DNA And RNA Replication Biochemistry Task 1

Topics: DNA, DNA replication, Protein Pages: 20 (849 words) Published: April 14, 2015
DNA and RNA
Replication
Deborah J Brooks
Biochemistry (GRT1) Task 1
Western Governors University

Objectives
DNA Replication at Biochemical Level
 Role of Ligase
 Role of mRNA
 Role of RNA Polymerase Inhibition related to
the death cap mushroom


Introduction
Nucleic acids are required for the storage and
expression of genetic information. There are
two chemically distinct types of nucleic acids.
 DNA

(deoxyribonucleic acid). The repository
of genetic information.



RNA (ribonucleic acid). “The working
copies” of DNA. The copying or translation
process in DNA synthesis.

DNA Replication
DNA replication at the biochemical level
involves the copying of doubled-stranded DNA
to produce a second double helix that is
identical to the first (“DNA Replication”).
The DNA being copied passes through several
proteins, and these unwind it and split into two
single strands; each of the two strands is copied
and become one-half of the new DNA doublehelix, in a process termed “semi-conservative” replication.

DNA Replication
Each of the proteins in the replication process
performs a specific function. For example,
helicase unwinds the double helix into two
individual strands, while single-stranded binding
proteins coat the DNA strands to keep them
from adhering back together.
Primase synthesizes the primers that will begin
the replication process, and polymerase- in
conjunction with the DNA clamp-strings
nucleotides together to create a DNA strand.

FA

DNA Replication Diagram
DNA REPLICATION

HELICASE
SINGLE-STRANDED
DNA BINDING PROTEINS

Name S AT THE
BEGIN
Title
THE REPLICA
TION
FORK
Name
LEADING TO LOCAL
SEPARATION OF
STRANDS

FACILITATED BY

Name S TO
LEAD

ALLOWING BINDING OF

POSITIVE
SUPERCOILS WHICH
ARE REMOVED BY

DNA TOPOISOMERASES

DNA POLYMERASES
WHICH SYNTHESIZE

Tit
le
NEW DNA STRA
N
DS IN THE 5'-3'
DIRECTION
Name

I

RNA PRIMER
SYNTHESIZE
BY
EXTENDING

PRIMASE

RESULTING IN

BIDIRECTIONAL
ELONGATION
INVOLVING

BOTH STRANDS
OF THE DOUBLE
HELIX

WHICH SERVES AS

TEMPLATES FOR
CONSTRUCTING

TWO COMPLEMENTARY
DAUGHTER STRANDS
CONSISTING OF

ONE LEADING
STRAND

A PROCESS CALLED

ONE LAGGING
STRAND
SYNTHESIZE IN

SEMICONSERVATIVE
REPLICATION

Ligase Enzyme in DNA
Replication
Ligase links shorter sections, known as
“Okazaki fragments,” together to create a
single long strand of DNA.
Since DNA polymerases are not able to seal up
nicks that occur when DNA replaces RNA
primers in the replication process, ligase comes
into the process to do that through the use of
phosphdiester bonds in ATP or NAD connecting
a free 3’ hydroxyl to the 5’ phosphate next to it.

Ligase in DNA Replication
Diagram

Role of mRNA

mRNA Diagram

Polymerase Inhibition and the
Death Cap Mushroom
 This

knowledge of biochemistry of DNA can
help to explain how the death cap
mushroom poisons an individual who
consumes it.

 The

poisonous effect of the death cap
mushroom is related to the biochemistry of
DNA and RNA and the process of RNA
polymerase inhibition.

Death cap mushroom/Amatoxins
 The

death cap mushroom gives off
amatoxins that are toxic to the liver as well
as being absorbed from the gastrointestinal
tract.

 The

main toxin given off by death cap
mushroom is ά- amanitine, and there are
also nine cyclic 900-Dalton molecular
weight octapeptide amatoxins.

Death cap/Polymerase
Inhibition


Shortly after an individual ingest άamanitine, the nucleoli of his/her liver cells will disintegrate, which in turn interferes
with DNA transcription because it inhibits
RNA polymerase II.



The way ά-amanitine does this is to bind to
the 140,000-Dalton RNA polymerase ll
subunit, inhibiting it.



This inhibition effectively stops protein
synthesis in the body, so the organs that
are most dependent on protein synthesis
are the ones that...

References: Clancy, Suzanne; Brown, William. “Translation:
DNA to mRNA to Protein.” Nature Education, 1.1.
http://www.nature.com/scitable/topicpage/translati
on-dna-to-mrna-to-protein-393
Richard, Harvey, Ferrier, Denise. (2010).
Biochemistry. Lippincott’s Illustrated Reviews 5th
ed. Baltimore, Maryland. Wolters Kluwer.
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