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Protein Synthesis
Genes  Proteins
Genes: a sequence of nucleotides in
DNA that performs a specific function.
Each gene contains the instructions to
build a specific protein.
It is the proteins that our bodies
make that give us our traits –
freckles, brown eyes, blond hair, etc.
Proteins
Proteins: complex molecules composed
of amino acids.
There are 20 different amino acids.
Different combinations of these 20
amino acids create different proteins.
Proteins are made outside the nucleus
by organelles called ribosomes.
Remember…
Genes are located on chromosomes.
Chromosomes are made up of coiled
DNA. Therefore, genes are made up of
sections of DNA.
Genes contain the instructions to make
specific proteins which give us our
genetic traits.
???
Proteins are not made inside the
nucleus, and DNA cannot exit the
nucleus!
So how can the instructions from the
genes actually make proteins to give
us our traits if they are in two
places?!
This is where the process of
Protein Synthesis comes in!
(without protein synthesis, our cells would
not operate, genes would not be
expressed, cells would die, etc.)
DNA, RNA, & Proteins
For proteins to be created - it starts
with the DNA.
DNA strand is transcribed into a language
that is understood outside the nucleus.
 It is transcribed into “messenger RNA”.
 The mRNA strand is able to exit the
nucleus, carrying the instructions from the
gene (DNA).
 Ribosomes translate the RNA code and
begin making the necessary proteins.

Transcription & Translation
Transcription: involves the copying of the
information in DNA into messenger RNA.

When you transcribe, you copy from one medium
to another.
Translation: involves ribosomes using the
messenger RNA as blueprint to synthesize a
protein composed of amino acids.

When you translate, you convert into a different
language.
The basics of protein synthesis
DNA is transcribed into complementary
messenger RNA, and ribosomes
translate messenger RNA into specific
sequences of amino acids, which are
used to build proteins!
Protein Synthesis – Two Stages
(the details)
Protein Synthesis involves two main
steps:
Transcription
 Translation

Step 1: Transcription
1.
2.
3.
4.
Occurs in the nucleus and results in the
formation of messenger RNA (mRNA)
Hydrogen bonds break and a portion of
DNA unzips
RNA nucleotides form a complement to
one side of the unzipped DNA
The RNA complement is called mRNA and
it leaves the nucleus carrying a copy of a
DNA gene.
The DNA zips back up, unchanged.
The Genetic Code
To code for all amino acids, a sequence
of three nucleotides must be used for
each amino acid.
Each triplet of nucleotides on RNA is
referred to as a codon.
One code serves as a start codon and
others serve as stop codons.
Refer to p. 240 in Nelson Biology 12
text for genetic code table
Universal Codes
The codons on the mRNA are universal.
In other words, GGG codes for the
amino acid glycine regardless of
whether it is in a human, a dog, or a
bacteria.
Transcription Animation
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/tra
nslation.swf
Step 2: Translation
Occurs in the cytoplasm on the
ribosomes.
Transfer RNA (tRNA) are clover-leaf
shaped molecules that carry 3 bases
on one end, called an anti-codon, and
a specific amino acid on the other end.
Step 2: Translation
1.
2.
3.
The ribosome moves along the mRNA
one codon at a time.
The tRNA with the complementary
anti-codon temporarily bonds with the
mRNA codon and brings its amino
acid with it.
The ribosome moves to the next
codon, the matching tRNA appears.
Step 2: Translation, cont’d
4.
5.
6.
The amino acids bond to each other.
This process continues until the
ribosome hits a “stop” codon.
The amino acids that bonded to each
other result in a protein (polypeptide
chain).
Translation Animation
http://highered.mcgrawhill.com/sites/0072943696/student_view0/chapter2/animation__p
rotein_synthesis__quiz_1_.html
Also see Figure 4, page 252 of Biology 12 Textbook
Interactive – Protein Synthesis!
http://learn.genetics.utah.edu/content/be
gin/dna/transcribe/
Complete the ‘TRY THIS Activity’ on page 233 of Biology 12
textbook. Complete questions on looseleaf.
Answer Question # 1 on page 236.
Compare and contrast DNA and RNA – in particular its shape,
sugar, bases, location. (Use your binder notes, these PPT
notes, and sections 4.2 and 5.2, and summary table on page
238.)
Complete # 2 and # 6 on page 249.
Complete # 6 on page 254.
Refer to Section 5.2 to answer the following:




Describe the role of the following molecules in protein synthesis:
ribosomes, mRNA, tRNA, rRNA.
Differentiate between transcription & translation in terms of their purpose
and location.
Differentiate between a stop codon and a start codon. Provide an
example of each.
Complete Questions # 10, 11, 13 on page 241.