cell drogma and genetic code

1. CENTRAL DOGMA &GENETIC CODE
CELL BIOLOGY AND BIOCHEMISTRY
Course code:BIT1004
Faculty:-- Gayathri M
Submitted by:
G.Ranga Manoj Kumar
REG no. 17BCB0021
SUBMISSION DATE: 12/02/2018
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2. INTRODUCTION:-
The ‘CENTRAL DOGMA’ is a process by which the instructions in the DNA are converted into a functional
product..It was first proposed in 1958 by the discoverer of the DNA structure named Francis Crick.
1) The central dogma of molecular biology explains the flow of genetic information,actually from DNA to
RNA,which makes a functional product protein.
2) The central dogma suggests that the DNA will contain the genetic information needed to make all our
protiens and RNA is messenger which carry information to ribosomes.
3) Gene expression is the process by which DNA instructions are converted to functional protiens.
4) The ribosomes help by serving as the factories in the cell where information is translated to functional
product from a code.
•A DNA molecule is divided into functional units called genes.
•Each gene is provided to give instructions on the functional product,that means a molecule need to perform
a particular job in the cell.In many cases functional product of genes are varieties of protiens,accurately
polypeptides.
•Polypeptides are nothing but amino acids and genes that specify polypeptides are called protein coding
genes.
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3. • Figure shows the basic idea of central dogma and its process
• Many genes provide instructions for building polypeptides. How,
exactly do you think that the DNA direct the construction of a
polypeptide? This process involves two major steps:
1)transcription
• In this process, the DNA sequence of a gene is copied to make an
RNA molecule. This step is called transcription because it involves
rewriting, or transcribing, the DNA sequence in a similar RNA
"alphabet”. Similarly in eukaryotes the RNA molecule must
undergo processing to become a messenger RNA also known as
mRNA
2)translation
• In this process, the sequence of the mRNA is decoded to specify
the amino acid sequence of a polypeptide. The name translation
refers to the nucleotide sequence of the mRNA sequence must be
translated into the completely different language of amino acids.
• Thus, during this expression of a protein-coding gene, the
information will flow from DNA to RNA and then to protiens.This
flow of information is known as cetral dogma.
• And for the non protein-coding genes they are still transcribed in
an RNA,but this RNA is not yet translated into polypeptides.The
process of translation of DNA to functional product is called as or
known as gene expression.
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4. • Three processes of the central dogma
1.REPLICATION
2.TRANSLATION
3.TRANSCRIPTION
REPLICATION
Genetic material in an organism needs
to be duplicated during the S phase of
cell-cycle. Duplication of DNA is done
usually by replication, utilizing the
sequence information of parent DNA.
The enzyme used for this purpose is
DNA dependent molecule known as
DNA polymerase.
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5. • TRANSCRIPTION
• In transcription, one strand of DNA which makes up the gene
called as non-coding strand will act as template for
synthesising of matching RNA strand by an enzyme known as
RNA polymerase. This is known as primary transcript.
• This primary transcript carrries the same information as that
of non transcribed DNA strand.
• However the primary transcript and the coding strand od
DNA are not identical and the basic difference is RNA
molecules do not have the base thymine. The RNA processing
and transcription in eukaryotes and bacteria are as follows
• In bacteria, the primary RNA transcript can directly serve as a
mRNA. Messenger RNAs get their name because they will act
as messenger between DNA and ribosomes. Ribosomes are
RNA and protein structures in the cytosol where protiens are
made actually.
• In eukaryotes such as humans, a primary transcript has to go
through some extra processing steps in order to become a
mature mRNA. During processing of this, caps are added to
the ends of RNA, and some pieces of it may be carefully
removed by a process named splicing. All these steps will not
happen in bacteria.
• The location of transcription is different for prokaryotes and
eukaryotes. Eukaryotic transcription will take place in the
nucleus, where the DNA is stored, while protein synthesis
takes place in the cytosol. Due to this reason, a eukaryotic
mRNA must be exported from the nucleus before it can be
translated into a polypeptide. Prokaryotic cells, on the other
side, don't have a nucleus, so they carry out both the
transcription and translation processes in the cytosol of the
cell.
