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DNA, RNA, and protein synthesis

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Jean Battinieri

on 11 May 2016

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Transcript of DNA, RNA, and protein synthesis

RNA
RNA
Much like DNA in that its monomer is a NUCLEOTIDE which consists of:
a 5 carbon sugar = RIBOSE
a phosphate group
4 nitrogen bases
Adenine
Guanine
Cytosine
Uracil - this replaces Thymine
3 types of RNA
messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomal RNA (rRNA)
Messenger RNA -
mRNA - goes to the nucleus to get the information from the DNA and takes it to the ribosomes
uses ONE DNA strand as a template to make the complementary mRNA
language is a codon "talks" to both DNA and tRNA
single stranded
Transfer RNA
tRNA - carries the amino acid from cytoplasm into the ribosomes
language anticodon
pairs with its complementary bases - codons of mRNA and anticodons of tRNA
clover or hair pin shaped
Ribosomal RNA
rRNA
helps in the synthesis of proteins
still more to learn about this type of RNA
found primarily in the ribosomes
globular in shape
Transcription
Transcription
is the synthesis of RNA under the direction of DNA
occurs in the cytoplasm of prokaryotes and in the nucleus of eukaryotes
the language of DNA is a triplet based on a series of 3 nucleotides ex. TAC CAC TGC ACT
What is the complimentary codons for the above triplets?
How mRNA and DNA go together
One side of DNA acts as a template in the formation of mRNA this is sometimes called the TEMPLATE, reader, or "sense" strand
A gene determines the sequence of base DNA triplets
mRNA is complementary to its DNA template
mRNA also follows the rules of base pairing except Adenine pairs with Uracil instead of with Thymine, Cytosine still pairs with Guanine
EX if DNA triplet ACC is the template for UGG in mRNA
THE PROCESS OF TRANSCRIPTION
a transcription factor recognizes the TATA box and binds to the DNA (a transcription factor is a group of enzymes that mediate the binding of RNA polymerase)
RNA polymerase II binds with the promoter; (promoter is the where transcription begins and acts as a binding site for RNA polymerase after a TATA box)as a result the DNA
as a result of this binding RNA polymerase II
- unwinds and and breaks Hydrogen bonds between the DNA nitrogen bases
-determines which side of the DNA is to act as the template
-pairs mRNA nucleotides one at a time with their DNA complement on the DNA template mRNA can only form in a 5'-3' direction from the free 3' end of DNA
-connects the mRNA nucleotides with covalent bonds
transcription continues until after the RNA polymerase transcribes a terminator sequence of DNA
mRNA strand breaks away from the DNA template and move from the nucleus if it is a Eukaryotic cell to the ribosome - if it is a Prokaryotic cell it goes from the cytoplasm to the ribosomes
Hydrogen bonds reform between the 2 DNA strands
DNA retwists
The formation of proteins involves 2 processes
TRANSCRIPTION - occurs in the nucleus of a eukaryotic cell and in the cytoplasm of a prokarytoic cell
TRANSLATION - occurs in the ribosomes in both eukaryotes and prokaryotes
In a prokaryote mRNA is immediately translated
In a eukaryote the pre-mRNA is processed
In eukaryotes pre-mRNA is made which needs to be altered.
the 5' end is capped off w/ a modified form a of guanine nucleotide
this cap helps to protect RNA from degradation
after the mRNA get to the cytoplasm is acts as an "attach here" sign for the ribosomes
the 3' end is also modified
an enzyme adds a poly (A) tail - a long string of Adenines
scientists think that this tail helps to:
prevent RNA degradation
helps ribosomes attach
seems to facilitate the export of mRNA from the nucleus
RNA splicing
removal of a large portion of the RNA molecule (cut and paste)
the RNA transcript is about 8000 nucleotides but an average protein is only about 400 amino acids long (1200 nucleotides)
pre-mRNA has long non-coding stretches of nucleotides - some even lay between coded segments these segments are called introns
the other segments are exons because they are expressed
Translation
Translation
ribosomes are make of 2 subunits called the large and small subunits which join only when attached to a mRNA molecule
mRNA enters the ribosome with the codon AUG
tRNA, with the complementary anticodon UAC, brings in the amino acid methionine and pairs with the codon
the second codon comes into the ribosome and the 2nd complementary tRNA comes in carrying the second amino acid
a peptide bond forms between the 1st and the second amino acid
