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Gene Expression at the Molecular Level - Coggle Diagram
Gene Expression at
the Molecular Level
Gene Expression
Central dogma states that most genes are transcribed into mRNA then it is translated into polypeptides. Eukaryotes modify RNA transcripts to make them functional.
Molecular expression of genes is an underlying factor that determines an organism's characteristics.
A polypeptide is a unit of structure, proteins are composed of 1 or more polypeptides- unit of function.
single gene controls the synthesis of a single enzyme
Transcription
Promoter is a site in a gene that specifies where transcription begins.
Terminator specifies where transcription
ends.
In bacteria, initiation of transcription begins when sigma factor binds to RNA polymerase and to a promoter.
RNA polymerase & RNA transcript separate
from DNA at terminator
In elongation, synthesis of an RNA transcript occurs by base pairing of nucleotides to the template strand of DNA as RNA polymerase slides along the DNA.
Genes along chromosomes are transcribed in different directions using either DNA strand as a template. RNA is always synthesized in 5' to 3' direction.
In eukaryotes, initiation of transcription includes assembly of RNA polymerase with 5 transcription factors.
RNA Modification in Eukaryotes
In eukaryotes, transcription produces a pre-mRNA that is capped, given a poly A tail & spliced
5' cap is methylated guanine base attached at 5' end of mRNA. Poly A tail is a string of adenine nucleotides that is summed to 3' end.
In RNA splicing, introns are removed from
eukaryotic pre-mRNA by a spliceosome.
Translation & Genetic Code
Each 64 codons specific a start codon (methionine), other amino acids, or a stop codon.
Template strand of DNA is used to make
mRNA that contain series of codons.
Recognition between mRNA & tRNA molecules determine amino acid sequences of polypeptides
Polypeptides have directionality where first amino acid is at N-terminus or amino end, whilst last amino acid has C-terminus or carboxyl end.
Machinery of Translation
tRNA molecules have 2D structure. Amino acid attachment side at 3' end & anticodon, which makes base pairs with codon in mRNA.
Enzyme aminoacyl-tRNA synthase attaches correct amino acid to tRNA molecule to make charged tRNA.
Translation needs mRNA, charged tRNAs,
ribosomes & many transcription factors.
Ribosomes are made up of small & large
subunit, each containing tRNA molecules & proteins.
Genes that code the small subunit rRNA is utilized to resolve evolutionary links between different species.
Stages of Translation
Intiation: mRNA assembles with ribosomal subunits & an initiator tRNA molecule, which carries methionine (first amino acid).
Bacteria & eukaryotes are similar in translation. Some antibiotics inhibit bacterial growth by interfering with translation
Elongation: Amino acids are added one at a time to a growing polypeptide.
Termination: Happens when binding of a release factor to a stop codon causes the release of a finalized polypeptide from tRNA.