12-3

12-3 RNA and protein synthesis

The Central Dogma

RNA and DNA

DNA• Double helix strands

• Deoxyribose

• A,T,C,G

• Nucleus

RNA• One strand

• Ribose

• A,U (uracil), C,G

• Cytoplasm & nucleus

Strands

Sugar

Base

Location

DNA ( A T C G)

RNA (A U C G)

A. messenger RNA (mRNA)B. transfer RNA (tRNA)C. ribosome RNA (rRNA)

Three types of RNA

A cooking book in French

A cooking book in Chinese

The Central Dogma

Steps from DNA to Proteins

Sequence of nucleotides

Sequence of nucleotides

Sequence of amino acids

Steps from DNA to Proteins

Nuclearmembrane

Transcription

RNA Processing

Translation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Transcription• Synthesize a mRNA molecule along one template

strand of DNA– In nucleus– Starts at promoter (TATA region of DNA)– Ends at terminator – Need enzyme RNA polymerase– When complete, pre-mRNA is released.

A T C G T A C G A A G T C T A C G G G A C T A T C G

T A G C G A T A G CA T G C T T C A G A T G C C C T

DNA

A C G A A G U C

mRNA

RNA polymerase

Direction of transcription

5 3

Transcription

• Steps– DNA unzipped by RNA polymerase– RNA polymerase builds RNA by base paring RNA

nucleotides to one strand of DNA– U is used instead of T– RNA is released and leaves the nucleus

Question

• What would be the complementary RNA strand for the following DNA sequence?

• DNA: GCGTATG

RNA: CGCAUAC

Question

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

• RNA Polymerase– Separates the DNA molecule by breaking the H-

bonds between the bases.

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

RNA processing

RNA processing

mature mRNA transcript5’ 3’

3’

poly-A tail

5’snipped out intron snipped out intron

cap

transcription into pre-mRNA

Part of a DNA strand

exon intron exon exonintron3’ 5’

Translation

• Synthesize a polypeptide chain using the genetic code on mRNA

Translation

• Key characters– 1) mRNA : provide code– 2) tRNA : bring building blocks– 3) Ribosome (rRNA) : provide site

1) mRNA

• A linear sequence of nucleotides

• Three nucleotides make a codon – Codon : the genetic code

for a amino acid– 64 codons– AUG: start– UAA, UAG, UGA: stop

methionine glycine serine isoleucine glycine alanine stopcodon

protein

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

startcodon

Primary 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

1) mRNA

2) tRNA

• Delivers amino acids to ribosomes

• One side attached with amino acid

• Another side with anticodon– Anticodon: 3 nucleotides

that can pair with a codon

– 20 different types of amino acids

amino acidattachment site

U A C

anticodon

methionine amino acid

2) tRNA

3) rRNA

• Major component of ribosomes

• Ribosome • Place where amino acids are

made into proteins• Small subunit + large subunit• Large subunit has 2 sites for

tRNA

PSite

ASite

Largesubunit

Small subunit

mRNA

A U G C U A C U U C G

Ribosome

3) rRNA

Translation

• Three Steps1. initiation: start codon (AUG)2. elongation:3. termination: stop codon (UAG, UAA, UGA)

• Let’s make a PROTEIN!!!!.

1) Initiation

PSite

ASite

Largesubunit

Small subunit

mRNA

A U G C U A C U U C G

1-tRNA

U A C

aa1

anticodon

codon

mRNA

A U G C U A C U U C G

2-tRNA

G

aa2

A U

Aanticodon

hydrogenbonds codon

1-tRNA

U A C

aa1

2) Elongation

mRNA

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

mRNA

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)

mRNA

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

mRNA

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

mRNA

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

mRNA

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

mRNA

A C A U G U

aa1

aa2

U

primarystructureof a protein

aa3

200-tRNA

aa4

U A G

aa5

C U

aa200

aa199

terminator or stop codon

3) Termination

4) End Product

• 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 aa4aa5

aa200

aa199

Question:

• The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid.

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

Answer:

• tRNA - UAC (anticodon)• mRNA - AUG (codon)• DNA - TAC