, produced by mitosis but could develop into any type of cell – PLURIPOTENT (Called embryonic stem cells when grown in a Lab.) At some point in development specific areas of the embryo formed. Those areas were fixed and the cells in specific areas could only perform specific functions. Cells had undergone differentiation. There was no going back for differentiated cells.

DNA and differentiation All somatic cells contain a full set of DNA. During normal embryo development organisation ensures the body develops correctly. Not all genes are needed to be expressed by all cells. Genes not required are ‘switched off’ or not expressed. Genes required by a cell will be expressed (active). This process is differentiation.

DNA and differentiation What genes will be expressed in most cells? Why? Will gene expression change over the lifetime of a human? How do cells know what genes to express and when? How complicated is the human body and life!

Cell division and mutation Cell division by mitosis in somatic cells produces diploid cells with 23 homologous pairs of chromosomes. Tissue stem cells (germline cells) divide by mitosis to produce more germline cells (diploid) or by meiosis to produce haploid gametes. Mutations in somatic cells only affect the human in which they occur. Mutations in gametic cells are passed to offspring.

Cancer caused by mutation Somatic cells that mutate can cause cancer. If the mutation causes a problem with the control of the cell life cycle then they can divide excessively. A mass of abnormal cells are produced (tumour) These cells do not respond to regulatory signals. If the cancerous cells become detached from each other they can spread around the body and cause secondary tumours.

Common cancers of somatic cells Skin cancer Lung cancer Bowel cancer

Stem cells and research Stem cells are researched for their therapeutic uses for the repair of damaged or diseased organs or tissues such as corneal transplants and skin grafts for burns Stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work. Stem cells can also be used as model cells to study how diseases develop or for drug testing. There are ethical issues for stem cell use. The regulation of stem cell research and use is quite significant.

Corneal transplants Stem cells can be used instead. Eye stem cells from the edge of the cornea are taken. Grown in culture and applied to the damage cornea. Or they can applied directly between eyes

Skin grafts for burns

Using stem cells to grow skin Skin stem cells are taken from patient. Grown in special conditions Placed over wounds Read Case study Therapeutic use of stem cells in textbook

Stem cell sources and ethics Sources of stem cells include embryonic stem cells, tissue stem cells and attempts to reprogram specialised cells to an embryonic state (induced pluripotent stem cells [iPS]). Embryos used for research must not be allowed to develop beyond 14 days, around the time a blastocyst would be implanted in a uterus. Ethical issues include regulations on the use of human embryos and the use of iPS cells. What do you think about the use of stem cells? Read Case study Embryonic stem cell debate in textbook

Consolidation Go over PPT and make your own notes Read chapter 1 in textbook and make own notes Complete questions on page 8 and 15 Look at this section on Scholar Complete multiple choice and matching exercises in book pages 2 to 9