RNA and Protein Synthesis
The Function of DNA
• 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
• Thus, a messenger http://www.accessexcellence.org/RC/VL/GG/images/genes.gif
molecule is needed.
Comparing DNA and RNA
• RNA is the nucleic acid that
acts as a messenger
between DNA and the
• The RNA produced during
transcription is structurally
different from DNA in 3
– 1. The sugar in RNA is ribose
whereas the sugar in DNA is
– 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
The Role of RNA
• RNA molecules have many functions, but
in the majority of cells, most RNA
molecules are involved in protein
• Protein synthesis is the assembly of
amino acids into proteins.
Types of RNA
• The RNA produced during transcription is modified into 3 basic
– 1. messenger RNA (mRNA) is responsible for copying one strand of
DNA in the nucleus and carrying that information to the ribosomes in the
– 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.
• 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).
Transcription and Translation
• Transcription occurs • Translation is
on the DNA in the completed by the
nucleus. ribosomes located in
• Transcription Demo the cell’s cytoplasm.
• All three types of RNA
work together during
translation to produce
• 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
• Each codon is matched to an anticodon, or
coplementary sequence on the tRNA to determine
the order of the amino acids.
• Translation Demo
Using a Codon Chart
• A codon chart can be used to determine
the sequence of the amino acids in the
• The mRNA bases or CODONS are used
to find the amino acid.
• For the following examples, give the appropriate
mRNA sequence and amino acid sequence.
(Remember: U replaces T in mRNA.)
DNA: TAC GCA TGG AAT
mRNA: AUG CGU ACC UUA
Amino Acids: Met Arg Thr Leu
DNA: CGT GGA GAT ATT
mRNA: GCA CCU CUA UAA
tRNA: CGU GGA GAU AUU
Amino Acids: Ala Pro Leu stop
What is a gene mutation?
• Sometimes during replication, an error is
made that causes subsequent changes in
the mRNA and proteins that are made
using that DNA.
• These errors or changes are called
Types of Gene Mutations
• Point mutation:
– changes in only 1 or a few nucleotides of
– Substitutions, in which one base is changes
to another, are a type of point mutation.
• Frameshift mutation:
– When one base is deleted (deletion) or
added (insertion) into a DNA sequence.
– This causes the entire sequence of codons to
shift over by one base.
What are Chromosomal Mutations?
• Mutations involving a long segment of
– These mutations can involve deletions,
insertions, or inversions of sections of DNA.
– In some cases, deleted sections may attach to
other chromosomes, changing both the
chromosomes that lost the DNA and the one
that gained it, also called a chromosomal
What is the significance of
• Mutations in DNA cause changes in the
sequence of amino acids which ultimately
creates changes in proteins and their