Download Ch 5

Ch 5.1: Protein Synthesis – pp. 328-330
DNA codes for the production of proteins.
Some functions of proteins in our bodies includes:



Act as chemical messengers
Catalysts in chemical reactions
Structural components of cells, tissues and organs
For protein synthesis, DNA is NOT replicated. Instead, it is copied by another nucleic
acid, messenger RNA (mRNA).
TRANSCRIPTION is the process of copying a sequence of DNA to a complementary
strand of RNA.


The enzyme RNA polymerase will unwind and unzip a DNA segment and bind
complementary RNA nucleotides together.
How is RNA different from DNA?
o RNA contains the nitrogen base uracil (U), instead of thymine, to bond
with adenine.
o RNA also has ribose sugar, not deoxyribose sugar.
o RNA is single-stranded, not double stranded.
Example of bonding:

DNA strand:
TAC
GGT
AAT
GTG
CAC
CCC
ATC
mRNA strand:
AUG
CCA
UUA
CAC
GUG
GGG UAG
mRNA is made with cap and tail sequences (like introductions and conclusions of
a story) that do NOT code for a protein. The mRNA will be corrected before the
protein is made.
o Introns are sections of nucleotides that are unnecessary for making
protein. Enzymes will remove these sections before mRNA leaves the
nucleus.
o Exons are then spliced together to make the final mRNA.
TRANSLATION is when the mRNA code is translated into protein molecules.









mRNA attaches to the ribosome.
Amino acids are transported to the mRNA by transfer RNA (tRNA).
mRNA has codons – a sequence of 3 nucleotides that codes for an amino acid.
tRNA has anticodons that are complementary to mRNA’s codons.
AUG is the universal ‘start’ codon that tells the ribosome to start translating.
There are three ‘stop’codons – UAA, UAG and UGA – that tell the ribosome to
stop translating the protein.
As tRNA bonds with mRNA along the ribosome, amino acids are lined up in the
sequence originally specified by the DNA template.
At the end, the amino acids are released to form a protein polymer and the tRNA
is released.
Enzymes will break up mRNA so those nucleotides can return to the nucleus to
transcribe another DNA sequence for protein.
Summary of Protein Synthesis:
Transcription
Translation
DNA code  mRNA copy  tRNA anticode  amino acid assemble  protein product
occurs in the nucleus
occurs in the cytoplasm
Ch 5.1: Mutations – pp. 331-333
Proteins created during protein synthesis are specific to the job they perform. Mistakes
in the gene code cause mistakes in the protein. Mistakes are called mutations.

Point mutations – are mutations involving one base. Some point mutations do
not affect the protein produced. Others can cause serious problems (ex. –
sickle-celled anemia and cystic fibrosis).
o An example of a point mutation is a substitution, where the correct base is
replaced with a different base.

Frameshift mutations – are when one or more bases are added or deleted from
the DNA strand. This shifts the base and codon pattern.
o Insertion is when one or more bases are added.
o Deletion is when one or more bases are missing.