Cell Division Flashcards
What is prokaryotic cell divison called?
Binary fission
Where does binary fission start?
The origin of the cell
What happens in binary fission?
The chromosomes are duplicated and the two DNA molecules are pulled to separate poles, as it increases in size. A new cell wall and plasma membrane form and pinches inwards, which divides the cell into two daughter cells
What are the purposes of cell division?
Restoring the nucleus-cytoplasm ratio, asexual reproduction, maintenance and repair, growth and development, development from a fertilised cell
What is cell replication in eukaryotes?
Mitosis then cytokinesis
What are chromosomes?
Packaging for DNA that carries all genetic information
What is the order of the cell cycle?
Interphase (G1, S, G2). Mitosis. cytokinesis. again.
At what stage does the cell arrest?
Potentially G0
What is mitosis?
The process in which the nucleus of a cell divides to create two new nuclei, each with identical copies of DNA
What is interphase?
The phase where chromosomes are duplicated and cell growth occurs.
What happens in G1?
Cell growth
What happens in S Phase?
DNA synthesis. Each chromosome makes an exact copy of itself, becoming double stranded. each strand is called a chromatid
What happens in G2?
Post-DNA synthesis. Cell increases in size and accumulates materials for mitosis
Features of interphase?
Nucleus is well defined, chromosomes not visible.
What is the longest phase of the cell cycle?
Interphase (12-24 hours in mammalian animals)
What is the first phase of mitosis?
Prophase
What happens in Prophase?
Chromosomes shorten and thicken. The chromosomes are held together by centromere. Centrioles move apart, with the microtubules of the mitoic spindle continues to extend from the centrioles
What is the second phase of mitosis?
Metaphase
What happens in metaphase?
The mitoic spindle is fully formed between the two pairs of centrioles at the two poles of the spindle. The double stranded chromsomes (two chromatids) lines up at the equator
What is the third phase of mitosis?
Anaphase
What happens in anaphase?
Each centrosome divides so that the chromatids move to the opposite sides of the cell as tubules shorten.
What is the fourth phase of mitosis?
Telophase
What is telophase?
The chromosomes become thinner and less obvious. A nuclear membrane forms around each group of chromosomes
What is cytokinesis?
The division of the cytoplasm which occurs towards the end of mitosis
What happens in cytokinesis in animal cells?
The plasma membrane moves in and pinches the daughter cells to form.
What happens in cytokinesis in plant cells?
The plant cells lay down a new cell membrane and wall
Where do the three checkpoints occur?
G1 (halfway), G2 (end), M (mitosis)
What checkpoint is at G1?
Cell growth. Checks if the cell was healthy and the cell has gone to a suitable size, S phase is intiated. if DNA is not favourable, it stops at G0 and it tries to grow again. Apoptosis can occur if it is damaged beyond repair
What is the G2 checkpoint?
DNA synthesis checkpoint, after DNA replication. DNA repair enzymes are triggered to check the results of DNA replication for errors. If this checkpoint is passed, proteins signal the cell
to begin mitosis
What happens at the mitosis checkpoint?
Checks to see if mitosis has been completed correctly. If it passes this, the protein signals trigger the cell to leave mitosis and enter G1
What is apoptosis?
Genetically programmed death that is controlled by particular cell signals from the inside/outside of the cell
Purposes of apoptosis
Maintenance of adult cell numbers
Defense against damaged or dangerous cells
The sculpting of embryonic tissue during development (e.g. formation of fingers)
What are some examples of apoptosis?
Sloughing of endometrium during menstruation
Sculpting fingers
Formation of synpases in brain
What happens during apoptosis?
Cell death occurs when the cell membrane shrinks, DNA fragments and lysosomes empty their contents in the cell. This causes the cellular fragments to be broken down. The nucleus condenses. The cell blebs and turns into vesicles, without spilling the contents out of the cell. Phagocytes then consume the dead cell
What is an apoptotic body?
Sealed sacs containing functional organelles and other features of dying cells
What can too much apoptosis lead to?
Degenerative conditons (e.g. Alzeimher’s, Huntingtons, Parkinsons’)
What can too little apoptosis lead to?
Cancer, webbed feet
What is necrosis?
Premature cell death, uncontrolled
What causes necrosis?
External factors e.g. trauma, infection, toxins
What is the process of necrosis?
Small blebs form and the structure of the nucleus changes. Blebs fuse and become larger; no organelles are located in the blebs. The cell ruptures
Why can necrosis be bad?
It can lead to the spilling of the cells contents to surrounding cells, potentially lethal
What lets cancer cells grow?
