BIOL 3451- Midterm Exam Guide - Comprehensive Notes for the exam ( 55 pages long!)

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6 Oct 2017
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BIOL 3451
MIDTERM EXAM
STUDY GUIDE
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RNA, Transcription, and the Genetic Code 3/2
How is genetic information encoded?
o GENETIC CODE is written in units of three letters-ribonucleotides in mRNA that
reflect the stored information in genes.
What is the MECHANISM OF TRANSCRIPTION?
o Complex process dependent on major polymerase enzymes and other proteins
RNA Molecules
o mRNA: template for protein synthesis (coding RNA)
o rRNA: functions as part of ribosomes
o tRNA: involved with protein synthesis
o snRNA: RNA processing, splicing
o snoRNA: chemical modification of RNAs
o miRNA: Regulation of gene expression (21-24 nt)
o piRNA: interact with piwi proteins, gene silencing function, suppression of DNA
transposable elements
o Other RNAs: Ex: those that work with proteins, like telomerase
TRANSCRIPTION
o The process by which RNA molecules are synthesized from a DNA template
o Transcription in E. coli
Transcription Components
RNA polymerase holoenzyme and subunit
Template binding and initiation of transcription
The subunit recognizes (binds) to the promoter region
Chain elongation
Occus i the 5’ to 3’ diectio
Transcription continues until it reaches a termination sequence
(stop codon), which is usually 40 bp in length
In bacteria, the RNA is often POLYCISTRONIC
o mRNA
DNA is the template used to produce RNA molecules
RNA processing occurs after transcription
An insertion of a single nucleotide causes the reading frame to shift,
referred to as a FRAMESHIFT MUTATION
Proved experimentally by Crick, Brenner, Watts-Tobin, and Barnett
The mRNA molecule is made up of RIBONUCLEOTIDE SEQUENCES
The ribonucleotide sequence is derived from the complementary
nucleotide bases in DNA
Each group of three ribonucleotides (codon) specifies one amino acid,
thus the code is TRIPLET
The code is UNAMBIGUOUS, thus each triplet specifies only a single
amino acid.
The code is DEGENERATE, meaning that a given amino acid can be
specified by more than one triplet codon (18 of the 20 amino acids)
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The code cotais a stat sigal AUG ad stop sigal UAA, UAG,
UGA)
The code is continuous; mRNA is read continuously, three nucleotides at
a time, without skipping any nucleotides of the message
The code is NON-OVERLAPPING, after translation commences, any single
ribonucleotide at a specific location within the mRNA is part of only one
triplet.
The code is nearly universal. A single coding dictionary is used by almost
all viruses, archaea, bacteria, and eukaryotes.
Khorana and Nirenberg won the Nobel Prize for experiments that led to
the understanding of the genetic code
Synthesis of polypeptides in a cell-free in vitro system
o RNA homopolymers were synthesized and used as
templates for in vitro assays to make polypeptides
o RNA heteropolymers were then synthesized and used as
templates for in vitro assays to make polypeptides
o Able to propose what codon used for any amino acid
o Used cell free system to examine various codons and
determine which amino acids were incorporated
THE WOBBLE HYPOTHESIS
The third base in an mRNA codon can undergo non-Watson-Crick
base pairing with the first base of a tRNA anticodon
The CODING REGION of genes can be overlapping
o Regulation of Gene Expression: Prokaryotic Promoter Regions
CONSENSUS SEQUENCES in DNA are sequences that are similar
(homologous) in different genes of the same organisms
Used to recruit RNA polymerase
5’ | TTGACA -35 region) | TATAAT (-10 region; TATA Box) | ATG (start
codon) | Coding Region
TATA Bo is highl coseed; ithout it tasciptio ould’t
really occur
o Transcription in Eukaryotes
Regulation of gene expression in eukaryotic systems is complex
Location: transcription in the nucleus, translation in the cytoplasm (or
with ribosomes on rough ER)
Regulation: upstream region consists of promoters and enhancer regions,
role of chromatin structure, transcription factors, monocistronic
Post transcriptional modifications of RNA molecules
RNA processing (splicing)
RNA polymerases in eukaryotes
Form I: rRNA; nucleolus
Form II: mRNA, snRNA; nucleoplasm
Form III: 5s rRNA, tRNA; nucleoplasm
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