Chapter 9:
Expressing
Genetic
Information
9.1 Genetic Material
DNA & RNA
- both nucleic acids (store genetic information)
- DNA- double stranded, deoxyribose
sugar, thymine
- RNA – single strand, ribose sugar, uracil
DNA sequence determines the structure of proteins
Proteins:
- made from amino acids (20 different a.a.
total)
- made in ribosomes
RNA exists in 3 forms:
– messenger RNA (mRNA)
– transfer RNA (tRNA)
– ribosomal RNA (rRNA)
mRNA is read in groups of 3
- 3 nitrogen bases = 1 amino acid
How do we know?
– 1 bases = 41 = 4 amino acids (not enough)
– 2 bases = 42 = 16 amino acids (not enough)
– 3 bases = 43 = 64 amino acids
Flow of Genetic Info. in a Cell
DNA
replication
RNA
protein
trait
9.2 Importance of Proteins
Proteins are responsible for carrying out
cellular activities
ex: enzymes, transport proteins,
hormones
Fainting Goats
9.3 RNA Synthesis
Transcription: uses DNA to create RNA
DNA
C
G
T
A
RNA
G
C
A
U
DNA: A C A G G A T A T C A A A C A T A T G
RNA: U G U C C U A U A G U U U G U A U A C
- mRNA is transcribed in the nucleus then
moves to the cytoplasm
- RNA polymerase = enzyme that creates the
complementary strand of mRNA
Stages of Transcription:
Initiation: RNA polymerase attached to
DNA at the promoter region (TATA box)
Elongation: RNA polymerase
partially unwinds DNA and creates
a complementary RNA strand
Termination: RNA poly. reaches the
terminator region & releases
Transcription
Simulation
9.4 RNA Processing
To prevent RNA degradation:
- methyl-guanine (mG) cap is
added to 5’ end
- poly A tail (~100-200 A’s) is
added to 3’ end
METHOLATED
CAP
mRNA is spliced before it leaves the nucleus:
introns  nonsense RNA that is
removed
exons parts of the gene that
will be expressed (translated)
9.5 Translation
Translation: Turns mRNA into a protein
- Takes place in the cell’s cytoplasm, in
a ribosome
String of amino acids are strung together
then folded up to create a protein.
codon (triplet): 3 mRNA bases which code for 1
amino acid
AUG= start codon
UAA, UAG, UGA = stop codons
Transcribe, then translate the DNA
strand below:
ATCTACAAGGGCTCAATCCAG
The Process of Translation
Involves 3 types of RNA:
mRNA- carries genetic code
tRNA- transports amino acids
-tRNA binds to mRNA with an
anticodon
rRNA- holds tRNA and mRNA together
tRNA molecule
G
(amino acid)
U
A (anticodon)
tRNA molecule
Protein Synthesis
Simulation
mRNA: A U G C C G A A G U A G C C G
tRNA:
amino acids:
mRNA: U U C A U G U U A C G U U G A
tRNA:
amino acids:
rRNA has 3 sites:
A site- holds the tRNA carrying a.a. to be
added to chain
P site- hold tRNA with growing polypeptide
chain
E site – exit site
P
Site
A
Site
mRNA
Steps of Translation: (review diagrams on p. 250-251)
Initiation: ribosome attaches to mRNA,
tRNA carrying methionine binds to P site
Elongation: ribosome moves down 1
codon, amino acids are added to
polypeptide chain
Termination: stop codon reaches A site, release
factor binds to stop codon, polypeptide is
released
Translation Simulation (mcgraw-hill)
Translation Video
9.6 Transport & Modification of Proteins
Modification:
- new proteins may not be functional
- must be chemically modified &
folded into active structure
- enzymes may cut polypeptide
into smaller segments (ex: pepsin &
trypsin)
Transportation:
- protein transported to where it will
function best
ex: insulin- protein moved outside
of cell
signal sequence part of the
protein’s a.a. sequence, determines
where the protein will be transported
start of a secretory pathway
9.7 Translation Errors
Mutation- any change in a cell’s DNA sequence
- Most caught and corrected by DNA
polymerase (during S phase of cell cycle)
- Basic types of mutations:
base insertion (can cause a frame-shift)
base deletion (can cause a frame-shift)
substitution
3 base insertion
Mutations can lead to a change in the a.a
sequence, or can create a partial
polypeptide
9.8 Genetic Information & Viruses
Viruses: made nucleic acids (DNA/RNA) and
protein
- not considered to be alive
- depends on host for reproduction
- no metabolism
- antibiotics are NOT effective
because viruses do not have
metabolism
retrovirus: forms DNA from its RNA
template using reverse transcriptase
ex: HIV, influenza
Viral replication (p.255-256)
- host cell’s organelles used to
make more viruses
- 2 reproduction patterns, lytic
(viruses reproduces and destroys
cell) and lysogenic (viral DNA
inserted into host cell’s DNA)
9.9 Impact of Viruses
The HIV life cycle. Howard
Hughes Medical Institute. YouTube
Life Cycle of the HIV Virus
(simulation link)
NOVA | 1918 Flu (6 min)
NOVA | Pandemic Flu (12 min)