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GENE EXPRESSION AT MOLECULAR LEVEL - Coggle Diagram
GENE EXPRESSION AT MOLECULAR LEVEL
CENTRAL DOGMA
DNA - mRNA- polypeptide
Undergoes process of transcription and translation
Proposed by Francis crick
For prokaryotes
Eukaryotes have a pre- mRNA which needs to under go RNA processings
Not all RNA undergoes translation
They aid in translation
tRNA
They help bring amino acids to form polypeptides
rRNA
Part of Ribosomes
Large subunit
Small subunit
Binds to the mRNA sequence
Initiates translation
GENE
Transcription
Features
An organized unit of DNA sequences that enables
A segment of DNA to be transcribed into RNA
Formation of a functional products
In eukaryotes
RNA processes after transcription
Splicing
Introns and exons are present in pre mRNA. Introns are removed
Method of removal
Alternative splicing
Splicing can occur more
than one way to produce different products
.
Spliceosome
Composed of snRNPs
Forms a lariet shaped structure for removal
Tailing
100-200 adenine nucleotides added to 3’ end.
Increases stability and lifespan in cytosol.
Not encoded in gene sequence
Capping
Modified guanosine attached to 5’ end.
Needed for mRNA to exit nucleus and bind
ribosome
.
3 different types of RNA polymerase
RNA polymerase II
Transcribes mRNA.
RNA polymerase III
Transcribes tRNA.
RNA polymerase I
Transcribes rRNA
Genetic Codes
Sequence of bases in an mRNA
molecule.
Codons
Three nucleotide bases
64 codons
3 stop codons
UAA, UGA, UAG
61 codons
Codes for amino acid
Includes AUG
AUG - start codon
Degenerate
More than one type of codon codes for the same amino acid
ORF- open reading frame
Has a 5 prime UTR - ribosomal binding site
Present before the ORF
3 prime UTR-
Present after the ORF
Genetic codons are complementary to coding strand
Genetic codons in tRNA is identical to template strand
tRNA has anti codons
Complementary to the codons in ORF
Has specific amino acids attached
Amino acid is attached through covalent bonds
This bond requires energy which ends up charging the tRNA
Done through Aminoacyl-tRNA synthetase
Will release a charged tRNA molecule
ATP is the source of energy
Binds to RNA codons through hydrogen bonds
2 loops
Amino Acid acceptor end
Forms a L shaped molecule
Anti codon loop
A genetic sequence that has four portions
Structural gene
Codes for polypeptides
May or may not form proteins
Determines the structure and function of the cell
Done through the process of elongation
Unwinding of the DNA segment
Reads the template strand
Reading of the strand is done from 3 prime to 5 prime direction
Done with RNA polymerase alone
Synthesis of the strand is done from 5 prime to 3 prime direction
Uracil is formed in place of thymine is RNA
Terminator region
Signals the end of transcription
Uses transcription factor -
Rho
Newly synthesized RNA is released
Promoter region
Signals the beginning of transcription
Uses RNA polymerase with transcription factor -
Sigma
Factor helps the polymerase to recognize the promoter sequence
Regulatory regions
A site where proteins binds to regulate the rate of transcription
TRANSLATION
Ribosomes
Forms 3 major sites
A- aminoacyl site
E- exit site
P- peptidyl site
Processes
Elongation
Reading and synthesis from start to stop codon
Charged tRNA brings amino acids first to the P site and subsequently moves to the A and E site
Charged tRNA helps in peptide bond formation
Done with peptidyl transfer reaction
Translocation
- ribosome movement
toward the 3’ end of the mRNA
Termination
Disintergration of the complex units
Polypeptide released through release factors
Binds to stop codon at the A site
Ribosomal unit Disintergrates
Stops translation with binds with stop codons
Initiation
mRNA, first tRNA- binds to AUG, and ribosomal subunits
Initiator tRNA binds second
mRNA binds to small subunit first
Large ribosomal subunit binds last
Makes use of GTP as energy source
Initiator tRNA is used