PROTEIN SYNTHESIS. Protein Synthesis proteinsThe production (synthesis) of proteins. 3 phases3...

PROTEIN SYNTHESISPROTEIN SYNTHESIS

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



DNA

mRNA

Ribosome

Protein

Prokaryotic CellProkaryotic Cell

DNA DNA RNA RNA ProteinProtein

Question:Question:

• How does RNARNA (ribonucleic acid) (ribonucleic acid) differ from DNA (deoxyribonucleic acid)DNA (deoxyribonucleic acid)?

RNARNA differs from DNADNA

1. 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




DNA

Pre-mRNA

mRNA

Ribosome

Protein



• 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 What enzymesenzymes are responsible are responsible for the production of the RNA for the production of the RNA molecule?molecule?

Answer:Answer: Helicase Helicase andand RNA RNA PolymerasePolymerase

• HelicaseHelicase separates the DNADNA molecule by breaking the H-bonds between the bases.

• RNA PolymeraseRNA Polymerase moves along one of the DNA DNA strandsstrands and links RNARNA nucleotides together.


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




DNA

Pre-mRNA

mRNA

Ribosome

Protein



• Maturation of pre-RNApre-RNA molecules.

• Also occurs in the nucleus.nucleus.

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

• End product is a messenger RNA molecule messenger RNA molecule (mRNA)(mRNA) that leaves the nucleusnucleus to the cytoplasm.cytoplasm.


pre-RNA molecule

intron

intronexon exon exon

exon exon exon

Messenger RNA moleculeMessenger 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. ribosomal RNA (rRNA)ribosomal 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 acidamino acid.

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 activating enzymeamino acid activating 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 (60%).proteins (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




DNA

Pre-mRNA

mRNA

Ribosome

Protein



• Synthesis of proteinsproteins in the cytoplasmcytoplasm

• Involves the following:Involves the following:

1. mRNA (codons)mRNA (codons)

2. tRNA (anticodons)tRNA (anticodons)

3. rRNArRNA

4. ribosomesribosomes

5. amino acidsamino acids


• Three parts:

1. initiationinitiation: start codon (AUG)

2. elongationelongation:

3. terminationtermination: stop codon (UAG)

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

mRNA Codon Translation Table


PSite

ASite

Largesubunit

Small subunit

mRNAmRNA


InitiationInitiation

mRNAmRNA


2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogenbonds codon

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

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)

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

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)


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

C C U

G G A

5-tRNA

aa5

mRNAmRNA

C 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

Question:Question:

• The anticodon The anticodon UACUAC belongs to a belongs to a tRNAtRNA that that recognizes and binds to a particular recognizes and binds to a particular amino amino acidacid..

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

Answer:Answer:

• tRNA tRNA - UAC (anticodon)- UAC (anticodon)

• mRNAmRNA - AUG (codon)- AUG (codon)

• DNA DNA - TAC- TAC

When things go wrong…• Mutations: changes in the DNA sequence,

that may be passed along to future generations.

• Point mutations: a single base substitutionTHE CAT SAW THE RATTHE CAT SAW THE HAT

• Deletion: a small DNA segment is lostTHE CAT SAW THE RATTHE ATS AWT HER AT

• Insertion: a segment of DNA is added THE CAT SAW THE HAT

THE CAT SAW THE BHAT

Mutations• Frame-shift mutation: modification of the reading

frame after a deletion or insertion, resulting in all codons downstreams being different.

For example:THE RAT SAW THE CAT AND RAN

If you take out the “R” in “RAT” and shift the frames, you get:

THE ATS AWT HEC ATA NDR AN

The resulting sentence (or mRNA message) is meaningless!

Mutations

• Somatic mutations: occur in body cells, or cells that do not lead to gametes.

• Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations… UNLESS the plant is reproduced asexually.

PROTEIN SYNTHESIS. Protein Synthesis proteinsThe production (synthesis) of proteins. 3 phases3...

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