G11S LH Bio DNA structure Video 20 21
Summary
TLDRThis educational video for grade 11 students delves into DNA's structure and function. It explains how DNA, a two-meter long molecule, is compactly packaged within a cell's nucleus using histone proteins, forming chromatin and chromosomes. The video details DNA's double helix structure, composed of nucleotides with phosphoric acid, deoxyribose sugar, and nitrogenous bases (adenine, thymine, guanine, cytosine). It emphasizes Chargaff's rule, where adenine pairs with thymine and guanine pairs with cytosine, highlighting the sequence's importance in determining an individual's genetic specificity.
Takeaways
- 🔬 DNA is located in the nucleus of a cell and can be visualized using the Feulgen stain, which colors DNA red.
- 🧬 A single DNA molecule is incredibly long, approximately 2 meters, and is compacted to fit within a cell nucleus measuring only 6 micrometers.
- 🌀 The DNA molecule is a double helix structure, composed of two strands that are coiled around each other.
- 🤔 DNA packaging involves wrapping the DNA around histone proteins to form nucleosomes, which are further compacted into chromatin and eventually chromosomes.
- 🧵 Chromatin is the less condensed form of DNA found during the interphase of the cell cycle, while chromosomes are the highly condensed form present during cell division.
- 🧬 Each DNA strand is made up of repeating units called nucleotides, which are the building blocks of DNA.
- 🔑 Nucleotides consist of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
- ⚖️ Chargaff's rules state that in DNA, the amount of adenine is equal to thymine, and the amount of guanine is equal to cytosine, reflecting the base pairing within the DNA structure.
- 🔄 The specificity of DNA, which determines the uniqueness of each individual, is due to the sequence of nucleotides along the DNA molecule.
- 🧪 The video concludes with an assignment for students to memorize key points and solve additional problems to reinforce their understanding of DNA structure and function.
Q & A
What is the main topic discussed in the video for grade 11 students?
-The main topic discussed is the structure and chemical composition of DNA, which is part of chapter 2 on DNA genetic information and the cell cycle.
Who is credited with the staining technique that helps visualize DNA in the cell?
-Robert Feulgen is credited with the staining technique named Feulgen stain, which colors DNA red, allowing its visualization within the cell.
How long is a single DNA molecule and how does it fit into a cell?
-A single DNA molecule is 2 meters long. It fits into a cell, which is only six micrometers in diameter, by being tightly packed and coiled around proteins.
What is the role of histone proteins in the packaging of DNA within the cell?
-Histone proteins play a crucial role in DNA packaging by allowing the DNA to wrap around them, forming nucleosomes, which are then further coiled into chromatin and eventually into chromosomes.
What is the final structure that DNA forms within the nucleus of a cell?
-The final structure that DNA forms within the nucleus of a cell is the chromosome, which is a condensed form of chromatin.
What is the basic unit of DNA called and what are its components?
-The basic unit of DNA is called a nucleotide, which is composed of a phosphoric acid, a deoxyribose sugar, and a nitrogenous base.
How many types of nitrogenous bases are there in a DNA molecule and what are they?
-There are four types of nitrogenous bases in a DNA molecule: adenine (A), thymine (T), guanine (G), and cytosine (C).
What is Chargaff's rule and how does it relate to the pairing of nitrogenous bases in DNA?
-Chagaff's rule states that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). This rule relates to the pairing of nitrogenous bases through hydrogen bonds, where A pairs with T by two hydrogen bonds and G pairs with C by three hydrogen bonds.
How does the sequence of nucleotides in DNA contribute to the uniqueness of an individual?
-The sequence of nucleotides in DNA determines the specificity of the DNA and thus the individual. Even a small change in the sequence can result in significant differences between individuals.
What is the significance of the double helix structure of DNA?
-The double helix structure of DNA is significant because it allows for the precise pairing and separation of the two strands during processes such as DNA replication and transcription, ensuring the accurate transmission of genetic information.
Outlines
🧬 DNA Structure and Packaging
This segment introduces the structure and chemical composition of DNA, emphasizing its importance in genetics. Students are guided to understand DNA's role in identifying individual identity and its presence in all body cells. The lesson begins with locating DNA within the cell nucleus, crediting Robert Feulgen for developing a staining technique that visualizes DNA. The script highlights the remarkable length of DNA molecules and how they are compacted into cells through proteins like histones, forming nucleosomes, chromatin, and eventually chromosomes. The process of DNA condensation is explained, illustrating how a two-meter DNA molecule fits into a microscopic cell nucleus.
🌀 DNA Molecule Components and Chargaff's Rule
This part delves into the components of the DNA molecule, describing its double helix structure composed of two strands. The strands are made up of repeating units called nucleotides, each consisting of a phosphoric acid, deoxyribose sugar, and a nitrogenous base. The four types of nitrogenous bases—adenine (A), thymine (T), guanine (G), and cytosine (C)—are identified. The video explains how these bases pair through hydrogen bonds, with A pairing with T and C with G, following Chargaff's rule. A practical calculation is provided to demonstrate how to determine the number of cytosine nucleotides based on the given number of adenine nucleotides, reinforcing the concept of base pairing.
