"Distrust any enterprise that requires new clothes'

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"Distrust any enterprise that requires new
clothes. Henry David Thoreau
(1817-62)
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Phenotype

• the expression of an individuals genetic
  makeup
• - the observable features of a cell or organism
• - Phenotype Genotype Environment

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platelets
All cells in an organism have the same genotype,
but diff genes are expressed in diff cells ? diff
cell phenotypes
neutrophil
monocyte
RBC
T-lymphocyte
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Gene

section of DNA that contains instructions for
making a polymer of RNA nucleotides
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REMEMBER!!!!Proteins are important molecules

• - make up 50 dry weight of cells
• - used for structural support, cell transport,
  signaling, etc.
• - act as enzymes drive all of the chemical
  reactions in an organism

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Gene Expression DNA ? Protein
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4 Steps of Gene Expression 1. RNA Synthesis
(transcription) 2. RNA Editing (in Eukaryotes
only) 3. Polypeptide Synthesis (translation) 4.
Protein Assembly
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1. Transcription (RNA Synthesis)

• In eukaryotes an RNA copy of one entire gene is
  made
• In Prokaryotes ? possibly multiple genes
• only one DNA strand, the template strand, is
  copied

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RNA ribonucleic acid
RNA is similar to DNA, except - RNA sugar
ribose - RNA has uracil (U) not thymine (T) -
RNA is single- stranded
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4 kinds of RNA
mRNA messenger RNA - carries the protein
recipe (protein coding genes) rRNA ribosomal
RNA - makes up ribosomes the place where
proteins are made (non-protein coding genes) tRNA
transfer RNA - assemble proteins translates
mRNA code into amino acid sequence
(N-PC-G) snRNA small nuclear RNA -makes up
spliceosomes (non-Protein coding genes)
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Steps of Transcription

• Initiation
• Elongation
• Termination

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A. Initiation

• Initiation complex forms
• Complex protein transcription factors RNA
  polymerase bind to promoter of gene
• RNA polymerase enzyme that unwinds DNA
  builds RNA
• Promoter TATA box signal for origin of
  transcription

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Transcription factors help eukaryotic RNA
polymerase recognize promoter sequences
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B. Elongation

• RNA polymerase grabs free nucleotides adds
  them forming a transcript

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RNA transcript is complimentary to DNA template
Guanine -- Cytosine Adenine -- Uracil
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C. Termination

• Differs in prokaryotes eukaryotes
• RNA polymerase reaches terminator complex
  disassembles

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• In prokaryotes, transcription and translation
  occur together

DNA
TRANSCRIPTION
mRNA
Ribosome
TRANSLATION
Polypeptide
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• In eukaryotes, RNA transcripts are modified
  before becoming true mRNA

Nuclear envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Ribosome
TRANSLATION
Polypeptide
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2. RNA Editing (not in Prokaryotes)
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Eukaryotes Poly-A tail phosphate cap
added to help move mRNA out of nucleus bind to
ribosome
A modified guanine nucleotide added to the 5? end
50 to 250 adenine nucleotides added to the 3? end
5?
3?
AAAAAA
G
P
P
P
Poly-A tail
5? Cap
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The mature mRNA then exits the nucleus
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3. Translation

• occurs on ribosomes (rRNA protein structures)
  in cytoplasm
• polypeptide (protein) is made by joining free
  amino acids from cytoplasm into a chain
• protein is built using the genetic code
  (recipe) carried in mRNA

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Genetic code

• each 3 nucleotides of mRNA codes for 1 amino
  acid
• nucleotide mRNA triplet codon
• each codon tells the cell to grab a different
  AA when building the protein chain

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Codon ? Amino Acid
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64 different codons exist (43 64) and they only
code for 20 different amino acids
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The genetic code is redundant

• the 3rd nucleotide position often doesnt
  affect the code
• ex. CCC proline
• CCA proline
• CCU proline
• CCG proline

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The genetic code is universal
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Summary of Gene Expression
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Steps of Translation

• Initiation
• Elongation
• Termination

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A. Initiation

• Initiation complex forms ribosome mRNA
  tRNA
• Translation begins at at the start codon (AUG)
• Start codon marks beginning of each gene

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Ribosome

• 2 subunits made of rRNA proteins
• ribosome has a tunnel that mRNA strand passes
  through during translation

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ribosome
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tRNA
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AA attachment site at top of tRNA molecule binds
to a specific amino acid
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Initiation
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B. Elongation

• mRNA passes through ribosome, one codon (3
  nucleotides) at a time
• As each codon passes, anticodon of tRNA binds to
  codon of mRNA
• tRNA carries the proper amino acid adds it to
  growing polypeptide

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Elongation
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Amino acids are chemically bonded to each other ?
AA chain (polypeptide)
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A mRNA transcript may pass through many ribosomes
make many copies of the same protein
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C. Termination

• Stop codon passes through ribosome
• Stop codon marks end of each gene
• 3 stop codons UAG or UAA or UGA
• Protein synthesis ends polypeptide (AA chain)
  is released

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Termination
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REMEMBER!! Prokaryotic cells lack a nuclear
envelope allowing translation to begin while
transcription is still in progress
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4. Protein Assembly

• Newly-made AA chain often modified by removing
  MET, adding carbs, lipids, minerals,etc.
• AA chain folds into a specific shape (2º 3º
  strux)
• AA chain joined with other AA chains to form
  complete protein (4º strux)
• Finished protein is shipped to where it is
  needed in/out of cell

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Protein Shapes
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Ex HEMOGLOBIN is made from two different AA
chains, encoded by two different genes (alpha
beta globins)
And four iron (heme) groups are added
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