RNA and the Genetic Code Flashcards
Central dogma of molecular biology
Doctrine that states the necessary steps for transfer of genetic information from generation to generation
Steps:
1. Replication
I. Production of DNA copies
2. Transcription
I. Formation of single stranded mRNA from
DNA through complementary and antiparallel
base pairing
3. Translation
I. Formation of proteins from mRNA codons
using ribosomes in a N- to COOH- terminal
orientation
Types of RNA
- mRNA / messenger RNA
I. The most abundant form of RNA
II. Formed in nucleus from complementary and
antiparallel transcription of DNA
III. Contains codons that code for amino acids
IV. Carries its information from nucleus to ribosome
in the cell’s cytoplasm to initiate translation - tRNA / transfer RNA
I. Second most abundant RNA that converts the
language of nucleic acids to amino acids
II. It contains contains amino acids that upon pairing
of its anticodons with mRNA’s codons add to the
polypeptide chain
III. Is found in the cytoplasm of cells - rRNA / ribosomal RNA
I. created in nucleolus but a vital part of ribosomal
machinery in the cytoplasm
II. It catalyzes the formation of polypeptide bonds as
a ribozyme
DNA Mutations and their Effects on Proteins
Mutations———————–Consequent Protein Changes
1. Silent/Degenerate——–None; change in wobble base
2. Point/Missense————None or change in amino acid
3. Point/Nonsense———–Premature protein truncation
4. Frameshift——————Change in amino acid
sequence
Important Codons to Remember
Start codon for all eukaryotic proteins
1. AUG--------corresponding to -----Methionine
Stop Codons
1. UAG
2. UGA
3. UAACodons
–mRNA reading frames in bases of 3 that code for
amino acids
–There are 64 codons–
I. 61 of which code for amino acids
II. 3 of which code for premature ending of protein
translation
–a single amino acid can be coded for by multiple
codons that share identical nucleotides for their first 2
bases, varying only at the wobble position
Wobble Position
Variable third base of a codon that allows for a silent mutation, preventing harmful changes in amino-acid sequence
Transcription
Process of converting genetic info from DNA to RNA to allow transportation of genetic info to ribosome in the cell’s cytoplasm where translation takes place
Reason for transcription:
1. DNA’s degradation upon leaving the nucleus
***Does not require a primer for its initiation and does not involve proceeding proofreading of the transcript as opposed to what’s seen in DNA replication
Template Strand
AKA anti-sense strand
DNA strand that serves as a template for mRNA transcription by RNA polymerase II
RNA polymerase II
DNA-dependent RNA polymerase that locates the promoter region on a DNA strand with the help of transcription factors before using the template strand to synthesize/transcribe mRNA
Promoter Region for Transcription
Region of DNA template strand with particular set of genes where RNA polymerase can bind to start transcription
Contains the TATA box
TATA box
Region of DNA template strand with high adenine and thymine content to which RNA polymerase II binds to start the transcription process
Various Types of RNA-Polymerases
- RNA polymerase I: responsible for rRNA [28S, 18S,
5.8S] synthesis in the nucleus - RNA-polymerase II: responsible for synthesis of
snRNA & hnRNA in the nucleus - RNA-polymerase III: responsible for synthesis of tRNA
and rRNA [5S]
No need for primer to start transcription
snRNA——->small number RNA
hnRNA——–>heterogenous nuclear RNA
hnRNA
heterogenous nuclear RNA is the pre-processed mRNA synthesized by RNA-polymerase II in the nucleus that upon post-transcriptional modifications turns into mRNA
Coding/Sense Template
DNA strand complementary to the template strand and identical to the mRNA strand except for including thymine instead of uracil
+1 Base of a Gene Region
The first base of a gene transcribed from DNA to RNA
Base-Numbering of a DNA Coding Region
1-Negative numbers: #s to the left of +1, upstream and
toward 5’; include -25 which is the
region where TATA box is located
2. +1 #: #of the first base on DNA that gets
transcribed
3. +2, +3, +4, etc #: #s downstream of +1 on which RNA
polymerase II moves until it
reaches a stop sequence, ending
transcription
Post-Transcriptional Processes
Define: Processes involved in preparing hnRNA to leave the nucleus and to interact with ribosome to participate in translation
- Splicing of Introns and Ligation of Exons on hnRNA
by spliceosome - Addition of 7-methylguanylate-triphosphate 5’Cap to
hnRNA to
1. protect it against ribosomal
degradation
2. to enable it to bind to ribosome - Addition of poly-A-[polyadenosyl] Tail to 3’ end of
mRNA to protect it against degradation in
cytoplasm before it reaches the ribosome
[the longer the tail, the longer the mRNA’s
survival time in the cytoplasm]
Spliceosome
Complexes of small nuclear RNA and small nuclear ribonucleoproteins [snRNA & snRNP] that recognize the 5’to3’ ends of introns on hnRNA and splice or snurp them before degrading them post-transcription
Introns vs. Exons
Non-coding vs. coding regions of mRNA
Evolutionary Significance of Introns
- Maintenance of genomic size
2. Rapid protein evolution
UTRs
Untranslated regions in mRNA’s 3’ and 5’ edges b/c translation starts at start codon (AUG) and ends at one of the stop codons [UAG, UGA, UAA]
