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Protein Synthesis
DNA Transcription and
Translation
What is the purpose for proteins? We
are made of protein!
•
•
•
•
•
•
•
antibody: fight diseases
Muscle contractions
Enzymes
Hormones
Hair, feathers, beaks, nails, horns, etc.
Egg whites
Transport proteins: blood(hemoglobin)
Protein Structure
• Made up of amino acids
• Polypeptide- string of amino acids
• ONLY 20 amino acids are arranged in
different orders to make a variety of
proteins!!!! Amino acids are in the
cytoplasm.
• Assembled on a ribosome
How Does Our Body Create
Proteins from DNA??
Its in the nucleus!!!!!!
Introduction
The Central Dogma
of Molecular Biology
Cell
DNA
Transcription
mRNA
Translation
Ribosome
Polypeptide
(protein)
DOGMA?
This central dogma(process) was develop
by Crick.
This was a hypothesis on how the code was
read from DNA then used to make
proteins. Scientists did not like this term
for this hypothesis because it sounds like
a problem!
Central Dogma of Biology
The flow of information in the cell starts at
DNA,
Location????
• Prokaryotic
Cyotoplasm and
ribosomes
• Eukaryotic
Nucleus and
ribosomes
DNA vs. RNA(players)
• DNA
• Double Helix
• Deoxyribose sugar
• Adenine pairs with
Thymine (A-T)
• Stays in nucleus
• RNA
• Single strand
• Ribose sugar
• Uracil replaces
Thymine!
• Leaves nucleus to
do the work
DNA vs. RNA
DNA
Deoxyribose
Thymine
RNA
Ribsose
Double Strand
Single Strand
Uracil is one of the
bases in RNA.
There is thymine no
thymine. This means
A goes with U and G
still goes with C.
Steps to Protein Synthesis
1. Transcription – process where
DNA message is changed into
mRNA then out of nucleus to the
ribosomes!!!
2. Translation – process when
mRNA is translated into amino
acid chains(protein) on the
ribosomes.
Transcription???
• Purpose?
• Creating?
• WHY WHY WHY!!!!!!
How does a protein get built??
• This is where RNA becomes
involved.
• DNA is too large to get out of the
nuclear membrane pores.
• SO RNA has to be made to go to
the ribosomes!!!
SO, HOW DOES AN AMINO
ACID CHAIN GET BUILT?
RNA stands for ribonucleic acid
Stars of Translation and
Transcription
1.
2.
3.
4.
5.
6.
mRNA
DNA
rRNA
tRNA
Ribsomes
RNA polymerase
•
•
•
•
Three types of RNA:
1. mRNA
• 2. tRNA
“messenger” RNA
• “transfer” RNA
Carries code for
• Attaches specific
proteins from DNA
Amino Acids to the
Carries “codon”
protein chain by
matching the mRNA
codon with the
anticodon.
RNA TRANSCIPTION
There are three (3) types RNA:
1. Messanger RNA – (mRNA) carries messages
from the DNA in the nucleus to the
ribosomes.
tRNA
2. Transfer RNA – (tRNA) 20 different
kinds which are only able to bond with
one (1) specific type of amino acid.
rRNA
3. Ribosomal RNA – (rRNA) major
component (part) of the ribosomes
3. Ribosomal
RNA - rRNA
• Where Protein
synthesis occurs
How Does RNA polymerase(complex)
know where to start and stop?
• Promoter site: starting and stopping
point on DNA. Specific base
sequences that represents a gene.
• Termination site: Place where RNA
polymerase stops!!!
• REMEMBER - only a gene is being
read to make mRNA not all of your
DNA.
Step 1:
• RNA polymerase complex attaches to DNA
at special places that serve as the start
signal(promoter sites). Only one gene!!!!!
Step 2:
• DNA splits at site of RNA polymerase.
• RNA polymerase attaches matching bases to
form new RNA strand from DNA template.
• RNA polymerase keeps adding bases
making the RNA strand grow…
Step 3:
• RNA polymerase leaves DNA when reaches
the termination site(stop signal).
• RNA strand is released and goes to
cytoplasm.
• DNA rewinds itself into the double helix.