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6. • TRANSLATION
• During the translation process, the nucleotide sequence
of an mRNA is translated into an amino acid sequence
of a polypeptide. Especially, the nucleotides of the
mRNA are read in triplets which means a group of
three known as condons. There are 61 codons that
specify the amino acids. One codon is a start codon
which indicates where to start the translation. The start
codon specifies the amino acid methionine, so most of
the polypeptides begin with this amino acid. Three
other stop codons signal at the end of a
polypeptide.These relation between codons and amino
acids are called genetic code. There are several steps
involved in translation which are as follows
• The process of translation takes place inside of
structure called ribosomes. Ribosomes are molecular
machines whose job is to build polypeptides. Once a
ribosome lays hold onto an mRNA and finds the start
codon, it will travel rapidly down the mRNA, single
codon at a time. As it goes, it will gradually build up a
chain of amino acids that will exactly mirror the
sequence of codons in the mRNA.
• You must be wandering that does the ribosomes know
which amino acid to add for each codon. This matching is
not done by the ribosome itself. Instead, it depends on a
group of specialized RNA molecules known as transfer
RNAS or shortly tRNA. Each tRNA has a three nucleotides
sticking out at one end, which can recognize just one or a
few particular codons. On the other side, the tRNA carries
an amino acid – specifically, the amino acid that matches
those codons.
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7. • There are many tRNAs floating around in a cell, but only a single tRNA that matches
(basepairs with) the codon that's currently being read and can bind it and deliver its
amino acid cargo. Once a tRNA is fit closely or bound to its matching codon in the
ribosome, its amino acid will be added the end of polypeptide chain.
• This process will repeat many times, with the ribosome moving to the mRNA with one
codon at a time. A chain of amino acids is built up one by one, with the amino acid
sequence that matches with the sequence of codons found in mRNA. Translation will end
when the ribosome reaches a stop codon and releases the polypeptide.
• After this process,the polypeptide which is completed it will be processed or modified,
combine with other polypeptides, or be shipped to a specific destination inside or outside
the cell. Finally, it will perform a specific job needed by the cell – perhaps as a signaling
molecule or structural element, or enzyme
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8. • There are special transfers of biological sequential information such
as
• 1)Reverse transcription
• Reverse transcription is the transfer of information from RNA to
DNA basically the reverse of transcription. This is known to occur in
the case of retroviruses, such as HIV as well as in eukaryotes , in the
case of retrotranspons. It is the process in which the genetic
information from RNA gets transcribed into a new DNA.
• Figure depicts the flow of information under special circumstances
in biological systems
• 2)RNA replication
• RNA replication is copying of one RNA to another. There are many
viruses which replicate this way.
• RNA has important role in central dogma such as
• The central dogma explains DNA codes for RNA,which codes for
certain protiens.
• Inside of the cells,there are tiny molecular machines are constantly
reading the information in DNA and using it to build proteins. In
exploring the activity below, you will learn about the three types of
RNA are essential to this process: messenger RNA (mRNA), transfer
RNA (tRNA), and ribosomal RNA (rRNA).
• 3)Direct translation from DNA to protiens
• Direct translation from DNA to protein has been demonstrated in a
cell-free system like in the case of test tube, using extracts from
E.coli that contained ribosomes, but not intact cells. These cell
fragments could synthesize proteins from single-stranded DNA
templates isolated from other organisms , and neomycin was found
only to enhance this effect. However, it was not clear whether this
mechanism of translation corresponded specifically to only the
genetic code
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9. • CONCLUSION
• During translation, the nucleotides of mRNA are read in groups of
three known as codons. Each codon specifies a particular amino acid or
a stop signal. This set of relationships is called as genetic code.
• Crick had written why he choosed the name as dogma and what are the
problems it has caused
• He called this idea the central dogma, for two reasons, One thing is he
had already used the word hypothesis in the sequential hypothesis,
and in extra to that he wanted to suggest that this new assumption was
more central and more powerful. As it turned out, the use of the word
dogma caused almost more trouble than it was worth. Many years later
Jaques monond pointed out to him that he did not appear to
understand the correct use of the word dogma, which is a belief that
cannot be doubted. He did apprehend this in a vague sort of way but
since he thought that all religious beliefs were without foundation, he
used the word the way he himself thought about it, not as most of the
world does, and simply applied it to a grand hypothesis that, however
plausible, had little direct experimental support.
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10. • REFERENCES
• Hellens, R. P., Moreau, C., Lin-Wang, K., Schwinn, K.
E., Thomson, S. J., Fiers
• Khan academy
• Wikipedia
• CyberBridge. (2007). RNA structure
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