Download Document

PROTEIN
SYNTHESIS
1
Protein Synthesis
 The production (synthesis)
of polypeptide chains
(proteins)
 Two phases:
Transcription & Translation
2
• SCI.9-12.B-4.3 - [Indicator] - Explain
how DNA functions as the code of life
and the blueprint for proteins.
• SCI.9-12.B-4.4 - [Indicator] Summarize the basic processes
involved in protein synthesis (including
transcription and translation).
3
• Transcription – mRNA copying
DNA, happens in the nucleus
and mRNA must be edited or
processed before it leaves the
nucleus
• Translation – when mRNA goes
to ribosome and tRNA brings
the correct amino acids to the
ribosome
4
DNA  RNA  Protein
Central Dogma
DNA
Eukaryotic
Cell
Transcription
Nuclear
membrane
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
5
Pathway to Making a
Protein
DNA
mRNA
tRNA (ribosomes)
Protein
6
Nucleic Acids
7
RNA
8
• SCI.9-12.B-4.1 - [Indicator] Compare DNA and RNA in
terms of structure,
nucleotides, and base pairs.
9
How DNA and RNA are alike:
• Both made of monomers
called nucleotides.
• Both had A, G and C
bases
10
*RNA Differs from DNA
1. RNA
DNA
2. RNA
DNA
3. RNA
DNA
has a sugar ribose
has a sugar deoxyribose
contains the base uracil (U)
has thymine (T)
molecule is single-stranded
is double-stranded
11
.
*Three Types of RNA
• Messenger RNA (mRNA) carries
genetic information to the
ribosomes
• Ribosomal RNA (rRNA), along
with protein, makes up the
ribosomes
• Transfer RNA (tRNA) transfers
amino acids to the ribosomes
where proteins are synthesized
12
Making a
Protein
13
*Genes & Proteins
 Proteins are made of amino
acids linked together by peptide
bonds
 20 different amino acids exist
 Amino acids chains are called
polypeptides
 Segment of DNA that codes for
the amino acid sequence in a
protein are called genes
14
Two Parts of Protein
Synthesis
 Transcription makes an RNA
molecule complementary to a
portion of DNA
 Translation occurs when the
sequence of bases of mRNA
DIRECTS the sequence of amino
acids in a polypeptide
15
• SCI.9-12.B-4.3 - [Indicator] - Explain
how DNA functions as the code of life
and the blueprint for proteins.
• SCI.9-12.B-4.4 - [Indicator] Summarize the basic processes
involved in protein synthesis (including
transcription and translation).
16
*Genetic Code
 DNA contains a triplet code
 Every three bases on DNA stands
for ONE amino acid
 Each three-letter unit on mRNA is
called a codon
 Most amino acids have more than
one codon!
 There are 20 amino acids with a
possible 64 different triplets
 The code is nearly universal among
living organisms
17
18
19
*What is the
enzyme
responsible for
the production of
the mRNA
molecule?
20
*RNA Polymerase
 Enzyme found in the nucleus
 Separates the two DNA
strands by breaking the
hydrogen bonds between the
bases
 Then moves along one of the
DNA strands and links RNA
nucleotides together
21
Question:
 What would be the
complementary RNA strand
for the following DNA
sequence?
DNA 5’-GCGTATG-3’
22
Answer:
• DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’
23
*Processing Pre-mRNA
• Also occurs in the nucleus
• Pre-mRNA made up of segments
called introns & exons
• Exons code for proteins, while
introns do NOT!
• Introns spliced out by splicesomeenzyme and exons re-join
• End product is a mature RNA
molecule that leaves the nucleus to
the cytoplasm
24
*Messenger RNA (mRNA)
• Carries the information for a
specific protein
• Made up of 500 to 1000
nucleotides long
• Sequence of 3 bases called codon
• AUG – methionine or start codon
• UAA, UAG, or UGA – stop codons
25
Messenger RNA (mRNA)
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
protein methionine
codon 2
codon 3
glycine
serine
codon 4
isoleucine
codon 5
codon 6
glycine
alanine
codon 7
stop
codon
Primary structure of a protein
aa1
aa2
aa3
peptide bonds
aa4
aa5
aa6
26
Transfer RNA (tRNA)
amino acid
attachment site
methionine
amino acid
U A C
anticodon
27
• SCI.9-12.B-4.3 - [Indicator] - Explain
how DNA functions as the code of life
and the blueprint for proteins.
• SCI.9-12.B-4.4 - [Indicator] Summarize the basic processes
involved in protein synthesis (including
transcription and translation).
28
*Ribosomes
• Made of a large and small
subunit
• Composed of rRNA (40%) and
proteins (60%)
• Have two sites for tRNA
attachment --- P and A
29
Translation
• Synthesis of proteins in the
cytoplasm
• Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. ribosomes
4. amino acids
30
*Translation
• Three steps:
1. initiation: start codon (AUG)
2. elongation: amino acids linked
3. termination: stop codon
(UAG, UAA, or UGA).