Results of Transcription
• Strand of mRNA made from the DNA
FYI
RNA polymerase doesn’t check for
mistakes in the code. Doesn’t cause
mutations when there is a few mistakes in
proteins unlike replication.
Protein Synthesis:
Transcription
Making mature mRNA
Original mRNA
transcribed is not
mature mRNA
Exons: readable
segments of mRNA that
will be spliced together
to make mature mRNA.
Introns: are non- readable
segments of mRNA that
must be removed before
it leaves the nucleus
Exons vs. Introns
Once introns removed, mRNA is ready
to leave the nucleus!!!!
Eukaryotic Transcription
Cytoplasm
DNA
Transcription
RNA
RNA
Processing
mRNA G
G
AAAAAA
Nucleus
Export
AAAAAA
Prokaryotic Protein Synthesis
• All occurs in the cyotplasm!!!
Transcription is done…what
now?
Now we have mature mRNA transcribed
from the cell’s DNA. It is leaving the
nucleus through a nuclear pore. Once in
the cytoplasm, it finds a ribosome so that
translation can begin.
We know how mRNA is made, but how do we
“read” the code?
Translation
Translation is the process of decoding a
mRNA molecule into a polypeptide chain
or protein.
ALWAYS read mRNA!!!!!!
Reading Frame
• Every 3 DNA bases pairs with 3 mRNA
bases
• Every group of 3 mRNA bases encodes a
single amino acid
• Codon- coding triplet of mRNA bases
Codons
• Each combination of 3 nucleotides
on mRNA is called a codon or threeletter code word.
• Each codon specifies a particular
amino acid that is to be placed in the
polypeptide chain (protein).
Protein Synthesis: Translation
Start codons and Stop codons
• For translation to begin, there is a START
codon.
• AUG: is the 3 letter codon that starts the
process.
• UAA, UGA, UAG: Stop codons.
A Codon
OH
P
HO
NH2
O
N
O
N
CH2
H
P
O
O
N
O
CH2
P
NH
N
Guanine
NH2
N
O
Arginine
H
O
HO
N
O
O
HO
Adenine
N
NH2
O
N
O
CH2
N
O
OH
H
N
N
Adenine
Protein Synthesis: Translation
Start Codon
• Start codon: codon AUG also serves
as the “initiator” codon, which starts
the synthesis of a protein.
Stop Codon
• STOP codon: Codon that signal the
end of the protein. (UAA, UAG, &
UGA
• Besides selecting the amino acid
methionine, the codon AUG also
serves as the “initiator” codon,
which starts the synthesis of a protein
Protein Synthesis: Translation
•A three-letter code is used because there
are 20 different amino acids that are
used to make proteins.
•If a two-letter code were used there
would not be enough codons to select all
20 amino acids.
•That is, there are 4 bases in RNA, so 42
(4x 4)=16; where as 43 (4x4x4)=64.
Translation
•Therefore, there is a total of 64 codons
with mRNA, 61specify a particular
amino acid.
• This means there are more than one
codon for each of the 20 amino acids.
Protein Synthesis: Translation
Transfer RNA (tRNA)
•Each tRNA molecule has 2 important
sites of attachment.
•One site, called the anticodon, binds to
the codon on the mRNA molecule.
•The other site attaches to a particular
amino acid.
•During protein synthesis, the anticodon of
a tRNA molecule base pairs with the
appropriate mRNA codon.
tRNA
• Transfer RNA
• Bound to one amino
acid on one end
• Anticodon on the
other end
complements mRNA
codon
Met-tRNA
Methionine
16 Pu
17
9
A
17:1
13 12 Py 10
1
2
3
4
5
6
U* 7
A
C
C
73
72
71
70
69
68
67
Py 59A*
66
65 64 63 62 C
Pu
49 50 51 52 G T C
y
Py
G*
22 23 Pu 25
G
26
2020:120:2A
27
1
28
29
30
31
Py*
47:16
47:15
43 44
42 45
41 46
47
40
47:1
39
38
Pu*
U
34
U 35
C
A 36
Anticodon
Protein Synthesis: Translation
Parts of a Ribosomes
• For translation to begin, 2 subunits of
ribsosomes must unite, separate in
cytoplasm
– Large
– Small
• Contain 3 binding sites – helps tRNA align
to codon.
–E
–P
–A
Protein Synthesis: Translation
RNA TRANSLATION
Protein Synthesis: the formation of a protein using
information coded on DNA and carried out by RNA in
the assembly of amino acids.
Proteins are:
a. Amino acids in chains – 20 kinds
b. Made of 10’s or 100’s or 1000’s of amino acids
c. Must be arranged in a specific sequence for each
type of protein
d. Function & type of protein is determined by amino
acid sequence
e. DNA makes RNA
f. RNA constructs amino acids
Steps of Translation
• 1. INITIATION:
A.The initiator(start) codon AUG binds
to the first anticodon of tRNA,
signaling the start of a protein.
B. Two parts of the ribosome join
around the tRNA and mRNA.
• The amino acid methionine, the
codon AUG also serves as the
“initiator” codon, which starts the
synthesis of a protein
Translation
• 2. ELONGATION: The anticodon
of another tRNA binds to the next
mRNA codon, bringing the 2nd
amino acid to be placed in the
protein. This will continue until stop
codon.
• As each anticodon & codon bind
together a peptide bond forms
between the two amino acids.
Protein Synthesis: Translation
3. Termination: The protein chain continues to
grow until a stop codon reaches the ribosome,
which results in the release of the new protein
and mRNA, completing the process of
translation. The amino acids are bonded with
a peptide bond to form a protein.
•Release factor causes the release of tRNA
and mRNA.
Summary of Translation
•
•
•
•
Ribosome 2 parts come together.
mRNA attaches to ribosome.
AUG – start codon.
tRNA brings in making anticodon with
amino acid.
• rRNA continues to read mRNA and
bring in
making tRNA.
*Stop codon will stop process. Peptide
bonds will form to make a protein.
tRNA Function
• Amino acids must be in the correct order
for the protein to function correctly
• tRNA lines up amino acids using mRNA
code
Protein Synthesis: Translation
Transfer RNA (tRNA)
•Each tRNA molecule has 2 important
sites of attachment.
•One site, called the anticodon, binds to
the codon on the mRNA molecule.
•The other site attaches to a particular
amino acid.
•During protein synthesis, the anticodon of
a tRNA molecule base pairs with the
appropriate mRNA codon.
Met-tRNA
Methionine
16 Pu
17
9
A
17:1
13 12 Py 10
1
2
3
4
5
6
U* 7
A
C
C
73
72
71
70
69
68
67
Py 59A*
66
65 64 63 62 C
Pu
49 50 51 52 G T C
y
Py
G*
22 23 Pu 25
G
26
2020:120:2A
27
1
28
29
30
31
Py*
47:16
47:15
43 44
42 45
41 46
47
40
47:1
39
38
Pu*
U
34
U 35
C
A 36
Anticodon
Translation - Initiation
fMet
Large
subunit
E
P
A
UAC
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
Small mRNA
subunit
3’
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ser
Gly
Arg
Ribosome
E
P
A
CCA UCU
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ser
Gly
Arg
Aminoacyl tRNA
Ribosome
E
P
A
CCA UCU
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ala
Ser
Gly
Aminoacyl tRNA
Arg
Ribosome
E
P
A
CCA
UCU
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ser
Gly
Arg
Ribosome
E
Ala
P
A
UCU CGA
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Protein Synthesis: Translation
The Genetic Code
ACGATACCCTGACGAGCGTTAGCTATCG
UGC
ACUG
UAUGGG
Protein
Synthesis:
Translation
Protein Synthesis
AMINE H
H
O
N
ACID
C
C
ANYTHING
R
H
Amino Acid
Alanine
OH
H
H
Serine
H
O
N
C
OH
H
C
H
H
H
H2O
H
H
C
H
H
C
H
O
C
C
C
C
HO
N
H
N
H
H
C
O
N
H
O
C
C
H
H C
H
H HO
H
OH
OH
Transcription And Translation
In Prokaryotes
5’
3’
3’
5’
RNA
Pol.
