Download chromosome

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Between cell divisions DNA is not tightly
coiled into chromosomes-called chromatin

Regions uncoil to be read to direct cell’s
activities

Prokaryotes have only 1 chromosome
attached to the inside of the cell membrane,
still compact to fit in cell but in a loop
When a eukaryotic cell
prepares to divide, the
DNA and the proteins
associated with the DNA
coil into a structure called
a chromosome
 Histones-aid in tight packing of DNA
and help maintain the shape of the
chromosome
 Nonhistone proteins are involved in
controlling the activity of specific
regions of the DNA
The 2 exact copies of DNA
that make up each
chromosome are called
chromatids
The 2 chromatids of a
chromosome are attached at
the centromere
The chromatids separate
during cell division and are
placed into each new cell
Each new cell will have the
same genetic information as
the original cell

Each species has a characteristic number of
chromosomes




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Sex chromosomes determine the sex of an
individual –XY
Autosomes are all other chromosomes
Chromosomes come in pairs – one member
from each parent
Chromosome pairs carry genes for the same
traits
Chromosome number (n) tells how many of
each type of chromosome is present in a cell; 2n
is diploid
 Sperm and egg cells are haploid
(1n)-have only ½ the number of
chromosomes of diploid cellswhy?
 Karyotype-a picture of the
condensed chromosomes of an
individual
Cell Division
 Three reasons why cells reproduce
by asexual reproduction:
1. Growth
2. Repair
3. Replacement
You make about 2 trillion new cells per day!
• Mitosis-eukaryotic nuclear divisionleads to the equal distribution of
DNA to 2 new nuclei of daughter
cells
• Prokaryotic cells reproduce
asexually (only 1 parent) by an
entirely different mechanism called
binary fission
G1 (Growth 1) –cell carries out
routine functions
S (Synthesis) - DNA copied, each
chromosome is 2 chromatids
attached at the centromere
G2 (Growth 2) - cell prepares for
division, microtubules rearranged
Mitosis – nucleus divided into 2
nuclei
Cytokinesis – cytoplasm divides
G0 phase-cell does not copy
DNA or prepare to divide
 Interphase
 Prophase
 Metaphase
 Anaphase
 Telophase &
Cytokinesis
•
•
Chromosome # doubles
Chromosomes appear as
threadlike coils (chromatin)
Animal Cell
Plant Cell
Mitosis (cell begins to divide)DNA tightens into
chromosomes, nuclear membrane breaks down and
disappears
• Centrosomes-dark spots that appear next to the
nucleus and begin to move to opposite end of the
cell-if an animal-then has a pair of centrioles
• Spindle fibers made of microtubules, form between
the poles-mitotic spindle-to equally divide the
chromatids
•
 Kinetochore fibers-attach to
centromeres-extend to the
centrosomes
 Polar fibers-extend across cell from
pole to pole, do not attach to
chromosomes
Animal Cell
Plant Cell
 Kinetochore fibers move
chromosomes to the center of
the cell
Animal Cell
Plant Cell
 Chromatids separate and
begin to move to opposite
ends of the cell.
Animal Cell
Plant Cell
Two new nuclei form
• Chromosomes appear as
chromatin (threads rather
than rods)
• Mitosis ends
•
Animal Cell
Plant Cell
 Cell membrane moves inward to
create two daughter cells – each
with its own nucleus with
identical chromosomes
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase