Ch. 10: Nucleic Acids and Protein Synthesis

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Ch. 10 Nucleic Acids and Protein Synthesis

• DNA controls the production of proteins within
  the cell.
• - These proteins form the structural units of
  cells and control the chemical processes.

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• DNAs 2 primary functions
• Store and use information to direct activities of
  the cell.
• Make an exact copy of itself to pass on to new
  cells.
• Where is DNA stored in the cell?
• In the cells nucleus.

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Structure of DNA

• DNA is an organic molecule made up of repeating
  subunits called nucleotides.
• Nucleotide 3 main parts
• 1) Sugar molecule called deoxyribose
• 2) Phosphate group
• 3) Nitrogen base

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• There are 4 nitrogen-containing bases found in
  DNA nucleotides
• 1. Adenine (A)
• 2. Cytosine (C)
• 3. Thymine (T)
• 4. Guanine (G)
• The 4 nitrogen bases are placed into 2 structural
  groups
• 1) Purines double ring of carbon (A,G)
• 2) Pyrimidines single ring of carbon
  (T,C)

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• DNA is a double helix (twisted ladder)
• Base Pairing Rules
• A-T
• C-G
• Or vice versa
• -Double ring always
• Bonds w/ single
• ring

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DNA Replication

• The process of duplicating a molecule of DNA
• An enzyme called DNA helicase attaches to the DNA
  molecule and breaks the bonds or unzips the
  double helix.
• In the nucleus of the cell, free-floating
  nucleotides bond to the unzipped portion of the
  DNA molecule.
• 3) The replication is complete after an enzyme
  called DNA polymerase bonds all nucleotides
  together forming 2 DNA molecules, both with one
  old strand and one new strand.

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Accuracy and Repair

• The cell has a built-in proof-reading function.
• About 1 error per billion nucleotides.
• Body heat, radiation, chemicals, etc. can damage
  your DNA.
• 4) A group of 20 or more enzymes designed to
  seek out and replace damaged nucleotides.

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Homework- due Tues.

• Research on the web, in magazines or
• books something interesting about DNA.
• Ex
• - How is DNA used to solve crimes?
• - What are some things that can happen as a
  result of DNA damage?
• - What is the human genome project?
• - What are some things modern science is studying
  about DNA?

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• Some helpful search words for the web
• - DNA
• - Nucleic Acids
• - Human genome project
• - DNA and forensic science
• - Neatly write or type 1-2 paragraphs describing
  what you found out. Be prepared to share in
  class on Tues.
• - Dont forget to cite your sources!

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Section 10-2 RNA

• How does RNA differ from DNA?
• RNA is a nucleic acid made up of repeating
• nucleotides. However, the sugar molecule of
  every RNA nucleotide is Ribose, whereas DNA
  nucleotides contain Deoxyribose Sugar.
• Uracil, a nitrogen-containing pyrimidine (one
  ring of carbon), usually replaces thymine in RNA.
  Therefore, uracil pairs with adenine in RNA.

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3 Types of RNA

• Type of RNA that consists of RNA nucleotides in
  the form of a single uncoiled chain. This RNA is
  responsible for carrying genetic information from
  the DNA in the nucleus to the cytosol of a
  eukaryotic cell
• Messenger RNA (mRNA).

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• This RNA consists of a single chain of about 80
  RNA nucleotides folded into a hairpin shape that
  binds to specific amino acids. There are about
  45 varieties of this RNA Transfer RNA (tRNA).
• This is the most abundant form of RNA. It
  consists of RNA nucleotides in a globular form.
  Joined by proteins, it makes up the ribosomes
  where proteins are made
• Ribosomal RNA (rRNA).

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Transcription

• Lets think of transcription as an analogy.
  Think of DNA as a reference book in a library.
  These books can not be taken out because they are
  very valuable and may risk getting damaged if
  they leave the confines of the library. If DNA
  were to leave the nucleus and enter the cytosol,
  it would enter an environment that would make it
  more vulnerable to getting damaged from radiation
  and chemicals.

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So, how do we get information from the reference
book/DNA without taking it out of the
library/nucleus?

• We make a copy.
• This is where mRNA enters the picture.
  The RNA is the messenger, or copier, responsible
  for carrying the genetic information from DNA in
  the nucleus to the cytosol, where it can be used
  to produce proteins.

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• Transcription is
• Process by which genetic information is copied
  from DNA to RNA
• We will now go through the process of
  transcription together. Please fill in notes
  where indicated.
• http//www-class.unl.edu/biochem/gp2/m_biology/ani
  mation/gene/gene_a2.html

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Some things to remember

• As in replication, a small section of the DNA
  double helix unwinds, and the bases on the 2
  strands are exposed.
• RNA nucleotides line up in the proper order by
  hydrogen-bonding to their complementary bases on
  DNA.
• The nucleotides are joined together by a
  DNA-dependent RNA polymerase enzyme, and mRNA
  results.

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How is Transcription different from Replication?

• In transcription, only 1 strand of DNA is
  transcribed into mRNA (remember that RNA is a
  single-stranded molecule).
• The DNA strand that is transcribed is called the
  template strand.

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What determines where transcription will begin
and end?

• In other words, where does one gene start and the
  next begin?
• The starting point of a gene is marked by a
  certain base sequence which is called a promoter
  site.
• These sites act as a start sign .
  Similarly, there are other base sequences at the
  end of a gene that signal a to mRNA
  synthesis.
• This DNA region is referred to as a termination
  signal.

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What are the products of transcription?

• The transcripts are the different types of RNA
  molecules, including mRNA, tRNA and rRNA.
• Even though the instructions are for making a
  protein are copied from DNA into mRNA, all 3
  types of RNA are involved in the synthesis of
  proteins.