Trait
Chapter 12
Section 3
1. RNA
Ribonucleic acid
Responsible for the
movement of genetic
information from the DNA
in the nucleus to the site
of protein synthesis in the
cytosol
A. Structure of RNA:
–Single-stranded
Nucleic acid made
up of repeating
units, like DNA
–Sugar molecule is
RIBOSE (not
deoxyribose)
–Thymine is replaced
with URACIL (U)
1. Messenger RNA (mRNA)
a. STRUCTURE= RNA
nucleotides in a single uncoiled
chain
b. FUNCTION= Carries
genetic info from the nucleus to
the ribosome
2.Transfer RNA (tRNA)
a. STRUCTURE= RNA
nucleotides in a single
chain folded into a
cloverleaf shape
b. FUNCTION= binds
to specific amino
acids and helps form
polypeptide chains
3. Ribosomal RNA (rRNA)
a. STRUCTURE = RNA
nucleotides in a globular
form
b. FUNCTION = makes
up the ribosomes where
proteins are made
• The production of proteins
• The amount and kind of
proteins produced in a cell
determine the structure and
function of the cell
• Protein’s carry out the genetic
instructions encoded in an
organism’s DNA
• Proteins are POLYMERS
• Made up of amino acids
• There are 20 different
amino acids that make
up proteins
a. Transcription
Transcription
• What is it???
–making mRNA from
DNA
• NOTE:
–Transcribe = to copy
Transcription
Steps
1. RNA polymerase binds to DNA
at the promoter and separates
the DNA strands.
2. RNA polymerase then uses one
strand of DNA as a template.
Using the template as a guide,
nucleotides are assembled into
a strand of mRNA.
DO NOW: Transcription
• 1. Where does Transcription occur?
• 2. What is produced at the end of
transcription?
• 3. What enzyme is used in
transcription?
b. T r a n s l a t i o n
STEP 2 of PROTEIN
SYNTHESIS
Translation
• The process TRANSLATING the
message encoded in mRNA to
assemble a protein.
• Process begins when mRNA
leaves the nucleus through
pores in the nuclear membrane
• The mRNA then migrates to a
ribosome in the cytosol, the site
of protein synthesis
THE GENETIC CODE
• The genetic information
necessary for making proteins
is encoded in series of three
mRNA nucleotides
• Each combination of 3-mRNA
nucleotides is called a CODON
• Each codon codes for a
specific amino acid
tRNA carries
the
“Anticodon”
. . . Allows
tRNA to match
up with mRNA
codon
Codons
in mRNA
If the mRNA sequence is
A-A-U (codon)
then the tRNA sequence is
U-U-A (anticodon)
T r a n s l a t i o n Steps
1. mRNA arrives at a ribosome
2. mRNA is pulled through the
ribosome
3. Start codon signals tRNA to start
arriving
4. One tRNA matches up to the codons
on mRNA to deposit an amino acid
5. Another tRNA comes in and adds
another amino acid to the chain.
6. Process continues until stop codon
is reached and enough amino acids
have been linked to form a protein.
Translation
Mutations
• Mutations = errors
–Mutations can occur as a “typo” in
the sequence of nitrogen bases.
–For example if a sequence should be
A-C-G, a mutation could occur and it
is now A-G-C . . . What affect could
this have on the protein produced?
PROTEIN SYNTHESIS
ANIMATION