Transcript The Cell Cycle

1. Of the images to the
left, select the one the
shows mutualism.
2. A human red blood cell
is placed in hypotonic
water. Predict what will
happen to the cell.
3. Write the
complimentary strand
for this sequence:
CTAAGTCGA
How do our wounds and injuries heal?
What is cancer, and how does it
form?
• Every cell has a set life cycle, known as the cell cycle. At
its simplest, the cell’s lifespan can be divided into two
separate phases:
• Interphase, where cells grow and develop
• Mitosis, where cells divide (e.g, reproduce)
• During interphase, the cell prepares for cell division
(mitosis). The cell gathers nutrients, makes an extra copy of
its DNA, and makes proteins.
• During mitosis, the mother cell divides, producing two
identical daughter cells.
• Interphase is itself
divided into three
different phases:
• G1, where the cell gathers
resources for DNA
replication and mitosis
• S, where the cell makes a
copy of its DNA
• G2, where the cell doublechecks its work and
prepares for mitosis
• So, the correct
sequence of events in
the cell cycle is:
G1→S→G2→M
• G1 and G2 refer to
“gap” phases.
• S refers to DNA
synthesis.
• M refers to mitosis.
1. Describe what
happens in S phase
of the cell cycle.
2. Describe what
happens in M phase
of the cell cycle.
3. Write the FULL
equation for cellular
respiration.
• DNA replication takes place
during S phase. During S
phase, the cell makes an
identical copy of its DNA,
producing two sets of DNA.
This way, each daughter cell
can have a complete and
identical set of DNA.
• DNA replication is catalyzed
by several different enzymes.
We will not discuss most of
these in detail, however.
• DNA Replication basically
takes place in three steps:
1. A strand of DNA is
“unzipped”. All base pairs
are spilt apart.
2. Free nucleotides bind to
each exposed half of the
DNA molecule. This creates
two new strands of DNA.
3. An enzyme rewinds each
strand of DNA, forming
two copies of DNA.
• The site where DNA is
unzipped is called the
origin.
• Each strand of DNA
that’s being copied is
called a replication fork.
• New nucleotides will
ALWAYS be added from
the 5’ to 3’ direction!
• Note that the new
strands of DNA are
IDENTICAL to the original
strand. This means that
ALL cells in your body
have the same DNA.
• This is true even if the cells
have different functions!
For instance, the cells in
your heart, bones and skin
have identical DNA!
• DNA replication is also
what we would call a
semiconservative process.
• This means that we reuse
the old strands of DNA
AND create two new
strands of DNA.
• This means that each
daughter DNA molecule
has one old and new
strand apiece.
1. Describe the daughter
strands formed after
DNA replication.
2. DNA replication requires
proteins – called
_________.
3. When DNA is copied,
each new molecule of
DNA has one old and
one new strand. DNA
replication is
________________.
• Cells divide because they CANNOT continue to grow
forever. As a cell grows, the inside grows faster than
the outside. The surface/volume ratio gets too small.
• Think of a balloon. As you pump air into a balloon, the inside
grows faster than the outside. Eventually, the balloon
explodes, because the walls can’t stretch enough to contain
the air inside!
• Cells don’t explode, but as the cell gets bigger, the cell
membrane can’t import or export materials effectively
anymore. The cell’s interior grows too quickly, so it demands
more materials than the cell membrane can provide.
• Mitosis or cell division
takes place in a clear
sequence:
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• In prophase, DNA
condenses into large
structures called
chromosomes.
• The centrioles also
appear. These structures
help pull the chromosomes
apart, which divides the
DNA in half.
• Finally, the nucleolus
disappears, and the
nuclear envelop dissolves.
This leaves the
chromosomes to float in
the cytoplasm.
• Prophase is the longest
phase of all. 50-60% of
mitosis consists of
prophase activity.
• During metaphase, the
chromosomes line up along
the middle of the cell.
• Also, microtubules connect
the centrioles to the center
of each chromosome.
• Metaphase only lasts a
few minutes.
• During anaphase, each
chromosome is pulled
apart, which produces
two sister chromatids.
• Each daughter cell will
receive one set of
chromatids.
• Anaphase ends when all
chromatids stop moving.
• In telophase, the
chromosomes disperse
back into strands of
genetic material.
• Also, the nucleus and
nucleolus begin to reform
and reappear.
• Finally, the cytoplasm
prepares for cell division.
• Cytokinesis is the final phase of mitosis.
• During cytokinesis, the cytoplasm pinches off, finally
separating the two daughter cells.
• This usually takes place during or right after
telophase.
1. List the steps of the
CELL CYCLE.
2. List the steps of
MITOSIS.
3. Mitosis results in two
________ cells.
4. What happens in
metaphase?
5. What phase of mitosis
is shown to the left?