Topic 11: Cell Growth And Differentiation

Question 1

How is a zygote formed?

Answer 1

• for fertilisation to occur, a sperm must penetrate the various layers that surround the egg and then enter the cytoplasm of the egg cell.
• the haploid sperm nucleus then fuses with the haploid egg nucleus to creat a single diploid cell known as a zygote.
• the DNA of the chromosomes of the zygote, half from the mother and half from the father creates a new genome that contains all the genetic information needed to form a unique human being

Question 2

What is a human embryo?

Answer 2

The entity that is produced by the first mitosis division of the zygote produced after completion of fertilisation of the egg by sperm, and this stage continues to the eighth week of fertilisation.

Question 3

What is a blastocyst?

Answer 3

By the fifth day or embryonic development the embryo is no longer a solid mass of cells but consists of hollow fluid file structure called a blastocyst, with an inner mass of cells surrounded by an outer layer of cells. The inner cell mass of the blastocyst will form the tissues of the embryo, while the cells of the outer layer will become the embryonic contribution to the placenta.

Question 4

What is gastrulation?

Answer 4

The complex cell migration that reorganise the inner cell mass of the embryo blastocyst into a three layered structure.

Question 5

What are the germ layers?

Answer 5

The cell migrations and the reorganisation produce three distinct layers of cells known as the primary germ layers which are composed of stem cell that can give rise to or differentiate into various specialised cells.

Question 6

When does and embryo become a foetus?

Answer 6

Nine weeks after fertilisation is regarded as the point at which the feral stage of development is reached, determined by the presence of all major body organs.

Question 7

What are stem cells?

Answer 7

Undifferentiated or unspecialised cells that have the ability to differentiate into organ or tissue specific cells with specialised functions such a muscle cells, skins cells etc.

Question 8

What are the two types of stem cells found in mammals?

Answer 8

EMBYRONIC STEM CELLS- isolated from inner cell mass of blastocysts
ADULT STEM CELLS- found in various tissues

Question 9

Define totipotent

Answer 9

Have the potential to give rise to all dell types

Found in fertilisation egg

Question 10

Define pluripotent

Answer 10

Cells of primary germ layers can differentiate into many cell types found in inner cell mass of embryonic blastocyst.

Question 11

Define multipotent stem cells

Answer 11

Can differentiate into closely related family of cells

Blood stem cells could become red or white blood cells or platelets.

Question 12

Define oligopotent

Answer 12

Can differentiate into w few cells

Adult somatic lymphoid or myeloid stem cells

Question 13

Define unipotent

Answer 13

Can produce cells only of their own type but they a termed stem cells because they can self renew
Adult somatic muscle stem cells

Question 14

Define cell based therapy

Answer 14

The use of stem cells to replace lost or damaged cells with the scope of treating or preventing a disease or condition

Question 15

Define therapeutic cloning

Answer 15

Involves the creation o fan embryo through the technique of somatic nuclear transfer for the purpose of obtaining stem cells from that embryo which can be used to treat a patient with degenerative disease

Question 16

What are ethical issues related to stem cells?

Answer 16

• creating an embryo for the purpose of obtaining stem cells will lead to the death of an embryo
• many donated eggs are required for this procedure. There is some concern that women might be coerced into providing eggs or be financially exploited if eggs can be purchased

Question 17

Define congenital malformation

Answer 17

Abnormalities arising cure antenatal development

Question 18

What factors cause abnormalities?

Answer 18

Genetic defects
Single gene defects, chromosomal defects
Environmental factors

Question 19

What is a single gene Defect?

Answer 19

Usually inherited and most commonly appearing in newborn of unaffected parents who are heterozygous carriers of the allele involved. Caused by mutation of the gametes in fertilisation

Dwarfism, cystic fibrosis

Question 20

What is chromosomal abnormality?

Answer 20

Presence of an extra copy of a chromosome (trisomy), results from disruption of the normal cell cycle

Down syndrome, Edwards syndrome, partial syndrome

Question 21

How is the cell cycle regulated to prevent mutations?

Answer 21

-checkpoints such as g1 ensure DNA replication is error free, if it needs to be repaired the process of the cell cycle is delayed.
-proteins cycling ensure chromosomes are attached to the correct spindle fibres so that an equal distribution of chromosomes to daughter cells occurs
-normal cells display so called contact inhibition which means they will stop dividing if they overgrow adjacent cells
-chemical signals convey information to cells about when to divide faster and when to slow down or stop
—> oncogene, continue dividing
Tumour suppressor genes, stop dividing

Question 22

Define apoptosis

Answer 22

If cells are chromosomally abnormal or damaged, they receive a signal to self destruct in a process known as programmed cell death

Question 23

What is cancer?

Answer 23

A disease in which cells divide in an uncontrolled manner, forming an abnormal mass of cells. It results from the loss of control in the cell cycle

Question 24

What causes cancer?

Answer 24

Carrying certain genes in your genome can increase risk of developing cancer

Environmental factors such as mutagens
Uv radiation
Carcinogenic chemicals in cigarettes
Viruses
Diet