🧬 DNA Specificity and Individuality
The final segment discusses the specificity of DNA, explaining how the sequence of nucleotides determines the uniqueness of each individual. Despite humans sharing a similar karyotype with 23 pairs of chromosomes, the variation in the sequence of nucleotides makes each person distinct. The video concludes by summarizing the key learnings: DNA's packaging within the nucleus, its double helix structure, the base pairing rules, and the significance of the nucleotide sequence in defining individuality. Students are encouraged to memorize the information and complete additional worksheets for practice.
Mindmap
Keywords
💡DNA
💡Chromosomes
💡Nucleotides
💡Histones
💡Chromatin
💡Condensation
💡Double Helix
💡Nitrogenous Bases
💡Chagaff's Rule
💡Specificity
Highlights
Introduction to the structure and chemical composition of DNA.
DNA's role in identifying an individual's unique genetic code.
Robert Feulgen's staining technique that locates DNA in the cell nucleus.
The surprising length of a single DNA molecule and its packaging into a cell.
Animation demonstrating how DNA is tightly packed within a cell.
The process of DNA wrapping around histone proteins to form nucleosomes.
Formation of chromatin from nucleosomes and its role in DNA packaging.
Condensation of chromatin into chromosomes during cell division.
DNA molecule's double helix structure made up of two strands.
Description of the components of a DNA strand: nucleotides, phosphoric acid, deoxyribose sugar, and nitrogenous bases.
Identification of the four types of nitrogenous bases in DNA: adenine, thymine, guanine, and cytosine.
Explanation of Chargaff's rule regarding the pairing of nitrogenous bases in DNA.
Calculation example demonstrating how Chargaff's rule applies to the composition of DNA.
The significance of the sequence of nucleotides in determining DNA specificity and individual uniqueness.
Summary of DNA's structure, composition, and the importance of its sequence in individual identity.
Assignment reminder to memorize the summary sheet and solve extra sheets for practice.
Transcripts
[Music]
welcome again grade 11 students we are
still discussing chapter 2 dna genetic
information and the cell cycle however
we will be starting with the most
important lesson of all activity 3 the
structure and chemical composition of
dna
at the end of this video you will be
able to describe the dna molecule deduce
the results of chargaff's rule
concerning the dna structure recognize
that the sequence of nucleotides
determines the specificity of the dna
make sure to prepare
your extra worksheet and the pencil case
previously we've learned about this cell
that contains chromosomes where if we
looked closely into each chromosome we
will find dna
let's ask some students what do they
know about this dna
is a long molecule that contain our
unique genetic code
dna identifies the identity of an
individual and it consists of body cells
and gm cells
dna is found in all our cells and is
made up of atoms
dna is a molecule that carry genetic
materials that are responsible for
development
functioning and growth now what about
you what do you think is dna and what
are the components of a dna molecule
let's start the lesson to answer these
questions
in our first step we must locate dna in
the cell and here comes robert folgen
who made a staining technique named
folgen stain that stained or colored dna
in red as you can see here in this way
folian found that dna is located in the
nucleus of a cell
now let me share some interesting
information with you did you know that
one dna molecule is 2 meters long
so that if you stretch all the dna
molecules found in your body they will
be as twice as our galaxy's length this
is quite long
how is this possible how do two meters
of dna fit in a six micrometer
cell
well the solution is in one protein
molecule what is this molecule watch the
following video in order to find how dna
is packaged inside the cell
in this animation we'll see the
remarkable way our dna is tightly packed
up so that six feet of this long
molecule fits into the microscopic
nucleus of every cell
the process starts when dna is wrapped
around special protein molecules called
histones the combined loop of dna and
protein is called a nucleosome
next the nucleosomes are packaged into a
thread
the end result is a fiber known as
chromatin
this fiber is then looped and coiled yet
again
leading finally to the familiar shapes
known as chromosomes
which can be seen in the nucleus of
dividing cells
chromosomes are not always present they
form around the time cells divide when
the two copies of the cell's dna need to
be separated
so how does two meters of dna become a
shorter chromosome let's explain what
you've seen in the video
starting from a dna molecule according
to what you've seen
this thread long thread of dna is being
wrapped or coiled around a protein
called histone protein forming what we
call a nucleosome so nucleosome is a
histone protein plus dna molecule that
is wrapped or coiled around those
proteins
in the next step those nucleosomes are
being packed one on the other forming
what we call a chromatin and of course
you've heard about this chromatin
previously
then what's happening is that this
chromatin is being wrapped
and wrapped again in order to form the
chromosome
let me remind you this chromatin is
found during interphase while this
chromosome is found during mitosis or
cell division so what's happening for
the chromatin to become a chromosome we
call it condensation
in short this two meters of dna will
become 0.2 micrometer chromosome with
the help of a protein called histone
protein
it's just like packing a long thread of
wool into a shorter scarf
now let's start with our second
objective by describing the components
of the dna molecule what is exactly
