DNA

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DNA Replication
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The Size of DNA...
If the DNA of one cell is stretched out, it makes
a 7 ft. long string
There are about 5 trillion cells in the human body
If you connected all the DNA together, it would
be long enough that it would take light over 10
hours to travel its length
(ruptured bacteria)
This is a whole lot of information
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The Basics of DNA
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DNA and Heredity

• Rosalind Franklins research was used in the
  discovery of DNA structure
• Francis Crick James Watson developed the first
  model of DNA
• Watson Crick concluded that all living cells
  contain DNA

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• Prokaryotes

• Genetic material is a single loop of DNA
• Located in the cytoplasm

• Eukaryotes

• Genetic material in the form of a chromosome
• Located in the nucleus

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Review the Cell

• Cells contain the nucleus
• The nucleus is the brains of the cell
• Chromatin DNA tightly wrapped around proteins
  (histones)
• Chromatin supercoils to form chromosome
• Chromosome visible during mitosis

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Review the Cell

• Chromosomes are found inside the nucleus
• Chromosomes contain genes
• Genes are made up of DNA

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DNA Structure

• DNA is a Double Helix - like a twisted rubber
  ladder made from three main components (like
  legos)
• Sides of the ladder are composed of alternating
  sugar and phosphate pieces
• Each rung of the ladder is made up of two
  complementary bases
• A bound to T
• C bound to G
• DNA is put together in chunks called NUCLEOTIDES
• Each nucleotide has a sugar, PO43- and base

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Nucleotides
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• A nucleotide is held together with strong
  molecular bonds
• Oxygens provide the hooks necessary to bind to
  other NTPs
• We identify where these Oxygens are by labeling
  the carbons of the deoxyribose sugar

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4
2
3
(see, no oxygen at 2)
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DNA Strand

• Each of the components of the nucleotide binds to
  another nucleotide to form a single DNA strand
• Since Oxygen easily forms two strong bonds, the
  phosphate and sugars both bind most strongly
• The Hydrogens on the base bind less strongly with
  an Oxygen or Nitrogen from another base to bind
  one strand to another

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ds DNA Helix

• Finally we have the characteristics of double
  stranded DNA
• STRONG bonds between the deoxyribose sugars and
  phosphates
• WEAK bonds between the Hydrogen and Oxygen or
  Nitrogen (weaker between A and T than C and G)
• Twisting of the two anti-parallel strands to form
  a double helix
• Heat it up, which bonds break first?...

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The Replicator

• We start with some ds DNA
• Replication The copying of DNA prior to the cell
  undergoing division
• It occurs at multiple sites along the DNA strand
  simultaneously
• DNA strands are complementary- that is each
  strand can be used to make the other strand.

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Replication 1

• DNA Helicase comes on the scene binds and
• UNWINDS the DNA upstream
• Then UNZIPS the hydrogen bonds between the base
  pairs This site is known as the replication
  bubble
• DNA single-stranded binding proteins stabilize
  the single strand structure.
• The sites on DNA where separation and replication
  occur are called replication forks.
• Replication takes place in both directions until
  each chromosomes is completely copied. In a 5?
  3 direction.

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Replication 1

• There are two replicating strands the leading
  strand and the lagging strand. The leading
  strand moves in a forward motion. The lagging
  strand move in a backwards motion.
• The lagging strand is made up of Okazaki
  fragments which replicate short pieces of DNA at
  a time.

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Replication 2

• DNA polymerase joins individual nucleotides to
  produce a DNA molecule, which is a polymer.
• Complementary Bases begin adding into both sides
  of the ds DNA
• A binds with T, C binds with G (no other
  possibility because of the shape of the bases!)
• The final job of the Polymerase is to Proofread
  the NTPs after they are added (back on the 5
  end) and to clip out any that are incorrectly
  paired

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Replication 3

• Primase is an enzyme that helps start DNA
  replication in an Okazaki fragment.
• DNA ligase removes the gaps that are in place due
  mainly to the use of primase in the lagging
  strand.
• Finally you have 2 identical copies of double
  stranded DNA
• The original strand serves as a template for the
  new strand
• The resulting DNA molecules are made up of one
  parent (original) strand and one daughter (new)
  strand

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DNA Structure
and Replication
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YouTube - DNA Transcription and Protein Assembly
YouTube - DNA Replication
YouTube - "The Gene Scene"
YouTube - BioRap (DNA Replication and Protein
Synthesis with a Beat)
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Review Questions
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Which of the following determines the traits of
an organism?
A cell nucleus
B chromosomes
C DNA
D eggs
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Which of the following determines the traits of
an organism?
A is incorrect because the nucleus does not
determine traits but contains information that
does.
B is also incorrect because chromosomes do not
determine traits but contain information that
does.
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Which of the following determines the traits of
an organism?
C is correct because DNA is the genetic
information, found in the nucleus, that
determines the traits of an organism.
D is incorrect because eggs are a cell that
contain genetic material that will be used to
determine traits, but does not determine an
organism's traits itself.
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DNA molecules separate into single strands, which
are then used to construct two identical strands
of DNA. This process ensures that the
A cytoplasm is in equilibrium
B mitochondria are genetically identical to
the chloroplasts
C parent cells use little ATP
D daughter cells are genetically identical
to the parent cells
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DNA molecules separate into single strands, which
are then used to construct two identical strands
of DNA. This process ensures that the
A is incorrect because cytoplasm is not part of
DNA molecules rather, cytoplasm is the
fluid-like substance that fills a cell.
B is incorrect because mitochondria are not
identical to chloroplasts further, animal cells
do not have chloroplasts, but do replicate DNA.
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DNA molecules separate into single strands, which
are then used to construct two identical strands
of DNA. This process ensures that the
C is incorrect because ATP is a high energy
molecule needed to provide energy for normal
cellular function and is not part of DNA.
D is correct because by producing identical
strands of DNA, it ensures that the daughter
cells are genetically identical to the parent
cell.
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The nucleus is the part of the cell that ?
A provides structure and support.
B supplies energy to the other organelles.
C changes sunlight into carbohydrates.
D contains genetic information about the
organism.
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The nucleus is the part of the cell that ?
A is incorrect because structure and support is
provided by cell membranes and cell walls.
B is incorrect because mitochondria are the parts
of the cell that provide energy.
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The nucleus is the part of the cell that ?
C is incorrect because chloroplasts are the
organelles that carry on photosynthesis.
D is correct because the nucleus contains
chromosomes that are made up of genes that
contain DNA which is the genetic information
about an organism.
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Which of the following is not a part of DNA?
A adenine
B citric acid
C deoxyribose
D phosphate
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Which of the following is not a part of DNA?
A is incorrect because adenine is one of the
bases that make up DNA.
B is correct because citric acid is not part of
DNA.
C is incorrect because deoxyribose is sugar which
is part of DNA
D is incorrect because phosphate is a part of DNA.
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