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BIOL 115 Study Guide - Midterm Guide: Tumor Suppressor Gene, Embryonic Stem Cell, Adult Stem Cell

Biology (Sci)
Course Code
BIOL 115
Robert Levine
Study Guide

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Biology Lecture Notes Midterm #2
(Lecture 10)
1. Divide cell contents cytokinesis
2. Faithfully reproduce interphase
3. Divide genetic material (genome) mitosis
Why Cell Division?
For prokaryotes and protists: reproduction
For plants, embryos and young animals: growth
Skin, blood, gut lining: maintenance (cells being replaced constantly in skin)
Immune system: clonal response
Injury: repair (healing cuts, etc)
Damage: regeneration (like skin, some animals regenerate whole limbs)
Prokaryotic chromosome is a single circular chromosome (single naked circle of DNA)
When bacteria replicate...
Replications starts at a certain point on the chromosome, continues around in both directions
Chromosomes actually attached to plasma membrane. Then there’s cell growth, and the two
chromosomes move apart from each other.
Eventually it starts to lay down new plasma membrane in between the two chromosomes, and then it
splits, builds new cell wall.
Cell division in prokaryotes is known as binary fission.
Bigger cells, a lot more DNA to deal with, Important to have accurate replication of genetic material
Chromosome undergoes DNA synthesis, creates two sister chromatids (2 copies identical of
chromosomes) central point where they’re stuck together is the centromere (Kinetochore: a protein
complex that binds the centromere, used to attach chromosomes for movement)

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And then, you have mitosis. Where the chromatids divide, and then you have daughter chromosomes
Each chromosome is a linear DNA molecule with tightly associated proteins
DNA synthesis occurs during interphase
In interphase, normally DNA is in the extended form.
Wrapping up (condensing/packaging DNA so it’s easier to separate/divide)
DNA wrapped around histones (proteins), this is what the DNA is coiled around.
The wrapped DNA+histones is known as the nucleosome
Then the beads on a string thing of DNA and histones coils again, and coils again and again (multiple
layers of coiling), and then it’s looped around scaffolding proteins.
Prior to mitosis is interphase.
During interphase: chromosomes are duplicated but still in extended form.
When we enter prophase (early stage of mitosis), chromosomes go into condensed form, the spindle
grows and develops (made up of microtubules) this is the mechanism for the movement of
chromosomes, they pull apart the chromosomes during mitosis. Centrioles/centrosome is the spindle
organizing center. Specific to animal cells. On either side of the spindles, spindles gathered around
them too, etc.
And then: nuclear membrane disintegrates (as do other endomembranes), and the spindle fibers bind
to the kinetochores.
ATP is involved in the movement of microtubules/spindles.
Next is metaphase: pairs of chromosomes line up, under tension at the spindle equator (also known as
the metaphase plate).
Next is anaphase: sister chromatids separate and migrate to the spindle poles (centrosomes)
Finally there’s telophase: end of mitosis. The nuclear membrane, ER and Golgi reform, chromosomes
After that is cytokinesis. (Cell division proper, not mitosis proper)
Cytokinesis (in animal cells): works a bit like muscles. The cleavage furrow. Actin and myosin. Like
pulling strings, pulls cell apart into two.

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Plant cells don’t do that, they just make a new cell wall.
There are 46 chromosomes in humans (2 x 23 chromosomes)
You have 22 sets of autosomes non-sex chromosomes, and 1 set of sex chromosomes
# of types of chromosomes, so 23 types, this is known as n
Humans are diploid 2 copies. 2n = 46.
Cells spend most of their time in interphase (getting ready for mitosis)
There are different stages of interphase.
1. G1 (Gap1): when cells just grow
2. Synthesis: DNA replication
3. G2: further cell growth
4. Mitosis
5. Cytokinesis, then back to G1
^ All this is tightly regulated, so cells divide only when needed. You don’t want cells dividing when
they’re not supposed to. If they go crazy, that’s cancer.
Oh wait. Cells can also stay in G0 for years. G0 is lack of cell division. It’s like Gap1, but cells don’t
proceed from there. Like nerve cells, blood cells, muscle cells, etc. Don’t really divide after embryo and
Self renewing, give rise to differentiated offspring (have the potential to become anything)
- Categorized by potential to make diff things, tissues, organs, etc.
At the very early embryo you have totipotent stem cells (at first few divisions). They can make all
structures. Anything! Including extraembryonic tissues (placenta, etc)
And then, what we have is a blastocyst, which has:
- Outer cells which make supporting tissue for embryonic development in mammals.
- Inside are pluripotent stem cells which can make everything except extraembryonic tissues.
And then, there are tissue specific stem cells, or multipotent stem cells. They can make multiple cell
types related to a specific tissue type. Sometimes referred to as adult stem cells, because we keep
these in our bone marrow, able to make all sorts of blood related cells, etc etc. Basically we still have
some stem cells as adults, but their ability to make diff things is more limited.
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