Wgu Biochemistry Task 1

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 are most sensitive to
this type of poisoning; these would be the gastrointestinal tract and the liver.



When protein synthesis shut down, cell metabolism also shuts down, and cells die.

Death cap mushrooms/Amatoxins 

These amatoxins then get absorbed into the gut and are then transported to the hepatocytes. 

Brent & Palmer note that boiling cyclopeptides like the amatoxins does not denature them, so cooking the death cap mushroom does not make it less poisonous.

In conclusion: Death cap mushroom 

It is estimated that the amount of amatoxin in just one death cap mushroom can be lethal to an adult.



Individuals poisoned by the death cap mushroom need to indicate to medical professionals that they have eaten mushrooms. Although newer treatments exist that have reduced deaths, and rapid treatment is essential.

Summary

References
“Definition: Amanita phalloides.” Webster’s Online
Dictionary.
http://www.websters-online-dictionary.org/definiti ons/Amanita+phalloides “DNA Replication Enzymes.” Cliffs Notes. http://www.cliffsnotes.com/study_guide/DNA-R eplication-Enzymes.topicArticleId-24594,arti cleId-24550.htlm References
“DNA Replication.” Wiley. http://www.wiley.com/college/pratt/0471393878/stu dent/animations/dna_replication/index.htlm
Brent, Jeffrey, Robert B. Shannon: Haddad and
Winchester’s Clinical Management of poisoning
Drug Overdose, 4th ed. Philadelphia, PA: Saunders,
2007. <http://www.mdconsult.com/books/page.do? eid=4-u1.0-B978-07216-0693-4..500281&isbm=978-0-7216-0693 4&type=bookpage&from=content&uniqId=313471
861-30>

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.