Protein synthesis2 ppt

1
PROTEINPROTEIN
SYNTHESISSYNTHESIS
byby
Hameedullah kakarHameedullah kakar
copyright cmassengale

DNADNA
andand
GenesGenes
2copyright cmassengale

DNADNA
• DNA contains genes,
sequences of nucleotide
bases
• These Genes code for
polypeptides (proteins)
• Proteins are used to build
cells and do much of the
work inside cells

4
Genes & ProteinsGenes & Proteins
 Proteins are made of
amino acids linked
together by peptide
bonds
 20 different amino acids
exist

5
Amino Acid StructureAmino Acid Structure

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PolypeptidesPolypeptides
• Amino acid
chains are
called
polypeptides

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DNA Begins the ProcessDNA Begins the Process
• DNA is found inside the
nucleus
• Proteins, however, are made
in the cytoplasm of cells by
organelles called ribosomes
• Ribosomes may be free in the
cytosol or attached to the
surface of rough ER

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Starting with DNAStarting with DNA
• DNA ‘s codeDNA ‘s code must bemust be copiedcopied
and taken to the cytosoland taken to the cytosol
• In the cytoplasm, thisIn the cytoplasm, this codecode
must be readmust be read soso amino acidsamino acids
can be assembled to makecan be assembled to make
polypeptides (proteins)polypeptides (proteins)
• This process is calledThis process is called
PROTEIN SYNTHESISPROTEIN SYNTHESIS

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Roles of RNA and DNA
• DNA is the MASTER
PLAN
• RNA is the
BLUEPRINT of the
Master Plan

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RNA Differs from DNARNA Differs from DNA
• RNA has a sugarRNA has a sugar riboseribose
DNA has a sugarDNA has a sugar deoxyribosedeoxyribose

12
Other DifferencesOther Differences
• RNA contains theRNA contains the
basebase uracil (Uuracil (U))
DNA hasDNA has thyminethymine
(T)(T)
• RNA molecule isRNA molecule is
single-strandedsingle-stranded
DNA isDNA is double-double-
strandedstranded
DNAcopyright cmassengale

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Structure of RNAStructure of RNA

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.
Three Types of RNAThree Types of RNA
• Messenger RNA (mRNA)Messenger RNA (mRNA) copiescopies
DNA’s code & carries theDNA’s code & carries the
genetic information to thegenetic information to the
ribosomesribosomes
• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), along, along
with protein, makes up thewith protein, makes up the
ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transferstransfers
amino acids to the ribosomesamino acids to the ribosomes
where proteins are synthesizedwhere proteins are synthesized

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Messenger RNA
• Long Straight chain
of Nucleotides
• Made in the Nucleus
• Copies DNA & leaves
through nuclear
pores
• Contains the
Nitrogen Bases A, G,
C, U ( no T )

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Messenger RNA (mRNA)Messenger RNA (mRNA)
• Carries the information for aCarries the information for a
specific proteinspecific protein
• Made up ofMade up of 500 to 1000500 to 1000
nucleotides longnucleotides long
• Sequence of 3 bases calledSequence of 3 bases called
codoncodon
• AUGAUG – methionine or– methionine or startstart
codoncodon
• UAA, UAG, or UGAUAA, UAG, or UGA –– stopstop
codonscodons copyright cmassengale

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Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)
• rRNA is a singlerRNA is a single
strandstrand 100 to 3000100 to 3000
nucleotidesnucleotides longlong
• GlobularGlobular in shapein shape
• Made inside theMade inside the
nucleusnucleus of a cellof a cell
• Associates withAssociates with
proteins to formproteins to form
ribosomesribosomes
• Site ofSite of proteinprotein
SynthesisSynthesis

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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

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The Genetic Code
•Use the
code by
reading from
the center to
the outside
•Example:
AUG codes
for
Methionine

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Name the Amino Acids
• GGG?
• UCA?
• CAU?
• GCA?
• AAA?

