DNA / RNA

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DNA / RNA

• Chapter 08

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DNA

• Deoxyribonucleic acid (DNA) is a nucleic acid
  that contains the blueprint for making the
  proteins the cell needs.
• DNA contains genes.
• Genes are specific messages instructing the cell
  on how to construct a protein.

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DNA

• DNA is the chemical used to pass genetic
  information on to the next generation of
  organisms.
• DNA controls the synthesis of proteins, which
  helps determine the characteristics of the
  organism and regulate the cells metabolism.

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DNA

• DNA contains the genetic instructions used in the
  development of all known living organisms and
  some viruses.
• DNA molecules are used for long term storage of
  information.
• DNA carries the instructions necessary to create
  RNA and proteins therefore, it is often compared
  to a blueprint.

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DNA Structure

• DNA is a nucleic acid.
• Nucleic acids are large polymers of nucleotides.

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DNA Structure

• DNA consists of two long polymers of simple units
  known as nucleotides.
• These two strands run in opposite directions to
  each other and are therefore known as
  anti-parallel.
• The strands have backbones made of sugars with
  phosphate groups attached.

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DNA Structure

• Attached to each sugar is one of four types of
  molecules called bases.
• Information is encoded in the sequence of these
  four bases along the backbone.
• The information is read using the genetic code.

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DNA Structure

• The genetic code specifies the sequence of amino
  acids within proteins.
• The code is read by copying stretches of DNA into
  RNA (A process known as transcription).

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DNA Structure

• A nucleotide consists of a sugar molecule, a
  phosphate group, and a nitrogenous base.
• There are four different nitrogenous bases in DNA

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DNA Structure

• Adenine (A), guanine (G), cytosine (C), and
  thymine (T).
• The DNA nucleotides can combine into a long
  linear DNA molecule that can pair with another
  linear DNA molecule.

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DNA Structure

• The two paired strands of DNA form a double helix
  with sugars and phosphates on the outside and the
  nitrogenous bases on the inside.
• The nucleotides form hydrogen bonds with one
  another, which helps to stabilize the helical
  structure.

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DNA Structure

• Adenine pairs with Thymine (A-T).
• Guanine pairs with Cytosine (G-C).

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Nitrogenous Bases

• The nucleotide bases are nitrogenous bases that
  are involved in pairing in DNA and RNA. This is
  known as base pairing.
• In genetics they are simply called bases.
• Adenine, Guanine, Cytosine, and Thymine are DNA
  bases.
• Adenine, Guanine, Cytosine, and Uracil are RNA
  bases.

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Adenine
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Guanine
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Thymine
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Cytosine
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Uracil
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Chromosomes

• Within cells, DNA is organized into structures
  called chromosomes.

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Chromosomes

• The chromosomes are duplicated before the cell
  divides, a process known as DNA replication.
• Within the chromosomes, chromatin proteins such
  as histones compact and organize DNA. The
  chromatins help determine which parts of the DNA
  are transcribed.

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Eukaryotes Vs. Prokaryotes

• Eukaryotic organisms (animals, plants, fungi, and
  protists) store their DNA inside the cell
  nucleus.
• Prokaryotic organisms (bacteria and archae) have
  no nucleus therefore, the DNA is found in the
  cytoplasm.

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DNA Replication

• When a cell grows and divides, two new cells
  result.
• DNA replication is the process by which a cell
  makes another copy of its DNA.
• Base pairing rules and many enzymes make
  replication possible.

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DNA Replication

• DNA replication is the process of copying a
  double-stranded DNA molecule to form two
  double-stranded molecules.

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DNA Replication

• Each DNA strand holds the same genetic
  information therefore, both strands can serve as
  a template for the reproduction of the
  complementary strand.
• The template strand is conserved in its entirety
  and the new strand is assembled from nucleotides.
  This is known as semiconservative replication.

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DNA Replication

• The resulting double-stranded DNA molecules are
  identical.
• DNA replication must happen before cell division
  can occur.

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DNA Replication

• Helicases are enzymes that bind to the DNA and
  separate the two strands of DNA.
• DNA polymerase incorporates DNA nucleotides into
  the new DNA strand. The nucleotides enter
  according to the base pairing rules.