Not being killed by apoptosis when they should
What are the mutated genes often present in cancer?
Proto-oncogenes (genes involved in the regulated of cell dvision)
tumour suppressor genes (genes involved in the slowing of cell divison, DNA repair and apoptosis)
What are mutagens?
Agents that alter the DNA molecule
What can mutagens lead to?
formation of developmental abnormalities/cancers
What are some mutagens?
Nitrate and nitrate preservatives
UV rays
X Rays
What is a stem cell?
A cell that is undifferentiated and can turn into many different types of cells. found in multicellular organisms
What is a zygote?
Diploid cell formed when a sperm fuses with an egg
How does a zygote become an embryo?
Divides many times by mitosis
What is an embryo?
First cells up until the first eight weeks of fertilisation
What are the cells up until there are eight?
Identical
What are identical stem cells called?
Embryonic stem cells
What happens to an embryonic stem cell when it is specialised?
Can’t become any other type of cell
What are the two things stem cells can do?
Self renew: make copies of themselves
Differentiate: make other specialised cells of the body
Can specialised cells make copies of themselves?
No, they need a stem cell to replace them
Why are stem cells important?
Specialised cells need copies made of them when they die/damaged/used up
What is a stem cell?
Undifferentiated cells of a multicellular organism
What is the ratio of stem cells to differentiated cells when created?
1 Stem Cell: 4 Differentiated Cell
What are embryonic stem cells?
Embryonic stem (ES) cells include those found within the embryo, the foetus or the umbilical cord blood. Depending upon when they are harvested, ES cells can give rise to just about any cell in the human body.
What are tissue stem cells?
Undifferentiated cells inside already developed tissue (e.g. brain, heart, kidney). Adult (__tissue___) stem cells can be found in infants, children and adults. They usually give rise to cells within their resident organs.
What are IPSC?
Induced pluripotent stem cells (IPSC) are adult, differentiated cells that have been experimentally “reprogrammed” into a stem cell-like.
What does potency mean?
A measure of how many different types of cells a stem cell can make
What does totipotent mean?
can differentiate into all types of specialized cells in the body PLUS cells that are needed during development of the embryo only: placenta, yolk sac, umbilical cord.
Where are totipotent cells found?
Zygote/embroynic stem cells within the first 8 cell divisons
What does pluripotent mean?
Can make all types of specialized cells in the body
What does multipotent mean?
can make multiple types of specialized cells, but not all types. Tissue stem cells are multipotent
Can make the cells on their layer
What does unipotent mean?
a stem cell that can make one type of specialised cell (e.g. spermatogonial)
How long is an embryo considered to be an embryo?
Until the first eight week of life
What is a foetus?
A growing baby, 8 weeks and onwards
What are the three germ layers of multipotency?
Ectoderm (outer), mesoderm (middle), endoderm (inner)
what is a blastocyst?
a clusture of dividing cells made by a fertilised cell
What does the ectoderm give rise to?
brain cells, hair cells, nerve cells
what does the mesoderm give rise to?
muscle cells, red blood cells, kidney cells
What does the endoderm give rise to?
lung cells, liver cells, stomach cells, pancreatic cells
Where are embryonic stem cells taken from?
Blastocyst (inner cell mass. outer cell mass becomes placenta, skin, etc). then they are grown in a fluid with nutrients in a lab
Where can stem cells be found?
Brain, breast, intestines, bone marrow, muscles, testicles, skin, surface of the eye
What do they do to adult stem cells to make them into IPSC?
genetic reprogramming: add a gene. behaves like an embryonic stem cell
What is a gastrula?
An embryo at a stage with three distinct layers
Where are multipotent cells found?
Gastrula, adult stem cells
Where are unipotent cells found?
Somatic cells
Why are iPSC exciting?
Promises a future where researchers may one day be able to treat diseases like Parkinson’s
How are iPSC currently being generated?
Isolate cells from a patient (skin or blood), treat the cell with reprogramming genes, wait a few weeks, turn the now pluripotent stem cells into certain cells by changing culture conditions
What is therapeutic cloning?
Method for creating patient-specific embryonic stem cells.
How is therapeutic cloning achieved?
Isolate cells from patient, remove a nucleus from an egg cell, transfer nucleus from a patient’s cell to an egg. Egg cell ‘reprograms’ the patient’s DNA, cell begins dividing. Isolate the inner cell mass from the blastocyst and grow it in a dish
What are the ethical considerations for stem cells?
Unless recently, the only way to get stem cells was from removing the cell mass of an embryo.
This could be seen as killing a human life.
Questions raised about ethics of stem cells
When does life begin?
Is killing one embryo worth it
