2.2 Cell division, Stem Cells and DNA

Question 1

What are chromosomes?

Answer 1

• Chromosomes are a length of DNA found in the nucleolus.

- They come in pairs and we inherit half of the genes (DNA) from each parent.

Question 2

How many chromosomes are in a human body cell?

Answer 2

There are 46 chromosomes in a standard body cell and 23 pairs of chromosomes.

Question 3

Which pair of chromosomes in a body cell codes for gender?

Answer 3

• The 23rd pair codes for gender with XX being female and XY being male.
• They are known as the sex chromosomes and the sperm decides the gender.

Question 4

What are genes?

Answer 4

• Genes are the instructions that code our characteristics/ features.
• They are located on the chromosome (the stripe pattern) and are made of a short section of DNA.

Question 5

What are Alleles?

Answer 5

• Alleles are different variations for the same gene.

- Blue eyes/ brown eyes would be the same gene but a different allele.

Question 6

What is the ‘cell cycle’ for a normal body cell?

Answer 6

• A normal body cell goes through the process of mitosis (cell division).
• ‘Cell Cycle’ = Growth > DNA duplication > Division (Cytokinesis)

Question 7

What is the function of mitosis?

Answer 7

Growth and repair

Question 8

What is the process of mitosis?

Answer 8

1) The mass of the cell increases as the cell grows.
2) The DNA replicates, creating two identical copies of each chromosome.
3) The 46 pairs of chromosomes (92 singles) line up across the centre of the cell.
4) The chromosome pairs split and move to either side of the cell’s poles.
5) The entire cell splits into two identical daughter cells.

MITOSIS CREATES MORE OF THE SAME!

Question 9

What happens when mitosis becomes uncontrolled?

Answer 9

Uncontrolled mitosis can lead to tumour and cancer can occur.

Extra information:
Benign tumour = Non cancerous
Malignant tumour = Cancerous

Question 10

What is the function of meiosis?

Answer 10

The production of 4 genetically unidentical gametes (egg/ sperm cell) for sexual reproduction.

Question 11

What is the process of meiosis?

Answer 11

Growth > DNA replication > Cell Division > Cell division again

1) The mass of the cell increases as the cell grows.
2) The DNA replicates, creating two identical copies of each chromosome.
3) Similar chromosomes pair up and swap sections of DNA randomly.
4) The 46 pairs of chromosomes divide
5) The 23 pairs of chromosomes divide randomly again.
6) In the end, there are 23 random selections of chromosomes in each of the 4 gamete cells. The egg and sperm cell will eventually combine to create 23 pairs of chromosomes as found in a normal body cell.

Question 12

What are stem cells?

Answer 12

• Stem cells are unspecialized body cells

- Depending on the chemical signals, they can turn into a number of different specialized cells

Question 13

What are the different states of stem cells?

Answer 13

Totipotent- can turn into almost any cell. They are fully undifferentiated but are found in embryonic tissues (ethical issues).

Multipotent/ pluripotent- Can become a variety of related cells. They are partially differentiated.

Specialized- Fully differentiated and can’t become any other cell

Question 14

What is DNA and where is it found?

Answer 14

• Deoxyribonucleic acid (DNA) is the code for proteins that write the genetic code in our bodies that tells it what to do and make.
• It is found in the genes of chromosomes and are different per individual.

Question 15

What is the structure of DNA?

Answer 15

A double helix made of two ‘sugar phosphate back bones’ joined together by the hydrogen bonds of the base pairings.

Question 16

What are the different bases and their pairs (A, T, C, G)?

Answer 16

• Adenine (A) ==== Thymine (T)
• Cytosine (C) ==== Guanine (G)
  They are ALWAYS opposite each other

Question 17

What does each triplet (3 base pairings) code for and what does it eventually create?

Answer 17

Each triplet codes for an amino acid (building blocks of a protein.
A chain of amino acids = a protein

Question 18

What are the clinical issues with stem cells?

Answer 18

• there is no guarantee how successful there therapies
• there is a difficulty in finding suitable stem cell donors
• there is a difficulty in in storing and obtaining a patient’s embryonic stem cells
• mutations can happen in stem cells
• some stem cells may be contaminated (with viruses)

Question 19

What are the ethical issues with (embryonic) stem cells?

Answer 19

• some believe it’s wrong to use embryos produced by vitro fertilisation
• is it right to create embryos just for therapy and destroy them in the process?
• when in the process should we consider an embryo as a person?
• Religious groups may see tampering with the birth process as ‘playing god’.
• Are we creating life just to destroy it and does an embryo count as living life?

Question 20

What are the social issues with stem cells?

Answer 20

• can the benefits of stem cells outweigh the risks?
• most the research is being carried out by commercial clinics , so reported successes are not subject to public review
• patients could be exploited by paying for expensive treatments and given false hope of a cure as stem cell therapies are only in their development stages

Question 21

Where does cell division in plants occur?

Answer 21

The meristems. Cells of the meristem can differentiate to produce all types of plants cells at any time during the life of a plant.
The main meristems are close to the tip of the shoot and the tip of the root.