Cell Cycle, Cell Death and Tissue Homeostasis

Question 1

What is the predominant cell type in the epidermis?

Answer 1

Keratinocytes

Question 2

What is the primary function of keratinocytes?

Answer 2

• formation of a barrier against environmental damage

Question 3

What are the keratinocyte cells called after they have completed differentiation?

Answer 3

Corneocytes

Question 4

What are the keratinocyte differentiation stages regulated by?

Answer 4

Ca

Question 5

Where do epidermal stem cells reside?

Answer 5

In the lower part of the epidermis (stratum basale) and are attached to the basement membrane through hemodesmosomes

Question 6

What are dendritic cels?

Answer 6

Antigen-presenting cells

Question 7

What is the main function of a dendritic cell?

Answer 7

To process antigen material and present it on the cell surface to the T cells
- act as messengers between innate and adaptive immune system

Question 8

What is tissue homeostasis?

Answer 8

Maintenance of normal tissue morphology and function under physiological or pathological conditions

Question 9

Regulation of which processes contributes to tissue homeostasis?

Answer 9

• balance of cell proliferation, differentiation and death

Question 10

What are the 2 key tasks of a cell cycle?

Answer 10

1. DNA Duplication

2. Accurate DNA segregation

Question 11

What are the 4 phases of the eukaryotic cell cycle and what happens in each stage?

Answer 11

G1/0:
G0- cell cycle arrest/ exit
G1 - growth and preparation for DNA synthesis
S:
DNA replication
- duplication of hereditary material and a copy of each chromosome is formed
G2:
Preparation for mitosis
- cell checks that DNA replications is completed
- make microtubules
M:
Mitosis occurs
- cell divides into 2 daughter cells

Question 12

What is the life cycle of the DNA during the cell cycle?

Answer 12

1. DNA replication occurs in the S phase
   - genetic material is duplicated
   - DNA in chromatin form
   - 2 identical sister chromatids are formed, held together by a centromere
2. During Prophase in mitosis, each DNA condenses and supercoils (becomes shorter and thicker)
3. During Anaphase the sister chromatids are pulled apart of separate poles of the cell

Question 13

How is DNA compacted into chromosomes?

Answer 13

1. starts with a short region of DNA double helix
2. Wrap DNA around the addition of histone proteins
3. The combined loop of DNA and protein is called a nucleosome
4. Next the nucleosomes are packaged into a thread, forming chromatin
   - “beads on a string”
5. The chromatin fiber is coiled into a structure called a “solenoid”

Question 14

What are the 5 stages of Mitosis?

Answer 14

Prophase, Prometaphase, Metaphase, Anaphase, Telophase

Question 15

What happens during Prophase?

Answer 15

• sister chromatids pairs disentangle and condense in the nucleus
• duplicated centrosomes move apart
• mitotic spindle assembly

Question 16

What happens during Prometaphase?

Answer 16

• breakdown of the nuclear envelope

- chromosomes attach to spindle microtubules and move

Question 17

What happens during Metaphase?

Answer 17

• chromosomes are aligned at the spindle equator

Question 18

What is the kinetochore?

Answer 18

The protein structure on the chromatids where the spindle fibers attach during cell division to pull sister chromatids apart.

Question 19

What happens during Anaphase?

Answer 19

• sister chromatids synchronously separate

- daughter chromosomes move apart towards the spindle poles

Question 20

What happens during Telophase?

Answer 20

• two sets of daughter chromosomes arrive at the spindle poles and decondense
• new nuclear envelopes assembly
• contraction of the contractile ring

Question 21

What happens at the end of mitosis?

Answer 21

• contractile cytokinesis
• completed nuclear envelope surrounds decondensing ring
• contractile ring creating cleavage furrow

Question 22

How can you study cell-cycle progression?

Answer 22

• look at cell morphology/ appearance
• DNA labelling (e.g. DNA-binding dyes)
• Antibodies recognising microtubules
• Incorporate artificial thymidine analog BrdU is incorporated into newly synthesised DNA
• analysis of DNA content with a flow cytometer (FACS)