CELL REPRODUCTION Chapter 8 Biology CPA Thank you, Miss
Colabelli!
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CHROMOSOMES Rod shaped structures made of DNA and proteins
Chromosomes are visible in cells undergoing division Chromosomes
are made by DNA coiling into tight structures Consist of two
identical halves
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CHROMOSOME STRUCTURE Histones are proteins that DNA wraps
around to make the chromosome shape Chromosomes are made of two
sister chromatids Identical to each other
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CHROMOSOME STRUCTURE Each chromosome is made of two sister
chromatids Near center of the chromosome is the centromere
Chromosomes are tightly coiled strings of DNA called chromatin
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CHROMOSOME NUMBERS There is a specific number of chromosomes in
each organism Ex: Humans have 46, chimpanzees have 48 Humans have
autosomes and sex chromosomes We have 2 sex chromosomes Either X or
Y We also have 44 autosomes Which do not code for gender
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CHROMOSOME NUMBERS Every cell of an organism produced by sexual
reproduction has two copies of each autosome One copy from mom and
one copy from dad The two copies of each pair is called homologous
chromosomes Same size and shape Carry genes for the same
traits
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KARYOTYPE A karyotype is a picture of one set of chromosomes
Shows you sex of organism Shows your any chromosomal disorders
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CHROMOSOME NUMBERS A diploid cell contains 2 sets of each
chromosome Prefix di = 2 Abbreviated as 2n n = number of
chromosomes A haploid cell contains only 1 set of each chromosome
Half of the total number Usually sex cells
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CELL DIVISION IN PROKARYOTES Prokaryotes No nucleus No
organelles Ex: Bacteria Reproduction is very fast Copy DNA Split
into two identical daughter cells Cell division is called binary
fission
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CELL DIVISION IN EUKARYOTES Eukaryotes Have a nucleus Have
organelles Ex: Humans, plants Both nucleus and cytoplasm need to
divide Process of making new cells is called mitosis Makes two
identical daughter cells Complex reproduction Everything needs to
be regulated! Much more complex process about 18 hours!
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CELL DIVISION AND REPRODUCTION Asexual Reproduction Produces
identical offspring from a single parent Used by many single-celled
organisms Ex: bacteria Occurs very quickly Sexual Reproduction
Produces genetically different offspring from two parents Fusion of
two parent cells Creates haploid gametes (sex cells)
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THE CELL CYCLE A repeating set of events in the life of a cell
A cell splits to make 2 identical copies This occurs in 3 main
stages 1.Interphase growth 2.Mitosis division of the cell
3.Cytokinesis Splitting of the cytoplasm
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INTERPHASE Cell growth Majority of cells life span is spent in
this phase 3 Part of Interphase: G 1, S, G 2
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G 1 PHASE Gap 1 Phase The cell is growing to mature size
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S PHASE S = synthesis of DNA DNA is copied so there is a set
for each new cell
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G 2 PHASE Gap 2 Phase Cell grows again Replication of
organelles Cell prepares for cell division
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MITOSIS Cell Division
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MITOSIS The part of a cells life cycle when the cells nucleus
divides into 2 identical nuclei 4 steps: Prophase Metaphase
Anaphase Telophase
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PROPHASE Shortening and tight coiling of chromatin into
chromosomes Nucleus breaks down and disappears Centrioles separate
and move to opposite poles of the cell Centrosomes in plant cells
Centrioles shoot off spindle fibers
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METAPHASE Spindle fibers are connected to centromere of
chromosomes Spindle fibers move chromosomes Chromosomes line up at
the equator of the cell Chromosomes are in the MIDDLE
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ANAPHASE Sister chromatids attach to the short spindle fibers
Chromatids of each chromosome separate at the centromere
Chromosomes are pulled APART Spindle fibers shorten and bring the
