protein synthesis

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PROTEIN PROTEIN SYNTHESISSYNTHESIS

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Protein SynthesisProtein Synthesis The production (synthesis) The production (synthesis)

of polypeptide chains of polypeptide chains (proteins)(proteins)

Two phases:Two phases: Transcription Transcription & & TranslationTranslation

• 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).

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•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

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DNA DNA RNA RNA ProteinProteinCentral DogmaCentral Dogma

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

EukaryotEukaryotic Cellic Cell

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Pathway to Making a Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProtein

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Nucleic Nucleic AcidsAcids

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RNARNA

• SCI.9-12.B-4.1 - [Indicator] - Compare DNA and RNA in terms of structure, nucleotides, and base pairs.

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How How DNA DNA andand RNA RNA are are alikealike::

•Both made of monomers called nucleotides.

•Both had A, G and C bases

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*RNA Differs from *RNA Differs from DNADNA1.1. RNARNA has a sugar has a sugar riboseribose

DNADNA has a sugar has a sugar deoxyribosedeoxyribose

2.2. RNARNA contains the base contains the base uracil uracil (U)(U)

DNADNA has has thymine (T)thymine (T)

3.3. RNARNA molecule is molecule is single-single-strandedstranded

DNADNA is is double-strandeddouble-stranded

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*Three Types of RNA*Three Types of RNA• Messenger RNA (mRNA)Messenger RNA (mRNA)

carries genetic information carries genetic information to the ribosomesto the ribosomes

• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA),, along with protein, makes along with protein, makes up the up the ribosomesribosomes

• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers amino acids to the transfers amino acids to the ribosomes where proteins ribosomes where proteins are synthesizedare synthesized

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Making a Making a ProteinProtein

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*Genes & Proteins*Genes & Proteins ProteinsProteins are made of are made of amino amino

acidsacids linked together by linked together by peptide bondspeptide bonds

2020 different amino acids different amino acids existexist Amino acids chains are called Amino acids chains are called

polypeptidespolypeptides Segment of DNA that codes Segment of DNA that codes

for the amino acid sequence for the amino acid sequence in a protein are called in a protein are called genesgenes

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Two Parts of Protein Two Parts of Protein SynthesisSynthesis

TranscriptionTranscription makes an RNA makes an RNA molecule complementary to molecule complementary to a portion of DNAa portion of DNA

TranslationTranslation occurs when the occurs when the sequence of bases of mRNA sequence of bases of mRNA DIRECTSDIRECTS the the sequence of sequence of amino acidsamino acids in a polypeptide in a polypeptide



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*Genetic Code*Genetic Code DNA contains a DNA contains a triplet codetriplet code Every three bases on DNA Every three bases on DNA

stands for stands for ONE amino acidONE amino acid Each three-letter unit on Each three-letter unit on mRNAmRNA

is called a is called a codoncodon Most amino acids have more Most amino acids have more

than one codon!than one codon! There are There are 20 amino acids20 amino acids with with

a possible 64 different tripletsa possible 64 different triplets The code is nearly The code is nearly universal universal

among living organismsamong living organisms

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*What is the *What is the enzymeenzyme

responsible for responsible for the production of the production of

the mRNA the mRNA molecule?molecule?

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*RNA Polymerase*RNA Polymerase

EnzymeEnzyme found in the found in the nucleusnucleus

Separates Separates the two DNA the two DNA strands by strands by breaking the breaking the hydrogen bondshydrogen bonds between between the basesthe bases

Then moves along one of Then moves along one of the DNA strands and the DNA strands and links links RNA nucleotidesRNA nucleotides together together

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Question:Question:

What would be the What would be the complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA 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-5RNA 3’-CGCAUAC-5’’

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*Processing Pre-*Processing Pre-mRNAmRNA

• Also occurs in the Also occurs in the nucleusnucleus• Pre-mRNA Pre-mRNA made up of segments made up of segments

called called introns & exonsintrons & exons• Exons code for proteins, while Exons code for proteins, while

introns do NOT!introns do NOT!• Introns spliced out by Introns spliced out by splicesome-splicesome-

enzymeenzyme and exons re-join and exons re-join

• End product is a End product is a mature RNAmature RNA molecule that leaves the nucleus molecule that leaves the nucleus to the cytoplasmto the cytoplasm

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*Messenger RNA *Messenger RNA (mRNA)(mRNA)

