D2.1 Cell and nuclear division HL

Question 1

mitotic index

Answer 1

Mitotic index = number of cells in mitosis / total number of cells

in mitosis = in PMAT

Question 2

what happens during interphase G1 phase

Answer 2

G1 phase (first gap phase): the cell grows physically and increases the volume of both protein and organelles , lasts around 11 hours

Question 3

what happens during interphase S phase

Answer 3

S phase: the cell copies its DNA to produce two sister chromatids and replicates its nucleosomes, centrioles + centrosomes, which help to separate DNA during M phase, last around 8 hours

Question 4

what happens during interphase G2 phase

Answer 4

G2 phase (second gap phase): further cell growth and organisation of cellular contents, replenish energy stores and proteins are synthesized for chromosome manipulation, lasts around 4 hours

Question 5

Checkpoints for interphase

Answer 5

Checkpoints: G1 - Decide to divide, checks for cell size, nutrients, DNA damage (else to G0)

G2 - checks for DNA damage and replication completeness (allow for repairs/apoptosis)

Question 6

cells spend most time in what phase during cell division

Answer 6

Cells spend most of their “lives” in interphase (90-96%) (24 hrs for human)

Question 7

what are cyclins

Answer 7

family of regulatory proteins that control the progression of the cell cycle (just like checkpoints)

Question 8

how do cyclins control the cell cycle

Answer 8

Each different cyclin reaches a certain concentration (threshold level) → trigger next stage of cell cycle (another cyclin)

Question 9

Mechanism of Cyclin Action

Answer 9

1) Activate enzymes (cyclin dependent kinases) → bind phosphate to other proteins (complex phosphorylates), (diff type of cyclin binds phosphate to diff protein) → trigger specific event

2) At the same time, When it reaches the threshold level, CDK releases phosphate → cyclin breaks down → CDK inactive
Ensures key processes (DNA replication/protein synthesis) to occur at correct time

Question 10

what is the hayflick limit?

Answer 10

Defines the number of possible cell divisions and depends on the length of chromosomal telomeres

~40-60 divisions for a typical human cell

Question 11

telomere

Answer 11

• Regions of repetitive DNA located at each end of a chromatid whose function is to prevent chromosomal deterioration
• Extreme ends of telomeres cannot be copied during DNA replication, so they get marginally shorter
• One of the explanation for cellular ageing and hayflick limit

Question 12

what turns normal cells into tumor cells?

Answer 12

Gene mutations caused by:
- Inheritance
random changes during - transcription,
- Mutagens (chemical that causes mutation) / carcinogen (causes cancer)
- X rays, gamma rays, alpha particles, beta particles and neutrons can cause changes in genes

Question 13

Proto-oncogenes

Answer 13

genes that cause normal division
Become oncogenes after mutation, causing rapid uncontrolled division

Question 13

Tumor-suppressor genes

Answer 13

genes that inhibit division

If mutated, nothing to control cell division

Question 14

Benign

Answer 14

tumors which do not spread, non cancerous, high chance of removal through surgery

Question 15

Malignant

Answer 15

will spread (no well-defined border), cancerous

Question 16

Metastasis

Answer 16

process which malignant tumours spread to other parts of the body through the bloodstream or lymphatic system

Question 17

primary tumor

Answer 17

where the cancer first starts, tumor first began to grow

Question 18

secondary tumor

Answer 18

tumors forming in other parts of the body when the cancer has spread through metastasis, often difficult to eliminate completely as they can spread and are hard to locate

Question 19

to diagnose cancer

Answer 19

Symptoms such as pain or nausea arise, CT or MRI scans to determine whether there are physical tumors

Biopsy is conducted to determine whether tumor is benign or malignant - sample of abnormal tissue removed, then examined under microscope

Question 20

types of biopsy

Answer 20

Open biopsy: a cut is made to extract part of the tumor surgically

Needle biopsy: part of the tumor is suctioned out using a needle, less invasive

Question 21

How are abnormal cells stopped by the body naturally?

Answer 21

1) Apoptosis (programmed cell death, occurs when a cell’s DNA is damaged beyond repair – ensures that it will not pass on the damaged DNA)

2) Lymphocytes in the immune system (cytotoxic T-cells, helper T-cells, B-cells)

Cytotoxic T-cells: kill cells infected with viruses and bacteria, and they also destroy tumor cells

Helper T-cells: send signals that tell other cells in your immune system how to coordinate an attack against invaders

B-cells are a type of white blood cell that makes infection-fighting proteins called antibodies

Question 22

process of apoptosis

Answer 22

Shrink and develop bubble-like protrusions (blebs) on their surface

The DNA in the nucleus gets chopped up into small pieces, and some organelles of the cell break down into fragments

Entire cell splits up into small chunks, each neatly enclosed in a package of membrane
Release signals that attract debris-eating (phagocytic) immune cells (e.g. macrophages)

The fragments of the dying cell display a lipid molecule called phosphatidylserine on their surface → lets the phagocytes bind and “engulf” the cell fragments

Intrinsic (when injury occurs within the cell) and extrinsic (when conditions in extracellular environment determine that a cell must die) pathways of apoptosis

Question 23

how is cancer stopped by conventional cancer treatment?

Answer 23

Surgery may be required to remove the mass of cancerous cells (tumour):
- Healthy tissue near the tumour will also be removed
- Lymph nodes in surrounding areas may also be removed and tested to see if they contain cancer cells, to prevent the spread of cancer cells to other parts of the body

Chemotherapy with radiation therapy:

Use of drugs and chemicals to kill rapidly proliferating cells

High intensity radioactive beams directed at cancer cells

Some may only require a one time treatment, while others may need therapy regularly

Immunotherapy - immune system activation:

Stimulate cytokines and inflammatory mediators→ encourage cancer cell destruction

Question 24

HeLa cells

Answer 24

HeLa cells: a line of human cells that were derived from the cervical cancer cells from a carcinoma biopsy performed on Henrietta Lacks in 1951

first human cells to be successfully cultured in a laboratory

Question 25

Importance of HeLa cells

Answer 25

can divide indefinitely, making an ideal model for studying human biology and diseases

instrumental in numerous scientific breakthroughs, including the development of vaccines, understanding the mechanisms of cancer, and testing the effects of drugs and toxins

contributed to advancements in genetics (utilized in studies on genetic disorders and have contributed to advancements in the field of genetics. provided insights into the structure and function of genes, gene expression patterns, and the effects of mutations), virology (poliovirus, HIV, and HPV), and cell biology, helping researchers gain insights into various aspects of human health and disease

used by scientists to develop a cancer research method that tests whether a cell line is cancerous or not