QOD 1/3/12 What is the shape of DNA?. DNA, RNA, and Protein Synthesis
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- QOD 1/3/12 What is the shape of DNA?
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- DNA, RNA, and Protein Synthesis
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- Discovery of DNA 1928- Fredrick Griffith He found that when
harmless bacteria are mixed with dead harmful bacteria, the
harmless will absorb the genetic material of the harmful and become
harmful themselves Transfer of genetic material is called
transformation
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- Discovery of DNA 1940s- Avery and colleagues Wanted to know
what caused transformation (DNA, RNA, or protein) They separated
these individual parts and tested them. They found DNA was the
cause of transformation In other words, they found if harmless
bacteria took in harmful bacterias DNA, the harmless became
harmful.
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- Discovery of DNA 1952- Hershey and Chase Wanted to test whether
DNA or protein was the genetic material that viruses pass on when
they infect an organism. They used viruses that infect bacteria
(called bacteriophages) They radioactively labeled the DNA and the
protein (this allowed them to trace the path of each) They found
DNA was injected into the bacteria to infect it, not protein. So
DNA was the genetic material
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- Discovery of DNA 1950s- Watson, Crick, Franklin, and Wilkins
Franklin and Wilkins discover DNA is helical Watson and Crick build
a model of DNA and determine it is a double helix
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- DNA Structure DNA is a double helix
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- DNA Structure It is made of nucleotides (so nucleotides are the
monomers of DNA!) Nucleotides have 3 parts: 1.Nitrogenous base
(there are 4 kinds) 2.Phosphate Group 3.5 carbon sugar called
deoxyribose
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- phosphate deoxyribose bases nucleotide
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- DNA Structure Nitrogenous bases: Contain nitrogen and is a base
Purines- (double ringed) Adenine (A) Guanine (G) Pyrimadines-
(single ringed) Cytosine (C) Thymine (T)
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- DNA Structure DNA is made up of 2 straight chains of
nucleotides The bases on each of those chains are attracted to each
other and form hydrogen bonds The force of thousands or millions of
hydrogen bonds keeps the two strands of DNA held tightly
together
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- DNA Structure If DNA was a spiral staircase The alternating
sugar and phosphates would be the hand rails. The bases would be
the steps But, they would be weak steps as they are only held
together by hydrogen bonds
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- DNA models Since the sugar- phosphate hand rails of DNA never
change, we often simplify DNA into the letters of the nitrogenous
bases. For example, this DNA strand can be simplified to TGAC
ACTG
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- DNA Structure Base pairing rules in DNA: Hydrogen bonds form
between specific pairs Adenine ALWAYS pairs with Thymine Cytosine
ALWAYS pairs with Guanine These pairs (A-T and C-G) are called
complementary base pairs Each complimentary pair contains one
single and one double ringed base
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- DNA Structure Because of the base pairing rules, one strand of
DNA is complementary to the other strand (otherwise they would not
stick together!) So if one strand has a base sequence of TGCC, the
other strand will have ACGG.
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- Lets Practice Right the complimentary DNA strand for TGACCGAT
ACTGGCTA
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- QOD 1/4/12 Which scientists built the first model of DNA?
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- DNA Replication DNA Replication is the process by which DNA is
copied in a cell before the cell divides.
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- DNA Replication First, enzymes called Helicases separate the
two strands of DNA Helicases break hydrogen bonds
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- DNA Replication Next, enzymes called DNA polymerases add
complimentary nucleotides to the separated strands of DNA
Nucleotides are found floating freely in the nucleus
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- DNA Replication When replication is finished, there are 2 DNA
molecules, each had one old strand and one new strand
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- DNA Replication Replication is usually very accurate There is
only about 1 error for every BILLION nucleotides added! The reason
is that DNA Polymerases also proofread the DNA and fix any errors
during replication
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- DNA Replication If an error does occur, it results in a
different nucleotide sequence in the new DNA strands This is called
a mutation A change in even one nucleotide can be very harmful to
an organism (for reasons we will see later) Some mutations can
affect the growth of cells, causing growth to accelerate, this
results in cancer Changes can be good- mutations sometimes lead to
adaptations and therefore evolution
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- Protein Synthesis DNA is the code for hereditary
characteristics. The genetic code is how organisms store hereditary
information and translate it into proteins
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- Protein Synthesis DNA codes for all of the bodies proteins
(like enzymes) Genes are sequences located in the DNA that code for
specific characteristics The code (or gene) for the production of
the protein melanin is in your DNA and creates your hair and skin
color The code or recipe for all of the enzymes that help you
digest your food is located in your DNA
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- Protein Synthesis The code or recipe within DNA cannot be read
directly- DNA cannot leave the nucleus and proteins are made in the
cytoplasm of cells So the code is transcribed (copied) and
translated (turned into something useful) by ribonucleic acid
(RNA)
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- Protein Synthesis Remember, proteins make us who we are They
are responsible for chemical reactions occurring in us (enzymes)
and for the hereditary characteristics that we have (such as eye
color) The building blocks (or monomers) of proteins are amino
acids DNA holds the recipe for the amino acid sequence of all the
proteins we need to make
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- Protein Synthesis RNA directs protein synthesis, which is the
making of proteins from DNA
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- DNA vs RNA Both are made of nucleotides Both are involved in
protein synthesis DNA has the sugar deoxyribose, while RNA has the
sugar ribose RNA uses the nitrogenous base uracil instead of
thymine (used in DNA) RNA is single stranded, while DNA is double
stranded RNA is usually MUCH shorter than DNA
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- Protein Synthesis There are several types of RNA involved in
protein synthesis Messenger RNA (mRNA) carries the genetic
instructions from the DNA to the ribosomes
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- Protein Synthesis Ribosomal RNA (rRNA) part of the ribosome
Remember ribosomes make proteins
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- Protein Synthesis Transfer RNA (tRNA) transfers the amino acids
to the ribosomes to make proteins
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- QOD 1/6/12 What type of RNA carries the genetic instructions
from the DNA to the ribosomes?