the 1st tRNA releases the 1st amino acid and returns to the cytoplasm to pick up another amino acid - methionine
a 3rd codon comes into the ribosome
a 3rd complementary tRNA comes in to the ribosome bringing the 3rd amino acid
the process continues until a stop codon is reached
the final product is a protein
Translation the process:
Initiation
The small ribosomal sub-unit binds to the 5' leader segment of the mRNA carrying the codon AUG
the small sub-unit also bonds to a special initiator tRNA, which carries the amino acid methionine, with the anticodon UAC that is complementary to the mRNA
with the union of the small subunit, the tRNA initiator and the mRNA the attachment of the large ribosomal subunit
the initiator tRNA moves to the middle of the ribosome making room for the 2nd tRNA
Transcription (cont)
Elongation
the mRNA codon in the middle of the ribosome forms hydrogen bonds with the anticodon of an incoming molecule of tRNA carrying its appropriate amino acid
an rRNA molecule of the large ribosomal subunit acts as a catalyst in the formation of a peptide bond that joins the 1st amino acid, methionine, to the 2nd amino acid
the 1st amino acid forms a peptide bond between the carbon of its carboxyl group the nitrogen of the 2nd amino acid's amino group
the amino acid, methionine, separates from the initiator tRNA
the 2nd tRNA now moves to the middle taking the mRNA with it and moving the initiator tRNA out of the ribosome
the third tRNA moves into the ribosome w/ its amino acid and pairs with the 3rd codon
a second peptide bond is formed between the 2nd and the 3rd amino acid, the 2nd tRNA is released into the cytoplasm and the process continues
Translation (cont)
Termination
a polypeptide protein continues to form until a stop codon UAA, UAG, UGA is reached
these signal to stop translation
the protein is released
proteins control chemical reactions in the cell
The end result is a polypeptide aka protein that can bond with others to form a larger protein
structure of a protein affects function
function of a protein is to control chemical reactions
So after learning all of this explain why the nucleus is the boss of eukaryotic cells.
Mutations
Two main types
gene mutation
includes point mutations: substitutions, deletions, insertion
chromosomal mutations
MUTATIONS are changes in genetic material of a cell (or virus)
Point mutations
a change in just one base pair
a change in a single nucleotide in the DNA's template strand leads to the production of an abnormal protein ie sickle cell anemia
three types
substitution
insertion
deletion
SUBSTITUTION
replacement of one DNA nucleotide and its complement with another
some of these will result in silent mutations and on effect on the protein due to the multiple codons for many amino acids Ex. triplet CCG mutates to CCA however both code for glycine
Insertions and Deletions
these are additions or losses of nucleotide pairs in a gene
both are considered a frameshift mutation
this occurs whenever the number of nucleotides inserted or deleted is not a multiple of three
Ways mutation can occur to DNA:
an error during DNA replication
physical (p) and chemical (c) agents called mutagens
xrays (p)
UV light produce disruptive thymine dimer (p)
base analogous - chemicals that are similar to normal DNA bases but that pair incorrectly during replication (c)
Chromosomal Mutations
4 main types
deletion
duplication
translocation
inversion
Alterations can also occur in chromosome structure
Alterations can also occur in chromosome number
Deletion
occurs when a chromosomal fragment lacking a centromere is lost in cell division - the chromosome where it came from will be missing a piece
often occurs during meiosis
Duplication
if during meiosis a fragment breaks from one sister chromatid and becomes attached to the other
Inversion
when a piece of a chromosome comes off and reattaches at the opposite end of the same chromosome
Translocation
when a fragment joins a non-homologous chromosome
Practical Applications of DNA Technology
DNA technology reshaping medicine
Human Genome Project
the identification of genes whose mutations could lead to ways of diagnosing, treating , and possibly preventing those conditions
other potential benefits
helps with the study of other non-genetic diseases from arthritis to HIV
is used to compare gene expression in healthy and diseased tissues - to look for genes that are turned on or off in certain diseases
for prevention or therapy
Gene Therapy
traceable genetic disorders may eventually be correctable
normal genes are introduced into a patients somatic cells
this has not proven beneficial or effective yet - mostly unsuccessful - may work for a short time
