NUCLEIC ACIDS AND PROTEIN SYNTHESIS
Nucleic acids: have been called the “molecules of life” or the “most extraordinary molecules on
earth”.
Why? As they have the capacity to store the information that controls cellular activity and
the development of entire organisms.
How do they do this? By controlling the synthesis of proteins.
Making proteins may not make an entire organism, but it is the first step in the process –
proteins not only make up much of the structure of the body, but as enzymes are proteins,
they also control the chemical processes inside cells. In this way, they ultimately control the
structure and functioning of all living organisms.
The two nucleic acids found in cells are:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
DEOXYRIBONUCLEIC ACID – DNA:
DNA’s discovery has been called the most important biological work of the last 100 years.
Who discovered the structure of DNA:
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin.
Background:
At King’s College in London in the early 1950’s, Maurice Wilkins and Rosalind Franklin were trying to work out the structure
of DNA. They took an experimental approach, looking at x-ray crystallography (ie: diffraction images of DNA).
At the same time at the Cavendish Institute at Cambridge University, graduate student Francis Crick and research fellow
James Watson also became interested in determining the structure of DNA. They analyzed the x-ray data collected by
Rosalind Franklin and others, and then built a model out of brass plates and clamps and other bits of laboratory equipment
and realized that nucleic acids are arranged like a twisted “ladder”, with two “runners” made of phosphates and sugars, and a
series of “rungs” made of pairs of organic compounds known as bases.
What about genetic replication?
Watson and crick developed their ideas about genetic replication in a second article in Nature, published on May 30, 1953.
The pairing of the bases (ie: A=T and C=G) suggested that given a sequence of bases in one strand, the other strand was
automatically determined.
This meant that when the two strands separated, each served as a template for a complementary new chain (ie: each strand
could replicate).
After the “double helix” model there were still questions about how DNA directed the synthesis of proteins.
In 1961, Francis Crick and Sydney Benner provided genetic proof that a triplet code was used in reading genetic material in
DNA and transferring this information from the nucleus to the cytoplasm via RNA to where proteins are made.
Crick and Benner had shown that in DNA, form is function:
The double-stranded molecule could both produce exact copies of itself (replicate) and carry genetic instructions (ie:
that the sequence of the bases in DNA forms a code by which genetic information can be stored and transmitted).
Who won the Nobel prize?
Of the four DNA researchers, only Rosalind Franklin had any degrees in chemistry. She worked mostly alone and suspected,
that through her x-ray diffractions, that all DNA molecules were helical in structure but was reluctant to announce this finding
until she had sufficient evidence. She died of cancer aged 37 before expressing her views.
In 1962, when Watson, Crick and Wilkins won the Nobel price for physiology/medicine, Franklin had died.
,Where is DNA found:
DNA is found mainly in the nucleus of a cell where it forms an important part of the chromosomes
that make up the chromatin network.
chromatin = chromosomal material made up of DNA, RNA and histone proteins as found in a non-
dividing cell.
The DNA molecule is coiled up so that these long structures can fit inside the nucleus. There are
nearly two meters of DNA squeezed into each human cell.
What is extranuclear DNA:
Small amounts of DNA are found inside the nucleus in mitochondria in plants and animals, and in
chloroplasts in plants. This is called extranuclear DNA.
How is DNA made up:
The shape of DNA is rather like a long, twisted ladder. The two strands twist to form a stable, 3-
dimensional double helix.
DNA double helix
What units make up DNA?
A DNA molecule is a long chain (polymer) made up
of small units (monomers,)
(ie: building blocks called nucleotides).
Each nucleotide is made up of a:
sugar molecule – deoxyribose (S)
phosphate molecule (P)
nitrogenous base, which may be:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
These four bases are the foundation of genetic
code, instructing cells on how to synthesize
enzymes and other proteins.
As there are four different nitrogenous bases, there
are four different nucleotides.
Eg: a thymine
nucleotide S T
P
, How is the double helix made up:
The outer two strands of the “ladder” are formed by a chain of alternating sugar/phosphate
links. The bonds between the sugar and phosphate molecules are strong.