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DNA Replication

• In prokaryotic cells, this replication process
  starts at only one place along the DNA molecule
  (origin of replication).
• In eukaryotic cells, the replication starts at
  the same time along several different places of
  the DNA molecule.

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DNA Replication

• Two new identical, double-stranded DNA molecules
  are formed.
• The new strands of DNA form on each side of the
  old DNA strands.

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DNA Replication

• The exposed nitrogenous bases of the original DNA
  serve as the pattern on which the new DNA is
  formed.
• Two double helices are formed with identical
  nucleotide sequences.
• A portion of the DNA polymerase molecule edits
  the newly created DNA molecule and makes
  corrections if needed.

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DNA Replication
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Repair of Genetic Information

• If an error or damage occurs to the DNA helix on
  one strand, the pairing arrangement of
  nitrogenous bases on the other undamaged strand
  can be read.
• This information is used to repair the damaged
  strand.

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DNA Code

• DNA stores information.
• The order of the nitrogenous bases is the genetic
  information that codes for proteins.
• The nucleotides are read in sets of three.
• Each sequence of three nucleotides is a codeword
  for a single amino acid.
• The information to code one protein can be
  thousands of nucleotides long.

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RNA Structure And Function

• Ribonucleic Acid (RNA) is important in protein
  production.
• RNAs nucleotides contain a ribose sugar whereas
  DNAs nucleotides contain a deoxyribose sugar.
• Ribose has an OH group and deoxyribose has an H
  group on the second carbon atom.

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RNA Structure And Function

• RNA contains the nitrogenous bases Uracil (U),
  guanine (G), cytosine (C), and adenine (A).
• DNA is found in the cells nucleus, while RNA is
  made in the nucleus and then moves out into the
  cytoplasm of the cell.

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RNA Structure And Function

• DNA directs protein synthesis by using RNA.
• RNA is made by enzymes that read the protein
  coding information in DNA.
• RNA nucleotides pair with DNA nucleotides.
• RNA contains Uracil instead of Thymine so adenine
  in DNA pairs with Uracil in RNA.

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Nucleic Acid Base Pairing Rules
DNA pairs with DNA DNA pairs with RNA RNA pairs with RNA
A pairs with T A pairs with U A pairs with U
T pairs with A T pairs with A U pairs with A
G pairs with C G pairs with C G pairs with C
C pairs with G C pairs with G C pairs with G
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Transcription

• Transcription is the process of using DNA as a
  template to synthesize RNA.
• The RNA polymerase enzyme reads the sequence of
  DNA nucleotides and follows the base pairing
  rules between DNA and RNA to build the new RNA
  molecule.

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Transcription

• The two strands of the double stranded DNA
  molecule are separated to expose the nitrogenous
  bases.
• The DNAs nitrogenous bases are read and paired
  with the RNA nucleotides.
• Only one strand of the DNA molecule is read (the
  coding strand). The other strand is referred to
  as the non-coding strand.

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Transcription

• Promoter sequences are specific sequences of DNA
  nucleotides that RNA polymerase uses to find a
  protein-coding region of DNA and to find out
  which strand of DNA is the coding strand.

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Transcription

• Termination sequences are DNA nucleotide
  sequences that indicate when RNA polymerase
  should finish making an RNA molecule.

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3 Types of RNA

• Messenger RNA (mRNA) carries the blueprint for
  making the necessary protein.
• Transfer RNA (tRNA) reads mRNA and brings in
  the necessary amino acids.
• Ribosomal RNA (rRNA) reads the mRNA and brings
  in the necessary amino acids.

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Translation

• Translation is the process of using information
  in RNA to direct protein synthesis.
• mRNA is read in sets of three nucleotides called
  codons.

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Translation

• A codon is a set of three nucleotides that codes
  for a specific amino acid.
• The ribosome is made up of proteins and ribosomal
  RNA (rRNA).
• The ribsome holds the mRNA in place and reads
  its codons.

