G11 S LH Video 9 Ch 2 Act 4 The cell cycle
Summary
TLDRThis educational video concludes Chapter 2 by exploring the cell cycle, focusing on interphase and mitosis. It explains the cell cycle's two phases: interphase, which includes G1, S, and G2, and mitosis. The video details DNA replication during the S phase, illustrating the semi-conservative model where each new DNA molecule consists of one old and one new strand. It also discusses the variation in DNA quantity throughout the cycle, emphasizing the cell's preparation for division during interphase and the importance of DNA replication in ensuring each daughter cell receives an identical genetic copy.
Takeaways
- 🔬 The cell cycle is divided into interphase and mitosis, with interphase further divided into G1, S, and G2 phases.
- 🌟 DNA replication, a critical process, occurs during the S phase of interphase, ensuring each new cell receives a complete set of genetic information.
- 🧬 The steps of DNA replication include unwinding the double helix, DNA polymerase binding, and the addition of complementary nucleotides to form two identical DNA molecules.
- 🔄 DNA replication is semi-conservative, meaning each new DNA molecule consists of one old and one new strand.
- 📈 The amount of DNA per cell doubles during the S phase and is restored to its original state after mitosis, maintaining the genetic integrity across cell divisions.
- 🌱 Interphase is a preparatory stage where the cell duplicates organelles during G1 and enlarges during G2, readying for division.
- 🧐 The video emphasizes the importance of understanding each phase of the cell cycle for grasping cellular reproduction and growth.
- 📚 Students are encouraged to take notes and compare cellular changes before and after each phase to deepen their understanding of the cell cycle.
- 🔍 The video uses a graphical representation to illustrate the variation in DNA quantity throughout the cell cycle, aiding in visual learning.
- 👩🏫 The lesson is designed to help students recognize, infer, and explain the processes involved in the cell cycle and DNA replication, enhancing their biological knowledge.
Q & A
What are the two main parts of the cell cycle mentioned in the script?
-The two main parts of the cell cycle mentioned are interphase and mitosis.
What happens during the S-phase of the cell cycle?
-During the S-phase of the cell cycle, DNA replication occurs, where the amount of DNA in the nucleus is doubled.
What is the purpose of DNA replication?
-The purpose of DNA replication is to copy the strands of DNA, resulting in two identical molecules of DNA from one original DNA molecule.
How does the DNA replication process work?
-DNA replication involves the unwinding of the double helix, the action of DNA polymerase to add complementary free nucleotides to the exposed bases, and the formation of two new DNA molecules, each with one new and one original strand.
What is the semi-conservative model of DNA replication?
-The semi-conservative model of DNA replication suggests that each of the resulting daughter DNA molecules will have one new strand and one old strand from the original DNA molecule.
What is the role of the enzyme DNA helicase in DNA replication?
-The enzyme DNA helicase unzips the DNA, separating the two strands, which is a necessary step for DNA replication to occur.
What happens to the organelles during the G1 phase of interphase?
-During the G1 phase of interphase, every organelle is duplicated, preparing the cell for division.
What is the significance of the G2 phase in the cell cycle?
-In the G2 phase, the cell enlarges and prepares certain enzymes to help in division, although no significant changes occur to the DNA or organelles.
How does the amount of DNA vary during the cell cycle?
-The amount of DNA per cell remains the same during G1, doubles during S-phase, and returns to the original amount after mitosis, maintaining the original quantity of DNA.
What is the final outcome of the cell cycle in terms of DNA content in the daughter cells?
-The final outcome of the cell cycle is that each daughter cell receives one copy of the DNA molecule, which refers to one chromatid per chromosome, maintaining the original DNA content.
Outlines
🔬 Introduction to the Cell Cycle and DNA Replication
This lesson is the final one in Chapter 2, focusing on the cell cycle and DNA replication. The main objective is to understand the cell cycle's two phases: interphase and mitosis. Students will learn to identify the cell cycle's components and infer that DNA replication occurs during the S-phase. The lesson also aims to describe the steps of DNA replication and deduce that it is semi-conservative. The variation of DNA amount per cell during the cell cycle is explained, highlighting the changes from one chromatid to two before mitosis. The importance of interphase, where cells prepare for division, is emphasized, and students are encouraged to take notes. The lesson discusses the cell cycle's stages, including G1, S, and G2 phases, and the process of DNA replication involving enzymes like DNA helicase and DNA polymerase.
