Cell Division Flashcards
Cancer is…
Uncontrolled Growth
Cell Division occurs for:
Growth
Cell Replacement
Healing
Reproduction
Binary Fission
How bacteria undergo cell division. Asexual reproduction. Lower likelihood of mutation per one replication than eukaryotic cells.
Binary Fission Process
DNA molecule is attached to the inner membrane.
DNA replication begins bidirectionally around the circle
New strand of DNA is also attached to the inner membrane near the attachment site of the initial plasmid
The entire cell then elongates symmetrically around the midpoint, separating the DNA attachment sites
Cell division begins with the synthesis of new membrane and wall material at the midpoint
Continued synthesis complete the constriction and separates the daughter cells.
Mitosis
Eukaryotic cell division
Interphase
The time between two successive M phases. Lasts 10-14 hours. Cell makes preparations for division.
G1
First “gap” phase in which size and protein content of the cell increase. Many regulatory proteins are made and activated, organelles are replicated
S
Synthesis phase, all DNA in the cell is replicated
G2
Second Gap phase in which the cell prepares for mitosis and cytokinesis
G0
No active preparation for cell division. Present in cell types that don’t actively divide. Liver, nerve, lens of the eye
Checkpoints
Spindle-Assembly Checkpoint: Are all chromosomes attached to the spindle (before Anaphase)
DNA damage checkpoint: (Before S phase)
DNA Replication Checkpoint: (At the end of G2), is all DNA replicated correctly?
Cyclins
Production caused by growth factors that arrived from other cells. Concentration fluctuates depending on the stage of cell cycle.
CDK’s
Cyclin-dependant kinases, bound to by cyclin, the Cyclin-CDK complexes phosphorylate target proteins that promote cell division. CDK is always at some observable level in the cell. CDK can be recycled even when cyclin is degraded.
Tim Hunt
Sea urchin embryos as they replicated, saw that the level of cyclin fluctuated as the embryo goes through mitosis/cell cycle. Cyclin peaks at every mitosis.
G1 Checkpoint
Growth factors arrive from other cells
Increase cyclin and E2F concentrations
Cyclin binds to CDK, and CDK is phosphorylated
Rb inactivates E2F by binding to it
Inactivating phosphate is removed from CDK and active CDK phosphorylates Rb.
Phosphorylated Rb releases E2F
E2F triggers production of S-phase proteins
G1 Checkpoint Significance
Subject to social control
E2F
Transcription Factor
p53
Found in the nucleus. Acts as a transcription factor that turns on genes that inhibit the cell cycle.
DNA damage activates protein kinases that phosphorylate p53. Inhibiting the cell cycle gives time to repair the DNA damage, or cause the cell to undergo apoptosis.
Peyton Raus
Experimented with chicken cancer. Took cancer from one chicken, filtered it, and injected into another chicken and found that the cancer grew. Determined that there are virus caused cancers.
Oncogene
Cancer-causing gene, E2F
Proto-oncogene
Normal genes important in cell division that have the potential to become cancerous if mutated, Cyclin
Tumor Suppressor
Encode proteins whose normal activities inhibit cell division, Rb
Karyotype
Shows an individuals complete set of chromosomes
Autosome
Non-sex related chromosome
Homologous Chromosomes
Paired chromosomes, each comes from one parent in the example of humans, and they have the same length and loci
Loci
Gene position
Sister Chromatids
Identical copies formed of each chromosome during replication, joined together by a centromere
Kinechore
Proteins that reside on either side of the centromere that attach to the mitotic spindle
Diploid
Two chromosomes of each type. Two (one from each parent) of chromosome 1, Two of chromosome 12, 2 of chromosome 19 etc.
Phases of Mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Prophase
Occurs after replication, chromosomes condense, centrosomes radiate microtubules and migrate to opposite poles, nuclear envelope starts to break down.
Chromatin Fibers
Condensed, tightly coiled DNA wrapped around histone proteins that makes up chromosomes
Prometaphase
Microtubules of the mitotic spindle attach to chromosomes, nuclear envelope breaks down
Metaphase
Chromosomes align along the middle of the cell. ‘Metaphase plate’. Spindle fibers coordinate movement.
Anaphase
Sister chromatids separated at kinechores and pulled apart. Poles of the cell move further apart.
Telophase
Spindle fibers disperse, nuclei and nucleoli form, chromosomes arrive at opposite poles.
Cytokinesis
ring of actin filaments called the contractile ring contracts around the equator, dividing the cell in two.
Phases of Meiosis
Prophase 1
Prometaphase 1
Metaphase 1
Anaphase 1
Telophase 1
Prophase 2
Prometaphase 2
Metaphase 2
Anaphase 2
Telophase 2
Prophase 1
Homologous chromosomes condense and pair together, goes through synapsis. Nuclear envelope breaks down
Synapsis
The matching up of homologous chromosomes for possible crossing over to occur.
Bivalent
The pairing of homologous chromosomes is called a bivalent.
Crossing Over
When parts of the chromosome can be switched between two paired homologous chromosomes. Creates two recombinant chromatids and two parent chromatids.
Chiasma
Where crossing over occurs between the homologous chromosomes in the bivalent
Meiosis 2
Steps are repeated, except the sister chromatids are separated, which give one cell the recombinant chromatid and the other the parent chromatid
Meiosis 1
Same steps as mitosis, except homologous chromosomes are separated, giving one cell the copy from one parent and the other cell the copy from the other parent.
Haploid
Only have one of each chromosme
Origins of mitosis and meiosis
Mitosis is present in all eukaryotes. Meiosis is present in most, but not all eukaryotes. Meiosis likely evolved in a common ancestor but was lost in some groups.
Oocyte
Can develop into a functional egg cell, where most of the cytoplasm is retained from meiosis
Polar body
The leftover cytoplasm/cell products from meiosis previously combined with the oocyte
Sperm development
Cytoplasm is eliminated, nucleus remains in the head and a flagellum
Zygote
Formed during fertilization, when a full two sets of chromosomes are restored
Nondisjunction
Failure of a pair of chromosomes to separate during anaphase of cell division. Gametes will have an extra copy or no copy of the chromosome. More common in the first division than the second division
