RNA

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RNA Protein Synthesis
Ribose
RNA
Hydrogen bonds
Mrs. Stewart Biology I
Uracil
Adenine
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Genes

• A gene is a section of the DNA sequence that
  codes for a protein.
• Each unique gene has a unique sequence of bases.
• This unique sequence of bases will code for the
  production of a unique protein.
• It is these proteins and combination of proteins
  that determine the phenotypes for our traits.

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DNA
How do we get from here, to there?
Trait
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DNA
GENE
RNA
Protein
Trait
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REVIEW Structure of RNA

• All forms of RNA have
• Single stranded chain of nucleotides
• RNA nucleotides composed of
• Phosphate
• Ribose sugar
• Nitrogenous base

• 4 Nitrogen bases of RNA
• Guanine
• Cytosine
• Adenine
• Uracil

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• Differences between DNA and RNA

DNA RNA
Structure Double Stranded Single Stranded
Bases- Purines Adenine (A) Guanine (G) Adenine (A) Guanine (G)
Bases - Pyrimidines Cytosine (C) Thymine (T) Cytosine (C) Uracil (U)
Sugar Deoxyribose Ribose

• RNAs JOB Make Proteins!!

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Types of RNA

• 1) messenger RNA (mRNA)- carries instructions
  (the message) from the DNA in the nucleus to the
  ribosome

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Types of RNA
2) ribosomal RNA (rRNA)- combines with proteins
to form the ribosome (proteins made here) 3)
transfer RNA (tRNA)- transfers each amino acid
to the ribosome as it is specified by coded
messages in mRNA during the construction of a
protein
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Protein Synthesis Overview

• There are two steps to making proteins (protein
  synthesis)
• 1) Transcription (occurs in the nucleus)
• DNA? RNA
• 2) Translation (occurs in the cytoplasm)
• RNA ? protein

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Transcription occurs in three main steps
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Initiation

• Transcription begins when the enzyme RNA
  polymerase binds to the DNA at a promoter site.
• Promoters are signals in the DNA strand (a
  certain sequence of bases) that indicate to the
  enzyme where to bind to make RNA.

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Elongation

• The enzyme separates the DNA strands by breaking
  the hydrogen bonds, and then uses one strand of
  DNA as a template from which nucleotides are
  assembled into a strand of RNA.
• RNA polymerase pairs up free floating RNA
  nucleotides with DNA template and joins the
  nucleotides together to form the backbone of the
  new mRNA strand.

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Termination
When mRNA hits a termination sequence, it
separates from the DNA
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Transcription vs. Replication

• The main difference
• Transcription results in one single-stranded mRNA
  molecule.
• Replication results in two double-stranded DNA
  molecules.

• Practice
• DNA template
• DNA Complement (replication)
• mRNA (transcription)

ATTCGGAGC
TAAGCCTCG
UAAGCCUCG
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mRNA synthesis animationtranscription animation
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What is the purpose of the genetic code in DNA?
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Transcription
Nucleus
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After we transcribe the message so it can leave
the nucleus, we then must have a way to read
the message.
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The Genetic Code

• The language of mRNA instructions is called the
  genetic code.
• This code is written in a language that has only
  four letters (A,G,C,U)
• How can a code with just 4 letters carry
  instructions for 20 different amino acids?

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The Genetic Code what does it code for?

• Proteins (polypeptides) - long chains of amino
  acids that are joined together.
• There are 20 different amino acids.
• The structure and function of proteins are
  determined by the order (sequence) of the amino
  acids

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The Genetic Code
The genetic code is read 3 letters at a time.
A codon consists of three consecutive nucleotides
that specify a single amino acid that is to be
added to the polypeptide (protein).
The four bases (letters) of mRNA (A, U, G, and C)
are read three letters at a time (and translated)
to determine the order in which amino acids are
added to a protein.
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The Codon Wheel

• 64 different mRNA codons are possible in the
  genetic code.

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• More than one codon can code for the same amino
  acid
• Example GGG, GGU, GGA, GGC Glycine
• Some codons give instructions
• Example AUG start
• Example UGA, UAA, UAG Stop

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Cracking the Secret Code

• To decode a codon
• start at the middle of the circle and move
  outward.
• Ex CGA Arginine
• Ex GAU Aspartic Acid

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Cracking the Code

• This picture shows the amino acid to which each
  of the 64 possible codons corresponds.
• To decode a codon, start at the middle of the
  circle and move outward.
• Ex CGA
• Arginine
• Ex GAU
• Aspartic Acid

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Translation

• rRNA and tRNA will decode the message on the mRNA
  strand to produce a polypeptide chain (protein).

• Translation takes place on ribosomes, in the
  cytoplasm or attached to the ER.

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http//www.youtube.com/watch?v5bLEDd-PSTQ
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Messenger RNA (mRNA)

• The mRNA that was transcribed from DNA during
  transcription, leaves the cells nucleus and
  enters the cytoplasm.

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Transfer RNA (tRNA)

• Transfer RNA (tRNA) molecules in the cytoplasm
  will bond with a specific amino acid
• Then, tRNA carries that amino acid to the
  ribosome
• Each tRNA molecule has three unpaired bases
  called an anticodon.
• These bases are complementary to one codon on the
  mRNA strand.

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tRNA molecule
Anticodon
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Translation
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Initiation

• Begins when an mRNA in the cytoplasm attaches to
  the ribosome.
• AUG the start codon
• AUG methionine

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The Polypeptide Assembly Line

• tRNA anticodon will temporarily bind to the
  complementary codon on the mRNA molecule in the
  ribosome.
• (This binding of codon to anticodon ensures the
  correct amino acid is being added)

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Elongation

• The ribosome has two binding sites, allowing two
  tRNA molecules to line up, side by side
• The ribosome forms a peptide bond between the
  first and second amino acids on those tRNA
  molecules
• At the same time, the ribosome breaks the bond
  that held the first tRNA molecule to its amino
  acid and releases the tRNA molecule.

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The Polypeptide Assembly Line
The tRNA floats away, allowing the ribosome to
move down the mRNA molecule and bind another
tRNA.
The ribosome continues to move along the mRNA,
attaching new tRNA molecules and adding more
amino acids to the polypeptide chain.
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Termination

• The process continues until the ribosome reaches
  one of the three stop codons on the mRNA.
• Then, the ribosome detaches from the mRNA.
• The result is a polypeptide (protein chain) that
  is ready for use in the cell.

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Practice

• DNA template
• mRNA (transcription)
• tRNA
• Amino Acid Sequence
• (translation)

TAC GGT CCA AAC ACT
AUG/CCA/GGU/UUG/UGA
UAC/GGU/CCA/AAC/ACU
Met-Pro-Gly-Leu-Stop
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Computer Practice for transcription and
translation

• http//learn.genetics.utah.edu/content/begin/dna/t
  ranscribe/
• http//www.youtube.com/watch?vIkq9AcBcohA

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• All organisms use the same genetic code
  (A,T,C,G).
• This provides evidence that all life on Earth
  evolved from a common origin.