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Bio 190 Exam #3
Topics:
1
...
Mitosis ✔
3
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Animal Reproduction
5
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Reproduction in spore-producing plants

Multicellularity
● Simple multicellularity
○ Rare among prokaryotes
○ Adhesion, but little communication
○ Minimal differentiation- most cells have full range of function, including
reproduction
○ Every cell contacts the outside environment
● Circumventing limits of diffusion
○ Ability to change shape
○ A transport system
● Complex multicellularity
○ Highly developed mechanisms for adhesion between cells
○ Specialized structures for cell communication
○ Cell and tissue differentiation
-genetic program to guide growth and development
-only some cells are reproductive
-cell/ tissue loss can be lethal
○ Presence of exterior and interior cells
● Adhesion molecules
○ Animal cells
-Cadherins: cell-to-cell, confer cell recognition
-Integrins: cell-to-extracellular matrix protein
○ Plant cells
-outer layer of cell wall has glue-like complex carbs (pectin)

Cellular Differentiation
● Differential gene expression (transcription/ translation)
○ Initially based on environmental gradients between exterior and interior cells
○ Concentration gradients of intercellular signals
● Tissue: collection of cells working together for a specific function
● Bulk transport: movement of molecules by active circulation of fluids
○ Circulatory system in animals (movement of O2 throughout body from lungs,
expulsion of CO2)
○ Vascular system in plants (transport water and nutrients from soil to leaves for
photosynthesis, move sugars from leaves to other parts of the plant)
● In order of evolution: adhesion → signaling → differentiation → bulk transport

Benefits of multicellularity
● Reduced predation
● Ability to occupy space
● Consume larger prey/ feeding efficiency
● Efficiency through specialization

Costs of multicellularity
● Energy costs (transport)
● Infections spread more easily
● Loss of some cells can be lethal to all
● “Cheating” i
...
cancer cells (use resources without benefit to whole organism)

Mitosis
● Traits (obtained through mutation) that make cells cancerous
○ Breakdown of the regulation of cell division
○ Ability to gain increased access to the organism’s resources
○ Ability to invade other tissues and migrate through the body
● Many cells in your body reproduce
● Cells in your body can evolve during your lifespan
● Cancerous traits allow cells to create more offspring, so cancer spreads
★ If cells in the body can individually evolve, they can become cancerous
Steps for a cell copying itself:
1) Replicate DNA
2) Movement of the 2 copies of the genome into opposite sides of the cell
3) Division of the cell into 2 parts

Binary fission
1
...
DNA replication- begins at 1 site and proceeds
in both directions
3
...
Cell elongates, separating the DNA attachment
sites
5
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Prophase- chromosomes condense
2
...
Metaphase- chromosomes line up in center of the cell
4
...
Telophase- nuclear envelopes form

Step

In Archea and Bacteria

In Eukarya Undergoing
Mitosis

DNA Replication

- begins at one site and
proceeds in both directions
- not necessarily attached

- S phase- begins at many
sites simultaneously
- sister chromatids
(chromosomes attached)

Movement of 2 copies of
genome to opposite sides of
the cell

- cell elongates, separating
the 2 attachment sites

- Anaphase- microtubules
pull sister chromatids to
opposite sides of the cell

Cell division

- membrane pinches inward
and new cell membranes and
cell walls are synthesized

-Telophase- nuclear
envelopes form

● Prokaryote cells typically reproduce faster than eukaryote cells
○ Human cells: 12-24 hrs
○ Yeasts: 90 mins
○ Embryo early cell divisions: 30 mins
○ Bacteria: 15-60 mins
★ Faster when there is no growth

● Cell-to-cell communication: healthy cells enter S phase only in response to external
signals (mitogens)
● Proto-oncogenes: promote passage through particular points in cell cycle
● Tumor-suppressor: genes that inhibit cell division
● For a cell to proceed to the next step in the cell cycle:
○ Proto-oncogenes turned ON
○ Tumor suppressors turned OFF
● Oncogene
○ Mutated proto-oncogene that is turned on too easily/ is on all the time
○ Typically will not be enough to cause cancer
○ Cancer usually requires multiple regulatory genes to fail

Meiosis
● Mutations are caused by
○ Mistakes in DNA replications
○ Damage that is not repaired correctly
○ Create new alleles of genes
● Recombination = generating new combinations of alleles
● Mutations can
○ Destroy or alter the functions of enzymes or proteins
○ Alter expression of genes
● Most mutations are not beneficial, but some are under the right circumstances

● Advantages of recombination- can get rid of damaging alleles
● Disadvantages of recombination
-requires 2 organisms
-can alter an already ideal combination
● Recombination in Bacteria = Horizontal Gene Transfer
1) Transformation
2) Transduction
3) Conjugation
★ Not related to reproduction

● 1N = 23 chromosomes, 2N = 46 chromosomes

● In meiotic division, chromosomes are duplicated to form pairs of sister chromatids, just
like in mitosis
● Meiosis 1: homologous pairs of chromosomes exchange genes and then are separated
● Meiosis 2: sister chromatids are separated, just like in mitosis

● Meiotic Cell Division
○ Results in 4 daughter cells
○ Each daughter cell has half the number of chromosomes
○ Each daughter cell is genetically unique
● Chromosomes are duplicated to form pairs of sister chromatids, just like in mitosis
● Meiosis I
○ Homologous pairs of chromosomes exchange genes
○ Homologous chromosomes are separated
● Meiosis II
○ Sister chromatids are separated, just like in mitosis
Humans have _____ pairs of chromosomes
...
At the end of meiosis II, each
daughter cell will have ____ copy/ies of _____ chromosomes

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