Transcript Protein Synthesis - Los Gatos High School

Protein Synthesis
Transcription & Translation
RNA is composed of 3 parts:
• Ribose: smaller sugar than
deoxyribose of DNA
• Phosphate
• 4 Bases
–
–
–
–
Adenine (A)
Guanine (G)
Uracil (U)* instead of T
Cytosine (C)
• RNA is single stranded and
thus smaller & able to leave
the nucleus of the cell
• These 3 parts
– ribose,
– phosphate and
– 1 base
• still form a nucleotide
• RNA is used by DNA to
carry the code and create
proteins that control the
functioning of the cell
• There are two main types
of RNA used: mRNA
(messenger RNA) and
tRNA (transfer RNA)
• DNA is the architect – it tells everyone else what to do,
how and when.
• mRNA is the messenger who carries the message from
DNA out of the nucleus to the ribosome.
• tRNA transfers (transports) amino acids to the ribosome
where they can be assembled into proteins.
Transcription
Writing of DNA Message to mRNA
• In the nucleus of the cell
• Information from DNA is
transferred to mRNA.
• DNA uncoils and unzips
(with the help of more
enzymes)
• The exposed DNA bases
match up with RNA
nucleotides to form an
mRNA strand.
• The mRNA strand will be
complementary to the
original DNA strand.
mRNA (Messenger RNA)
• The DNA strands
rejoin.
• The mRNA will
detach, move out
of the nucleus into
the cell cytoplasm
and go to the
ribosome.
Transcription
Translation
• In the cytoplasm at
the ribosomes.
• The mRNA binds to a
ribosome.
• The strand of mRNA
is pulled through the
ribosome three bases
at a time, in triplets.
• Each of these triplets
on the mRNA strand
is called a codon.
• Each triplet of
complementary tRNA
is called an
anticodon.
Translation
tRNA (Transfer RNA)
• Transfer RNA (tRNA), reads the
strand of mRNA and translates it into
a strand of amino acids.
• If the 3 base anticodon of the tRNA
complements the 3 base codon of
the mRNA, they briefly combine.
• The amino acid is left behind when
the tRNA leaves.
• As each codon is read, the next
tRNA brings in a new amino acid and
the polypeptide (protein) chain
grows.
• This requires enzymes and ATP.
mRNA to amino acid
First letter/
second letter
U
C
A
G
U
C
A
G
Third Letter
phenylalanine
serine
tyrosine
cysteine
U
phenylalanine
serine
tyrosine
cysteine
C
leucine
serine
stop
stop
A
leucine
serine
stop
tryptophan
G
leucine
proline
histadine
arginine
U
leucine
proline
histadine
arginine
C
leucine
proline
glutamine
arginine
A
leucine
proline
glutamine
arginine
G
isoleucine
threonine
asparagine
serine
U
isoleucine
threonine
asparagine
serine
C
isoleucine
threonine
lysine
arginine
A
methionine,
start codon
threonine
lysine
arginine
G
valine
alanine
aspartate
glycine
U
valine
alanine
aspartate
glycine
C
valine
alanine
glutamate
glycine
A
valine
alanine
glutamate
glycine
G
mRNA to amino acid
Codons code for particular
amino acids
• Each codon will
correspond to one amino
acid.
• These amino acids when
put together form
polypeptides or proteins.
• The genetic code is
redundant. There are 64
possible codons but only
20 amino acids.
Translation
http://www.nobel.se/medicine/educational/dna/b/translation/translation_ani.html
Review