The “rungs” of the “ladder” are formed from pairs of bases linked by weak hydrogen bonds.
The base pairs are attached to the sugar molecules.
How do these four base pairs link up:
The shape and size of the four base pairs differ so that:
Adenine will only bond with thymine or uracil by means of two hydrogen bonds (eg: A=T,
A=U).
Cytosine will only bond with guanine by means of three hydrogen bonds (eg: C≡G).
How are the base pairs classified:
There are two groups of nitrogenous bases – purines and pyrimidines.
Purines: Made up of two fused rings of nitrogen, carbon, and hydrogen atoms.
Eg: guanine and adenine.
Pyrimidines: Made up of one ring of similar atoms and are therefore smaller than purines.
Eg: thymine, cytosine, and uracil.
Do the bases differ in different organisms?
These four nucleotides are the same in all animals and plants.
An adenine nucleotide of a human is the same as the adenine nucleotide of a frog.
How do organisms differ?
What makes the difference is the sequence in which the nucleotides are strung together.
Eg: the sequence ACCTGA represents different information than the sequence AGTCCA.
The sequence in certain sections of DNA in a human is very different from the same sections
in every other human being (except in identical twins).
It is the sequence of the nucleotides (bases) therefore that determines the genetic code of
an organism.
The role of DNA:
DNA molecules:
carry hereditary information in each cell in the form of genes.
provide a blueprint for an organism’s growth and development by coding for protein
synthesis.
can replicate (ie: make a copy of itself) so that a copy of the genetic information is passed
on to each daughter cell formed during cell division. This ensures that the genetic code is
passed on from generation to generation.
What is non-coding DNA:
Less than 2% of a human DNA codes for proteins: the rest consist of non-coding DNA.
Protein-coding regions of a DNA molecule: called exons.
Non-coding regions of a DNA molecule: called introns (they interrupt the coding regions).
Complex organisms contain much more of this non-coding DNA than less complex
organisms.
The non-coding regions were thought to be “evolutionary junk”, but they are now known to
form functional RNA molecules which have regulatory functions.
Nucleic acids: have been called the “molecules of life” or the “most extraordinary molecules on
earth”.
Why? As they have the capacity to store the information that controls cellular activity and
the development of entire organisms.
How do they do this? By controlling the synthesis of proteins.
Making proteins may not make an entire organism, but it is the first step in the process –
proteins not only make up much of the structure of the body, but as enzymes are proteins,
they also control the chemical processes inside cells. In this way, they ultimately control the
structure and functioning of all living organisms.
The two nucleic acids found in cells are:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
DEOXYRIBONUCLEIC ACID – DNA:
DNA’s discovery has been called the most important biological work of the last 100 years.
Who discovered the structure of DNA:
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin.
Background:
At King’s College in London in the early 1950’s, Maurice Wilkins and Rosalind Franklin were trying to work out the structure
of DNA. They took an experimental approach, looking at x-ray crystallography (ie: diffraction images of DNA).
At the same time at the Cavendish Institute at Cambridge University, graduate student Francis Crick and research fellow
James Watson also became interested in determining the structure of DNA. They analyzed the x-ray data collected by
Rosalind Franklin and others, and then built a model out of brass plates and clamps and other bits of laboratory equipment
and realized that nucleic acids are arranged like a twisted “ladder”, with two “runners” made of phosphates and sugars, and a
series of “rungs” made of pairs of organic compounds known as bases.
What about genetic replication?
Watson and crick developed their ideas about genetic replication in a second article in Nature, published on May 30, 1953.
The pairing of the bases (ie: A=T and C=G) suggested that given a sequence of bases in one strand, the other strand was
automatically determined.
This meant that when the two strands separated, each served as a template for a complementary new chain (ie: each strand
could replicate).
After the “double helix” model there were still questions about how DNA directed the synthesis of proteins.
In 1961, Francis Crick and Sydney Benner provided genetic proof that a triplet code was used in reading genetic material in
DNA and transferring this information from the nucleus to the cytoplasm via RNA to where proteins are made.
