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Summary Bsc 1010 Unit 3 Study Guide
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This is a comprehensive and detailed study guide on unit 3 for BSC 1010. *Essential Study Material!!
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BIO PRINCIPLES UNIT 3I. Core Concepts
A. Cells must reproduce either to perpetuate the species or create a multi-
celled individual.
B. Cell reproduction involves mitosis (duplication and division of the nucleus) and
cytokinesis (division of the rest of the cell).
C. Cells produced in this fashion are identical (clones).
D. But evolution by natural selection requires variation in the offspring.
The diversity of life is a result of this variation.
E. Meiosis is a form of cell reproduction involved in organisms that
reproduce sexually.
F. Along with random mutations that can occur, meiosis scrambles the genetic
information from both of the parents and reduces the chromosome number by ½
to produce eggs and sperm.
G. At fertilization, the full complement of paired chromosomes is restored.
H. Once fertilized, a zygote frequently shows evolutionary links to other closely
related groups as development occurs (e.g., tail in humans is relatively long
embryonically compared to the rest of the body: i.e., ontogeny
recapitulates phylogeny).
II. Mitosis
A. Cell reproduction
a. Mitosis not synonymous with cell division; cytokinesis doesn’t always
occur after mitosis; division of nuclear material
b. Cytokinesis can occur without mitosis; cell division; division of
remaining cellular contents of the ctoplasm
c. A normal cell has 46 chromosomes
i. Ploidy tells us what kind of chromosomes are present
1. Haploid (n) = 23 1 set
2. Diploid (2n) = 46 2 sets
B. Cell Cycle
a. Interphase between mitosis; chromosomes referred to as chromatin (a
diffuse, loosely scattered arrangement of chromosomes)
i. G1 most active part of the cell (where life occurs); active
growth and metabolism
ii. S duplication and synthesis of DNA
iii. G2 synthesis of molecules in preparation for cell division
b. Mitosis/Meiosis both cycles are between interphase; mitosis is cell
replication and meiosis is for cell reproduction
c. Mitosis and cytokinesis mitotic chromosomes in mitosis-cytokinesis
stage are highly condensed and coiled and thus distinct
C. DNA Replication
a. DNA “unzips” old DNA unzips in the middle to form two strands, and
those two strands create a new “zipper” in order to complete their base
pairing
b. Base pairing
, i. A => T
ii. C => G
D. Eukaryotic Chromosomes
a. Histones protein; core
i. H1 clamps DNA to the core
ii. Two loops = DNA
iii. Nucleosome unit of DNA, Histone and H1
1. What DNA usually looks like
iv. Uncoiled is messy, but when its coiled it forms the shape of a
chromosome
b. Non-Histones nonprotein
c. Chromosomes
i. Unduplicated monad
ii. Duplicated dyad
1. Chromatids monad; 2 chromatids form a dyad
2. Centromere place where the two dyads meet
3. Monad (C) = Chromatid = DNA strand = chromosome
4. Dyad (X) = Sister chromatids = chromosomes
d. Chromosome pairs – Homologues
i. Karyotyping the way you determine the number of the
chromosome; the link and position of the centromere will tell you
which chromosome it is
E. Mitosis Events
a. Interphase
i. Tubulin (protein that separates dyads and forms microtubules)
Microtubules (form spindle and asters) Spindle & Asters
ii. The daughter cells formed are genetically (and usually physically)
identical to the parent cell except for size
iii. Chromatin
iv. Leave this phase once nuclear membrane is gone and
chromosomes appear
b. Stages
i. PROPHASE chromosomes condense and organize; nuclear
membrane and nucleoli disappear; spindle apparatus is assembled
and attaches to centromeres of duplicated chromosomes
ii. METAPHASE spindles line up duplicated chromosomes along
equator of cell, one spindle to each half, or chromatid, of
duplicated chromosome
iii. ANAPHASE centromere of each duplicated chromosome is
separated and paired chromatids are pulled apart
iv. TELOPHASE chromosomes uncoil, nucleoli reappear,
cytokinesis occurs, and two genetically identical daughter cells are
produced
F. How the Spindle Works
a. Sliding filament hypothesis
, i. Continuous (polar) spindle fibers spindles that don’t attach to
chromosomes (don’t catch any fish); spindle elongates,
chromosomes pulled apart; poles pushed apart
b. Subunit disassembly hypothesis
i. Centromeric (kinetochore) spindle fibers kinetochore
microtubules shorten; chromosomes pulled to poles (catch fish)
c. Microtubule organizing center
G. Cytokinesis
a. Animal
i. Cleavage Furrow microfilaments form ring around equator of
spindle; microfilament ring contracts, pinching in “waist” of cell;
waist completely pinches off, forming two daughter cells
b. Plant cannot pinch in because of cell wall
i. Cell Plate separates from the inside out; vesicles forming cell
plate; vesicles fusing to form new cell wall and plasma membranes
between daughter cells; complete separation of daughter cells
ii. Golgi bodies
1. Pectin creates cell plate
H. Mitosis & Multicellularity zygote divides via mitosis (trillions of cells because
many divisions)
a. Start as blob
b. Cells know where they are
c. Circle hand, cells in between fingers die
d. Different species same genes, different programming
e. All start out as fertilized egg
f. Information all passes through “S” phase (duplication of DNA)
g. Multicellularity almost always occurs through mitotic divisions
I. Bacterial Mitosis
a. Bacteria have more divisions than humans they are good and fast at this
b. Called “Binary Fission,” cannot be called division of mitosis because they
have no nuclei
c. Most common process of division on the planet
III. Meiosis the process by which the chromosome number is reduced by half,
resulting in new genetic combinations in the gametes
A. Sexual Processes
a. Sexual reproduction involves the fusion of genetic material (gametes)
from two parental organisms
b. To ensure the proper chromosomal numbers in the zygote (fertilized egg),
each gamete must have haploid, or half (N, or one set of chromosomes), of
the original diploid (2N, or two sets of chromosomes) amount of DNA
B. Versus Mitosis
a. Meiosis requires two divisions
b. Meiosis reduces chromosome # (Meiosis I)
c. Meiosis results in new genetic varieties (Meiosis I) infinite
combinations
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