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PROTEIN SYNTHESIS
Protein Synthesis
• The production (synthesis) of proteins.
proteins
• 3 phases:
phases
1. Transcription
2. RNA processing
3. Translation
• Remember: DNA → RNA → Protein
DNA → RNA → Protein
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
DNA → RNA → Protein
DNA
Transcription
mRNA
Ribosome
Translation
Protein
Prokaryotic Cell
Question:
• How does RNA (ribonucleic acid) differ
from DNA (deoxyribonucleic acid)?
acid)
RNA differs from DNA
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains uracil (U)
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded
1. Transcription
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
1. Transcription
• The transfer of information in the nucleus from a
DNA molecule to an RNA molecule.
• Only 1 DNA strand serves as the template
• Starts at promoter DNA (TATA box)
• Ends at terminator DNA (stop)
• When complete, pre-RNA molecule is released.
Question:
• What is the enzyme responsible
for the production of the RNA
molecule?
Answer: RNA Polymerase
• Separates the DNA molecule by breaking the Hbonds between the bases.
• Then moves along one of the DNA strands and
links RNA nucleotides together.
1. Transcription
DNA
RNA Polymerase
pre-mRNA
Question:
• What would be the complementary
RNA strand for the following DNA
sequence?
• DNA 5’-GCGTATG-3’
Answer:
• DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’
2. RNA Processing
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
2. RNA Processing
• Maturation of pre-RNA molecules.
• Also occurs in the nucleus.
• Introns spliced out by splicesome-enzyme
and exons come together.
• End product is a mature RNA molecule that
leaves the nucleus to the cytoplasm.
2. RNA Processing
pre-RNA molecule
exon
intron
exon
intron
exon
intron
intron
exon
exon
splicesome
splicesome
exon
exon
exon
exon
Mature RNA molecule
Types of RNA
• Three types of RNA:
RNA
A. messenger RNA (mRNA)
B. transfer RNA (tRNA)
C. ribosome RNA (rRNA)
• Remember: all produced in the nucleus!
A. Messenger RNA (mRNA)
• Carries the information for a specific protein.
protein
• Made up of 500 to 1000 nucleotides long.
• Made up of codons (sequence of three bases:
AUG - methionine).
• Each codon,
codon is specific for an amino acid.
acid
A. 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
B. Transfer RNA (tRNA)
• Made up of 75 to 80 nucleotides long.
• Picks up the appropriate amino acid floating in
the cytoplasm (amino acid activating enzyme)
enzyme
• Transports amino acids to the mRNA.
mRNA
• Have anticodons that are complementary to
mRNA codons.
codons
• Recognizes the appropriate codons on the
mRNA and bonds to them with H-bonds.
B. Transfer RNA (tRNA)
amino acid
attachment site
methionine
U A C
anticodon
amino acid
C. Ribosomal RNA (rRNA)
• Made up of rRNA is 100 to 3000 nucleotides
long.
• Important structural component of a ribosome.
• Associates with proteins to form ribosomes.
Ribosomes
• Large and small subunits.
• Composed of rRNA (40%) and proteins (60%).
• Both units come together and help bind the
mRNA and tRNA.
• Two sites for tRNA
a. P site (first and last tRNA will attach)
attach
b. A site
Ribosomes
Large
subunit
P
Site
A
Site
mRNA
A U G
Small subunit
C U A C U U C G
3. Translation
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
3. Translation
• Synthesis of proteins in the cytoplasm
• Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. rRNA
4. ribosomes
5. amino acids
3. Translation
• Three parts:
1. initiation:
initiation start codon (AUG)
2. elongation:
elongation
3. termination:
termination stop codon (UAG)
• Let’s make a PROTEIN!!!!.
PROTEIN!!!!
3. Translation
Large
subunit
P
Site
A
Site
mRNA
A U G
Small subunit
C U A C U U C G
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
Elongation
peptide bond
aa3
aa1
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
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
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
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
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
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
aa4
aa5
Termination
aa199
aa3 primary
structure
aa2 of a protein
aa200
aa1
200-tRNA
A C U
mRNA
terminator
or stop
codon
C A U G U U U A G
End Product
• The end products of protein synthesis is a
primary structure of a protein.
protein
• A sequence of amino acid bonded together
by peptide bonds.
bonds
aa2
aa1
aa3
aa4
aa5
aa199
aa200
Polyribosome
• Groups of ribosomes reading same mRNA
simultaneously producing many proteins
(polypeptides).
incoming
large
subunit
1
incoming
small subunit
2
3
4
polypeptide
5
6
7
mRNA
Question:
• The anticodon UAC belongs to a tRNA that
recognizes and binds to a particular amino
acid.
• What would be the DNA base code for this
amino acid?
Answer:
• tRNA
• mRNA
• DNA
- UAC (anticodon)
- AUG (codon)
- TAC