RNA and Protein
Synthesis
The Function of DNA
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The DNA molecule contains
all of your hereditary
information in the form of
genes.
Genes are portions of the
DNA molecule that code for
the production of specific
types of proteins.
However, DNA is confined to
the nucleus, while proteins are
made by ribosomes in the
cytoplasm.
Thus, a messenger molecule is
needed.
http://www.accessexcellence.org/RC/VL/GG/images/genes.gif
Comparing DNA and RNA
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RNA is the nucleic acid that acts
as a messenger between DNA
and the ribosomes.
The RNA produced during
transcription is structurally
different from DNA in 3 basic
ways:
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1. The sugar in RNA is ribose
whereas the sugar in DNA is
deoxyribose.
2. RNA is single stranded while
DNA is double stranded.
3. RNA contains a base called
uracil instead of thymine.
http://www.dkimages.com/discover/previews/769/85011519.JPG
Protein Synthesis
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During protein synthesis, genes copied onto
RNA are expressed by the production of
specific types of proteins.
Protein synthesis involves two processes:
1. Transcription – the process where a portion of the
DNA sequence is copied into a complementary
RNA sequence.
 2. Translation – the decoding of an mRNA message
into a polypeptide chain (protein).
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Transcription
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Transcription occurs on the DNA in the
nucleus.
Transcription Demo
Types of RNA
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The RNA produced during transcription is modified into 3 basic types:
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1. messenger RNA (mRNA) is responsible for copying one strand of DNA in the
nucleus and carrying that information to the ribosomes in the cytoplasm.
2. ribosomal RNA (rRNA) makes up a large part of the ribosome and is
responsible for reading and decoding mRNA.
3. transfer RNA (tRNA) carries amino acids to the ribosome where they are joined
to form proteins.
http://images.encarta.msn.com/xrefmedia/zencmed/targets/illus/ilt/T068340A.gif
Translation
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Translation is completed by the ribosomes
located in the cell’s cytoplasm.
All three types of RNA work together during
translation to produce polypeptides (proteins).
Translation Demo
Decoding mRNA
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The sequence of bases in an mRNA molecule serves as
instructions for the order in which amino acids are joined to
produce a polypeptide.
Ribosomes decode these instructions by using codons, sets
of 3 bases that each code for 1 amino acid.
Each codon is matched to an anticodon, or coplementary
sequence on the tRNA to determine the order of the amino
acids.
http://www.gwu.edu/~darwin/BiSc150/One/codon.gif
Using a Codon Chart
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When given a sequence of mRNA bases, a
codon chart can be used to determine the
sequence of the amino acids in the polypeptide.
http://www.safarikscience.org/biologyhome/7_dna/codon_qu
estion.png
Decoding Practice
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For the following examples, give the appropriate mRNA
sequence and amino acid sequence. (Remember: U replaces T in
mRNA.)
Example 1:
DNA:
TAC GCA TGG AAT
mRNA:
AUG CGU ACC UUA
Amino Acids:
Met
Arg
Thr
Leu
Example 2:
DNA:
CGT GGA GAT ATT
mRNA:
GCA CCU CUA UAA
tRNA:
CGU GGA GAU AUU
Amino Acids:
Ala
Pro
Leu
stop