PROTEIN PROTEIN SYNTHESISSYNTHESIS

Used and Modified with permission from Used and Modified with permission from

Robert GoodmanRobert Goodman, , Biology Department,Citrus Community CollegeBiology Department,Citrus Community College

Protein SynthesisProtein Synthesis• The production (synthesis) of proteinsproteins.

• 3 phases3 phases:

1.1. TranscriptionTranscription

2.2. RNA processingRNA processing

3.3. TranslationTranslation

• Remember: Remember: DNA DNA RNA RNA ProteinProtein

DNA DNA RNA RNA ProteinProtein

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

TranscriptionTranscription

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Prokaryotic CellProkaryotic Cell

DNA DNA RNA RNA ProteinProtein

Question:Question:

How does RNARNA (ribonucleic acid) (ribonucleic acid) differ

from DNA DNA (deoxyribonucleic acid)(deoxyribonucleic acid)?

RNARNA differs from differs from DNADNA1. RNARNA has a sugar ribosesugar ribose

DNADNA has a sugar deoxyribosesugar deoxyribose

2. RNARNA contains uracil (U)uracil (U)

DNADNA has thymine (T)thymine (T)

3. RNARNA molecule is single-strandedsingle-stranded

DNADNA is double-strandeddouble-stranded

1. Transcription1. Transcription

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

1. Transcription1. Transcription• The transfer of information in the

nucleusnucleus from a DNADNA molecule to an RNARNA molecule.

• Only 1 1 DNADNA strand serves as the templatetemplate

• Starts at promoter DNADNA (TATA box)• Ends at terminator DNADNA (stop)• When complete, pre-RNApre-RNA molecule is

released.

Question:Question:

• What is the What is the enzymeenzyme responsible for the responsible for the production of the RNA production of the RNA molecule?molecule?

Answer:Answer: RNA Polymerase RNA Polymerase• Separates the DNADNA molecule by

breaking the H-bonds between the bases.

• Then moves along one of the DNA DNA strandsstrands and links RNARNA nucleotides together.

1. Transcription1. Transcription

DNADNA

pre-mRNApre-mRNA

RNA PolymeraseRNA Polymerase

Question:Question:• What would be the complementary

RNARNA strand for the following DNADNA sequence?

• DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’

Answer:Answer:

• DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’

• RNA 3’-CGCAUAC-5’RNA 3’-CGCAUAC-5’

2. RNA Processing2. RNA Processing

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

2. RNA Processing2. RNA Processing• Maturation of pre-RNApre-RNA molecules.

• Also occurs in the nucleus.nucleus.

• IntronsIntrons spliced out by splicesome-splicesome-enzymeenzyme and exonsexons come together.

• End product is a mature RNA mature RNA moleculemolecule that leaves the nucleusnucleus to the cytoplasm.cytoplasm.

2. RNA Processing2. RNA Processing

pre-RNA molecule

intron

intronexon exon exon

exon exon exon

Mature RNA moleculeMature RNA molecule

exon exon exon

intron intron

splicesome splicesome

Types of RNATypes of RNA• Three types ofThree types of RNARNA:

A.A. messenger RNA (mRNA)messenger RNA (mRNA)

B.B. transfer RNA (tRNA)transfer RNA (tRNA)

C.C. ribosome RNA (rRNA)ribosome RNA (rRNA)

• Remember: all produced in theRemember: all produced in the nucleusnucleus!!

A. Messenger RNA (mRNA)A. Messenger RNA (mRNA)• Carries the information for a specific

proteinprotein.

• Made up of 500 to 1000 nucleotides nucleotides long.

• Made up of codons codons (sequence of three bases: AUG - methionine).

• Each codoncodon, is specific for an amino amino acidacid.

A. Messenger RNA (mRNA)A. Messenger RNA (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

B. Transfer RNA (tRNA)B. Transfer RNA (tRNA)• Made up of 75 to 80 nucleotides long.

• Picks up the appropriate amino acid amino acid floating in the cytoplasm (amino acid amino acid activating enzymeactivating enzyme)

• Transports amino acids amino acids to the mRNAmRNA.

• Have anticodonsanticodons that are complementary to mRNAmRNA codonscodons.

• Recognizes the appropriate codonscodons on the mRNAmRNA and bonds to them with H-bonds.

B. Transfer RNA (tRNA)B. Transfer RNA (tRNA)

amino acidamino acidattachment siteattachment site

U A C

anticodonanticodon

methionine amino acidamino acid

C. Ribosomal RNA (rRNA)C. Ribosomal RNA (rRNA)• Made up of rRNArRNA is 100 to 3000

nucleotides long.

• Important structural component of a ribosome.ribosome.

• Associates with proteins proteins to form ribosomes.ribosomes.

RibosomesRibosomes• Large and small subunits.Large and small subunits.

• Composed of rRNA (40%) rRNA (40%) and proteins proteins (60%).(60%).

• Both units come together and help bind the mRNAmRNA and tRNA.tRNA.

• Two sites forTwo sites for tRNAtRNA

a. P siteP site (first and last tRNA will attachtRNA will attach)

b. A siteA site

RibosomesRibosomes

PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

3. Translation3. Translation

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

3. Translation3. Translation• Synthesis of proteinsproteins in the

cytoplasmcytoplasm

• Involves the following:Involves the following:1. mRNA (codons)mRNA (codons)2. tRNA (anticodons)tRNA (anticodons)3. rRNArRNA4. ribosomesribosomes5. amino acidsamino acids

3. Translation3. Translation• Three parts:

1. initiationinitiation: start codon (AUG)

2. elongationelongation:

3. terminationtermination: stop codon (UAG)

• Let’s make a PROTEIN!!!!PROTEIN!!!!.

3. Translation3. Translation

PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

InitiationInitiation

mRNAmRNA

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

mRNAmRNA

A U G C U A C U U C G

1-tRNA 2-tRNA

U A C G

aa1 aa2

A UA

anticodon

hydrogenbonds codon

peptide bond

3-tRNA

G A A

aa3

ElongationElongation

mRNAmRNA

A U G C U A C U U C G

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)

mRNAmRNA

A U G C U A C U U C G

2-tRNA

G

aa1

aa2

A UA

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

mRNAmRNA

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 codon

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

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

Ribosomes move over one codon

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

End ProductEnd Product• The end products of protein synthesis

is a primary structure of a proteinprimary structure of a protein.

• A sequence of amino acid amino acid bonded together by peptide bondspeptide bonds.

aa1

aa2 aa3 aa4aa5

aa200

aa199

PolyribosomePolyribosome• Groups of ribosomes reading same

mRNA mRNA simultaneously producing many proteins (polypeptides).proteins (polypeptides).

incominglargesubunit

incomingsmall subunit polypeptidepolypeptide

mRNAmRNA1 2 3 4 5 6 7

Question:Question:• The anticodon The anticodon UACUAC belongs to belongs to

a a tRNAtRNA that recognizes and that recognizes and binds to a particular binds to a particular amino amino acidacid..

• What would be the What would be the DNA base DNA base code code for this for this amino acid?amino acid?

Answer:Answer:• tRNA - UAC (anticodon)tRNA - UAC (anticodon)

• mRNA - AUG (codon)mRNA - AUG (codon)

• DNA - TACDNA - TAC