From DNA to Protein:

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From DNA to Protein
Transcription and Translation

• Each gene is the information to build one
  protein (or polypeptide chain) that the organism
  needs.
• The first step in producing the protein is
  making a mRNA copy of the gene. This process is
  called transcription.

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Differences between DNA and mRNA

• While DNA is a double helix, mRNA is a single
  strand of nucleotides.
• mRNA nucleotides have the sugar ribose instead of
  deoxyribose
• mRNA has the nitrogen base uracil instead of
  thymine.

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The Process of Transcription

• The process of transcription is similar to DNA
  replication in that the DNA is unwound and
  complementary nucleotides are added.
• Differences
• Only a gene is copied, not the whole chromosome.
• RNA nucleotides are added instead of DNA
  nucleotides.
• Uracil is paired with adenine instead of thymine.
• Transcription occurs on an ongoing basis
• as proteins needed, replication only occurs
  prior to cell division.

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Transcription

• The enzyme RNA polymerase unwinds the DNA
  double helix and adds the complementary RNA
  nucleotides.
• If the sequence of a gene is CGGCAT what mRNA
  transcript will be produced?
• DNA C G C A T A
• mRNA

G
C
G
U
A
U
In RNA, the nucleotide uracil is used in place of
thymine.
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DNA Transcription VideoClick once on image to
start
http//www.youtube.com/watch?vztPkv7wc3yU
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Transcription Animation

• http//www.stolaf.edu/people/giannini/flashanimat/
  molgenetics/transcription.swf

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Modification of mRNA in Eukaryotic Cells

• Genes in eukaryotic organisms contain non-coding
  segments called introns.
• The coding portions of the gene are called exons.
• The noncoding introns need to be removed before
  the mRNA leaves the nucleus.

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Prokaryotic Cells

• In prokaryotic cells, there is no nuclear
  membrane.
• So mRNA transcripts can not be modified before
  being translated.

So in prokaryotes, transcription of mRNA and
translation to produce the protein can occur
simultaneously
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