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DNA

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by

Gabriel Higdon

on 31 March 2015

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Transcript of DNA

DNA
What is it?
Deoxyribonucleic acid is a molecule made up of deoxyribose sugar, phosphate groups, and nitrogenous bases that contains the genetic information in most living organisms.
DNA must replicate, transcribe, and translate in order to sustain the genetic information needed for life.
Replication occurs in four simple steps:
1. Initiation
2. Unwinding
3. Elongation
4. Termination
In order for replication to occur, we must make our double-stranded DNA into single-stranded templates.
1. Initiation
First, an
initiator protein
binds to the replication origin
A short piece of DNA then unwinds.
2. Unwinding
DNA helicase
then comes in and breaks the remaining hydrogen bonds between the two nucleotide strands.
5' -----> 3'

Single-stranded-binding proteins (SSBs)
then attach to the single strands to prevent secondary structures from forming.

DNA gyrase/topoisomerase
is another essential enzyme that helps relieve torque built up in the unwinding DNA.
3. Elongation

The enzyme
primase
adds a RNA
primer
because a 3' -OH group has to be present in order to initiate DNA synthesis.

A primer is added before every Okazaki fragment begins.
An
Okazaki fragment
is the gap between continuous and discontinuous DNA or the leading and lagging strand.
3. Elongation...continued
DNA polymerase III
then adds new nucleotides to the growing 3' end.

DNA polymerase I
is also an important enzyme that removers RNA primers and replaces them with DNA.

After DNA polymerase I has replaced a primer,
DNA ligase
is then used to seal up the gaps in the new DNA strand.
=
What DNA
replication
is proposed
to look like.
------------>
4. Termination
Two ways:
Two replication forks meet
Termination sequence blocks helicase from moving down a DNA strand
So what's next??
TRANSCRIPTION!!!
Replication
- DNA doubling before cell division
Transcription
- synthesis of an RNA molecule from DNA
A transcription unit must be present which includes the following:
1.
Promoter
- recognizes template DNA and start site
2.
RNA-coding region
- sequence of DNA being copied into RNA
3.
Terminator
- end site
1. Initiation
The
transcription apparatus,
which consists of several important enzymes, binds to the promoter region.

RNA polymerase
is then able to bind to the promoter to begin synthesizing RNA.

RNA synthesis occurs from the 3' end of the RNA molecule and is
complementary
and
antiparallel
to the template DNA strand.

Similar to replication, transcription occurs in three steps:
1. Initiation
2. Elongation
3. Termination
2. Elongation
RNA polymerase continues to unwind DNA as nucleotides join to the growing RNA strand.
3. Termination
Once RNA polymerase transcribes the terminator, transcription stops.

RNA polymerase detaches from the DNA template

RNA detaches from RNA polymerase
Translation
- the process of assembling amino acids into proteins (protein synthesis)
Translation occurs in four steps:
1. tRNA charging
2. Initiation
3. Elongation
4. Termination
1. tRNA charging
tRNA binds to a specific amino acid on its 3' end
Recognition of the appropriate amino acid (AA) is based on size, charge, and R-group of the AA
2. Initiation
mRNA
binds to the small subunit of a ribosome.
Initiator tRNA binds to the mRNA by base pairing between the codon and anticodon.
The large subunit of a ribosome then binds and forms the initiation complex.
2. Elongation
A ribosome has three sites that a tRNA can occupy:
E (exit), P (peptidal), and A (aminoacyl) sites
.
The initiator tRNA starts out occupying the P site
Another charged tRNA comes and binds to the A site
The amino acids on each of the tRNAs form a peptide bond which allows the amino acid to be released from the tRNA in the P site
2. Elongation...continued
The last part of elongation is
translocation
.

The ribosome moves down the mRNA strand to the next codon.

The tRNAs in the existing P and A sites then shift to the E and P sites to allow another tRNA to come occupy the A site.

The new amino acid forms a peptide bond to the other existing amino acids resulting in a growing chain.
3. Termination
Elongation continues until a termination codon is translated.

Once this codon is translated, a
release factor
binds to the A site in the ribosome.

The release factor causes the tRNA and the mRNA to be released from the ribosome.
Recap of translation
This Prezi was made by Gabriel Miner in hopes of receiving much needed bonus points for Genetics at UAB with Dr. Mukhtar.


Next up is....
Translation!!!
Full transcript