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3 Phases of Translation

• Initiation
• Elongation
• Termination

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Initiation

• The small ribosomal subunit binds to the mRNA and
  moves along until it reaches an AUG codon to
  signal the beginning of translation.
• Transfer RNA (tRNA) carries amino acids to the
  mRNA complex.

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Initiation

• The anticodon portion of the tRNA interacts with
  the mRNA to match the correct amino acid to the
  codon in the mRNA nucleotide sequence.
• The tRNA that binds to the AUG codon that signals
  the beginning of translation carries the amino
  acid methionine therefore, every protein begins
  with this amino acid.

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Elongation

• The ribosome functions as an assembly line.
• New amino acids are carried by tRNA to the
  corresponding mRNA segment.
• The anticodon on tRNA matches with the codon on
  mRNA.
• The amino acid is then attached to the end of the
  chain and the protein becomes elongated.

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Termination

• The ribosome will continue to add new amino acids
  until a stop signal is reached on the mRNA
  molecule.
• The stop codon can be either UAA, UAG, or UGA.

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Termination

• When these codons are encountered, a release
  factor enters the ribosome. The ribosomal
  subunits release mRNA.
• The mRNA can then either be reused or broken down
  to stop protein production.

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Translation
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Nearly Universal Genetic Code

• The code for making protein from DNA is the same
  for nearly all cells.
• Bacteria, protists, plants, fungi, and animals
  all use DNA to store their genetic information.
• They all transcribe information in DNA to RNA.
• They all translate the RNA to synthesize protein
  using a ribosome.

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Nearly Universal Genetic Code

• Almost all use the same three nucleotide codons
  to code for the same amino acid.
• In eukaryotic cells, transcription always occurs
  in the nucleu, and translation always occurs in
  the cytoplasm.

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Nearly Universal Genetic Code

• These similarities make it possible to use
  bacteria to synthesize human proteins (i.e.
  insulin).
• Some viruses use RNA to store their genetic
  information (retroviruses). HIV is an example of
  this. Retroviruses use RNA to make DNA, which is
  then used to make proteins.

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Gene Expression

• Gene expression occurs when a cell transcribes
  and translates a gene.
• Cells control which genes are used to make
  proteins.
• The different cell types in the human body are
  due to which proteins the cell is producing.

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Controlling Protein Quantity

• An enzymes activity can be regulated by
  controlling how much of that enzyme is made.
• The cell controls how much mRNA is available for
  translation, which in turn determines the
  quantity of the protein produced.

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Controlling Protein Quantity

• Enhancer and silencer sequences affect the
  ability of RNA polymerase to transcribe a
  specific protein.
• Enhancer sequences increase protein synthesis by
  increasing transcription.
• Silencer sequences decrease protein production by
  decreasing transcription.

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RNA Degradation

• Cells regulate gene expression by limiting the
  length of time that mRNA is available for
  translation.
• Enzymes in the cell break down mRNA.

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Mutations

• A mutation is any change in the DNA sequence of
  an organism.
• Errors during DNA replication can cause mutation.
• External factors can cause mutation

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Mutations

• Radiation, carcinogens, drugs, viruses.
• Not all mutations cause a change in the organism.
• If the mutation occurs away from the
  protein-coding sequence of the DNA, it is
  unlikely to be harmful to the organism.

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Silent Mutation

• A silent mutation is a change that does not
  change the amino acids used to build a protein.

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Nonsense Mutation

• A nonsense mutation causes a ribosome to stop
  protein synthesis by introducing a stop codon too
  early.
• This prevents the formation of functional
  proteins.

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Missense Mutation

• A missense mutation causes the wrong amino acid
  to be used in making a protein.
• This will change the shape of the protein and
  affect its active sites.
• This can cause an abnormally functioning protein.

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Insertions And Deletions

• Some mutations involve larger spans of DNA than a
  change in a single nucleotide.
• An insertion mutation adds one or more
  nucleotides to the normals DNA sequence.

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Insertions And Deletions

• This can add amino acids to the protein and
  change its function.
• A deletion mutation removes one or more
  nucleotides.
• This can delete amino acids from the protein and
  change its function.