Transcript lecture notes-molecular biology-central dogma

Basics of Molecular Biology
Central Dogma:
- DNA replication
- Transcription
- Translation
Metabolic regulation:
- Genetic level
- Metabolic pathway control
Central Dogma
Central Dogma: universal
molecule.
is stored on the DNA
: The genetic information can be
replicated directly to form a second identical
molecule.
: Segments information on the
DNA molecule can be transcribed to yield m-, t, r-RNAs.
: Using RNAs, this information is
translated into proteins.
DNA Replication in
Cell Division Cycle (Mitosis)
Transcription
The primary product of transcription:
m-RNA, t-RNA and r-RNA.
Transcription requires: RNA polymerases
- Growth of RNA polymers is energy requiring.
e.g. ATP, GTP,
The base-sequence of RNA is the precise
complement
DNA template
RNA product
A
U
T
A
G
C
C
G
.
Transcription
DNA template
Promoter
Operator
Gene 1
Gene 2
Gene 3
m-RNA
RNA polymerase
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
Transcription Process
- Initiation:
The sigma factor of RNA polymerase recognizes a specific
sequence of nucleotides on a DNA strand – promoter
region.
the strands unwound.
- Elongation:
Transcription starts with the core enzyme of the RNA
polymerase then the sigma factor is released.
- Termination:
RNA polymerase encounter a stop signal or transcription
terminator (e.g. rho protein in procaryotes).
- the RNA polymerase dissociate from the DNA template
- the RNA transcript is released.
Translation
Translation is the final step on the way from DNA
to protein.
- It is the synthesis of proteins directed by a
mRNA template.
- The information contained in the nucleotide
sequence of the mRNA is read as three letter
words (triplets), called codons.
- Each word stands for one amino acid.
- During translation
are linked together
to form a
chain which will later be
folded into a protein.
Translation
Translation: Message to Product
Universal
-letter codons on mRNA: A, G, C, U
- 64 codes for 20 standard amino acids
- more than one codon can specify a particular
amino acids.
- Nonsense codons: UAA, UAG and UGA
- Do not encode normally for amino acids.
- Act as stop points in translation.
- encoded at the end of each gene.
Translation
Important Components:
R
:
The ribosome is the cellular factory responsible for the
protein synthesis.
It consists of two different subunits, one small and one
large and is built up from rRNA and proteins.
Inside the ribosome the amino acids are linked
together into a chain through multiple biochemical
reactions.
Translation-Components
t-RNA:
The charged t-RNA (aminoacyl-t-RNA) carries an amino
acid at one end and has a triplet of nucleotides, an
anticodon, at the other end.
It is formed by the energy from two phosphate bonds and
enzymes (aminoacyl-t-RNA synthetases)
The anticodon of a t-RNA molecule can basepair, i.e form
chemical bonds, with the m-RNA's three letter codon.
The t-RNA acts as the translator between m-RNA and
protein by bringing the specific amino acid coded for by
the m-RNA codon.
t-RNA
Translation-Components
• m-RNA template
• The translation process also involves a
large number of protein factors that
facilitate binding of mRNA and tRNA to the
ribosome.
• Protein synthesis consumes a large part of
the energy produced in the cell.
Translation Processes
Translation consists of Initiation, Elongation and
Termination.
http://www.phschool.com/science/biology_place/biocoach/translation/init.html
Initiation results in the formation of an initiation complex in
which the ribosome is bound to the specific initiation (start)
site on the mRNA while the initiator tRNA charged with (Nformyl)methionine is annealed to the initiator codon and
bound to the ribosome.
- Protein synthesis begins with a AUG codon (less frequently
GUG) on the m-RNA
AUG encodes for a modified methionine, N-formylmethionine
(fMet).
In the middle of protein, AUG encodes for methionine.
Translation Processes
Elongation joins amino acids to the growing
polypeptide chain according to the sequence
specified by the message.
- The formation of the peptide bond between the two
amino acids occurs on adjacent sites on the
ribosome: the P or peptidyl site and the A or
aminoacyl site.
- The growing protein occupies the P site, while the
next amino acid to be added occupies the A site.
- As the peptide bond is formed, the t-RNA
associated with the P site is released.
http://www.phschool.com/science/biology_place/biocoach/translation/elong1.html
Translation Processes
Termination
- At a stop codon, a release factor reads the triplet,
and polypeptide synthesis ends.
- the polypeptide is released from the tRNA.
- the tRNA is released from the ribosome, the two
ribosomal subunits separate from the mRNA.
http://www.phschool.com/science/biology_place/biocoach/translation/term.html
Posttranslation
• Posttranslational modification means the
chemical
of a protein after its
translation. It is one of the later steps in protein
biosynthesis.
• It may involve the
of a proper structure,
the formation of disulfide bridges and attachment
of any of a number of biochemical functional
groups, such as phosphate, acetate, various
lipids and carbohydrates.
e.g. phosphorylation catalyzed by enzymes such
as with kinase.
(e.g. phosphorylated TP53 protein functions as
tumor suppressor).
Summary of Central Dogma
•
•
•
•
DNA replication
DNA-RNA transcription
RNA-Protein translation
Posttranslation
components, processes, features