From Genes to Proteins
Grade 10 Biology
Spring 2011
 Complete
this table as we take a journey
learning about RNA:
Property
Bases
Backbone
Number of strands
Base Pairing
Full name
Sugar
Function
DNA
RNA
 Compare
the structure of RNA with that of
DNA
 Summarize the process of transcription
 Relate the role of codons to the sequence of
amino acids that results after translation
 Outline the major steps of translation
 Discuss the evolutionary significance of the
genetic code
http://www.youtube.com/watch?v=983lh
h20rGY
 Traits
are determined by proteins that are
built according to instructions coded in DNA

Ex. Eye colour
 Proteins

are not built directly from DNA
Ribonucleic acid is involved (RNA)
 RNA:
nucleic acid, molecule made of
nucleotides linked together
 RNA
differs from DNA in 3 ways:
Single strand of nucleotides
Contain 5-Carbon sugar Ribose
Has bases A, G, C and U
1.
2.
3.


URACIL
A = U; G = C
 Transcription:
process where instructions for
making a protein are transferred from a gene
(DNA) to an RNA molecule
 Translation:
cells use two different types of
RNA (rRNA and tRNA) to read the instructions
made on mRNA and put together the amino
acid that makes up the protein
 Gene
expression: entire process by which
proteins are made based on information
encoded in DNA

Aka: protein synthesis
 RNA
polymerase: enzyme that adds and links
complementary RNA nucleotides during
transcription
 Steps
of TRANSCRIPTION:
RNA polymerase binds to the genes promoter
1.

Promoter: specific sequence of DNA that acts as a
“start” signal for transcription
 Steps
2.
of TRANSCRIPTION:
RNA polymerase then unwinds and separates
the two strands of the double helix, exposing
the DNA nucleotides on each strand
 Steps
3.
of TRANSCRIPTION:
RNA polymerase adds and then links
complementary RNA nucleotides as it “reads”
the gene.
RNA moves along the nucleotides of the DNA
strand that has the gene (only one of the
strands).
Follows base pairing rules. A = U, G = C
 RNA
polymerase eventually reaches “stop”
signal in DNA
 “Stop” is sequence of bases that marks the
end of the gene
 RNA
nucleotides linked by covalent bonds
 Behind RNA, DNA strands close (zip) back up
 Transcription uses DNA nucleotides as a
template
 Only part of one strand (the gene) of DNA
serves as the template
 Prokaryotes:

Transcription occurs in cytoplasm…why?

No nucleus
 Eukaryotes:

Transcription occurs in nucleus
 During
transcription many copies of RNA are
made simultaneously from a single gene
http://www.youtube.com/watch?v=ztPkv7wc3yU
http://www.youtube.com/watch?v=5bLEDd-PSTQ
 Messenger
RNA (mRNA) is
made when a cell needs a
particular protein
 mRNA: form of RNA that
carries the instructions for
making a protein from a gene
and delivers it to the site of
translation
 Translation:
information translated from the
language of RNA (nucleotides) to the
language of proteins (amino acids)
 Codons: RNA instructions are written as a
series of 3-nucleotide sequences on the
mRNA
 Each
codon along mRNA strand corresponds
to an amino acid or signifies a start or stop
signal for translation
 Genetic
Code: the amino acids and start and
stop signals that are coded for by each of the
possible 64 mRNA codons
1.
2.
3.
Find the first base of the mRNA codon along
the left side of the table
Follow that row to the right until you are
beneath the second base of the codon
Move up or down in that section until you
are even, on the right side of the chart,
with the third base of the codon
 Translate
this
mRNA sequence
into amino acids:
 Translation
takes place in the cytoplasm
 Transfer RNA (tRNA): single strands of RNA
that temporarly carry a specific amino acid
on one end

Each has an Anticodon: a three nucleotide
sequence on a tRNA that is complementary to an
mRNA codon
 Transfer
this mRNA sequence into its tRNA
anticodon and its amino acid
tRNA anticodons:
•CAA
•UGG
•CUA
•GUC
 Ribosomes:
composed of both proteins and
ribosomal RNA

Each ribosome temporarily holds one mRNA and
two tRNA molecules
 rRNA:
RNA molecules that are part of the
structure of ribosomes
 Lets
make a small poster that summarizes
the 7 steps of translation!
 Step




1:
Translation begins when mRNA leaves nucleus and
enters cytoplasm
mRNA, two ribosomal subunits, and tRNA carrying
the amino acid methionine form a functional
ribosome
mRNA “start” codon AUG, signals beginning of
protein chain, is oriented in ribosome in the P
site
tRNA molecule carrying methione can bind to the
start codon
 Step



2:
Codon in the area of the ribosome called the A
site is ready to receive the next tRNA
tRNA with complementary anticodon arrives and
binds to the codon in the A site
tRNA is carrying its specific amino acid
 Step


3:
Both A and P site have tRNA molecules, each
carrying an amino acid
Enzymes help form a peptide bond between
adjacent amino acids
 Step


#4:
tRNA in P site detaches
Leaves behind its amino acid, and moves away
from the ribosome
 Step




#5:
tRNA (with its protein chain) in A site, moves to P
site
Because anticodon remains attached to codon,
tRNA molecule and mRNA molecule move as a
unit
Result: new codon is present in A site, ready to
receive the next tRNA molecule and its amino
acid
Amino acid is carried to A site by a tRNA and then
bonded by a peptide bond to the growing protein
chain
 Step

#6:
tRNA in the P site detaches and leaves its amino
acid
 Step


Steps 2 through 6 are repeated until a stop codon
is reached
Stop codon is one of three codons




#7:
UAG, UAA, UGA
No tRNA molecule with a complementary anticodon
Because there is no tRNA molecule to fit into the
empty A site, protein synthesis stops
Newly made protein is released into the cell
 Many
copies of the same protein are made
from a single mRNA molecule
 Once ribosome has moved past the start
signal another ribosome can come in and
start translating
 Genetic
code is nearly universal
 With few exceptions the genetic code is the
same in all organisms
 Evidence for common ancestor
The gene is part of the DNA,
The gene is TRANSCRIBED by the mRNA,
The mRNA goes to the ribosome,
rRNA is part of the ribosome,
TRANSLATION occurs on the ribosome,
tRNA has an anticodon,
The anticodon matches to the mRNA codon,
The tRNA brings in the amino acid,
First to the P then the A site,
The amino acids are connected by a peptide bond,
And that’s how we make a protein!
 Lets
watch a video of transcription and
translation for review!
 http://www.youtube.com/watch?v=bpMhgAG
ybe4&feature=related