scientist have modified how they use this therapy - heart disease with this stimulate new blood vessels
Is it ethical
many say no to changing genes even in people with life threatening diseases is wrong
they believe that it will eventually lead to a deliberate effort to control the genetic makeup of human populations
others think this no different than regular medicine or transplant of organs
do we try to treat germ-line cells in the hope of correcting the defect in future generations?
do we interfere with evolution? Damaged Genes under some conditions may be helpful - sickle cell
We need genetic variety - if genes are eliminated we are reducing variety
Pharmaceutical Products
culture organisms that can produce large amount of proteins that can be used in medicine
ex. human insulin,
human growth hormone
a protein that helps to dissolve blood clots
using genetically engineered proteins that either block or mimic surface receptors on cell membranes - HIV blocked like this
vaccines - viruses - are inactivated by chemicals called attenuated (nonpathogenic) viral strains OR subunit vaccine - one that has a protein produced from the virus and that is used to trigger an immune response
Forensic uses of DNA Technology
DNA testing can compare the blood or tissue found at a crime scene with a suspect due to a DNA fingerprint or specific banding pattern
Environmental Uses of DNA technology
genetic engineering - scientist modify organisms to help with some environmental problems - used in mining minerals or cleaning up highly toxic mining wastes
sewage treatment plants rely on microbes to break down organic compounds into nontoxic forms
help to clean up oil spills
Agricultural Uses of DNA Technology
use vaccines and hormones to treat animals
transgenic organism - genomes carry genes from another species - goal breed sheep with better quality wool, pig with leaner meat etc
adding a gene for a desired human protein to an animal's genome - product of that animal - like milk will contain that protein which can be purified from the milk
creating a transgenic animal - remove eggs cells from female and fertilize them - clone the desired gene - inject the cloned DNA directly into the nuclei of the eggs which incorporate the genes into their own - eggs get implanted into a surrogate mother
Recombinant DNA technology
technique for recombining genes from different sources in vitro then transferring the recombinant DNA into a cell for gene expression
has allowed us to develop the Biotechnology Industry
Biotechnology refers to the use of living organisms or their components to do practical tasks such as:
the use of microorganism to make wine and cheese
selective breeding of livestock and crops
production of antibiotics from microorganism
production of monoclonal antibodies
Using recombinant DNA
genes can be moved between species
scientists better understand how eukaryotic cells work
the human genome project - transcribed and translated the entire human DNA
the goal is to improve human health and food production
Genetic engineering in plants
easier in plants because many plants can be generated from just one somatic cell
most times scientists use a virus or bacteria to add the DNA into the host
useful traits that came from genetic engineering
40% of crops have a gene that are herbicide resistant - benefit - can kill weeds with out killing crops
some fruits have a gene to suppress ripening and retard spoilage.
insect resistant - reduces the need for pesticide
increase of nitrogen fixation
Safety and ethical questions of DNA technology
would hazardous new pathogens be created? if so what if those pathogens would escape the lab? - to prevent this government regulations and monitoring occur
Genetic engineering has much potential for improving health but ethical questions include:
Who should have the right to examine someone else's genes?
Should a person's genome be a factor in their suitability for a job?
Should insurance companies have the right to examine an applicant's genes?
Genetic engineering can provide solutions to environmental problems such as oil spills but what is their impact on native species?

New medical products - will they have harmful side effects?
Agricultural products - what are the potential dangers of introducing new genetically engineered organisms into the environment?

What if genetically modified crops hybridize with native plants and pass their new genes into the wild?
non-disjunction -when chromosomes fail to separate causing either a missing or extra chromosome in the gamete
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