Protein Synthesis DNA codes for RNA which guides the synthesis of proteins! 10 Step 1 TRANSCRIPTION...

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PROTEIN SYNTHESIS

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DNA and

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Roles of RNA and DNA

• DNA is the MASTER PLAN

• RNA is the BLUEPRINT of the

Master Plancopyright cmassengale

RNA Differs from DNA

• RNA has a sugar ribose

DNA has a sugar deoxyribose

Other Differences

• RNA contains the base uracil (U)DNA has thymine (T)

• RNA molecule is single-strandedDNA is double-stranded

DNAcopyright cmassengale

Structure of RNA

Central Dogma of Biology

DNA codes for RNA which guides

the synthesis of proteins!7

. Three Types of RNA

• Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes

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

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

amino acidattachment site

anticodon

Central Dogma of Biology

DNA codes for RNA which guides

the synthesis of proteins!10

Step 1

TRANSCRIPTION IS HAPPENING AT THE SAME TIME AS DNA

REPLICATION!

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Transcription - 1

• A portion of the DNA molecule unzips

• Recall: DNA helicase is the enzyme responsible for this!

Transcription - 2

• RNA polymerase joins RNA nucleotides using the DNA strand as a template

• This strand of DNA read by the RNA is the “template strand” read in the 3’ to 5’

• This new strand of RNA is the mRNA strand made in the 5’ to 3’ direction

Transcription - 3

• The mRNA strand is released through nuclear pores (exits the nucleus) and the DNA strand rejoins

RNA Polymerase

mRNA Processing

• After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional

• Introns, non-functional segments of DNA are snipped out of the chain

mRNA Editing

• Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase

• The newly processed mRNA can then leave the nucleus

19CAP TailNew Transcript

Result of Transcription

mRNA Transcript - 4

•mRNA leaves the nucleus through its pores and goes to the ribosomes

The Genetic Code

• A codon designates an amino acid

• An amino acid may have more than one codon

• There are 20 amino acids, but 64 possible codons

• Some codons tell the ribosome to stop translating

The Genetic Code

•Use the code by reading from the center to the outside•Example: AUG codes for Methionine

Name the Amino Acids

• GGG?

• UCA?

• CAU?

• GCA?

• AAA?

Remember the Complementary Bases

On DNA:A-TC-G

On RNA:A-UC-G

Question:

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

DNA 5’-GCGTATG-3’

Answer:

•DNA 5’-GCGTATG-3’

•RNA 3’-CGCAUAC-5’

Translation

• Translation is the process of decoding the mRNA into a polypeptide chain to create proteins

• Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

Transcription

Translation

Ribosomes

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

• Have two sites for tRNA attachment --- P and A

Step 1- Initiation

• mRNA transcriptstart codon AUGattaches to the small ribosomalsubunit

• Small subunit attaches to large ribosomal subunit

mRNA transcriptcopyright cmassengale

Ribosomes

Largesubunit

Small subunit

A U G C U A C U U C G

Step 2 - Elongation• As ribosome moves, two tRNA with

their amino acids move into site A and P of the ribosome

• Peptide bonds join the amino acids

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Initiation

2-tRNA

1-tRNA

anticodon

hydrogenbonds codon

34mRNA

1-tRNA 2-tRNA

U A C G

aa1 aa2

anticodon

hydrogen

bonds codon

peptide bond

3-tRNA

Elongation

1-tRNA

2-tRNA

peptide bond

3-tRNA

Ribosomes move over one codon

(leaves)

2-tRNA

peptide bonds

3-tRNA

4-tRNA

2-tRNA

aa1aa2

peptide bonds

3-tRNA

4-tRNA

(leaves)

Ribosomes move over one codoncopyright cmassengale

G C U A C U U C G

aa1aa2

peptide bonds

3-tRNA

4-tRNA

5-tRNA

G C U A C U U C G

peptide bonds

3-tRNA

4-tRNA

5-tRNA

Ribosomes move over one codoncopyright cmassengale

A C A U G U

primary

structure

of a protein

200-tRNA

terminator

or stop

Termination

End Product –The Protein!

• The end products of protein synthesis is a primary structureof a protein

• A sequence of amino acidbonded together by peptide bonds

aa2 aa3 aa4aa5

Messenger RNA (mRNA)

methionine glycine serine isoleucine glycine alanine stop

codonprotein

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

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

Protein Synthesis DNA codes for RNA which guides the synthesis of proteins! 10 Step 1 TRANSCRIPTION...

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