21
Remember theRemember the
Complementary BasesComplementary Bases
On DNA:
A-T
C-G
On RNA:
A-U
C-G

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Transfer RNA (tRNA)Transfer RNA (tRNA)
• Clover-leaf shape
• Single stranded molecule with
attachment site at one end
for an amino acid
• Opposite end has three
nucleotide bases called the
anticodon

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Transfer RNATransfer RNA
amino acidamino acid
attachment siteattachment site
U A C
anticodonanticodoncopyright cmassengale

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Codons and Anticodons
• The 3 bases of an
anticodon are
complementary to
the 3 bases of a
codon
• Example: Codon ACU
Anticodon UGA
UGA
ACU

TranscriptionTranscription
andand
TranslationTranslation

26
Pathway to Making aPathway to Making a
ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProteincopyright cmassengale

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Protein SynthesisProtein Synthesis
 The production or
synthesis of polypeptide
chains (proteins)
 Two phases:
Transcription & Translation
 mRNA must be processed
before it leaves the nucleus
of eukaryotic cells

28
DNADNA →→ RNARNA →→ ProteinProtein
Nuclear
membrane
RNA ProcessingRNA Processing
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryoticEukaryotic
CellCell

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• The process of copying
the sequence of one
strand of DNA, the
template strand
• mRNA copies the template
strand
• Requires the enzyme RNA
Polymerasecopyright cmassengale

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Template Strand

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Question:Question:
 What would be theWhat would be the
complementary RNA strandcomplementary RNA strand
for the following DNAfor the following DNA
sequence?sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’

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Answer:Answer:
• DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’RNA 3’-CGCAUAC-5’

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• During transcription, RNA
polymerase binds to DNA and
separates the DNA strands
• RNA Polymerase then uses
one strand of DNA as a
template to assemble
nucleotides into RNA

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• Promoters are regions on
DNA that show where RNA
Polymerase must bind to
begin the Transcription of
RNA
• Called the TATA box
• Specific base sequences act
as signals to stop
• Called the termination signalcopyright cmassengale

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RNA PolymeraseRNA Polymerase

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mRNA ProcessingmRNA 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 chaincopyright cmassengale

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mRNA EditingmRNA Editing
• Exons, segments of DNA that
code for proteins, are then
rejoined by the enzyme ligase
• A guanine triphosphate cap is
added to the 5” end of the
newly copied mRNA
• A poly A tail is added to the 3’
end of the RNA
• The newly processed mRNA can
then leave the nucleuscopyright cmassengale

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CAP
TailNew Transcript
Result of TranscriptionResult of Transcription

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mRNA Transcript
•mRNA leaves the nucleus
through its pores and goes to
the ribosomes

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• Translation is the process
of decoding the mRNA
into a polypeptide chain
• Ribosomes read mRNA
three bases or 1 codon at
a time and construct the
proteins

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RibosomesRibosomes
• Made of a large and small
subunit
• Composed of rRNA (40%)
and proteins (60%)
• Have two sites for tRNA
attachment --- P and A

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Step 1- InitiationStep 1- Initiation
• mRNA transcript
start codon AUG
attaches to the
small ribosomal
subunit
• Small subunit
attaches to large
ribosomal subunit
mRNA transcript

44
RibosomesRibosomes
P
Site
A
Site
Large
subunit
Small
subunit
mRNAmRNA
A U G C U A C U U C G

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

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InitiationInitiation
mRNAmRNA
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogen
bonds codon

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mRNAmRNA
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
ElongationElongation

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mRNAmRNA
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)

49
mRNAmRNA
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

50
mRNAmRNA
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
(leaves)

51
mRNAmRNA
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

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mRNAmRNA
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

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mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimary
structurestructure
of a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator
or stopor stop
codoncodon
TerminationTermination

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End Product –The Protein!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
aa1
aa2 aa3 aa4
aa5
aa200
aa199

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Messenger RNAMessenger RNA
(mRNA)(mRNA)
methionine glycine serine isoleucine glycine alanine stop
codon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
start
codon
Primary structure of a proteinPrimary 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

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