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BIOB11H3 (13)
Dan Riggs (8)
Chapter 11

Chapter 11 notes

11 Pages
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Department
Biological Sciences
Course Code
BIOB11H3
Professor
Dan Riggs

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Chapter 11
Garrod discovered the relationship between a genetic defect, a specific enzyme, and
a specific metabolic condition - "inborn errors of
metabolism".
Beadle and Tatum first proposed the "one gene-one enzyme" hypothesis. It was
modified to "one gene-one poplypeptide". Then it was
discovered that a single gene often generates more than one polypeptide.
Ingram demonstrated that a mutation in a single gene had caused a single
substitution in the amino acid sequence of a single polypeptide
(valine in place of glutamic acid caused sickle cell anemia).
The use of mRNA allows the cell to separate information storage from information
utilized. It also allows the cell to greatly amplify its
synthetic output.
DNA is always double-helical while RNAs may fold into different structures and
thus perform many functions.
With the help of transcription factors, RNA polymerase binds to the promoter site
on DNA, which contains information that determines which
strand is going to be transcribed and where to begin. Polymerase moves 3'-5' on
DNA, so assembles RNA 5'-3'.
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Bacteria like E.Coli contain a single type of RNA polymerase composed of 5 subunits
that are tightly associated to from a core enzyme.
An accessory polypeptide called sigma factor attached to core enzyme increases its
affinity for promoter sites in DNA and so,
transcription only begins at selected locations.
After 10-12 nucleotides have been transcribed, the enzyme undergoes a
conformation change -> transcriptional elongation complex that can
move processively along the DNA. This is when sigma factor is released.
Two stretches of DNA are similar in bacteria genes: TTGACA (-35 element;
consensus sequence) and TATAAT (-10 element; Pribnow box) which
is responsible for identifying the precise nucleotide at which transcription begins.
Bacterial cells possess a variety of different sigma factors that recognize different
versions of the promoter sequence, e.g. sigma 70
the "housekeeping" sigma factor initiates transcription of most genes.
For termination of transcription, a ring-shaped protein called rho is required -
separates the RNA transcript from the DNA.
Sometimes, transcription is terminated when polymerase reaches a terminator
sequence and releases the RNA chain (no additional factors).
Eukaryotic cells have 3 distinct transcribing enzymes in the nucleus (Table 11.1
P.437).
www.notesolution.com
Transcription in eukaryotes requires accessory proteins called transcription factors.
The 3 major types of RNAs are derived from precursor RNA molecules that are
considerably longer than the final RNA product, called primary
transcript or pre-RNA and is transcribed from transcription unit in DNA.
80% of RNA in most cells consists of ribosomal RNA. DNA-sequences encoding
rRNA are repeated hundreds of times (rDNA). Nucleoli's function
is to produce ribosomes. The bulk of a nucleolus is composed of nascent ribosomal
subunits that give it a granular appearance.
Nontranscribed spacer are present between tandemly repeated genes, including
those of tRNA and histones.
Eukaryotic ribosomes have 4 ribosomal RNAs: 3 in the large subunit (28S, 5.8S, 5S)
and 1 in the small subunit (18S). 28S, 5.8S, 18S come
from the same 45S pre-rRNA. pre-rRNA undergoes some posttranslational
modification (i.e. addition of methyl groups and pseudouridines)
for unclear reasons - unaltered sections are discarded during processing.
Experiment: Pulse -> add labeled methionine to 45S pre-rRNA. Chase -> remove
and add in normal medium, take them out at various times.
Results: 45S cleaved into 32S and another product in nucleolus. This other product
leaves the nucleolus and appears as 18S in the cytoplasm
after 40 minutes. 32S leaves to the cytoplasm and is cleaved into 28S and 5.8S more
slowly. So, 18S is formed first, and then 28S and 5.8S.
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Description
Chapter 11 Garrod discovered the relationship between a genetic defect, a specific enzyme, and a specific metabolic condition - inborn errors of metabolism. Beadle and Tatum first proposed the one gene-one enzyme hypothesis. It was modified to one gene-one poplypeptide. Then it was discovered that a single gene often generates more than one polypeptide. Ingram demonstrated that a mutation in a single gene had caused a single substitution in the amino acid sequence of a single polypeptide (valine in place of glutamic acid caused sickle cell anemia). The use of mRNA allows the cell to separate information storage from information utilized. It also allows the cell to greatly amplify its synthetic output. DNA is always double-helical while RNAs may fold into different structures and thus perform many functions. With the help of transcription factors, RNA polymerase binds to the promoter site on DNA, which contains information that determines which strand is going to be transcribed and where to begin. Polymerase moves 3-5 on DNA, so assembles RNA 5-3. www.notesolution.comBacteria like E.Coli contain a single type of RNA polymerase composed of 5 subunits that are tightly associated to from a core enzyme. An accessory polypeptide called sigma factor attached to core enzyme increases its affinity for promoter sites in DNA and so, transcription only begins at selected locations. After 10-12 nucleotides have been transcribed, the enzyme undergoes a conformation change -> transcriptional elongation complex that can move processively along the DNA. This is when sigma factor is released. Two stretches of DNA are similar in bacteria genes: TTGACA (-35 element; consensus sequence) and TATAAT (-10 element; Pribnow box) which is responsible for identifying the precise nucleotide at which transcription begins. Bacterial cells possess a variety of different sigma factors that recognize different versions of the promoter sequence, e.g. sigma 70 the housekeeping sigma factor initiates transcription of most genes. For termination of transcription, a ring-shaped protein called rho is required - separates the RNA transcript from the DNA. Sometimes, transcription is terminated when polymerase reaches a terminator sequence and releases the RNA chain (no additional factors). Eukaryotic cells have 3 distinct transcribing enzymes in the nucleus (Table 11.1 P.437). www.notesolution.com
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