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Hello friends!
Cells, made up of thousands of
different kinds of molecules,
have just 4 kinds of molecules that contribute
upto 90% of the weight of a dried cell.
These are called macromolecules as these are large and heavy,
These are called macromolecules as these are large and heavy,
and can be seen as a chain of specific smaller molecules.
and can be seen as a chain of specific smaller molecules.
and can be seen as a chain of specific smaller molecules.
These macromolecules are:
Nucleic Acids -
DNA & RNA
Proteins
Carbohydrates and Lipids.
Today we will discuss the first two,
Today we will discuss the first two,
the understanding of which will
be key to learning biology.
be key to learning biology.
First, let's learn about DNA
The genetic material in the nucleus,
called chromosomes,
is mainly made up of DNA.
It was first found only
in the nucleus of a cell,
hence named as nucleic acid.
From a bacterium to a human being,
From a bacterium to a human being,
molecules of DNA are found in nearly every organism.
DNA works as the master molecule,
DNA works as the master molecule,
controlling the functioning, growth,
and division of the cell.
What does this master molecule look like?
DNA has the same structure in all organisms.
DNA has the same structure in all organisms.
In the year 1953,
Watson and crick gave a model of the structure.
Watson and crick gave a model of the structure.
Watson and crick gave a model of the structure.
This model had two anti-parallel strands
coiled around a common axis.
coiled around a common axis.
This structure is known as double helix.
It could be compared with a flexible, twisted ladder.
It could be compared with a flexible, twisted ladder.
Each strand in the DNA molecule
is a chain of smaller molecules called nucleotides.
is a chain of smaller molecules called nucleotides.
is a chain of smaller molecules called nucleotides.
Each nucleotide
contains a nitrogenous base,
contains a nitrogenous base,
a sugar molecule
a sugar molecule
and a phosphate group.
and a phosphate group.
Based on the nitrogenous base present in them,
nucleotides can be classified into 4 types.
A-Adenine,
G -guanine,
T - thymine,
C-cytosine
are the nitrogenous bases found in DNA.
A, G are purines
A, G are purines
and T, C are known as pyrimidines.
and T, C are known as pyrimidines.
and T, C are known as pyrimidines.
Nucleotides are arranged
in a chain inside the DNA.
The two strands of DNA can be considered
as two pillars of a ladder.
Each pillar is made up of alternately
bonded sugar molecule and phosphoric acid.
bonded sugar molecule and phosphoric acid.
Each step of the ladder
is the nitrogenous base pair
connected by hydrogen bonds.
connected by hydrogen bonds.
A of one pillar
always bonds with T of another
and G of one pillar always
bonds with C of another.
bonds with C of another.
Just how, your phone number
is a string of numbers from 0-9,
is a string of numbers from 0-9,
DNA is a string of the nucleotides ATGC,
DNA is a string of the nucleotides ATGC,
this is referred to as the genetic code,
with the difference that this string
is nearly a billion characters long in humans.
This huge code is divided into
smaller segments called genes.
smaller segments called genes.
These genes control the
structure and functions of cells and thus body.
How? We will discuss that shortly.
How? We will discuss that shortly.
Now, let's study about RNA.
RNA is another important nucleic acid found in a cell.
RNA is another important nucleic acid found in a cell.
RNA is another important nucleic acid found in a cell.
Its discovery began with the discovery of nucleic acids in 1868
Its discovery began with the discovery of nucleic acids in 1868
but it was only after 1890
but it was only after 1890
that RNA was found to be distinctly different from DNA.
that RNA was found to be distinctly different from DNA.
It was later discovered that this molecule
has a role to perform in the manufacture of proteins.
What does an RNA molecule look like?
What does an RNA molecule look like?
Its molecular components
are similar to those of DNA.
What does an RNA molecule look like?
Its molecular components
are similar to those of DNA.
One nucleotide of RNA
has a nitrogenous base,
a sugar molecule
(slightly different than the one in DNA),
and a phosphoric acid.
The 4 nitrogenous bases present in RNA are
The 4 nitrogenous bases present in RNA are
A-adenine, C-cytosine,
G-guanine and U-uracil.
The two prime differences between DNA and RNA
The two prime differences between DNA and RNA
are the presence of different sugars
and the T and U in DNA and RNA respectively.
