• Click here to read the case study about
protein synthesis.
Big Question:
How do cells use the genetic
information stored in DNA to
make millions of different
proteins the body needs?
Key Concept:
• Genetics shows that genes code for
proteins.
Remember: each gene consists of a
linear sequence of nucleotides arranged in
a specific order according to our genetic
ancestry.
C
sugar-
T
G
A
...
phosp
phosp
phosp
phosp
sugarsugarsugar...
hatehatehatehate-
The order of these nucleotides makes up
the genetic information or “code” which
determines the sequence of amino acids
that will be assembled.
Proteins are made up of a linear sequence of
amino acids that get twisted up.
Ribosome
And, in all cells, except for bacteria, DNA is
stored in the nucleus and protein synthesis
takes place in the ribosome (located in
the cytoplasm)…
• If a gene is used to make a protein, we say that gene is
“expressed”.
Be able to answer the following questions.
You will have to answer a question at the
start of class tomorrow:
• What is a gene?
• What is a protein made of?
• What do we mean when we say a gene is
expressed?
Key Concept:
• The genetic code carried by RNA is
translated into amino acid sequences of
proteins.
Problem:
• DNA cannot leave the nucleus (it is TOO
BIG!)
How can we get DNA’s information from
the nucleus to the ribosomes (site of
protein synthesis)?
We use RNA to move DNA’s code from the
nucleus to the ribosome!
3 Types of RNA:
• 1. mRNA
• 2. tRNA
• 3. rRNA
• RNA: ribonucleic acid. Takes DNA information to
the ribosome and uses information from DNA to
make proteins.
Comparison of DNA and RNA:
Nucleotide Components
Sugar
DNA
RNA
Deoxyribose
Ribose
Function
Form/Structure
Nitrogen Base
Adenine,
Guanine,
Cytosine,
Thymine
Store and
transmit
genetic info.
that tells cells
which proteins
to make and
when.
2 strands of
nucleotides.
Adenine,
Guanine,
Cytosine,
Uracil
Move genetic
info. from DNA
to ribosomes;
assemble
polypeptide
chains.
Single strand of
nucleotides.
Double Helix
Single Helix
Hey kids…RNA
differs from DNA
in several ways.
•An RNA molecule
has only one side of
the ladder shape.
•RNA has the bases
A, G, and C.
However, it has a
base U or Uracil,
instead of base T or
thyamine.
•So when forming
base pairs, base A
pairs with base U.
1. mRNA (Messenger RNA)
• Structure-single, uncoiled strand of RNA nucleotides.
• Function-takes information from DNA (in nucleus) to
ribosome to use during protein synthesis. Used as a
template for the assembly of amino acids during protein
synthesis.
• mRNA is made from
DNA in the nucleus.
• mRNA is “read” in order in 3 base “groups”.
• Each called a CODON- a 3-base sequence of mRNA
that codes for a specific amino acid.
• 3 mRNA bases=1 codon= code for 1 amino acid
• 64 different codons exist…several will code for the
SAME amino acid.
Two Important Types of Codons:
• START CODON-tells the ribosome to begin reading
the mRNA and to bring and assemble a chain of amino
acids (begin translation).
• This codon and amino acid is the same in EVERY
PROTEIN.
• STOP CODON-tells the ribosome to stop reading the
mRNA. No more amino acids are brought and
assembled (stop translation-ends the assembly of the
protein).
Stop and Think:
3 mRNA bases = code for 1 amino acid
If you have 450 mRNA bases, how many
amino acids would you code for?
How many codons would you have?
2. tRNA (Transfer RNA)
• Structure-single strand of RNA nucleotides folded into
a hairpin shape.
• Function-pairs with mRNA to transfer amino acids into
the growing polypeptide chain in the correct sequence.
• How does the tRNA know where to bring the amino
acids (what order)?
• One end of the tRNA is an ANTICODON-3-base
sequence of tRNA that complements (fits into) an
mRNA codon.
• The tRNA brings the amino acid to the codon
that it fits into.
