Ch.10: Protein
Synthesis, Gene
Regulation, &
Mutations
Biology
 DNA controls protein synthesis.
 Proteins control most all chemical rxns.
in living organisms.
 DNA is located in the nucleus and does
not leave.
 Protein synthesis occurs in the
ribosome in the cytoplasm.
If DNA controls protein synthesis, How
does the info get to the ribosome when
DNA can’t leave the nucleus?
RNA
 RNA acts as a messenger b/t DNA and
ribosomes.
RNA differs from DNA in 3 ways.
1) RNA contains ribose sugar.
2) Uracil replaces thymine as a nitrogen
base.
3) RNA is single strand molecule, DNA is
double stranded.
3 Kinds of RNA
1) mRNA (messenger RNA) carries
sequence of nucleotides that code for
protein from nucleus to ribosome
2) tRNA (transfer RNA) picks up
individual aa in the cytoplasm & carries
them to ribosome (where they are
joined together in proper order)
3) rRNA (ribosomal RNA) plays a
structural role in ribosomes
Protein Synthesis
1) Transcription-process where the
hereditary info in nucleotide sequence of
DNA is transferred and encoded in
nucleotide sequence of RNA. The RNA
molecule that is formed is called mRNA.
RNA polymerase binds to a promotor
(start signal) and unwinds & separates the
2 strands of DNA molecule, exposing the
nitrogen bases. One of the 2 separated
strands serves as the pattern for making
mRNA. Transcription continues until a
terminator (stop signal) is reached.
The sequence of nucleotides forming
mRNA is determined by nucleotide
sequence of DNA strand on which it is
formed.
EX: DNA: AGCT
mRNA:UCGA
Introns-noncoding sequences which are cut
out
Exons-coding sequences that are joined
together to form single mRNA molecule
which travels to cytoplasm
2) Translation-the formation of a protein
under the control of mRNA in the
cytoplasm; translate RNA base
sequence into the aa sequence of a
protein, takes place at the ribosome.
The tRNA carries specific aa to
ribosomes where protein is assembled.
Codon-sequence of nucleotide bases as
combination of 3; each codon is coding
for a specific aa; carried by mRNA
Anticodon-complementary to the mRNA
codon; carried by tRNA
EX: mRNA: CCU (codon)
tRNA: GGA (anticodon)
Translation begins w/ the 1st codon of
mRNA (AUG). The stop codon
(terminator) can be UAA, UAG, or UGA.
Gene Regulation in
Bacteria

1)
2)
3)
Scientists first studied gene expression in bacteria (specifically
E.coli and lactose sugar).
In bacteria (prokaryotes), the basic mechanism that controls
gene regulation is the “operon”.
Operon-cluster of genes that code for proteins with related
functions. (Ex: lac operon code for enzyme beta-galactosidase).
Regions of Lac operon
Promoter-binding site that signal start of gene for RNA
polymerase
Operator-acts like on/off switch for operon
Structural genes- genes that code for structurally making the
proteins.
A repressor switches off the lac operon and an inducer switches on
the lac operon.
Gene Regulation in
Eukaryotes
 Operons are not found in eukaryotes.
 More DNA found in eukaryotes than
prokaryotes.
 Eukaryotic cells are specialized for
specific functions and therefore produce
different proteins.
Genes and Mutations
1) Mutations-changes in the DNA of a gene or
chromosome
2) Point mutations-chemical changes in just 1 nucleotide
or a few nucleotides in a single gene. In gamete, may
be passed to offspring. In somatic cell, will not be
passed to offspring.
3) Base-pair substitutions-replacement of 1 nucleotide &
its partner from the DNA strand with another pair of
nucleotides (may or may not be harmful).
4) Frame-shift mutation-insertion of deletion of a
nucleotide which causes reading to be out of phase
resulting in the production of an abnormal protein.