cell biology ; unit 2. cell cycle and transport

differentiation

As an organism develops, (stem) cells differentiate to form different types of cells - to carry out specific functions in the body

• Most types of animal cell differentiate at an early stage.

• Many types of plant cells retain the ability to differentiate throughout life

in adult animals, diff. is limited to replacement and repair

what happens during differentiation

As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell

chromosomes and gametes

EUKs have chromosomes in nucleus and they are made of DNA molecules. Body cells contain two of each chromosome. Human cells contain 23 pairs of chromosomes (for the eg. cell there are 2 pairs of c.somes - 4 )

however gametes - sperm, egg only contain half the chromosomes (genetic material) as they fuse together

the pairs are genetically identical - homologous , and are matched based on size and shape

genes and multicellular need

each chromosome carries a large number of genes (coding for a specific protein) , and these determine many of our features

DNA carry the code that controls cellular functions and activities

animals and plants are multicellular so have lots of cells so they must be able to divide - Cells divide in a series of stages called the cell cycle

cell stuff b4. mitosis

Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome.

They are also checked so that they are correct

chromosomes explanation of the e.g. cell when being copied

The copies stay attatched

(for the e.g cell, that is still two pairs of chromosomes in an x shape - but one end of the x shape is a chromatid that will eventually break off into its own chromosome - so as of now it as 2 copies of 2 pairs that have two potential chromosomes (chromatids) - 8P as 2×2×2

mitosis (stage 2) :

In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus (membrane) divides.

Final stage of the CC the cytoplasm and cell membranes divide to form two genetically identical cells.

functions and importance of mitosis

essential for growth and development of multicellular organisms (plants and animals)

takes place when an organism repairs or replaces damaged or worn-out cells

happens during asexual reproduction

cell cycle time phase length formula + explanation

= observes no. of cells at that stage / total no. of cells observed (physically there at whatever stage) * (length in time of one cycle)

this method takes into account the proportion of cells in a stage out of the total number of cells relative to the time it takes for one division

(less cells there are the faster it takes)

humans progression from fertilisation + embryonic S cells.

humans start as a zygote (fertilised egg cell). the zygote undergoes mitosis to form a ball of cells called the embryo. they furtherly divide to get more, and diff. into specialised cells e.g. muscle and nerve → which then forms the final organism

cells in the early embro have not differentiated. Any cells is capable of diff. into any type of body cell - are called embryonic stem cells.

SC defenition

A stem cell is an undifferentiated cell which can give rise to more cells of the same type and can diff to form other types of cells

embryonic (early age) vs. adult SCs

(embryonic can diff into any - however SCs of the organ and only diff into related cells (few types of cells) e.g. Bone M → RBCs, WBCs + platelets) - adult stem cells cannot diff. into any other type of cell

|→ This is why most animals diff. at an early age , and why diff in adults is js limited to repair and replacement of cells

some specialised cells cannot be re diff.ed into

bone marrow transplant

Leukaemia is a cancer of the bone marrow

To treat this, the patients first existing bone marrow is destroyed using radiation

The patient then recieves a transplant of the bone marrow from a donor

the SCs in the bone marrow now divide and form new bone marrow. They also diff. and form blood cells

problems w bone marrow transplant

donor has to be genetically compatible with the patient or else the WBC produced by the donated BM could attack the patients body. → immunosuppressant drugs that could make it easier to contract infection

Risk of viruses being passed down from donor to patient

therapeutic cloning

In therapeutic cloning, an embryo is produced with the same genes as the patient.

Stem cells from the embryo can be transplanted into the patient (stimulated for division) without being rejected by the patient's immune system.

Once inside the patient, the stem cells can then differentiate to replace cells which have stopped working correctly.

(can be used to treat lots of medical conditions like diabetes or paralysis - some ppl have ethical or religious objections to the procedure)

plant stem cells

shoots and toots tips and buds contain meristem tissue. These stem cells can differentiate into any type of plant tissue, at any point in the life of the plant.

Stem cells from meristems in plants can be used to produce genetically identical clones of plants quickly and economically.

• Rare species can be cloned to protect from extinction.

• Crop plants with special features such as disease resistance / appearance / taste / or certain nutrients can be cloned to produce large numbers of identical plants for farmers.