Be able to answer the following questions.
You will have to answer a question at the
start of class tomorrow:
• How is RNA able to move DNA’s information out of the
nucleus?
• If a strand of mRNA has 1500 bases, how many codons is
that? How many amino acids does it call for?
Key Concept(s):
• DNA Expression begins with its
transcription to RNA.
• Translation of the genetic code is
mediated by tRNA and ribosomes.
Protein Synthesis takes place in two
steps:
1. Transcription
2. Translation
Like copying a cookie
recipe from a cookbook,
then baking the cookies.
• 1. TRANSCRIPTION-mRNA is made from
DNA in the nucleus.
How does mRNA get made?
1. RNA polymerase (enzyme) unzips section of
DNA.
• This section is a GENE-piece of DNA that
codes for a protein.
2. RNA polymerase moves along one side of the
DNA causing complementary mRNA nucleotides
floating in the nucleus to be assembled.
3. RNA polymerase reaches the termination
sequence of the gene and releases mRNA and
DNA.
4. DNA zips back up; mRNA leaves the nucleus.
How does the mRNA only assemble for one
section of DNA (one gene)?
• PROMOTER-beginning of the gene being transcribed.
Tells transcription to begin.
• TERMINATION SEQUENCE-end of the gene being
transcribed. Tells the RNA polymerase “let go”.
Making Proteins
Now, how does the template of bases found in
the mRNA get used to assemble the protein?
This requires “translating” the nucleotide-base
language of mRNA to the new, amino acid
language of protein synthesis.
TRANSLATION:
the second step of protein synthesis; (enzyme
assisted!!) the ribosomes ‘read’ the mRNA base
sequence in groups of three bases (called a
codon). Amino acids are transferred to growing
chain by tRNA.
Remember: the tRNA anticodon (sequence of 3
bases) fits into an mRNA codon; when they fit
together, that is the spot in the chain the amino
acid will occupy.
How does the amino acid chain get assembled?
1. mRNA goes to ribosome (proteins made here).
2. Ribosome reads mRNA from start codon to stop codon.
3. As the ribosome reads each codon, the corresponding
tRNA will come and match its anticodon to the correct
codon.
4. The amino acid carried by the tRNA will be linked to the
prior amino acid in the chain.
5. Ribosome repeats 2-4 until itreads the stop codon and
the process stops.
mRNA codon
and
corresponding
amino acids.
The diagram below shows a ribosome attach to
mRNA, and then move along the mRNA adding
amino acids to the growing polypeptide chain.
Part 2: Translation
Let’s Review:
DNA makes RNA makes PROTEIN.
It is a 2 - step process
Transcription - when DNA makes a copy of the protein
recipe. The copy is called mRNA.
Translation - when the ribosome makes the protein.
Has helper molecules called tRNA that carry the
amino acids.
Except for bones, fat, and water, the rest of your
body is made of protein.
Examples of protein functions
Function
Antibody
Enzyme
Description
Antibodies bind to specific foreign particles,
such as viruses and bacteria, to help protect
the body.
Enzymes carry out almost all of the
thousands of chemical reactions that take
place in cells. They also assist with the
formation of new molecules by reading the
genetic information stored in DNA.
Example
Immunoglobulin G
(IgG)
Phenylalanine
hydroxylase
Messenger
Messenger proteins, such as some types of Growth hormone
hormones, transmit signals to coordinate
biological processes between different cells,
tissues, and organs.
Structural
component
These proteins provide structure and
Actin
support for cells. On a larger scale, they also
allow the body to move.
Transport/storage
These proteins bind and carry atoms and
small molecules within cells and throughout
the body.
Ferritin
Summary:
• Let’s watch protein synthesis in
ACTION!
Be able to answer the following
questions. You will have to answer
a question at the start of class
tomorrow:
• Why is protein synthesis important to your
life?
• What are the two parts of protein synthesis –
summarize them VERY BRIEFLY.
• What is tRNA’s role in protein synthesis?