Transcription and translation Flashcards
Central Dogma of Biology
Theclassic view of the central dogma of biologystates that “the coded genetic information hard-wired into DNA is transcribed into individual transportable cassettes, composed of messenger RNA (mRNA); each mRNA cassette contains the program for synthesis of a particular protein (or small number of proteins).“
Transcription and Translation
The primary role of DNA is to provide instructions that direct cell activities.
This is accomplished by regulating protein synthesis and activity within the cell .
Enzymes, hormones, and other similar biomacromolecules are proteins that are utilized to accomplish various homeostatic, synthesis, and life functions in the cell. Protein synthesis is carried out in various stages that begin with transcription and translation.
Transcription
TheDNAcontains the master plan for the creation of theproteinsand other molecules and systems of the cell, but the carrying out of the plan involves transfer of the relevant information toRNAin a process called transcription. The RNA that bears this information is transcribed is messenger RNA (mRNA).
DNA Transcription
RNA polymerase unzips the DNA helix.
One of the 2 DNA strands acts as a template.
RNA nucleotides line up along one strand of the DNA following the base-pairing rules.
No T, Instead U
RNA polymerase forms covalent bonds between nucleotides.
Transcription continues until one entire gene has converted to RNA.
The single-stranded messenger RNA separate and the DNA strands rejoin
RNA types
There are 3 different types of RNA:
Messenger RNA: (mRNA) Transcription Product
Single strand
Transported from nucleus to cytoplasm
Ribosomal RNA: (rRNA)
Translation
Structural & Functional
component of Ribosomes
Transfer RNA: (tRNA) Translation
Bring AA to Ribosomes for protein assembly
Transfer RNA:
. Amino acids are carried to the ribosomes by smaller RNA molecules called transfer RNA (tRNA).
2. Single strands folded back on themselves:
“Clover Leaf structures”
3. Role = Carry AA to the ribosomes
-amino acid attachment site
-anticodon – codon attachment site
Anticodon
Asequenceof threeadjacentnucleotideslocated on one end oftransfer RNA. It binds to the complementary codingtripletofnucleotidesinmessenger RNAduringtranslationphase ofprotein synthesis.
Codon
A set of three adjacentnucleotides, also calleda triplet, inmRNAthat base-pair with the correspondinganiticodonoftRNAmoleculethat carries a particularamino acid specifying the type and sequence ofamino acidsforprotein synthesis.
Exons
Theprotein-codingregionin theDNA. Thenucleic acidsequencein theDNA, orRNAtranscriptfollowinggenetic splicing.
Introns
Non-coding, interveningsequencesofDNAthat are transcribed, but are removed from within theprimarygenetranscript and rapidlydegradedduringmaturationofmessenger RNA mostgenesin thenucleiofeukaryotescontainintrons, as domitochondrialandchloroplastgenes
Translation: Process
mRNA binds the small subunit of the ribosome.
tRNA molecules are present, each one carrying a specific AA and anticodon sequence.
tRNA binds to the ribosome at the site where the anticodon matches the codon on the mRNA.
Two tRNAs bind at once and the first one transfers the growing polypeptide chain to the second one.
The tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is “read” by the ribosome.
- The ribosome moves along the mRNA and the process continues until a stop codon is reached when the polypeptide is released.
4 phases of Translation
(1) activation– the correctamino acidis covalently bonded to the correcttRNA; a step required for translation to proceed
(2) initiation- the smallsubunitof theribosomebinds to 5’ end ofmRNAwith the help of initiation factors (IF)
(3) elongation– the next aminoacyl-tRNA in line binds to theribosomealong with GTP and an elongation factor.
(4) termination- the A site of theribosomefaces astop codon(UAA, UAG, or UGA)
Polypeptide Theory
proposed byGeorge BeadleandEdward Tatum
One gene is transcribed and translated to produce one polypeptide.
Some proteins are composed of a number of polypeptides and in this theory each polypeptide has its own gene.
e.g. hemoglobin is composed of 4 polypeptides (2 of each type)
and there is a gene for each type of polypeptide.
This theory, like many in biology has exceptions.
Some genes code for types of RNA which do not produce polypeptides.
2) Some genes control the expression of other genes.
