Cell Division Flashcards
Unit 1, Cell Biology
Importance of cell production
New cells need to be produced for growth, maintenance and reproduction
What is zygote
Zygote is the original mother cell in a human that through division leads to the trillion of other cells in a human
Define Mitosis
Nuclear cell division that produces identical cells.
Daughter cells have the same amount of chromosomes and genes as their mother
Define Meiosis
Nuclear cell division that produces genetically unique cells.
Daughter cells have half amount of chromosomes than their mother. Genetic diversity allowing evolution.
What is the first step of eukaryotes cell division
They must first divide their nucleus to avoid creating new cells that are lacking a nucleus
Define cell proliferation
It is a rapid increase in the number of cells (cell division is faster than cell death)
Importance of cell proliferation
in multicellular organisms it is needed for growth, cell replacement and tissue repair
Example of growth
In animals, proliferation occurs at a high rate during embryonic phases of growth and continues in juvenile phases
In plants, it is confined to growth regions called meristems
Cell replacement example
Skin epidermis cells are replaced throughout a humans life, continuous division below the skin’s surface gradually pushes older cells to the surface.
Example of tissue repair
It occrs in undifferentiated stem cells are present such as in the skin, repair can happen in a matter of days
Define cell cycle
It is the series of events that occur during the life of a cell. Cells proliferate in the mitosis phase of the cell cycle.
Different phases of mitosis
Prophase, metaphase, anaphase and telophase
What is mitotic phase
Process of mitosis (nuclear division) followed by cytokinesis (divides the cytoplasm and its contents)
What is Interphase
Time between one mitosis and the next
Interphase = G1+S+G2
What is a G1 phase?
Phase afer mitosis and before DNA replication, active growth, each chromosome is a single DNA molecule (unduplicated)
What is a S phase?
All DNA in the nucleus is replicated or copied resulting in identical pairs of DNA
What is a G2 phase?
More growth and preparation for division, DNA still duplicated
What happens to chromosomes after S phase
After S phase, there will be pairs of idential molecules (chromosomes) due to the repliction of DNA
What is a cohesin?
Cohesin complex holds the chromatids together until anaphase of mitosis
What is centromere?
A constricted region of a chromosome where cohesin loops join the chromatids
What happens to chromosomes during mitosis
Chromosomes are in a condensed and organized form
What is chromosomes made up of?
Chromosomes are made up of DNA wrapped around proteins called histones
Define Cyclins
They are a group of proteins that help progress the cell through the cell cycle
Function of each cyclins
Cyclin activates a different group of proteins, and the group of proteins is specific to the desired actions of that point in the cell cycle.
Metaphase Checkpoint?
Chromosome spindle attachment
G1 Checkpoint?
- Nutrients
- Growth factors
- DNA damage
G2 Checkpoint?
- Cell size
- DNA replication
What do chromosomes need ot be condensed?
During mitosis they need to be moved and condensing them prevents them from getting tangled or broken
Processs of condensing of the DNA?
Condensing begins by DNA wrapping around histone proteins forming nucleosomes and linking them together
Define Kinetechore
They attach chromosomes to the spindle in order to move the chromosomes during mitosis
What are chromosomes moved by?
Chromosomes are moved by microtubles (made of protein tubulin) that assemble and reassemble quickly
What happens to DNA during interphase?
DNA during interphase is decondensed and dispersed in the nucleus in a form called chromatin, which directs many cell activities.
What happens during interphase?
Volume of cytoplasm increases so many organelles must be chemically produced
Metabolic reactions are occuring
Many proteins and molecules needed for growth are being made
Define heterochromatin
DNA that lacks genes necessary for cell activities, during interphase it remains condensed
What are different phases of mitosis?
Prophase, Metaphase, Anaphase and Telophase
What happens during prophase
It is the beginning of the phase, chromosomes condense (becomes visible in microscopes)
What happens during metaphase?
Chromosomes align at the center (equator or metaphase plate)
What happens during anaphase?
Duplicated chromosomes are split, chromatids pulled to each pole
What happens during Telophase?
Chromosomes reach poles, decondense and spread out
Fomula to find Mitotic index
Mitotic index= number of cells dividing/Total number of cells
Define cytokinesis
Cytokinesis is a division of the cytoplasm and all its contents (organelles etc.) between the two daughter cells.
Quick Note
Mitosis + Cytokinesis = Cell Division
Is it okay for cytokinesis division to be unequal?
Some organelles can only be produced from pre-existing organelles and the daughter cells will survive if they have at least a nucleus and one of such organelles
What happens to animal cells during cytokinesis?
A ring of contractile protein immediately inside the plasma membrane at the equator pulls the plasma membrane inward.
The inward pull on the plasma membrane produces the characterstic cleavage furrow (The seperating line)
When the cleavage furrow reaches the centre of the cells it is pinched apart to form two daughter cells.
What happens to plant cells during cytokinesis
During telophase, membrane-enclosed vesicles derived from the Golgi apparatus migrate to the centre of the cell.
The tubular structures merge to form two layers of plasma membrane, cell plate
The cell plate continues to develop until it connects with the existing cell’s plasma membrane.
Two daughter cells are formed
Vesicles deposit, by exocytosis, pectins and other substances in the lumen between the daughter cells to form the middle lamella
Both daughter cell secrete cellulose to form their new adjoining cell walls.
Example of unequal cytokinesis?
Yeast, they reproduce asexually, called budding and an outgrowth of the mother cell receives a nuclei but only small amounts of cytoplasm. A wall forms separating them, small outgrowth splits them.
Define Mutagen
A substance that increases the chances of tumor formation
Effects of Mutation
Mutation to genes in a cell can cause the loss of control over cell division (can be passed on)
It can result in cells increasing exponentially forming tumors
Two main types of mutagens?
- Chemicals, labelled as carcinogenic
- High energy radiation (xrays, uv rays)
What are two main groups of genes that can change a normal cell into a tumor?
- Proto-oncogene
- Tumor suppressor genes
What are proto-oncogene genes?
They are genes that regulate expression (turning genes on/off) of genes involved with cell proliferation, pathways involved in cell cycle control, or growth factors.
How can proto-oncogene cause cancer?
Proto-oncogenes can mutate into a oncogenes, meaning the mutations (cahnges to the gene) make it activate when it is not supposed to, causing cancer
What is tumor suppressor genes?
They are genes that prevent cell proliferation (putting a break at the cell cycle checkpoints), correct errors in DNA replication, have roles in apoposis (programmed cell deaths)
How can mutations to tumor suppressor genes cause cancer?
It can make the tumor suppressor genes not function properly and increase risk of tumor formation. Often many mutations are required before forming of tumors.
Define primary tumor
The cells that divide to form a tumor at the original location it was formed (the cells often stick to each other forming a single mass)
Characteristics of primary tumor
They are unlikely to cause harm
Not yet considered cancerous
Define secondary tumor
When cells detach from a primary tumor and invade neighboring tissue or move to other tissue locations throught he blood/lymph
Characteristics of secondary tumor
The cells will continue to divide and form more tumor
Define malignant tumor
Tumors that spread to form secondary tumors
Define apoptosis
Self distrupting of damaged cells to ensure that irreparable cells will not divide
