PROTEIN SYNTHESISPROTEIN SYNTHESIS

Higher Level

Lesson ObjectivesAt the end of this lesson you should be

able to

1. Outline the steps in protein synthesis

2.Understand that a strand of DNA is copied by transcription

3.Understand the role of mRNA

4.Know the function of a ribosome in protein synthesis

5.Understand the process of translation that leads to the formation of a new protein

6.Know that the shape of a protein determines its function

For Protein Synthesis You need:

1. A supply of amino acids – cytoplasm

2. Instructions as how to join the amino acids together – genetic code

3.An assembly line – ribosomes

4.A messenger to carry information from DNA to ribosomes

Protein Synthesis - StepsProtein Synthesis - Steps

3 stages3 stages:

1.1. TranscriptionTranscription

2.2. RNA processingRNA processing

3.3. TranslationTranslation

• Remember:Remember: DNA DNA RNA RNA ProteinProtein

RNA is composed of 3 parts

1. Ribose: smaller sugar than deoxyribose of DNA

2. Phosphate

3. 4 Nitrogenous Bases A,G,U,C

RNA is single stranded and thus smaller & able to leave the nucleus of the cell

DNA DNA RNA RNA ProteinProtein

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

Transcription Translation

TranscriptionTranscription

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Prokaryotic Cell – No nucleusProkaryotic Cell – No nucleus

DNA DNA RNA RNA ProteinProtein

Learning CheckLearning Check• What is RNA composed of?

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

• What are the three stages in Protein synthesis?

1. Transcription1. Transcription

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

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 (AUG)

• Ends at terminator DNADNA (stop)

• When complete, mRNAmRNA molecule is released into the cytoplasm

Video Clip available in extra material folder

Transcription

• Takes places in the nucleus of the cellThe process by which the information from DNA is transferred to RNA. DNA uncoils and unzips.

• The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

1. Transcription1. Transcription

DNADNA

mRNAmRNA

RNA PolymeraseRNA Polymerase

Enzyme

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

This is a molecule of messenger RNA.

It was made in the nucleus by transcription from a DNA molecule.

mRNA molecule

codon

Learning CheckLearning Check

• What type of RNA molecule is responsible for taking the DNA copy from the nucleus into the cytoplasm

• What parts of the cell do you find RNA in?

• Can you outline the stages in transcription?

2. RNA Processing2. RNA Processing

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

2. RNA Processing2. RNA Processing

• Occurs in the nucleus.nucleus.

• Non- Coding Non- Coding regions taken out by enzymeenzyme and Coding regions Coding regions come together.

• End product is a mRNA moleculemRNA molecule that leaves the nucleusnucleus to the cytoplasm.cytoplasm.

mRNA

• Takes places in the nucleus of the cellThe process by which the information from DNA is transferred to RNA. DNA uncoils and unzips.

• The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

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)

• Each codoncodon is specific for one 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

• Transports amino acids amino acids to the mRNAmRNA.

• Has anticodonsanticodons that are complementary to mRNAmRNA codonscodons.

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

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.

RibosomesRibosomes

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

Learning Check

• What are the three types of RNA?

• Where is each type produced?

• What is the function of each type of RNA?

3. Translation3. Translation

Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Eukaryotic Eukaryotic CellCell

Video Clip available in extra material folder

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. rRNArRNA

4. ribosomesribosomes

5. amino acidsamino acids

3. Translation3. Translation

Three parts:

1. initiationinitiation: start codon (AUG)

2. elongationelongation:

3. terminationtermination: stop codon (UAG)

Translation• In the cytoplasm, translation occurs.

The mRNA binds to a ribosome.

• The strand of mRNA is pulled through the ribosome three bases at a time, in triplets.

• Each of these triplets on the mRNA strand is called a codon.

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

This is a molecule of messenger RNA.

It was made in the nucleus by transcription from a DNA molecule.

mRNA molecule

codon

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

A ribosome on the rough endoplasmic reticulum attaches to

the mRNA molecule.

ribosome

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

It brings an amino acid to the first three bases (codon) on the mRNA.

Amino acid

tRNA molecule

anticodon

U A C

A transfer RNA molecule arrives.

The three unpaired bases (anticodon) on the tRNA link up with the codon.

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

Another tRNA molecule comes into place, bringing a second amino acid.

U A C C C G

Its anticodon links up with the second codon on the mRNA.

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

Another tRNA molecule brings the next amino acid into place.

C C G

A A U

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

A peptide bond joins the second and third amino acids to form a polypeptide chain.

C C G C C G

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

The polypeptide chain gets longer.

G U C

A C G

The process continues.

This continues until a termination (stop) codon is reached.

The polypeptide is then complete.

tRNA Transfer RNA (tRNA), reads the strand

of mRNA and translates it into a strand of amino acids.

A molecule of tRNA has at one end a set of three bases that will complement the mRNA strand; this is called the anticodon.

tRNA• If the 3 base anticodon of the tRNA

complements the 3 base codon of the mRNA, they briefly combine.

• The amino acid is left behind when the tRNA leaves.

• As each codon is read, the next tRNA brings in a new amino acid and the polypeptide (protein) chain grows.

• This requires enzymes and ATP.

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

Functional ProteinFunctional Protein

• The protein now has to undergo folding and the addition of bonds

• Folding allows the Protein to reach its 3D (Tertiary Shape) which influences its Function.

Learning CheckLearning Check

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

What have you learned?Can you ………………

1. Outline the steps in protein synthesis

2. Understand that a strand of DNA is copied by transcription

3. Understand the role of mRNA

4. Know the function of a ribosome in protein synthesis

5. Understand the process of translation that leads to the formation of a new protein

6. Know that the shape of a protein determines its function

End