PROTEIN SYNTHESIS
(A) DNA  RNA  PROTEIN
 DNA is the ___________________ of __________
 DNA contains a __________ which produces
___________________ proteins
A gene is a section/segment of DNA
 The process of DNA producing a protein involves
_____ steps:
(1) Transcription
 a gene segment of DNA is copied into a mobile
molecule called __________ in the nucleus
(2) Translation
 mRNA travels to the cytoplasm and is used by __________________ to produce proteins
through a process called ____________________
 at the ribosome, the mRNA __________ is read and used to ________________ a specific
sequence of______________________
 when finished, the mRNA is _______________________ and the parts are
_________________
(B) RIBONUCLEIC ACID (RNA)
 we have already looked at the
structure of DNA and RNA and we
know that DNA has all the
instructions for cell activities
QUESTION: HOW DO THE DNA
INSTRUCTIONS GET COMMUNICATED
AND MADE INTO PROTEIN?
 Molecules of RNA
,
_______________, ________________
the messages
Different Types of RNA
 there are ____ different types of RNA used in the process of making _____________
(protein synthesis)
(i) Messenger RNA (mRNA)
 ________________ the genetic code contained in the sequence of bases in the cell's DNA
from the _________________ to the ___________________
 acts as a "go-between" for DNA in the nucleus and the ribosomes in the cytoplasm.
 constitutes 5% to 10% of the cell's RNA.
(ii) Transfer RNA (tRNA)
 is used to deliver
from the cytoplasm to the ribosome.
 There is a ___________________ tRNA for
each amino acid.
 The function of each type of tRNA is to bring its
__________________ amino acid to a
ribosome
 The tRNA molecules consist of about 80
nucleotides and are folded into a clover-leaf
structure
 They constitute about 5% of the cell's total RNA
(iii) Ribosomal RNA (rRNA)
 becomes a ______________________ part of ribosomes
 Ribosomes are the sites of _____________________________________
 varies in size and is the most plentiful RNA. It constitutes 85% to 90% of the cell’s RNA
(C) PROTEIN SYNTHESIS
 the cellular process of making proteins from the genetic instructions encoded in DNA
 occur in two main steps:
and
(1) Transcription
 mRNA is produced from DNA by a process called
 The steps of transcription are as follows:
(i) A specific section of DNA unwinds, exposing a set of bases. Unzipped by an
_____
(ii) Along
strand of the DNA (called the "____________" strand), ____________________
RNA bases are paired with the DNA on the sense strand.
 In RNA, U replaces T, cytosine still binds to guanine)
 The other strand of the DNA molecule, the “
” strand, isn’t read in
eukaryotic cells.
 Adjacent RNA
_____________________________bond
 covalently between the sugar and phosphates
(iii) The mRNA strand is released from DNA (mRNA
is a single-stranded nucleic acid)
 Once produced, the mRNA strand may be
_____________________
 certain sections called “introns” are cut out
(iv) RNA then leaves the ____________________
through the nuclear
and goes to the
_____________________
(iv) The DNA molecule ______________________, and returns to its normal double helix form.
NOTES: (i) The ____________ involved in transcription is known as
__________________________
INSTANT PRACTICE:
G
III
 In the table below, write the complimentary RNA bases that would pair with the DNA “sense” strand.
A
C
A
A
C
T
G
G
A
T
C
G
A
C
DNA
II
III
II
II
III
II
III
III
II
II
III
III
II
III
mRNA
(2) Translation
 the process that translates the mRNA message
into the actual __________________
 It occurs at the ____________________
 The _____________________ of the bases in DNA,
and then subsequently mRNA, determines
the
sequence of the
protein being made.
 Each amino acids is coded for by ____ bases
 There are _____ different amino acids, but only ____ different bases in DNA/RNA.
 Each three-letter unit of mRNA is called a _______________ and calls for 1 amino acid
NOTE: There are 43 ( = 64) codons possible --> there are more codons than amino acids.
 Therefore, the same amino acid is often specified by _________ than one codon.
NOTE: The reverse is never true: that is, any one codon only specifies ONE amino acid there is no vagueness in the code (e.g. CCU will always produce proline).
AAU
AAC
AAA
AAG
ACU
ACC
ACA
ACG
AGU
AGC
AGA
AGG
AUU
AUC
AUA
AUG
ASPARAGINE
LYSINE
THREONINE
SERINE
ARGININE
ISOLEUCINE
METHIONINE
*START
CAU
CAC
CAA
CAG
CCU
CCC
CCA
CCG
CGU
CGC
CGA
CGG
CUU
CUC
CUA
CUG
HISTIDINE
GLUTAMINE
PROLINE
ARGININE
LEUCINE
GAU
GAC
GAA
GAG
GCU
GCC
GCA
GCG
GGU
GGC
GGA
GGG
GUU
GUC
GUA
GUG
ASPARTIC ACID
GLUTAMIC ACID
ALANINE
GLYCINE
VALINE
UAU
UAC
UAA
UAG
UCU
UCC
UCA
UCG
UGU
UGC
UGA
UGG
UUU
UUC
UUA
UUG
TYROSINE
STOP
STOP
SERINE
CYSTEINE
STOP
TRYPTOPHAN
PHENYLALANINE
LEUCINE
 The code also contains “
reading the gene for a particular protein)
 Each codon corresponds to an
"
" signal
.” (Telling when to start & stop
, or a “___ " or
 The genetic code is __________________: the same codons stand for the same amino
acids in all living things (well, almost all living things). This "Biochemical Unity" suggests
that all living things have a common evolutionary ancestor.
STEPS OF TRANSLATION (there are 3 sub-processes)
(a) INITIATION
(b) the ribosome (small subunit) binds to a
and travels along it until it
i.
reaches the
(
joined by the initiator
, which carries the
amino acid
).
(met)
o tRNA molecules have a complementary 3 base
sequence to the mRNA codon called the
(at the
base of the “clover-leaf”)
ii. the tRNA binds to the
site of the ribosome
 large subunit joins to complete the ribosome
NOTE: The AUG codon always initiates translation and codes
for the amino acid methionine.
(b) ELONGATION
 during elongation, amino acids are connected together to
form a _______________, as specified by the mRNA
i.
an tRNA carrying the next amino acid (as called for by the
next mRNA codon) enters the _____ site
ii. a
bond forms between the amino acids
carried by the tRNA’s in the P and A sites
iii. the
is released from the P site and the ribosome
one codon
(this shifts the tRNA with the growing polypeptide into the P site, & the A site open for
the next tRNA)
iv. a tRNA with the anticodon to the next mRNA codon enters the A site and another
forms.
v.
this process of elongation continues until a
is reached
(c) TERMINATION
i.
Elongation stops when a STOP codon is reached (There are 3 Stop codons: UAA, UAG,
UGA)
 the stop codons do _____ code for amino acids but instead act as signals to stop
translation.
ii.
a protein ____________________
_ binds directly to the stop codon in the A site.
iii.
 The release factor causes a water molecule to be added to the end of the polypeptide
chain, and the chain then separates from the last tRNA.
the protein is now complete and is sent for final processing in the
and
 The mRNA is usually broken down, & the ribosome splits into its large and small
subunits
NOTE: Often, many ribosomes will simultaneously transcribe the same mRNA. In this way,
many copies of the same protein can be made quickly. These clusters of ribosomes are
called polysomes.
Animations:
http://www.youtube.com/watch?v=NJxobgkPEAo&feature=related
http://www.youtube.com/watch?v=vJSmZ3DsntU&feature=related