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Cell Cycle
6.4 – 6.9
1
2
The Cell Cycle
 alternation
of activities between cell division
and other processes


describes series of phases leading to cell division
mitosis and three phases of interphase—Gap 1,
DNA synthesis, and Gap 2
 cell
division phase – mitosis
 phase of growth and non-reproductive
activities – interphase
3
4
In which part of the cell cycle
does the cell spend most of its
time?
1.
2.
3.
4.
Interphase
Mitosis
G2
DNA synthesis
5
DNA Review
 DNA
= deoxyribonucleic acid
 long, spiraling “ladder” with a sugarphosphate backbone
 Four bases – thymine (T), adenine (A),
cytosine (C), guanine (G) form the
“rungs” of the DNA ladder. (2 bases form
a rung -- one for each side of the ladder)
 Sugar + base + phosphate = nucleotide
6
Chromosome Structure
 Single
strand of DNA
forms a chromosome
 DNA is wrapped
around spools of a
protein called histone
 Therefore, DNA is
much, much longer
than the chromosome
it makes up
7
8
DNA Replication
 Copy
double-stranded DNA
 Necessary for cell division
 Replication is termed semiconservative since
each new cell contains one strand of original
DNA and one newly synthesized strand of
DNA
9
DNA Replication
 Special
enzymes move up along DNA ladder
and “unzip” the molecule as it moves along
 New nucleotides move in to each side of the
unzipped ladder
 Cytosine (C) pairs with guanine (G), adenine
(A) pairs with thymine (T).
 Arrangement of bases is what determines
genetic code
10
DNA Replication




When enzyme has passed the end of the DNA,
two identical molecules of DNA are left behind
Each contains one side of the original DNA and
one side made of "new" nucleotides
It is possible that mistakes were made along the
way -- in other words, that a base pair in one
DNA molecule doesn't match the
corresponding pair in the other molecule
On average, one mistake may exist in every
billion base pairs
11
12
Mutation
Variety of errors can occur during replication
 Several DNA repair processes occur after
replication
 If error remains sequences in a replicated
DNA molecule (including the genes) can be
different from those in parent DNA molecule

13
Review: If an incorrect base is
placed in the DNA during
replication, the mutation would
be called a:
1.
2.
3.
4.
deletion
insertion
substitution
chromosomal breakage
14
Reason for Mitosis

To enable cells to generate
new, genetically identical cells
– why?
1.
2.
Growth
Replacement
15
16
17
Apoptosis
 Apoptosis
: Pre-planned cell “suicide”
called apoptosis



parts of body where the cells are likely to
accumulate significant genetic damage
over time,  high risk of becoming cancer
cells
cells lining the digestive tract, liver, etc
cells are almost constantly in contact with
harmful substances
18
Mitosis
# of (somatic) cells that must be replaced
by mitosis every day is huge
 Rate @ which mitosis occurs varies
dramatically




average RBC ~ 6 weeks
cells lining the intestines ~ 3 weeks
hair follicles also divide rapidly
19
What cellular process listed
below might involve mitosis?
1.
2.
3.
4.
Wound healing
Making insulin
Glucose transport
Muscle contraction
20
Mitosis – Overview
 Parent
cell duplicates DNA  duplicate
copy of each chromosome
 Remaining organelles duplicate
 Cell divides into two new duplicate cells
(daughter cells)
 Usually the shortest period in eukaryotic
cell cycle
21
Mitosis – Overview
22
Interphase
 In
preparation for mitosis, chromosomes
replicate



DNA synthesis (S) part of interphase, every
chromosome creates an exact duplicate of itself
by replicating
Before replication, each chromosome was a
single long linear strand of genetic material
After replication, each chromosome is a pair of
identical long linear strands, held together at the
center, a position called the centromere
23
Interphase
24
Sister Chromatids
25
Mitosis – The Details
Prophase
 chromosomes
condense, coil,
become visible
 official beginning of mitosis
26
27
Mitosis – The Details
Prophase
 chromosomes
condense, coil,
become visible
 official beginning of mitosis
28
Mitosis – The Details
 Metaphase

chromatids separate and move in opposite
directions
 Anaphase



pairs of sister chromatids are all simultaneously
pulled apart by the spindle fibers
one full set of chromosomes goes to each side
of the cell
chromosome sets will eventually reside in
nucleus of new daughter cells
29
Mitosis – The Details
 Telophase
 New
nuclear membranes re-form
around the two complete chromosome
sets.
 chromosomes begin to uncoil and fade
from view
 nuclear membrane is reassembled
 cell begins to pinch into two
30
31
32
 Cytokinesis
 cell’s
cytoplasm is also
divided into
approximately equal
parts
 some of organelles go to
each new cell
 two new daughter cells
(each w/identical
nucleus) enter interphase
33
Cancer
unrestrained
cell growth and
division
can lead to tumors
second leading cause of death
in the United States (heart
disease is #1)
34
Cancer
 Disruption
of DNA in a normal cell
interferes with cell’s ability to
regulate cell division
 caused
by :
 chemicals that mutate DNA
 sources of high energy (X-rays, sun,
nuclear radiation)
 viruses
35
Cancer
36
Cancer: Benign vs. Malignant
Benign
etc.)
tumors (moles, warts,
 masses
of normal cells that do not
spread
 usually be removed safely without
any lasting consequences
37
Cancer: Benign vs. Malignant
Malignant
tumors
 cancerous
 grow
continuously
 shed cells
shedding of cancer cells from
malignant tumors is how cancer
spreads (metastasis
38
39
Cancer Treatment
 Rapidly
dividing cells must be removed
surgically, killed, or slowed down
 Chemotherapy
 anti-mitoticdrugs are administered that
interfere w/cell division.
 Slows growth of tumors, but because
the drugs interfere with cell division
throughout the body they have terrible
side effects.