Let’s Make a Protein !
31
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf
::535::535::/sites/dl/free/0072437316/12
0077/micro06.swf::Protein%20Synthesi
s
32
http://sciencenetlinks.com/interactives/pro
tein.html
33
mRNA Codons Join the
Ribosome
Large
subunit
P
Site
A
Site
mRNA
A U G
Small subunit
C U A C U U C G
34
Initiation
aa1
aa2
2-tRNA
1-tRNA
anticodon
hydrogen
bonds
U A C
A U G
codon
G A U
C U A C U U C G A
mRNA
35
Elongation
peptide bond
aa1
aa3
aa2
3-tRNA
1-tRNA
anticodon
hydrogen
bonds
U A C
A U G
codon
2-tRNA
G A A
G A U
C U A C U U C G A
mRNA
36
aa1
peptide bond
aa3
aa2
1-tRNA
3-tRNA
U A C
(leaves)
2-tRNA
A U G
G A A
G A U
C U A C U U C G A
mRNA
Ribosomes move over one codon
37
aa1
peptide bonds
aa4
aa2
aa3
4-tRNA
2-tRNA
A U G
3-tRNA
G C U
G A U G A A
C U A C U U C G A A C U
mRNA
38
aa1
peptide bonds
aa4
aa2
aa3
2-tRNA
4-tRNA
G A U
(leaves)
3-tRNA
A U G
G C U
G A A
C U A C U U C G A A C U
mRNA
Ribosomes move over one codon
39
aa1
peptide bonds
aa5
aa2
aa3
aa4
5-tRNA
U G A
3-tRNA
4-tRNA
G A A G C U
G C U A C U U C G A A C U
mRNA
40
peptide bonds
aa1
aa5
aa2
aa3
aa4
5-tRNA
U G A
3-tRNA
G A A
4-tRNA
G C U
G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon
41
aa4
aa5
Termination
aa199
aa3 primary
structure
aa2 of a protein
aa200
aa1
200-tRNA
A C U
terminator
or stop
codon
C A U G U U U A G
mRNA
42
*End Product –The Protein!
• The end products of protein
synthesis is a primary structure of
a protein
• A sequence of amino acid bonded
together by peptide bonds
aa2
aa1
aa3
aa4
aa5
aa199
aa200
43
• SCI.9-12.B-4.3 - [Indicator] - Explain
how DNA functions as the code of life
and the blueprint for proteins.
• SCI.9-12.B-4.4 - [Indicator] Summarize the basic processes
involved in protein synthesis (including
transcription and translation).
44
*Types of Mutations
1. Point mutation – one DNA bases
changes. Sometimes this mistake is
corrected by an enzyme.
Types:
a. insertion – where a base is added
b. deletion – where a base is lost
c. substitution – where a base is
changed
45
Substitution
Wild type
A
mRNA
U
G
A
5
Protein
A
G
U
U
G
G
C
U
A
A
3
Lys
Met
U
Phe
Gly
Stop
Amino end
Carboxyl end
Base-pair substitution
No effect on amino acid sequence
U instead of C
A
U
G
A
A
G
U
Lys
Met
U
G
G
Phe
Missense
A
U
U
U
Gly
A
A
Stop
A instead of G
U
G
A
A
G
U
Lys
Met
U
U
A
Phe
G
U
U
Ser
A
A
Stop
Nonsense
U instead of A
A
U
Met
G
U
A
G
U
U
U
G
G
C
U
A
A
Stop
46
• *The change of a single nucleotide in the
DNA’s template strand
– Leads to the production of an abnormal
protein
Wild-type hemoglobin DNA
3
Mutant hemoglobin DNA
5
C T
T
In the DNA, the
mutant template
strand has an A where
the wild-type template
has a T.
G U A
The mutant mRNA has
a U instead of an A in
one codon.
3
5
T
C A
mRNA
mRNA
G A
A
5
3
5
3
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Figure 17.23
The mutant (sickle-cell)
hemoglobin has a valine
(Val) instead of a glutamic
acid (Glu).
48
*
2. Frameshift mutation – insertion or
deletion of a nucleotide (or base)
changes the group of three bases
that code for the amino acid
ACT CAT TAG GAG (first T is
deleted)
ACC ATT AGG AG
49
Wild type
mRNA
5
A
A
G
U
A
Met
Protein
G
U
U
Lys
G
U
G
C
U
Gly
Phe
A
A
3
Stop
Amino end
Carboxyl end
Base-pair insertion or deletion
Frameshift causing immediate nonsense
Extra U
A
G
U
A
U
Met
A
G
U
U
U
G
C
U
A
Stop
Frameshift causing
extensive missense
Missing
U
A
G
G
U
A
A
Met
G
U
Lys
U
G
G
C
U
A
A
Ala
Leu
Insertion or deletion of 3 nucleotides:
no frameshift but extra or missing amino acid
A
A
U
Met
A
G
Missing
G
U
U
Phe
U
G
G
Gly
C
U
A
A
Stop
50