Download Protein Synthesis

Do Now:
1. What structure makes proteins?
2. Where are these found?
3. Where is DNA stored?
4. Why not in cytoplasm?
• Homework: read 12-3 and
complete packet
DNA is safe inside the nucleus, but
ribosome are in the cytoplasm!!
RNA is a “messenger molecule” that can
take the code into the cytoplasm.
Trait
Overview of Protein Synthesis
Transcription
Translation
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
*STEP 1 of PROTEIN
SYNTHESIS*
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.
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.
• 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
**Start codon=AUG**
If the mRNA sequence is
A-A-U (codon)
then the tRNA sequence is
U-U-A (anticodon)
All three types of RNA are
involved in Translation
rRNA
tRNA
mRNA
Phase 1: Initiation
• mRNA leaves nucleus
• mRNA attaches to a ribosome
• tRNA attaches to a start codon (AUG)
Phase 2: Elongation
• tRNA anticodon binds with next mRNA codon
• adjacent amino acids bond (begin a polypeptide chain)
• Ribosomal unit shifts down to next codon, first tRNA leaves
Phase 3: Termination
•
•
Ribosomal unit stops when reaches stop
codon
All units detach,
and polypeptide
folds into 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