1 PROTEIN SYNTHESIS copyright cmassengale. DNA DNA contains genes, sequences of nucleotide bases These Genes code for polypeptides (proteins) Proteins

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PROTEIN PROTEIN SYNTHESISSYNTHESIS

copyright cmassengale

DNADNA

•DNA contains genes, sequences of nucleotide bases

•These Genes code for polypeptides (proteins)

•Proteins are used to build cells and do much of the work inside cells

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Genes & ProteinsGenes & Proteins

Proteins are made of amino acids linked together by peptide bonds

20 different amino acids exist


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This is a generic amino This is a generic amino acidacid


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PolypeptidesPolypeptides

•Amino acid chains are called

•polypeptides


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DNA Begins the DNA Begins the ProcessProcess

• DNA is found inside the nucleus

• Proteins, however, are made in the cytoplasm of cells by organelles called ribosomes

• Ribosomes may be free in the cytosol or attached to the surface of rough ER


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Starting with DNAStarting with DNA• DNA’s codeDNA’s code must be must be copiedcopied

and taken to the cytoplasmand taken to the cytoplasm• In the cytoplasm, this In the cytoplasm, this code code

must be readmust be read so so amino amino acidsacids can be assembled to can be assembled to make polypeptides make polypeptides (proteins)(proteins)

• This process is called This process is called

PROTEIN SYNTHESISPROTEIN SYNTHESIScopyright cmassengale

What is RNA?What is RNA?Ribonucleic Ribonucleic acid!acid!


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Roles of RNA and DNA

•DNA is the MASTER PLAN

•RNA is the BLUEPRINT of the

Master Plancopyright cmassengale

Structure of RNAStructure of RNA

1. Phosphate group1. Phosphate group

2. 5-carbon sugar- ribose2. 5-carbon sugar- ribose

3. Bases3. Basesi. Adeninei. Adenine

ii. Uracilii. Uracil

iii. Cytosineiii. Cytosine

iv. Guanineiv. Guanine

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Structure of RNAStructure of RNA


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. Three Types of Three Types of RNARNA

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

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

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


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Messenger RNA (mRNA)Messenger RNA (mRNA)• Carries the information for a Carries the information for a

specific proteinspecific protein• Made up of Made up of 500 to 1000 500 to 1000

nucleotides longnucleotides long• Sequence of 3 bases called Sequence of 3 bases called

codoncodon• AUGAUG – methionine or – methionine or start codonstart codon• UAA, UAG, or UGAUAA, UAG, or UGA – – stop codonsstop codons


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The Genetic Code

• A codon is a group of 3-nucleotides that 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


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The Genetic Code

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


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Name the Amino Acids

•GGG?•UCA?•CAU?•GCA?•AAA?


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Remember the Remember the Complementary Complementary

BasesBasesOn DNA: A-T C-GOn RNA: A-U C-G


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Transfer RNA Transfer RNA (tRNA)(tRNA)

• Clover-leaf shape• Single stranded molecule

with attachment site at one end for an amino acid

• Opposite end has three nucleotide bases called the anticodon


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Transfer RNATransfer RNAamino acidamino acid

attachment siteattachment site

U A C

anticodonanticodoncopyright cmassengale

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Codons and Anticodons

• The 3 bases of an anticodon are complementary to the 3 bases of a codon

• Example: Codon ACU

Anticodon UGA

UGA

ACU


TranscriptiTranscription and on and

TranslationTranslation


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Pathway to Making a Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProteincopyright cmassengale

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Protein SynthesisProtein Synthesis

Definition:Definition:

The production or synthesis of polypeptide chains (proteins) Two phases:

Transcription & Translation mRNA must be processed

before it leaves the nucleus of eukaryotic cellshe


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TranscriptionTranscription

• The process of copying the sequence of one strand of DNA, the template strand

• mRNA copies the template strand

• Requires the enzyme RNA Polymerase


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Template Strand


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Question:Question:

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

DNA 5DNA 5’’--GCGTATGGCGTATG-3-3’’RNA 3RNA 3’’-CGCAUAC-5-CGCAUAC-5’’


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Answer:Answer:

• DNA 5DNA 5’’-GCGTATG-3-GCGTATG-3’’• RNA 3RNA 3’’-CGCAUAC-5-CGCAUAC-5’’


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TranscriptionTranscription• During transcription, RNA

polymerase binds to DNA and separates the DNA strands

• RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA


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Transcription, Transcription, con.’tcon.’t

• Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA

• Called the TATA box

• Specific base sequences act as signals to stop

• Called the termination signal


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RNA PolymeraseRNA Polymerase


mRNA Processing

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• 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


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mRNA EditingmRNA Editing

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

• A cap is added to the 5’ end of the newly copied mRNA

• A poly A tail is added to the 3’ end of the RNA

• The newly processed mRNA can then leave the nucleus



Introns

Exons

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TailNew Transcript

Result of TranscriptionResult of Transcription


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mRNA Transcript

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


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TranslationTranslation• Translation is the process of

decoding the mRNA into a polypeptide chain

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


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TranscriptioTranscriptionn

TranslatiTranslationon


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Step 1- InitiationStep 1- Initiation

• mRNA transcript start codon AUG attaches to the small ribosomal subunit

mRNA transcript




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End Product –The End Product –The Protein!Protein!

• 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


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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


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1 PROTEIN SYNTHESIS copyright cmassengale. DNA DNA contains genes, sequences of nucleotide bases These Genes code for polypeptides (proteins) Proteins