42
1 PROTEIN SYNTHESIS copyright cmassengale
1
PROTEIN SYNTHESIS
copyright cmassengale
DNA and
Genes
2copyright cmassengale
3
Roles of RNA and DNA
• DNA is the MASTER PLAN
• RNA is the BLUEPRINT of the
Master Plancopyright cmassengale
4
RNA Differs from DNA
• RNA has a sugar ribose
DNA has a sugar deoxyribose
copyright cmassengale
5
Other Differences
• RNA contains the base uracil (U)DNA has thymine (T)
• RNA molecule is single-strandedDNA is double-stranded
DNAcopyright cmassengale
6
Structure of RNA
copyright cmassengale
Central Dogma of Biology
DNA codes for RNA which guides
the synthesis of proteins!7
8
. Three Types of RNA
• Messenger RNA (mRNA) copies DNA’s code & carries the 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
copyright cmassengale
9
amino acidattachment site
UA C
anticodon
mRNA
rRNA
tRNA
Central Dogma of Biology
DNA codes for RNA which guides
the synthesis of proteins!10
Step 1
TRANSCRIPTION IS HAPPENING AT THE SAME TIME AS DNA
REPLICATION!
copyright cmassengale 11
12
Transcription - 1
• A portion of the DNA molecule unzips
• Recall: DNA helicase is the enzyme responsible for this!
copyright cmassengale
13
Transcription - 2
• RNA polymerase joins RNA nucleotides using the DNA strand as a template
• This strand of DNA read by the RNA is the “template strand” read in the 3’ to 5’
• This new strand of RNA is the mRNA strand made in the 5’ to 3’ direction
14
15
Transcription - 3
• The mRNA strand is released through nuclear pores (exits the nucleus) and the DNA strand rejoins
16
RNA Polymerase
copyright cmassengale
17
mRNA Processing
• After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
• Introns, non-functional segments of DNA are snipped out of the chain
copyright cmassengale
18
mRNA Editing
• Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase
• The newly processed mRNA can then leave the nucleus
copyright cmassengale
19CAP TailNew Transcript
Result of Transcription
copyright cmassengale
20
mRNA Transcript - 4
•mRNA leaves the nucleus through its pores and goes to the ribosomes
copyright cmassengale
21
The Genetic Code
• A codon designates an amino acid
• An amino acid may have more than one codon
• There are 20 amino acids, but 64 possible codons
• Some codons tell the ribosome to stop translating
copyright cmassengale
22
The Genetic Code
•Use the code by reading from the center to the outside•Example: AUG codes for Methionine
copyright cmassengale
23
Name the Amino Acids
• GGG?
• UCA?
• CAU?
• GCA?
• AAA?
copyright cmassengale
24
Remember the Complementary Bases
On DNA:A-TC-G
On RNA:A-UC-G
copyright cmassengale
25
Question:
What would be the complementary RNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’
copyright cmassengale
26
Answer:
•DNA 5’-GCGTATG-3’
•RNA 3’-CGCAUAC-5’
copyright cmassengale
27
Translation
• Translation is the process of decoding the mRNA into a polypeptide chain to create proteins
• Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
copyright cmassengale
28
Transcription
Translation
copyright cmassengale
29
Ribosomes
• Composed of rRNA (40%)and proteins (60%)
• Have two sites for tRNA attachment --- P and A
copyright cmassengale
30
Step 1- Initiation
• mRNA transcriptstart codon AUGattaches to the small ribosomalsubunit
• Small subunit attaches to large ribosomal subunit
mRNA transcriptcopyright cmassengale
31
Ribosomes
P
Site
A
Site
Largesubunit
Small subunit
mRNA
A U G C U A C U U C G
copyright cmassengale
Step 2 - Elongation• As ribosome moves, two tRNA with
their amino acids move into site A and P of the ribosome
• Peptide bonds join the amino acids
32copyright cmassengale
33
Initiation
mRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
copyright cmassengale
34mRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A U
A
anticodon
hydrogen
bonds codon
peptide bond
3-tRNA
G A A
aa3
Elongation
copyright cmassengale
35
mRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A U
A
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
copyright cmassengale
36
mRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
copyright cmassengale
37
mRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codoncopyright cmassengale
38
mRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
copyright cmassengale
39
mRNA
G C U A C U U C G
aa1
aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codoncopyright cmassengale
40
mRNA
A C A U G U
aa1
aa2
U
primary
structure
of a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminator
or stop
codon
Termination
copyright cmassengale
41
End Product –The Protein!
• The end products of protein synthesis is a primary structureof a protein
• A sequence of amino acidbonded together by peptide bonds
aa1
aa2 aa3 aa4aa5
aa200
aa199
copyright cmassengale
42
Messenger RNA (mRNA)
methionine glycine serine isoleucine glycine alanine stop
codonprotein
A U G G G C U C C A U C G G C G C A U A AmRNA
start
codon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
copyright cmassengale