• Carries the information for a Carries the information for a specific proteinspecific protein

• Made up of Made up of 500 to 1000500 to 1000 nucleotides longnucleotides long

• Sequence of 3 bases called Sequence of 3 bases called codoncodon• AUGAUG – methionine or – methionine or start start codoncodon• UAA, UAG, or UGAUAA, UAG, or UGA – – stopstop codons codons

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Messenger RNA Messenger RNA (mRNA)(mRNA)

methionine glycine serine isoleucine glycine alanine stopcodon

proteinprotein

A U G G G C U C C A U C G G C G C A U A AmRNAmRNA

startcodon

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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Transfer RNA (tRNA)Transfer RNA (tRNA)

amino acidamino acidattachment siteattachment site

U A C

anticodonanticodon

methionine amino acidamino acid



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*Ribosomes*Ribosomes

•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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TranslationTranslation

• Synthesis of proteinsSynthesis of proteins in the in the cytoplasmcytoplasm

• Involves the following:Involves the following:

1.1. mRNA (codons)mRNA (codons)

2.2. tRNA (anticodons)tRNA (anticodons)

3.3. ribosomesribosomes

4.4. amino acidsamino acids

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*Translation*Translation• Three steps:Three steps:

1.1. initiationinitiation: start codon (AUG): start codon (AUG)

2.2. elongationelongation: amino acids : amino acids linkedlinked

3.3. terminationtermination: stop codon : stop codon (UAG, UAA, or UGA).(UAG, UAA, or UGA).

Let’s Make a Protein !Let’s Make a Protein !

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein%20Synthesis

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http://sciencenetlinks.com/interactives/protein.html

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mRNA Codons Join the mRNA Codons Join the RibosomeRibosome

PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

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InitiationInitiation

mRNAmRNA


2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogenbonds codon

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mRNAmRNA


1-tRNA 2-tRNA

U A C G

aa1 aa2

A UA

anticodon

hydrogenbonds 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 UA

peptide bond

3-tRNA

G A A

aa3

Ribosomes move over one codon

(leaves)

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mRNAmRNA


2-tRNA

G

aa1

aa2

A UA

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

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mRNAmRNA


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)


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mRNAmRNA

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

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mRNAmRNA

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


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mRNAmRNA

A C A U G U

aa1

aa2

U

primaryprimarystructurestructureof 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 *End Product –The Protein!Protein!

• The end products of protein The end products of protein synthesis is a synthesis is a primary structureprimary structure of a proteinof a protein

• A A sequence of amino acidsequence of amino acid bonded together by peptide bonded together by peptide bondsbonds

aa1

aa2 aa3 aa4aa5

aa200

aa199



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*Types of Mutations1. 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

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Substitution

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Wild type

A U G A A G U U U G G C U A AmRNA

5Protein Met Lys Phe Gly

Stop

Carboxyl endAmino end

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A U G A A G U U U G G U U A A

Met Lys Phe Gly

Base-pair substitution

No effect on amino acid sequenceU instead of C

Stop

A U G A A G U U U A G U U A A

Met Lys Phe Ser Stop

A U G U A G U U U G G C U A A

MetStop

Missense A instead of G

NonsenseU instead of A

• *The change of a single nucleotide in the DNA’s template strand– Leads to the production of an

abnormal protein

Figure 17.23

In the DNA, themutant templatestrand has an A where the wild-type template has a T.

The mutant mRNA has a U instead of an A in one codon.

The mutant (sickle-cell) hemoglobin has a valine (Val) instead of a glutamic acid (Glu).

Mutant hemoglobin DNAWild-type hemoglobin DNA

mRNA mRNA

Normal hemoglobin Sickle-cell hemoglobin

Glu Val

C T T C A T

G A A G U A

3 5 3 5

5 35 3

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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

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mRNA

Protein

Wild type

A U G A A G U U U G G C U A A5

Met Lys Phe Gly

Amino end Carboxyl end

Stop

Base-pair insertion or deletion

Frameshift causing immediate nonsense

A U G U A A G U U U G G C U A

A U G A A G U U G G C U A A

A U G U U U G G C U A A

Met Stop

U

Met Lys Leu Ala

Met Phe GlyStop

MissingA A G

Missing

Extra U

Frameshift causing extensive missense

Insertion or deletion of 3 nucleotides:no frameshift but extra or missing amino acid

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protein synthesis

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