G11S LH Bio DNA structure Video 20 21

Summary

This 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

00:00

🧬 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.

05:02

🌀 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.

10:07

🧬 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.

Keywords

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for the development, functioning, and reproduction of all known living organisms and many viruses. In the video, DNA is described as a long molecule that contains our unique genetic code, identifying the identity of an individual. It is found in all our cells and is made up of atoms, playing a crucial role in development, functioning, and growth.

💡Chromosomes

Chromosomes are thread-like structures located inside the nucleus of animal and plant cells, consisting of DNA and proteins. They carry genetic information in the form of genes. The video mentions that if we look closely into each chromosome, we will find DNA, which is essential for the cell's genetic makeup.

💡Nucleotides

Nucleotides are the building blocks of DNA, consisting of a nitrogenous base, a sugar molecule, and a phosphate molecule. The video explains that DNA is made up of nucleotides, which are the monomers that repeat to form the polymeric structure of DNA.

💡Histones

Histones are proteins that play a crucial role in the packaging of DNA within the cell's nucleus. The video describes how DNA is wrapped around histone proteins to form nucleosomes, which are then further packaged into chromatin, allowing the long DNA molecule to fit into the cell.

💡Chromatin

Chromatin is a complex of DNA and protein that makes up chromosomes. It is a form of DNA packaging that allows the long DNA molecule to be organized and fit into the cell nucleus. The video illustrates the process of DNA packaging into chromatin and how it condenses to form chromosomes.

💡Condensation

Condensation refers to the process by which DNA is tightly packed into a more compact form, such as chromatin becoming a chromosome. The video uses the term to describe how the two-meter-long DNA molecule becomes a shorter chromosome with the help of histone proteins.

💡Double Helix

The double helix is the structure of DNA, where two strands of nucleotides are wound around each other. The video explains that DNA is a double helix made up of two strands, which are stabilized by hydrogen bonds between the nitrogenous bases.

💡Nitrogenous Bases

Nitrogenous bases are the part of the nucleotide that varies between adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair specifically with each other (A with T, and C with G) to form the rungs of the DNA ladder. The video highlights the importance of these bases in determining the specificity of DNA.

💡Chagaff's Rule

Chargaff's Rule states that in DNA, the amount of adenine is equal to thymine, and the amount of cytosine is equal to guanine. This rule is crucial for understanding the structure of DNA and how the two strands are complementary. The video uses Chargaff's Rule to explain the pairing of nucleotides in the DNA molecule.

💡Specificity

Specificity in the context of DNA refers to the unique sequence of nucleotides that determines the genetic information of an individual. The video emphasizes that while all humans have a similar karyotype, the sequence of nucleotides in their DNA makes each person unique.

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