Cell Differentiation and Tissues

Question 1

What is cell differentiation?

Answer 1

The natural process by which an unspecialised cell (e.g. stem cell) changes to become a specialised or differentiated cell.

Question 2

What are the two main parts of the cell cycle?

Answer 2

Interphase and Mitosis

Question 3

What are the 3 phases of interphase? Explain each?

Answer 3

G1 phase- Longest phase, cell grows, Organelles synthesise proteins and produce energy
S Phase- DNA is replicated. S phase begins with 1 chromatid and ends with 2 chromatids (DNA is doubled)
G2 phase- Cells duplicate organelles

Question 4

What are the 4 stages of mitosis?

Answer 4

Prophase- Nuclear membrane disintegrates and chromosomes condense and become visible
Metaphase- Chromosomes align at the centre of each cell
Anaphase- Spindle fibres contract and pull one of each type of chromatid to opposite poles of the cell
Telophase- Nuclear membrane reforms and chromosomes decondense

Question 5

What stage immediately follows mitosis?

Answer 5

Cytokinesis- Cell membranes separate and two identical daughter cells are formed

Question 6

What is cell potency?

Answer 6

The ability of stem cells to differentiate into specialised cell types. The more potent a cell is, the greater the types of different cells this stem cell can differentiate to.

Question 7

What is the hierarchy of cell potency?

Answer 7

Totipotent- Cell can differentiate into any type of cell
Pluripotent- Cells can differentiate into all cell types of the body (but not the placenta)
Multipotent- Stem cells can develop into cells only a few different types of cell
Unipotent- Can differentiate into only one type of cell. Are still stem cells as they can self-renew and are not terminally differentiated

Question 8

What are constitutive genes (housekeeping) and non-constitutive (luxury) genes?

Answer 8

Constitutive genes- Constantly expressed. Code for proteins that are essential for cellular maintenance (e.g. ribosomal RNA’s)
Non-constitutive genes- expressed only when needed. Code for proteins that are considered specialised in function (e.g. Alcohol dehydrogenase). If you switch these cells off, the cell will still survive

Question 9

What is a stem cell?

Answer 9

They are unspecialised, can specialise into many different cell types, they can self-renew.

Question 9

How do cells become specialised?

Answer 9

Different genes with a cell become silenced and others are expressed resulting in the cell being able to carry out a different function

Question 9

What is the stem cell niche?

Answer 9

This is the microenvironment surrounding stem cells. If you damage tissue, it is the stem cell niche that detects this and sends signals to stem cells to differentiate into the type of cell that was damaged.

Question 9

What are induced pluripotent stem cell?

Answer 9

This is reprogramming specialised cells using transcription factors to become undifferentiated cells.

Question 10

What effect does methylation of DNA have?

Answer 10

Causes a conformational change in the structure of the DNA so proteins are not able to bind to the DNA as easily so the gene is not expressed.

Question 11

What is histone modification?

Answer 11

This is where histones wrap around the DNA to make it easier for proteins to bind to the DNA and transcribe it.

Question 12

What are microRNA?

Answer 12

They are a type of RNA that destroys mRNA which means that the protein that the mRNA would code for, is no longer produced?

Question 13

What are the 2 main chromatin states?

Answer 13

Euchromatin- Less condensed, in areas where there are lots of genes, more easily transcribed.
Heterochromatin- Highly condensed, in areas where there are less genes, transcriptionally silent

Question 14

What is haematopoiesis?

Answer 14

This involves the formation of the cellular component of blood. For example, this involves Multipotent haemopoietic stem cells, that are within the bone marrow, being able to differentiate into all cell types required by the blood (red blood cells and platelets) and immune system (white blood cells). HSCs go through an intermediate progenitor differentiation step (Myeloid or Lymphoid) making true HSCs a rare population in the bone marrow.

Question 15

What is CD34+?

Answer 15

It is a cell surface marker that can be used to distinguish how differentiated a cell is. A HSC (Haematopoietic stem cell) contains a greater number of CD34+ compared to a myeloid progenitor cell for example. These more differentiated cells, then turn on other cell markers such as CD14+ so they have a higher concentration. This means we can use this to identify what type of cell it is and how far differentiated it is.

Question 16

What does blast and cyte mean?

Answer 16

blast= immature form
cyte= mature form

Question 17

How do people have different types of leukaemia cancer?

Answer 17

This is because different stages of the stem cell differentiation process is affected resulting in different phenotypes being produced.

Question 18

What is Stem cell therapy/bone marrow transplants?

Answer 18

This is where stem cells are extracted from the bone marrow and then replicated in a culture. The patient then undergoes chemotherapy to destroy these bad cells. The patient is then re-injected with the stem cells into the bloodstream.