sister chromatids to opposite poles After chromatids separate, they
are called individual chromosomes
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TELOPHASE Chromatids become chromatin Spindle fibers
disassemble Nuclear envelope forms around each set of chromatin
Nucleolus reappears
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CYTOKINESIS Once mitosis has finished! Last stage of cell cycle
Process is when the cytoplasm splits apart
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CYTOKINESIS IN PLANT CELLS A cell plate forms between the two
nuclei The cytoplasm divides A cell wall forms two daughter
cells
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CYTOKINESIS IN ANIMAL CELLS Cell membrane pinches in at equator
Cleavage furrow
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CELLS IN VARIOUS STAGES OF THE CELL CYCLE
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CONTROL OF CELL DIVISION Checkpoints (Regulatory Proteins)
Repair enzymes fix any mutations G 1 Checkpoint Proteins check to
see if cell will be able to divide Check for cell size G 2
Checkpoint DNA repair enzymes check results of DNA replication
during S phase Mitosis checkpoint If all is correct, proteins will
signal cell to exit mitosis Cell will renter interphase after
cytokinesis and start process over again If a cell does not meet
requirements for checkpoints, the cell will be programmed to die
Apoptosis is controlled cell death
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THE CELL CYCLE CLOCK: CYCLINS AND CYCLIN- DEPENDENT KINASES Two
types of regulatory proteins are involved in cell cycle control:
cyclins and cyclin-dependent kinases (Cdks) Cdks activity
fluctuates during the cell cycle because it is controled by
cyclins, so named because their concentrations vary with the cell
cycle MPF (maturation-promoting factor) is a cyclin-Cdk complex
that triggers a cells passage past the G 2 checkpoint into the M
phase
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FIGURE 12.17 (a) Fluctuation of MPF activity and cyclin
concentration during the cell cycle (b) Molecular mechanisms that
help regulate the cell cycle MPF activity Cyclin concentration Time
M M M S S G1G1 G2G2 G1G1 G2G2 G1G1 Cdk Degraded cyclin Cyclin is
degraded MPF G 2 checkpoint Cdk Cyclin M S G1G1 G2G2
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STOP AND GO SIGNS: INTERNAL AND EXTERNAL SIGNALS AT THE
CHECKPOINTS An example of an internal signal is that kinetochores
not attached to spindle microtubules send a molecular signal that
delays anaphase Some external signals are growth factors, proteins
released by certain cells that stimulate other cells to divide For
example, platelet-derived growth factor (PDGF) stimulates the
division of human fibroblast cells in culture
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A clear example of external signals is density-dependent
inhibition, in which crowded cells stop dividing Most animal cells
also exhibit anchorage dependence, in which they must be attached
to a substratum in order to divide Cancer cells exhibit neither
density- dependent inhibition nor anchorage dependence
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FIGURE 12.19 Anchorage dependence Density-dependent inhibition
(a) Normal mammalian cells (b) Cancer cells 20 m
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LOSS OF CELL CYCLE CONTROLS IN CANCER CELLS Cancer cells do not
respond normally to the bodys control mechanisms Cancer cells may
not need growth factors to grow and divide They may make their own
growth factor They may convey a growth factors signal without the
presence of the growth factor They may have an abnormal cell cycle
control system
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A normal cell is converted to a cancerous cell by a process
called transformation Cancer cells that are not eliminated by the
immune system, form tumors, masses of abnormal cells within
otherwise normal tissue If abnormal cells remain at the original
site, the lump is called a benign tumor Malignant tumors invade
surrounding tissues and can metastasize, exporting cancer cells to
other parts of the body, where they may form additional tumors
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FIGURE 12.20 Glandular tissue Tumor Lymph vessel Blood vessel
Cancer cell Metastatic tumor A tumor grows from a single cancer
cell. Cancer cells invade neighboring tissue. Cancer cells spread
through lymph and blood vessels to other parts of the body. Cancer
cells may survive and establish a new tumor in another part of the
body. 4321
