D2.1 Cell and nuclear division HL Flashcards
mitotic index
Mitotic index = number of cells in mitosis / total number of cells
in mitosis = in PMAT
what happens during interphase G1 phase
G1 phase (first gap phase): the cell grows physically and increases the volume of both protein and organelles , lasts around 11 hours
what happens during interphase S phase
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
what happens during interphase G2 phase
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
Checkpoints for interphase
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)
cells spend most time in what phase during cell division
Cells spend most of their “lives” in interphase (90-96%) (24 hrs for human)
what are cyclins
family of regulatory proteins that control the progression of the cell cycle (just like checkpoints)
how do cyclins control the cell cycle
Each different cyclin reaches a certain concentration (threshold level) → trigger next stage of cell cycle (another cyclin)
Mechanism of Cyclin Action
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
what is the hayflick limit?
Defines the number of possible cell divisions and depends on the length of chromosomal telomeres
~40-60 divisions for a typical human cell
telomere
- 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
what turns normal cells into tumor cells?
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
Proto-oncogenes
genes that cause normal division
Become oncogenes after mutation, causing rapid uncontrolled division
Tumor-suppressor genes
genes that inhibit division
If mutated, nothing to control cell division
Benign
tumors which do not spread, non cancerous, high chance of removal through surgery
Malignant
will spread (no well-defined border), cancerous
Metastasis
process which malignant tumours spread to other parts of the body through the bloodstream or lymphatic system
primary tumor
where the cancer first starts, tumor first began to grow
secondary tumor
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
to diagnose cancer
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
types of biopsy
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
How are abnormal cells stopped by the body naturally?
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
process of apoptosis
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
how is cancer stopped by conventional cancer treatment?
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