🧬 DNA Replication Process and its Significance
This section delves into the process of DNA replication, which is crucial for the cell cycle. The DNA double helix unwinds, and DNA helicase separates the strands. DNA polymerase then adds complementary nucleotides to form two new DNA molecules, each with one original and one new strand. This results in two identical DNA molecules, demonstrating the semi-conservative model of DNA replication. The lesson clarifies the importance of DNA replication in preparing the cell for division by doubling the DNA content. It also explains the changes in DNA quantity during the cell cycle, with G1 phase having one DNA molecule per chromosome, S phase doubling it to two molecules, and G2 phase maintaining this doubled state. After mitosis, each daughter cell has one DNA molecule, returning to the original state.
📊 Summarizing the Cell Cycle and Assignment
The final part of the lesson summarizes the steps of the cell cycle, emphasizing the graphical representation of DNA quantity changes throughout the cycle. It reiterates that the cell cycle consists of interphase (G1 and G2) and mitosis, with DNA replication occurring during the S phase. The video concludes with an assignment for students to memorize the summary sheet, which encapsulates the key points of the lesson. The lesson is prepared and recorded by Teacher Zahara Shari and supervised by Teacher Assange Hassan, concluding with a thank you note for the students' attention.
Mindmap
Keywords
💡Cell Cycle
💡Interphase
💡Mitosis
💡DNA Replication
💡Synthesis (S Phase)
💡G1 and G2 Phases
💡Chromatids
💡DNA Polymerase
💡Semi-conservative Replication
💡Chromosomes
Highlights
Lesson focuses on the cell cycle, including interphase and mitosis.
Students will learn to recognize the cell cycle's two main phases.
Understanding that DNA replication occurs during the S-phase of the cell cycle.
Describing the steps of DNA replication and the role of DNA helicase and polymerase.
Deduction that DNA replication is semi-conservative.
Explanation of DNA amount variation per cell during the cell cycle.
Interphase is divided into G1, S phase, and G2 phases.
G1 phase involves the duplication of cellular organelles.
S phase is characterized by DNA replication within the nucleus.
G2 phase is marked by cell enlargement and preparation for division.
DNA replication results in two identical DNA molecules, each with one old and one new strand.
The cell cycle's graphical representation shows DNA quantity changes over time.
DNA replication is essential for maintaining the original DNA quantity after cell division.
Assignment to memorize the summary sheet for a deeper understanding of the cell cycle.
The video is prepared and recorded by Teacher Zahara Shari, supervised by Teacher Assange Hassan.
Transcripts
[Music]
how are you doing dear students this
lesson will be our final lesson in
chapter 2 titled by activity for
identical reproduction and the cell
cycle
at the end of this video you will be
able to recognize that the cell cycle
consists of interphase and mitosis
infer that dna replication occurs during
s-phase of the cell cycle describe the
steps of dna replication deduce that the
dna replication is semi-conservative
and explain the variation of the dna
amount per cell during this cell cycle
don't forget to prepare your notebook in
order to take notes
this cell is found during mitosis having
chromosomes with two chromatids however
after and before mitosis this cell
normally have chromosomes with only one
chromatid so how is this possible how
does one chromatid become two for each
chromosome the solution lies in the
process happening before mitosis the
interphase
so our talk in this lesson will be
mainly about what's happening during
interface
when checking again the title of this
lesson we find the important term the
cell cycle
let's see what's a cell cycle looking at
this cell cycle here we find mitosis
that results in two daughter cells after
division
and of course interphase that occurs
before mitosis
as we divided mitosis into prophase
metaphase anaphase and telophase we will
also divide interphase into g1 or gap 1
s phase also known as synthesis and g2
also known as gap 2 phase
and this is in short the cell cycle now
let's concentrate on interphase where
this cell prepares itself for division
how and what's happening in each step of
interface
to find the importance of each step i
must ask for your help pause the video
and compare each cell before and after
each step gap 1
sentences and gap 2.
