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Ribonucleic Acid (RNA)
and Protein Synthesis
Section 12-3
Outline of today’s information
RNA - basics
1
Summary
Translation
2
Transcription
3
4
Replication
5
Outline of today’s information
RNA - basics
1
2
3
4
5
The DNA/RNA connection
DNA and RNA are partners in the business
of making proteins.
DNA is a specialist.
It provides stable, permanent storage of
the code (or recipe) for making proteins
RNA is a generalist (more versatile).
It serves a variety of roles (including the
“chef”) to make (synthesize) proteins.
Structure of RNA (ribonucleic acid)
*Notice the differences (in red) from DNA*
A long chain of nucleotides
 SINGLE stranded
 Phosphate, sugar (ribose), nitrogenous
base


Adenine, guanine, cytosine, URACIL
3 Types of RNA

messenger RNA (mRNA)


ribosomal RNA (rRNA)


Instructions for assembling proteins out of
amino acids – code is copied from DNA and
taken to the rest of the cell.
The main pieces that make up ribosomes (along
with some protein components). Ribosomes
assemble proteins.
transfer RNA (tRNA)

Transfers (delivers) amino acids to ribosomes.
Checkpoint

What are three differences
between RNA and DNA?

What are the three types of
RNA?

What does each kind of RNA
do?
RNA makes proteins from the information stored in
the cell’s nucleus (DNA). This requires two different
processes — transcription and translation.
process
types of RNA involved
location
function
transcription
messenger RNA
mRNA
nucleus
copy DNA
translation
messenger RNA
mRNA
On a
ribosome
in the
cytoplasm
make proteins
transfer RNA
tRNA
ribosomal RNA
rRNA
Outline of today’s information
RNA - basics
1
2
Transcription
3
4
5
Transcription
Transcription - the conversion of information
from one form to another.
In molecular genetics, transcription is
when the “code” found in DNA is
transcribed (or copied) into a
complementary sequence of RNA.
Cooking/Kitchen analogy of
transcription of DNA into RNA
If DNA is like a treasured cookbook in
your grandmother’s house that is filled
with dozens of family recipes,
 Then, the process of transcription is like
copying down one recipe from
Grandmother’s cookbook (let’s say, pecan
pie) onto an index card that you can take
home to use.
 The mRNA is the “index card with one
copied recipe.”

A brief description of transcription
The enzyme RNA
polymerase binds
to a particular
part of the DNA
that says “the
gene starts here.”
1.
•
This location is
called the
promoter site.
RNA polymerase - the
enzyme that makes an
RNA copy of the DNA gene
A brief description of transcription
After the RNA
polymerase binds to
the promoter site,
the 2 strands of the
DNA begin to unzip
to form a “bubble” of
unpaired DNA
strands.
2.
•
This allows space for
the mRNA to be
assembled.
RNA polymerase - the
enzyme that makes an
RNA copy of the DNA gene
A brief description of transcription
The mRNA transcript
is built nucleotide by
nucleotide by the
RNA polymerase as it
moves over the DNA
(gene).
3.
•
The assembled RNA
nucleotides are
complementary to
the nucleotides on the
DNA.
RNA polymerase
transcribing the
gene
RNA/DNA base-pairing rules
(for making the mRNA)
Complementary nucleotides
In the new strand of RNA,
___________ pairs
With
__________ on the
DNA template
Guanine (G)
Cytosine (C)
Cytosine (C)
Guanine (G)
Adenine (A)
Thymine (T)
Uracil (U)
Adenine (A)
Example of base-pairing
What would the
mRNA sequence be
if the DNA
template strand
were:
 ATTGGCGCTAAC ?

A brief description of transcription
4.
The end of transcription
occurs when
•
the end of the gene is
reached
•
the mRNA is cut loose
•
the mRNA is edited
(in eukaryotes) to
make it ready for use
•
the mRNA is exported
out of the nucleus and
into the cytoplasm.
RNA polymerase
transcribing the
gene
Checkpoint
If the DNA sequence is:
ATT GTC CAC TGG AGC
What will the mRNA be after
transcription?
Can you now describe what is going on
in this picture?
nucleus
mRNA
RNA polymerase
DNA
Outline of today’s information
RNA - basics
1
Translation
2
Transcription
3
4
5
Translation
 mRNA
(messenger RNA) is DECODED
by a RIBOSOME to make…

Proteins

 mRNA
attaches
to a ribosome
 mRNA is read 3
bases at a time
by the
ribosome.
 This three-base
unit is called a
codon.
Translation
 As
each codon
(3 N-bases)
moves through
the ribosome
like a ribbon…
 The tRNAs with
the correct
anticodon
bring the
required amino
acids.
Translation
(continued)
Translation
 Anticodon
-
the 3-base
sequence on
each different
tRNA that is
complementary
to a codon on
mRNA.
(codon)
From Wikipedia commons
The relationship between tRNAs
and amino acids
 Each
amino acid (a.a.) is carried
by tRNAs that have anticodons
complementary to the mRNA
codons.
 We will look at how this genetic
code works a little later.
Translation
 The
ribosome forms a
peptide bond between
this newly delivered
amino acid and the
previous a.a. in the
chain.
 This makes the
polypeptide chain (what
will be the protein) one
a.a. longer.
ribosome
Translation
 tRNA
(minus its amino
acid) is released
 The ribosome moves to
next codon
 This continues until a
Stop Codon is reached
 New polypeptide is
released 
ribosome
Can you now describe what is
going on in this picture?
Proteins
The whole purpose of the genetic code
is to assemble complicated proteins
perfectly, over and over, millions of times.
 Proteins (polypeptides) are long chains of
amino acids (20 different ones) that are
connected in a specific order.
How can just four “letters” (the four Nbases in RNA) code for the correct amino
acid (if there are 20 different ones)?

