G11 S LH Video 9 Ch 2 Act 4 The cell cycle

Summary

This 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

00:00

🔬 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.

05:02

🧬 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.

10:02

📊 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.

Keywords

💡Cell Cycle

The cell cycle is the series of events that take place in a cell, leading to its division and duplication. It is central to the video's theme as it sets the stage for understanding how cells grow and reproduce. The video explains that the cell cycle consists of interphase and mitosis, with interphase further divided into G1, S, and G2 phases. This cycle is crucial for the cell's preparation for division, ensuring that each new cell receives a complete set of genetic material.

💡Interphase

Interphase is the phase of the cell cycle where the cell grows and prepares for division. It is highlighted in the video as the period before mitosis where most of the cell's activities take place. Interphase includes G1, S, and G2 phases, with the S phase being particularly important for DNA replication. The video emphasizes that during interphase, the cell duplicates its organelles and grows in size, readying itself for the upcoming division.

💡Mitosis

Mitosis is the process of cell division that results in two daughter cells, each having the same number and kind of chromosomes as the parent nucleus. The video discusses mitosis as the culmination of the cell cycle, where the cell actually divides. It is divided into prophase, metaphase, anaphase, and telophase, and it is the phase where the duplicated DNA is segregated into the two new cells, maintaining the genetic integrity.

💡DNA Replication

DNA replication is the process of copying a cell's DNA to produce two identical DNA molecules, each consisting of one old and one new strand. The video describes this process in detail during the S phase of interphase, emphasizing its importance for genetic continuity. The video script mentions that DNA replication involves the unwinding of the double helix, the action of DNA polymerase, and the pairing of complementary bases, resulting in two identical DNA molecules.

💡Synthesis (S Phase)

The S phase, also known as the synthesis phase, is a stage in the cell cycle where DNA replication occurs. The video explains that during this phase, the cell's DNA content is doubled, which is essential for ensuring that each daughter cell receives a complete set of genetic information after cell division. The script provides a step-by-step account of DNA replication, including the role of enzymes like DNA helicase and DNA polymerase.

💡G1 and G2 Phases

G1 and G2 phases are the gap phases that occur before DNA synthesis (S phase) and before mitosis, respectively. The video script describes G1 as the phase where the cell duplicates its organelles and G2 as the phase where the cell enlarges in preparation for division. These phases are crucial for the cell's growth and the preparation of necessary cellular machinery for the upcoming processes.

💡Chromatids

Chromatids are the two identical copies of a chromosome formed during DNA replication. The video script uses the term to explain how, after DNA replication, a chromosome that originally had one chromatid (one DNA molecule) ends up with two chromatids (two DNA molecules). This concept is key to understanding how genetic material is duplicated and distributed during cell division.

💡DNA Polymerase

DNA polymerase is an enzyme that plays a critical role in DNA replication by adding complementary nucleotides to the DNA strands. The video script describes how DNA polymerase binds to the separated DNA strands and helps in the formation of two new DNA molecules, each with one old and one new strand. This enzyme is essential for the semi-conservative model of DNA replication discussed in the video.

💡Semi-conservative Replication

Semi-conservative replication is a model of DNA replication where each of the two resulting DNA molecules consists of one original (parental) strand and one newly synthesized (daughter) strand. The video script explains this model as the correct mechanism of DNA replication, where the old and new strands pair up to form two identical DNA molecules, ensuring that each daughter cell receives an exact copy of the parental DNA.

💡Chromosomes

Chromosomes are structures within the cell nucleus that contain the genetic material. The video script mentions chromosomes in the context of cell division, explaining how they condense and are distributed to daughter cells during mitosis. Chromosomes are made up of DNA and proteins, and their correct segregation is crucial for maintaining genetic information in dividing cells.

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