what do you notice
after comparing the steps you can find
that during gap 1 every organelle is
duplicated for example the vacuole here
becomes two the mitochondria here
becomes two also and every organelle is
being duplicated so in gap one the cell
copies organelles and what's happening
during synthesis is that the amount of
dna found in the nucleus here is being
doubled so here the dna duplicates and
finally in gap 2
nothing important is happening inside
the cell however what's happening is
that this cell enlarges so that the cell
will grow and certain enzymes are
prepared to help in division
for now what's happening during gap 1
and gap 2 is clear during gap 1 the cell
copies organelles and during gap 2 the
cell enlarges however during synthesis
how is this dna inside the nucleus is
being doubled what's exactly happening
here is in our next title dna
replication please watch the following
video and find the purpose and result of
this dna replication occurring during
synthesis during dna replication the
double helix unwinds
then an enzyme called dna helicase
unzips the dna so the two strands are
separated this happens at several points
along the dna
an enzyme called dna polymerase attaches
itself to the dna strands and is used to
add complementary free nucleotides to
the now exposed basis on both strands a
pairs with t and c pairs with g this
forms two dna molecules each of which
have one brand new strand and one from
the original dna
these two strands twist to form a double
helix the two new dna molecules are both
identical to the original dna molecule
it's clear from what you've watched in
the video that the purpose of this dna
replication is to copy the strands of
dna where in the results you will get
two identical molecules of dna as you're
seeing in the adjacent figure so dna
replication is the biological process to
produce two identical molecules of dna
starting from one original dna molecule
those two strands of the dna molecule
will become two brand new dna molecules
each one identical to the other so let's
list the steps of dna replication where
in the first step the two strands of the
double helix unwind
an enzyme called dna polymerase bonds to
each strand of the dna molecule then
this dna polymerase will start
replicating or duplicating the strands
of dna by adding complementary base
pairs a is complementary to t and g is
complementary to c
then finally you will get two identical
molecules of dna
now i will ask for your help again
please compare the all the strand and
the new strand of the dna after
replication there are two important
things to notice here what are they
let's first start by comparing the two
strands of the same dna molecule and as
we've been saying from the beginning of
the video that each strand is
complementary to the other t is
complementary to a in the second strand
and c is complementary to g in the
opposite strand and now when comparing
the two dna molecules you can find that
they have the same sequence
where the new strand in one dna molecule
is the same as the old strand in the
other dna molecule the sequence tg is
same as the sequence in the other strand
tg
and for now you understood the parts of
the cell cycle you defined the dna
replication and described each step now
let's deduce the form of dna replication
scientists propose two models of dna
replication the semiconservative where
the resulting daughter dna molecules
will have one new strand and one old one
and the conservative model where you
have one totally all dna molecule and
one totally new dna molecule the old one
is conserved by looking again at this
image what is the correct model of dna
replication is it semi-conservative or
conservative remember the two resulting
dna molecules have one old original
strand and one new strand well it's
obvious that the correct model here is
semi-conservative where one strand of
dna is conserved and the other strand is
the new replicated one
so in short you have this cell and
before s phase of interphase it contains
simple d condensed chromosomes each with
one chromatid and one chromatid refers
to one dna molecule
during s phase you will get replication
fork a replication fork is formed when
the dna unwinds and replication is
occurring and finally after s-phase or
during d2 you will get double
d-condensed chromosome each with two
chromatids two chromatids refer to two
dna molecules
here we've answered our important
question how do we get two chromatids
for each chromosome
the answer is in dna replication where
you had chromosomes with one chromatid
or one dna molecule after dna
replication this chromosome will contain
two chromatids or two dna molecules and
finally after division or mitosis it
will return to its original state having
one chromatid or one dna molecule so how
does this amount of dna vary during the
cell cycle first you had this cell this
cell originally or during g1 will
contain a chromosome with one chromatid
which refers to one dna molecule
however when this cell passes through
the s phase replication fork will occur
where dna is being replicated
as a result and after s-phase this this
cell will contain d-condensed
chromosomes with two chromatids which
refers to two dna molecules now finally
when passing through mitosis the cell
will give two daughter cells each having
one copy of the dna molecule which
refers to one chromatid pair one
chromosome now let's explain the idea
again graphically
where you have this graph that
represents the amount of dna in a cell
progressing through the stages of the
cell cycle
pause the video and remember what we've
explained then try to label the line
segments between those hatch marks to
show g1 s g2 and mitosis where does each
step or phase occur
as we explained previously the first
step of the cell cycle is known as g1
where the quantity of dna remains the
same per cell q this quantity increases
when dna replication occurs during s
phase after s phase the amount of dna
per cell will become 2q double the
amount of the original dna quantity and
here comes g2 after g2 we have mitosis
where after cell division everything
will return to its original quantity q
so here we've listed simply the steps of
the cell cycle
referring to the variation of the
quantity of dna in progress with time g1
s g2 and finally mitosis remember that
during g1 we have d condensed chromosome
with one dna molecule one chromatid
after s phase and during g2 you will get
two chromatids or two dna molecule per
chromosome and finally after mitosis
this quantity will return to being one
chromated per one chromosome
so you can conclude that the starting
amount is the same as the final amount
after mitosis the original quantity of
dna is maintained and here we've
summarized the steps of the cell cycle
graphically in this video you've learned
that the cell cycle is of two parts
interphase g1 as g2 and mitosis with its
several phases
during s-phase dna replication occurs
where dna is duplicated
the phases of dna replication are
summarized by
first the double helix unwants then dna
polymerase bonds to both strands of the
dna
dna polymerase replicates the dna by
adding complementary bases and finally
you will get two dna molecules according
to the semiconservative models
as an assignment please make sure to
memorize the summary sheet this video is
prepared and recorded by teacher zahara
shari and supervised by teacher assange
hassan thank you for your time
5.0 / 5 (0 votes)