Crick and Benner had shown that in DNA, form is function:
The double-stranded molecule could both produce exact copies of itself (replicate) and carry genetic instructions (ie:
that the sequence of the bases in DNA forms a code by which genetic information can be stored and transmitted).
Who won the Nobel prize?
Of the four DNA researchers, only Rosalind Franklin had any degrees in chemistry. She worked mostly alone and suspected,
that through her x-ray diffractions, that all DNA molecules were helical in structure but was reluctant to announce this finding
until she had sufficient evidence. She died of cancer aged 37 before expressing her views.
In 1962, when Watson, Crick and Wilkins won the Nobel price for physiology/medicine, Franklin had died.
,Where is DNA found:
DNA is found mainly in the nucleus of a cell where it forms an important part of the chromosomes
that make up the chromatin network.
chromatin = chromosomal material made up of DNA, RNA and histone proteins as found in a non-
dividing cell.
The DNA molecule is coiled up so that these long structures can fit inside the nucleus. There are
nearly two meters of DNA squeezed into each human cell.
What is extranuclear DNA:
Small amounts of DNA are found inside the nucleus in mitochondria in plants and animals, and in
chloroplasts in plants. This is called extranuclear DNA.
How is DNA made up:
The shape of DNA is rather like a long, twisted ladder. The two strands twist to form a stable, 3-
dimensional double helix.
DNA double helix
What units make up DNA?
A DNA molecule is a long chain (polymer) made up
of small units (monomers,)
(ie: building blocks called nucleotides).
Each nucleotide is made up of a:
sugar molecule – deoxyribose (S)
phosphate molecule (P)
nitrogenous base, which may be:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
These four bases are the foundation of genetic
code, instructing cells on how to synthesize
enzymes and other proteins.
As there are four different nitrogenous bases, there
are four different nucleotides.
Eg: a thymine
nucleotide S T
P
, How is the double helix made up:
The outer two strands of the “ladder” are formed by a chain of alternating sugar/phosphate
links. The bonds between the sugar and phosphate molecules are strong.
The “rungs” of the “ladder” are formed from pairs of bases linked by weak hydrogen bonds.
The base pairs are attached to the sugar molecules.
How do these four base pairs link up:
The shape and size of the four base pairs differ so that:
Adenine will only bond with thymine or uracil by means of two hydrogen bonds (eg: A=T,
A=U).
Cytosine will only bond with guanine by means of three hydrogen bonds (eg: C≡G).
How are the base pairs classified:
There are two groups of nitrogenous bases – purines and pyrimidines.
Purines: Made up of two fused rings of nitrogen, carbon, and hydrogen atoms.
Eg: guanine and adenine.
Pyrimidines: Made up of one ring of similar atoms and are therefore smaller than purines.
Eg: thymine, cytosine, and uracil.
Do the bases differ in different organisms?
These four nucleotides are the same in all animals and plants.
An adenine nucleotide of a human is the same as the adenine nucleotide of a frog.
How do organisms differ?
What makes the difference is the sequence in which the nucleotides are strung together.
Eg: the sequence ACCTGA represents different information than the sequence AGTCCA.
The sequence in certain sections of DNA in a human is very different from the same sections
in every other human being (except in identical twins).
It is the sequence of the nucleotides (bases) therefore that determines the genetic code of
an organism.
The role of DNA:
DNA molecules:
carry hereditary information in each cell in the form of genes.
provide a blueprint for an organism’s growth and development by coding for protein
synthesis.
can replicate (ie: make a copy of itself) so that a copy of the genetic information is passed
on to each daughter cell formed during cell division. This ensures that the genetic code is
passed on from generation to generation.
What is non-coding DNA:
Less than 2% of a human DNA codes for proteins: the rest consist of non-coding DNA.
Protein-coding regions of a DNA molecule: called exons.
Non-coding regions of a DNA molecule: called introns (they interrupt the coding regions).
Complex organisms contain much more of this non-coding DNA than less complex
organisms.
The non-coding regions were thought to be “evolutionary junk”, but they are now known to
form functional RNA molecules which have regulatory functions.