Ribosome
mRNA
5’
Ribosome
Transcription vs. Translation Review
Transcription
• Process by which
genetic information
encoded in DNA is
copied onto
messenger RNA
• Occurs in the nucleus
• DNA
mRNA
Translation
• Process by which
information encoded in
mRNA is used to
assemble a protein at a
ribosome
• Occurs on a Ribosome
• mRNA
protein
Protein Synthesis
AMINE H
H
O
N
ACID
C
C
ANYTHING
R
H
Amino Acid
Alanine
OH
H
H
Serine
H
O
N
C
OH
H
C
H
H
H
H2O
H
H
C
H
H
C
H
O
C
C
C
C
HO
N
H
N
H
H
C
O
N
H
O
C
C
H
H C
H
H HO
H
OH
OH
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ser
Gly
Arg
Ribosome
E
P
A
CCA UCU
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Prokaryotic - Protein synthesis
• Location – cytoplasm
• At the same time.
• Eukaryotic – Protein synthesis
Transcription And Translation
In Prokaryotes
5’
3’
3’
5’
RNA
Pol.
Ribosome
mRNA
5’
Ribosome
(1961)
Watson & Crick proposed…
• …DNA controlled cell function by
serving as a template for PROTEIN
structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
See p.303
• AMINO ACIDS are the building blocks
of proteins.
MUTATIONS
Changes in DNA that affect genetic
information
Gene Mutations
• Point Mutations – changes in
one nucleotides
1. Substitution – base is replaced
• THE FAT CAT ATE THE RAT
• THE FAT HAT ATE THE RAT
Gene Mutations
2. Insertion – a base is added
• THE FAT CAT ATE THE RAT
• THE FAT HCA TAT ETH ERA T
3. Deletion – delete a base
THE FAT CAT ATE THE RAT
TEF ATC ATA TET GER AT
Point Mutations that cause
Frameshift Mutations – shifts the
reading frame of the genetic
message so that the protein may
not be able
to perform its
H
function.
Effects of Mutations
• Silent – When a base pair is substituted
but the change still codes for the same
amino acid in sequence. NO CHANGE!!!
Effects 0f Mutations
• Missense –Mutation that causes a
changed amino acid. Usually harmful!!!
• EX: sickle cell amenia
Effects of Mutations
• Nonsense – Mutation that does not allow
protein to form because of early stop
codon
Sex Chromosome Abnormalities
• XYY Syndrome
– Normal male traits
– Often tall and thin
– Associated with antisocial and behavioral
problems
Chromosome Mutations
• Changes in number and structure of entire
chromosomes
• Original Chromosome ABC * DEF
• Deletion
AC * DEF
• Duplication
ABBC * DEF
• Inversion
AED * CBF
• Translocation
ABC * JKL
GHI * DEF
Significance of Mutations
• Most are neutral
• Eye color
• Birth marks
• Some are harmful
• Sickle Cell Anemia
• Down Syndrome
• Some are beneficial
• Sickle Cell Anemia to Malaria
• Immunity to HIV
What Causes Mutations?
• There are two ways in which DNA can
become mutated:
– Mutations can be inherited.
• Parent to child
– Mutations can be acquired.
• Environmental damage
• Mistakes when DNA is copied
Chromosome Mutations
• Down Syndrome
– Chromosome 21 does
not separate correctly.
– They have 47
chromosomes in stead of
46.
– Children with Down
Syndrome develop
slower, may have heart
and stomach illnesses
and vary greatly in their
degree of inteligence.
Chromosome Mutations
• Cri-du-chat
– Deletion of material on 5th
chromosome
– Characterized by the cat-like
cry made by cri-du-chat
babies
– Varied levels of metal
handicaps
Sex Chromosome Abnormalities
• Klinefelter’s Syndrome
–XXY, XXYY, XXXY
–Male
–Sterility
–Small testicles
–Breast enlargement
Sex Chromosome Abnormalities
• XYY Syndrome
–Normal male traits
–Often tall and thin
–Associated with antisocial and
behavioral problems
Sex Chromosome Mutations
• Turner’s Syndrome
–X
– Female
– sex organs don't
mature at adolescence
– sterility
– short stature
Sex Chromosome Mutations
• XXX
–Trisomy X
–Female
–Little or no visible differences
–tall stature
–learning disabilities
–limited fertility