inside this dna
looking at this dna molecule how can you
describe its structure well you can see
that this dna is made up of two strands
one in purple here and the other one in
yellow and those two strands have a
helix shape so we can say here that this
dna molecule is a double helix made up
of two strands
now let's unwind this dna molecule and
straighten the two strands in order to
find what's the component of each strand
looking carefully into each strand you
can find that there's some kind of
repetition here what is the molecule
that is being repeated
this structure here is being repeated
once twice and several times
what do we call a molecule that has
several repeating units let me remind
you here about a molecule called a
polymer the polymer is made up of
several smaller monomers so looking
again at this dna molecule we can say
that it's a polymer
made up of small monomers where we call
each monomer of these nucleotides
what is a nucleotide made up of the
nucleotide is made up of smaller three
structures which are the phosphoric acid
the deoxyribose sugar and a nitrogenous
base
now again we need to find the types of
those nitrogenous bases
looking at this dna molecule how many
types of nitrogenous bases can you find
we can find a that refers to adenine g
that refers to guanine
t that refers to thymine and c that
refers to cytosine so let's make a kind
of a map to memorize what we've said a
dna molecule is a polymer made up of
monomers called the nucleotides
each nucleotide is made up of phosphoric
acid nitrogenous base and deoxyribose
sugar and we have four different types
of nitrogenous bases
a refers to adenine t thymine g guanine
and c cytosine
and this is our complex dna molecule
d refers to deoxyribo and to nucleic or
the nucleus a to acid so dna is
deoxyribonucleic acid for our last
question concerning the structure of dna
we said that those two helices makes one
double helix so how does the first helix
and the second helix combine in order to
form one double helix
the answer lies in those bonds between
the two dna strands as you can see here
so dna is stabilized by the hydrogen
bonds between the nitrogenous bases and
the two strands as you can see
where we have two types of those bonds a
always pairs with t by two hydrogen
bonds and c always pairs with g by three
hydrogen bonds
continuing up from here looking at this
dna strand what can you notice
concerning those base pairs
look carefully at each base pair in the
two strands
by looking at each base you can find
that when we have adenine we have
thymine in the opposite strand
so adenine always pairs with thymine
and where you have guanine we have
cytosine in the opposite strand so we
can say that guanine always pairs with
cytosine
now this rule is discovered by chargaff
that's why it's called chargapp's rule
where a should be equal to t and g
should be equal to c
how is that look at those two strands
and start counting each nucleotide in
the first strand and in the opposite
strand is the rule applied here let's
see in the first strand you have two
thyme nucleotides so that in the second
strand you have two adenine molecules
same goes for the adenine in the first
strand two adenine then we have two
thymine in the opposite strand one
guanine will fit with one cytosine and
finally if you have three cytosine you
will have three guanine there will a
simple g must be equal to c and a must
be equal to t
now let's have some kind of calculation
if a dna molecule has 180 base pairs and
20 adenine how many cytosine nucleotides
are present in this molecule of dna
pause the video and remember the rule
carefully and try to find the cytosine
nucleotides
well if we said that 20
adenine are found in this dna molecule
then also 20 percent of thymine are
present since a should be equal to t now
the whole dna molecule is hundred
percent
and the percent of a and t will be 40 20
plus 20 is 40
then what's left for the percentage of
cg nucleotides is 60 percent and again
charge rule says that the percentage of
c should be g and if c g is 60 then each
one of them will be 30 percent hence it
contains 54 cytosine nucleotides since
30
of 180 bays refers to 54 cytosine
nucleotides
up to our final objective concerning the
specificity of a dna
well you know by now that all humans
karyotype is similar they all have 23
pairs of chromosomes however each human
is so much different from the other why
is that and how is that possible well if
we studied one type of chromosome in two
individuals and then we looked at the
sequence of the nucleotides in each one
we can find that they are similar
however a change in only one nucleotide
or in only one base will make those two
individuals very different
so the sequence of nucleotides
determines the specificity of dna we are
different not because we have different
chromosomes it's because we have
different sequence of these nucleotides
and that's how dna makes us in this
video you've learned that dna is packed
inside the nucleus with the help of
histone protein and that this chromosome
is a condensed form of chromatin
you've also learned that this dna is a
double helix made up of different
nucleotides each nucleotide is made up
of phosphoric acid deoxyribose sugar and
one of four nitrogenous bases adenine
thymine guanine and cytosine where
according to charge of guanine always
pairs with cytosine by three hydrogen
bonds and t always pairs with a by two
hydrogen bonds which makes the two
strands complementary finally this
sequence of nucleotides determines the
specificity of the dna and thus the
individual as an assignment please make
sure to memorize the summary sheet and
solve the extra sheets this video is
prepared and recorded by teacher
zaracharya and supervised by teachers
thank you for your time
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