From Gene To Protein

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From Gene To Protein

• A PowerPoint presentation by Gene Tempest

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Table of Contents

• Overview
• Transcription
• RNA Processing
• Translation
• Differences in protein Synthesis Between
  Prokaryotes and Eukaryotes
• Point Mutations
• Bibliography

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Overview
The one gene-one polypeptide hypothesis Main
processes in protein production in
eukaryotes 1. Transcription 2. RNA
processing 3. Translation
The synthesis of RNA under the direction of DNA
Yields the finished mRNA
Actual synthesis of a polypeptide, under the
direction of mRNA
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Animation 17.1
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Terms
Triplet Code Template Strand Codon Initiation
Codon Termination Codons
Series of three-nucleotide words that contain
the instructions for making polypeptide chains.
The one out of the two DNA strands that is
transcribed.
mRNA base triplet
AUG (also codes for amino acid methionine)
UAA UAG UGA
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Fig. 17.3
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Fig. 17.4
Note Based on mRNA Codon
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Transcription
Pries the two strands of DNA apart and hooks
together the RNA nucleotides, as they base-pare
along the DNA template
In eukaryotes, a collection of proteins that
mediate the binding of RNA polymerase and the
initiation of transcription
A closer look
Stretch of DNA that is transcribed into an RNA
molecule
Terms
RNA polymerase Transcription unit Promoter
Transcription factors
Terminator
RNA sequence that functions as the actual
termination signal
Region of DNA where RNA polymerase attaches and
initiates transcription
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Stages
1. RNA polymerase unwinds the two DNA strands.
RNA synthesis begins at the starting point on
the template strand. 2. The RNA polymerase
works its way downstream. 5 3
3. RNA polymerase transcribes a terminator.
RNA is released.
RNA
polymerase dissociates from DNA
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Fig. 17.6
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Animation 17.2
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RNA Processing
The removal of a large portion of the originally
synthesized RNA molecule
A closer look
Non-coding segments of nucleic acid that lie
between coding regions
Terms
Small nuclear ribonucleoproteins joins with
proteins to form the spliceosome
RNA splicing Introns Exons
snRNPs
Spliceosome
Cuts at specific points to release the intron,
then joins the two exons together
Eventually expressed--or translated into amino
acid sequences
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Stages
1. The ends of each pre-mRNA molecule are
modified

- the 5 end is capped off with a
modified form of a guanine (G)
nucleotide ( 5 cap ) - a poly(A) tail,
consisting of adenine nucleotides,
attaches to the 3 end 2. The spliceosome
removes the introns and
produces joined exons, now mRNA
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Animation 17.3
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Translation
Transfer RNA Function to transfer amino acids
from the cytoplasm to a ribosome
Holds the tRNA carrying the growing polypeptide
chain
A closer look
Relaxation of the base-paring rules
Terms
tRNA Wobble rRNA
P Site A Site E
Site
Sites on the large ribosomal subunit
Ribosomal RNA Function structural and catalytic
role in ribosomes
Holds the tRNA carrying the next amino acid to be
added to the chain
Exit for discarded tRNAs
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Stages
I. Initiation 1. Small ribosomal subunit
binds to a molecule of mRNA 2. A large
ribosomal subunit complex completes
it II. Elongation 1. Codon
Recognition 2. Peptide bond formation 3.
Translocation III. Termination
1. The ribosome accepts a
release factor instead of tRNA 2.
The release factor hydrolyses the bond
between tRNA and P site 3. Ribosomal subunits
dissociate
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Animation 17.4
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Differences between Prokaryotes and
Eukaryotes

• Can simultaneously transcribe and translate the
  same gene
• Newly made proteins can diffuse to their sites of
  function

• Nuclear envelope segregates transcription from
  translation
• Have complicated mechanisms for targeting
  proteins to their appropriate destinations

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Point Mutations
Chemical changes in just one or a few base pairs
in a single gene
Substitutions Insertions and deletions
Replacement of one nucleotide and its partner in
the complementary DNA strand with another pair of
nucleotides
Vocabulary Missense Mutation Nonsense Mutation
Frameshift Mutation
The altered codon still codes for an amino acid
Addition or loss of one or more nucleotide pairs
in a gene
Alterations that change amino acids to a stop
signal
Alters the reading frame of the genetic message
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Bibliography

• Campbell, Mitchell, Reece. Biology Fifth
  Edition. Illinois, USA. 1999
• Biology Fifth Edition CD-ROM
• http//www.animationfactory.com
• http//occawlonline.pearsoned.com/bookbind/pubbook
  s/campbell_awl/chapter17/deluxe.html