The sugar in RNA is more reactive
The sugar in RNA is more reactive
(remember this,
you will understand why later)
you will understand why later)
RNA, being functionally more active,
does not have a single structure.
And yes,
it can form the double helix too.
it can form the double helix too.
More on this in the next video.
Now, let's learn about proteins.
Proteins are large biomolecules
performing a variety of functions.
They were discovered by J.J. Berzelius in 1838.
They were discovered by J.J. Berzelius in 1838.
They were discovered by J.J. Berzelius in 1838.
The name protein was derived from 'potas'
The name protein was derived from 'potas'
(a Greek word meaning- 'of primary importance').
Proteins are essential for every organism.
Proteins are essential for every organism.
From cell signalling to performing muscle activity,
From cell signalling to performing muscle activity,
From cell signalling to performing muscle activity,
From cell signalling to performing muscle activity,
they participate
in almost every biological process.
What do these life-sustaining molecules look like?
What do these life-sustaining molecules look like?
Proteins contain one or more polypeptide.
Proteins contain one or more polypeptide.
Each polypeptide is a linear chain of amino acids.
Each polypeptide is a linear chain of amino acids.
In nature, 20 different kinds
of these amino acids are found.
Adjacent amino acids are linked
together by peptide bonds.
together by peptide bonds.
Proteins differ from one another
primarily in their sequence of amino acids.
There are different aspects of structure of a protein
like primary, secondary
and so on…
the amino acid sequence is referred
to as the primary structure of a protein.
to as the primary structure of a protein.
These primary structures are further
stabilised by special bonds and form
secondary structure of a protein.
Spatial relationship of these secondary structures
Spatial relationship of these secondary structures
gives a protein its unique 3-D shape.
gives a protein its unique 3-D shape.
Individual cells build their
specific proteins in the following way-
specific proteins in the following way-
Proteins are assembled from amino acids using information encoded in genes.
Proteins are assembled from amino acids using information encoded in genes.
Proteins are assembled from amino acids using information encoded in genes.
Proteins are assembled from amino acids using information encoded in genes.
Each protein has its own unique
amino acid sequence that is specified
by the nucleotide sequence of the gene encoding this protein.
by the nucleotide sequence of the gene encoding this protein.
by the nucleotide sequence of the gene encoding this protein.
by the nucleotide sequence of the gene encoding this protein.
Genes encoded in DNA
are first transcribed into mRNA.
are first transcribed into mRNA.
mRNA is then used
as a template for protein synthesis by ribosome.
as a template for protein synthesis by ribosome.
All required amino acids are assembled together by ribosome to form protein.
All required amino acids are assembled together by ribosome to form protein.
All required amino acids are assembled together by ribosome to form protein.
All required amino acids are assembled together by ribosome to form protein.
The number of proteins the genome
encodes correlates well with the organism complexity.
encodes correlates well with the organism complexity.
encodes correlates well with the organism complexity.
Well developed organisms like human beings
have nearly 15000 proteins encoded in their genome,
have nearly 15000 proteins encoded in their genome,
bacteria have nearly 3200,
bacteria have nearly 3200,
while viruses have only 42!
while viruses have only 42!
To summarise all this,
think of a cell to be a restaurant,
think of a cell to be a restaurant,
and the DNA in your cell
to be like a recipe book
to be like a recipe book
to be like a recipe book
but in an obscure language
that no one can read,
with each gene to be a different recipe.
with each gene to be a different recipe.
First, it needs to be translated into a language the chef knows.
First, it needs to be translated into a language the chef knows.
First, it needs to be translated into a language the chef knows.
This is the RNA's role.
Then the ribosome, acting as the chef,
reads the recipe and cooks the dish,
reads the recipe and cooks the dish,
reads the recipe and cooks the dish,
here the protein, from its ingredients, the amino acids.
here the protein, from its ingredients, the amino acids.
here the protein, from its ingredients, the amino acids.
here the protein, from its ingredients, the amino acids.
The recipe book governs
what will be served to the customers
but it cannot do anything alone.
Hence, we study all the molecules
and how they perform all the processes
to run a sophisticated restaurant.
to run a sophisticated restaurant.
Until then goodbye from Synkranti!
Until then goodbye from Synkranti!
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