Download Protein Synthesis Notes

You have been given a mission:
 You must crack the code that you
have been given. How many letters
does it look like it requires to make
just one English Letter?
 What information did you use to crack
the code?
Protein Synthesis
-The process of making a protein from a
gene
What is a gene?
 A gene is a specific section of DNA
along the length of a chromosome.
 It has a beginning (the “promoter”) and
an end (the “termination signal”).
 A gene holds the instructions for making
a specific protein.
The path from DNA to protein
1.) DNA
2.) Process of Transcription
3.) RNA
4.) Process of Translation
5.) Protein
DNA vs. RNA
 Similarities
 Nucleic acids
 Made of nucleotides with a sugar,
nitrogen base, and phosphate groups
 Differences
 RNA has ribose sugar (instead of
deoxyribose)
 RNA has uracil instead (U) of
thymine (T)
 RNA is single-stranded
Base-pairing between DNA & RNA
during transcription
Videos:
 http://www.californiastreaming.org/pl
ayer.asp?mediaID=12495&segmentI
D=20846
Types of RNA
-messenger RNA
-transfer RNA
-ribosomal RNA
Messenger RNA (mRNA)
 Location: nucleus & cytoplasm
 Structure: single, unfolded chain of
nucleotides. Contains a series of
codons.
 3 bases = codon = code for an amino
acid
 Function: to carry the instructions for
making the protein from inside the
nucleus to the ribosomes.
Transfer RNA (tRNA)
 Location: cytoplasm
 Structure: single chain folded into
“cloverleaf” shape. Has an anticodon
on one end and binds an amino acid
on the opposite end.
 Function: to transfer (deliver) the
correct amino acids to the ribosome.
 There are many different tRNAs; each
carries a different a.a.
Ribosomal RNA (rRNA)
 Location: cytoplasm (“free” or on the
rough ER)
 Structure: rRNA, combined with
proteins. Has two subunits.
 Function: coordinates the building of
a protein. Binds mRNA and tRNA;
catalyzes peptide bond formation.
 http://www.teachersdomain.org/reso
urce/tdc02.sci.life.gen.proteinsynth/
 http://www.youtube.com/watch?v=4
1_Ne5mS2ls&safe=active
Transcription & Translation
 Warm Up:
 1. What are the
building blocks
(monomer) of a
protein?
 2. What acts as a
messenger
between DNA &
ribosomes?
 3. Define a codon.
Transcription: Gene to message
 Creating the “messenger”
 Making a strand of mRNA using DNA as a
template.
 mRNA = copy of gene
 Allows for transfer of info from DNA to
site of protein synthesis (cytoplasm)
Transcription
 DNA contains the instructions for making
protein but cannot leave the nucleus
 Proteins are made by the ribosomes, which
are found outside the nucleus
 Somehow the info held by the DNA must
make it’s way outside the nucleus to the
ribosome, done by creating the “messenger”
Steps of Transcription:
1. The enzyme RNA polymerase binds to a
promoter on specific gene in DNA
2. DNA molecule in that region “unzips”
3. RNA nucleotides are paired to
complementary bases on the DNA template
strand

Complementary base-pairing: C-G, G-C, T-A,
A-U
Transcription, cont’d…
5. mRNA strand lengthens until RNA
polymerase reaches a “termination
signal”
6. Single stranded mRNA strand is made &
seperates from the DNA template.
 DNA re-twists into double-helix.
mRNA Carries Message from
Nucleus to Cytoplasm
http://nobelprize.org
/educational/medicin
e/dna/b/transcriptio
n/transcription_ani.h
tml
http://www.teachersd
omain.org/resource/ls
ps07.sci.life.stru.celltr
ans/
Problem Solving
 If you know the DNA sequence, you
can determine the mRNA sequence
More Practice
 Use the DNA sequence below to
determine the mRNA sequence:
DNA: T-A-C-G-A-T-A-T-C
mRNA: A-U-G-C-U-A-U-A-G
Translation
Making a protein using an mRNA
template.
 mRNA = copy of gene
 Every 3 letters on mRNA = codon = codes for a
specific amino acid (a.a.).
e.g.: the codon AUG codes for methionine
(“met”)known as the “start” codon.
 Amino acids will be bonded together in a specific
sequence. Correct a.a. sequence is critical to the
protein being functional (having the right shape).
mRNA-tRNA connection
 mRNA contains the “codes” for the
amino acids.
 tRNA delivers the amino acids.
 tRNA brings the right a.a. to the right
place in the protein by binding to the
mRNA.
 Codon and anticodon are
complementary.
The “Genetic Code”
 The a.a.
brought by
tRNA is
specified by the
mRNA codon,
NOT the
anticodon.
mRNA, tRNA, and a ribosome work
together in constructing a protein
 mRNA = “messenger”; it contains the
message that is being translated.
 tRNA = “transfer”; it transfers (delivers) the
right a.a. to the right codon. It is the
“interpreter”.
 When you translate an mRNA sequence, you are
the “interpreter”. You determine the correct a.a.
for each codon by looking at the Genetic Code
table.
 rRNA = “ribosomal”; as part of the structure
of the ribosome, it helps bond amino acids
together.
Steps of Translation
1. mRNA attaches to a ribosome in the
cytoplasm.
2. A tRNA, carrying the amino acid
“met”, binds to the start codon (AUG)
on mRNA. A second tRNA w/an a.a.
binds to the ribosome.
3. A peptide bond is formed between the
a.a.
Translation, cont’d
4. The process of a.a. delivery by tRNA and
peptide bond formation continues until the
chain is 100+ amino acids long.
5. When a stop codon is reached, translation
ends and the polypeptide (protein) is
released.
6. The polypeptide’s a.a. sequence will determine
how the protein folds into a 3-D functional
shape.
http://nobelprize.org/educational/medicine/dna/b/translation/translation_ani.html
Finish your “steps in Protein
Synthesis” and answer the
following questions on the back.
 What is the end result of Translation?
 What RNA codon or anticodon will you
use to find the amino acid?
 What chart will you use to find the
amino acid?
The amino acid “Tyr” is
carried by a tRNA, but it is
coded for by the mRNA
codon (UAC)