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- Protein Synthesis - Transcription The first step in protein
synthesis is transcription: An Enzyme called RNA polymerase binds
to a genes promoter region A promoter is just a specific nucleotide
sequence where the RNA polymerase can attach The RNA attaches to
the RNA polymerase and the DNA begins to uncoil
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- Protein Synthesis - Transcription The RNA polymerase adds
complimentary nucleotides resulting in a straight chain RNA
molecule The DNA code determines what bases will be added (A with
U, T with A, and G with C) For example if the DNA code for a gene
is ATCCGTT, then the RNA will be UAGGCAA Remember, RNA does not
have thymine, it has Uracil!!
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- The copying of DNA continues until the RNA polymerase reaches a
STOP signal That is a specific sequence of nucleotides that tells
the RNA polymerase to STOP and release the RNA and DNA The RNA is
mRNA, because it is the messenger of the code from the DNA to the
ribosomes Protein Synthesis - Transcription
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- Lets Practice What is the mRNA strand for the following DNA
sequences?? DNA - ATCGGT mRNA - UAGCCA
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- Lets Practice What is the DNA sequence that the following mRNA
strands came from?? mRNA - GUCAUG DNA - CAGTAC
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- Once the newly made RNA leaves the nucleus it attaches to a
ribosome at the promoter region. Ribosomes will read 3 nucleotides
in the RNA code at a time These 3 nucleotides are called codons.
Each Codon codes for an amino acid, a START signal, or a STOP
signal Protein Synthesis - Translation
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- For example, the sequence AUG codes for the amino acid
Methionine and means START(it is the only one that means start) ALL
mRNA molecules start with AUG, otherwise, they would have a start
region for protein synthesis Protein Synthesis - Translation
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- So, in translation, the RNA is translated into amino acids,
which are put together to form proteins (or polypeptides) The
translation occurs with the help of tRNA, which carries the amino
acids Protein Synthesis - Translation
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- When the ribosome reads the start sequence (AUG), a tRNA
molecule comes along with the anticodon The anticodon is the
complementary sequence, which would be UAC. The complementary bases
bond with each other and the amino acid methionine begins the
protein synthesis within the ribosome tRNA transfers amino acids to
the ribosome Protein Synthesis - Translation
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- There are only 20 amino acids Most amino acids have more than
on codon For example, Leucines codons are UUA, UUG, CUU, CUC, CUA,
and CUG But each codon codes for ONLY 1 amino acid For example, CUU
only codes for Leucine and nothing else Protein Synthesis -
Translation
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- After the start sequence, the ribosome moves to the next codon.
Lets say the next codon is GUC Now a tRNA that has the anticodon
CAG would attach to the ribosome and it would carry the amino acid
Valine. The amino acid Valine would attach to the Methionine from
before (now we have a dipeptide!) Protein Synthesis -
Translation
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- This process continues and the polypeptide grows until the STOP
codon is reached UAA, UAG, and UGA are the only stop codons The
protein, ribosome and all RNA is released to perform other needed
functions Protein Synthesis - Translation
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- Protein Synthesis - Summary Lets learn how to BREAK THE
CODE!!
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- Protein Synthesis - Summary This is an mRNA strand- figure out
what the DNA code was that it came from:
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- Protein Synthesis - Summary 1 - TAC 2 - TGC 3 - CTC 4 - GAA 5 -
GCC 6 - TCG 7 - ATC
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- Protein Synthesis - Summary Now figure out the anticodons
(which will be found on the tRNA)
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- Protein Synthesis - Summary 1 - UAC 2 - UGC 3 - CUC 4 - GAA 5 -
GCC 6 - UCG 7 - AUC
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- Protein Synthesis - Summary Now use the CODON chart to figure
out the amino acid sequence
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- Protein Synthesis - Summary 1 Methionine (start) 2 - Threonine
3 Glutamic Acid 4 - Leucine 5 - Arginine 6 - Serine 7 - STOP
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- QOD 1/11/12 What is the amino acid for AUG?
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- Genetic Mutations Can effect reproductive and body cells.
Reproductive cells: Offspring may have genetic disease. Body cells:
Can cause cancer or may have no effect. Can change the entire
structure of a protein, and effect the shape of the protein. MYTH:
All mutations are bad.
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- Point mutations Occurs when a single base changes. Types:
Silent mutation- no amino acid change Missense- changes amino acid
that is coded. Nonsense- changes sequence to a stop codon.
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- Frameshift is a shift in the reading frame of DNA sequence
changes everything downstream (after) Types: Insertions- adding
base(s) Deletions- losing base(s) Frameshift mutations