REVIEW OF DNA DNA stands for Deoxyribonucleic Acid. DNA
contains the genetic code and the working instructions for a
cell.
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Structure of DNA DNA, which is a nucleic acid, is made up of
monomers known as nucleotides. Parts of a DNA nucleotide - 5 carbon
sugar called Deoxyribose - Phosphate group - Nitrogen Base Adenine
(A), Thymine (T), Guanine (G), Cytosine (C)
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Bonding Hydrogen bonds form between the nitrogen bases of two
strands. These hydrogen bonds occur between 2 specific nitrogen
base pairs: A T and G C Memory Helper for base pairing rules:
straight letters pair together (A T) and curved letters pair
together (G C)
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DNA Replication DNA replicates during S phase of interphase.
This occurs before cell division (mitosis). DNA replicates in the
nucleus, while in the form of chromatin. DNA replicates according
to Chargaffs base pairing rules : A T, G C
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DNA Replication The Process Replication takes place in a 2 Step
Process: 1. An enzyme breaks the hydrogen bond that is between the
nitrogen bases, unzipping DNA. The DNA molecule is unzipped in
several places ~ like a broken zipper.
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2. After DNA is unzipped, a second enzyme, called DNA
polymerase helps bind free nucleotides to the exposed nitrogen
bases. They bind according to Chargaffs rules, so A T, G C. This
continues along both strands of DNA in both directions.
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The end result is 2 identical DNA molecules. Each new DNA
molecule consists of one original strand and one newly formed
strand. These 2 DNA molecules are the sister chromatids that
undergo mitosis. Remember this???
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RNA RNA stands for Ribonucleic acid RNA carries out the
instructions of DNA by protein synthesis. DNA is too large (double
stranded) to leave the nucleus, so RNA (which carries the code of
DNA), leaves the nucleus through the nuclear pores and help make
proteins at ribosomes out in the cytoplasm.
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Structure RNA, which is a nucleic acid, is made up of monomers
known as nucleotides. Parts of a RNA nucleotide 5 carbon sugar
called ribose Phosphate group Nitrogen Base Adenine (A), Uracil
(U), Guanine (G), Cytosine (C). RNA is a single helix molecule.
Nucleotide
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Compare & Contrast of DNA & RNA CharacteristicDNARNA
SugarDeoxyriboseRibose BaseThymineUracil StructureDouble
HelixSingle Helix
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Types of RNA There are 3 forms of RNA involved in carrying out
the genetic instructions of DNA: 1. mRNA messenger RNA; It carries
the instructions (message) from DNA in the nucleus to the
Ribosomes. 2. tRNA transfer RNA; It carries (transfers) the amino
acids to the ribosome according to the message of mRNA. 3. rRNA
ribosomal RNA; It is part of the structural component of the
ribosomes; it also produces enzymes needed to bond the amino acids
together to form the proteins.
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Protein Synthesis Protein synthesis occurs in 2 steps: The
genetic material contained in DNA must be transcribed (rewritten)
onto an RNA molecule. The message contained in RNA must be
translated (converted) into a specific molecule.
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Transcription (DNA transferred to RNA) Transcription takes
place in the nucleus and allows for the genetic code of DNA to be
carried out to the ribosome. This happens in G1 of interphase.
(Remember G1 where normal cell activities take place?)
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Steps of Transcription 1. The enzyme, RNA polymerase, unzips
part of the DNA molecule.
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2. RNA polymerase adds nucleotides (A,U,G,C) according to
Chargaffs rules (A U, G C), and RNA is synthesized.
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Initially mRNA has too many nucleotides, some code for proteins
and some do not. Nucleotides in mRNA are classified as introns or
exons. Introns not required for protein synthesis they are removed
from mRNA. Exons required for protein synthesis kept and bonded
together once the introns are removed. EXONS = EX pressed INTRONS =
IN between the good stuff
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3. Then the new mRNA strand breaks apart from DNA, leaves the
nucleus through the nuclear pores and goes to the ribosomes, the
site of protein synthesis.
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There are 2 important ways that transcription differs from
replication: Only one side of the DNA molecule is copied in
transcription, both sides are copied in replication. In
transcription, RNA is used, so the nitrogen base that pairs with
adenine is uracil, in DNA replication, adenine pairs with
thymine.
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http://www.johnkyrk.com/DNAtranscription.html RNA being made! -
transcription
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Translation (RNA transferred to Proteins) Translation takes
place in the cytoplasm at ribosomes. The message is carried by
mRNA, it is interpreted by tRNA, and the final product is a
protein.
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Codon Codon = a group of 3 nucleotides on mRNA that codes for a
specific amino acid. A codon can be made up of any combination of
the 4 nucleotides (A, U, G, C), therefore there are up to 64
possible codons. (b/c 4 x 4 x 4 = 64) Ex: AAA, AAU, AAG, AAC Many
different codons represent the same amino acid b/c there are 64
possible codons, and only 20 amino acids. Amino acids are the
building blocks (or monomers) of proteins. Even though there are
only 20 amino acids, there are many, many proteins. It is the
number and arrangement of the amino acids that makes every protein
unique.
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Start codon: AUG starts the making of the amino acid chain.
Stop codon: signal to stop the making of the amino acid chain.
Genetic Code is universal, therefore the codons codes for the same
amino acid in all organisms.
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The mRNA message is translated by the ribosome using these
codons. 1 st letter 2 nd letter 3 rd letter
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Practice: AUG _________ UCA _________ CGG _________GAG
_________ GAA _________AAU _________
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tRNA The tRNA molecule (which is out in the cytoplasm) has an
amino acid on one end and an anticodon on the other end.
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Anticodon an anticodon is a group of 3 nucleotides on tRNA that
pairs up to the codon on mRNA. Acts as a binding site - The
anticodon binds to the mRNA codon according to base pairing rules
(A-U, G-C) and insures that the proper amino acid is brought to the
ribosome. tRNA - transfers the amino acids specified by the mRNA
codon to the inside of the ribosomes for protein synthesis. The
amino acid is then transferred to the growing polyopeptide chain.
(polypeptide chain = becomes a protein)
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Building of a protein The mRNA molecule slides through the
ribosome one codon at a time. The specified amino acids are carried
to the ribosome by tRNA. As another tRNA arrives at the ribosome,
the tRNA already there is bumped off, but leaves its amino acid
behind. This process continues and a chain of amino acids forms
until a stop codon is reached. Then the ribosome releases the amino
acid chain, which coils and folds to form a protein.
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Steps for translation: mRNA attaches to the ribosome mRNA
message in the form of codons is read by the ribosome. Amino acids
are made as the mRNA is being read tRNA transfers these amino acids
to the inside of the ribosome Amino acid chains form in the
ribosome Stop codon is reached Protein (amino acid chain) is
released and tRNA and mRNA is released.