STEM CELLSNoadswood Science,

2012

Stem Cells

To understand chromosomes, genes and stem cells

Wednesday, April 19, 2023

Key Terms

Complete the key terms worksheet

Key Terms

DNA

What is DNA?

DNA (deoxyribose nucleic acid) molecules are large and complex – they carry the genetic code that determines the characteristics of a living thing

Except for identical twins, each person’s DNA is unique allowing people to be identified using DNA fingerprinting

DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next

Gene

What is a gene?

A gene is a short section of DNA

Each gene codes for a specific protein by specifying the order in which amino acids must be joined together

Chromosomes

The cell’s nucleus contains chromosomes made from long DNA molecules

Allele

Some characteristics, such as eye colour and the shape of the earlobe, are controlled by a single gene

These genes may have different forms which are called alleles

Alleles are dominant or recessive…

The characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair

The characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair

Chromosomes

How many chromosomes do humans have?

A human nucleus contains 23 pairs of chromosomes – the 23rd pair determines sex (XX = female and XY = male)

Gametes only have 1 copy of each chromosome – this allows combing of the two sex cells from mother and father resulting in the correct number of chromosomes

Normal cell – 46 chromosomes (23 pairs) Gametes – 23 chromosomes

Mitosis – Identical

First the cell makes a copy of each chromosome and then divides…

Each new cell has a full set of chromosomes and is identical to the original cell

Each new cell can keep on dividing by mitosis

Mitosis makes new cells for growth and repair in all living things – that’s how you get from one cell to 50 billion!

Mitosis

Mitosis

Meiosis – Single Set Of Chromosomes First the cell makes a copy

of each chromosome followed by two stages of cell division…

Meiosis produces four new sex cells with half the original number of chromosomes

In animals, meiosis produces ova in females and sperm cells in males and in plants, the gametes produced by meiosis are pollen grains and ovules

Meiosis

Meiosis

Stem Cells

Embryonic stem cells can turn into any type of cell (they are undifferentiated and can develop into different types of cell depending upon the instructions they’re given)

Stem cells are found within human embryos (adults do have stem cells but they are only found in a few places such as bone marrow and are not as versatile as embryonic stem cells)

Stem Cells & Disease

Medicine has for many years used stem cells (e.g. sickle cell anaemia is treated by bone marrow transplants)

Embryos can have their stem cells extracted and grown specifically for medical purposes, such as… To develop into heart muscle for heart disease To develop into insulin producing cells for diabetes To develop into nerve cells for paralysed individuals

The research remains in its infancy, but the possibilities for medical improvements are vast…

Negative Press

Some individuals are against stem cell research because they feel human embryos should not be used (as they can potentially become a human life)

The counter to this is stem cells can sure patients who already exist and are suffering already

Embryos used in research are normally unwanted ones from fertility clinics, which if they were not used for research would be destroyed…

Stem cell research is allowed in the UK, though it must adhere to strict guidelines