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Chp: 12
Transcription &
Translation
Genes and Proteins
 Proteins function as Enzymes, build
and repair cells, transport proteins
 Genes code for proteins (genetic
code)
 Proteins are built from amino acids
 Each nucleotide is composed of 3
nitrogen bases representing an
amino acid called a codon
 There are 64 different codons in the
genetic code
 Genetic code was figured out by
studying E. coli.
 Codons represent the same amino
acids in all organisms.
Transcription
 RNA differs from DNA in that it is
only a single strand, contains a
different sugar (ribose), and
contains Uracil instead of Thymine
 In RNA A binds with U
How to read the Amino Acid
chart
Transcription
 Enzymes make an RNA copy of a DNA
strand. Results in the formation of a single
stranded RNA molecule
 Messenger RNA (mRNA)- the RNA copy
that carries the information from DNA out
into the cytoplasm of the cells
 Carries info to the ribosomes so that
proteins can be synthesized
 Ribosomal RNA (rRNA)- portion of
the DNA code for the RNA that makes
up ribosomes
 Helps to produce enzymes needed to
bond amino acids together during
protein synthesis
Steps in transcription
1. DNA helicases (enzymes) unzip DNA
2. Free RNA nucleotides pair with the
complementary DNA by using RNA
polymerases
3. When the base pairing is complete, mRNA
breaks away from the DNA strand, leaves
the nucleus, and enters the cytoplasm,
then ribosome
4. If the DNA strand is
AGC TAG CGA
the RNA strand would be
UCG AUC GCU
Translation
 The process of converting the information in a
sequence of nitrogen bases in mRNA into a
sequence of amino acids that make up a
protein
 Occurs on the ribosomes
 Transfer RNA (tRNA)- brings amino acids to
the ribosomes so they can be assembled into
proteins
 Each mRNA codon (3 letters) joins w/the
anticodons of tRNA
 End result of translation is the production of
proteins
Steps in translation
1. The 1st codon of the mRNA strand attaches
to the ribosome. The tRNA approaches
the ribosome, the anticodon from tRNA
binds w/the codon on mRNA.
2. The first codon of mRNA is AUG (start
codon for protein synthesis), mRNA slides
along the ribosome to the next codon
3. A new tRNA carrying an amino acid will pair
w/the mRNA codon
4. When the 1st and 2nd amino acids are in
place an enzyme will join them.
5. A chain of amino acids is formed until the
ribosome reaches the stop codon on the
mRNA (UAA)
6. The bond that holds the amino acids
together is called a Peptide Bond.