A, U, C, G
vs. 20 different amino acids?
Proteins
 RNA is read 3 letters at a time
 Like “3 letter words”
 These 3 letter words are called
codons.
 Examples
 AUG
 GGC
 UUA
Cracking the Code
mRNA
UCGCACGGU
 UCGCACGGU


Codons: UCG
CAC
GGU
Translation



These strings of codons are
then translated into proteins
by the interaction of
ribosomes and tRNA’s.
tRNA’s only deliver their
specific amino acid to the
ribosome when the mRNA
has the appropriate
complementary codon.
We can use a chart to
determine which amino acids
are coded for by a given
codon.
Codons: UCG
CAC
GGU
Note the
20 amino
acids plus
the 3 stop
codons
Proteins

Example:





If a DNA sequence is GGCTATCTA,
The complementary mRNA sequence is…
CCG AUA GAU
Using a genetic code chart (like on pg. 303),
one can determine that these three codons
correspond to the following amino acids:
Proline Isoleucine Aspartic Acid
Checkpoint
If the DNA sequence is:
GTAGGCCTCTGGTGCACT
What will the mRNA be after
transcription?
What will the amino
sequence be?
Outline of today’s information
RNA - basics
1
Translation
2
Transcription
3
4
Replication
5
DNA transcription and translation
compared with DNA replication

DNA transcription and translation




One small gene at a time
Nearly constant throughout cell’s life
For assembling the proteins of which we, and
all living things, are made.
DNA replication



Requires the copying of the cell’s entire
collection of DNA.
Is only performed once in the cell’s life.
For reproduction where all the instructions
for making an organism must be passed on.
DNA replication
 Before
a cell can divide, it needs
to have two complete set of
instructions, one for each of the
two new daughter cells.
 The duplication of the cell’s DNA
is called DNA replication.
DNA replication
 This
copying of DNA is very
efficient and elegant because
each strand has all the
information needed to make the
other strand (the base pairing
rules allow you to reconstruct
what the complementary
sequence was).
Base-pairing Rules
• Adenine (A) always pairs with Thymine (T)
• A •• T or T •• A
• Connected by 2 Hydrogen bonds
• Cytosine (C) always pairs with Guanine (G)
• C ••• G or G ••• C
• Connected by 3 Hydrogen bonds
Steps in DNA Replication

Step 1 The two strands of DNA are
“unzipped” by the enzyme helicase.
Steps in DNA Replication

Step 2 Now, each separate strand of DNA
can serve as a template to make a new
complementary strand of DNA. The new
strands are formed by the enzyme DNA
polymerase which adds the correct
nucleotides one at a time to make the new
strands.
Replication of DNA is semiconservative. That is, one side of each
new DNA strand is "old" and the other
side is "new".
Outline of today’s information
RNA - basics
1
Summary
Translation
2
Transcription
3
4
Replication
5
Central Dogma of
Molecular Biology
transcription
replication
DNA
translation
RNA
Protein
Summary Checkpoint
What does each type of RNA do?
Describe what happens in transcription.
Describe the process of translation.
Beginning with a DNA sequence, you need
to be able to figure out the amino acid
sequence it codes for.
If the DNA sequence is TGAGGGAGA…
Mutations
Cells do rarely make mistakes copying
their own DNA resulting in a change in the
DNA.
 Mutation – a change in genetic material.
 Types of mutations



Gene mutations – mutations that produce
changes in a single gene.
Chromosomal Mutations

Changes in the number or structure of chromosomes.
Results of mutations
Can be very harmful
 Can be neutral (neither harmful nor good)
 Also result in genetic variability



Good for changing environments
Plant and Animal Breeders


Polyploidy = extra sets of chromosomes (3N,
4N, 6n, 8n, 10n, etc.)
Bananas, citrus fruits, seedless fruit
Protein synthesis animations

http://www.stolaf.edu/people/giannini/flas
hanimat/molgenetics/transcription.swf

http://www.stolaf.edu/people/giannini/flas
hanimat/molgenetics/translation.swf

http://student.ccbcmd.edu/~gkaiser/biotu
torials/protsyn/translat.html
Protein synthesis animations
http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a1.html
 http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a2.html
 http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a3.html


http://student.ccbcmd.edu/~gkaiser/biotu
torials/protsyn/translat.html

http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a3.html
http://www.biostudio.com/demo_freeman
_protein_synthesis.htm
 http://www.wisconline.com/objects/index_tj.asp?objID=AP
1302
 http://www.abdn.ac.uk/~clt011/flash/sam
ples/protein.swf
