Protein SynthesisProtein Synthesis

The production (synthesis) The production (synthesis) of polypeptide chains of polypeptide chains (proteins)(proteins)

Two phases:Two phases: Transcription Transcription & & TranslationTranslation

mRNA must be mRNA must be processed processed beforebefore itit leaves leaves thethe nucleus nucleus of eukaryotic cellsof eukaryotic cells

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Pathway to Making a Pathway to Making a ProteinProtein

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProtein

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RNA Differs from DNARNA Differs from DNA1.1. RNARNA has a sugar has a sugar riboseribose

DNADNA has a sugar has a sugar deoxyribosedeoxyribose

2.2. RNARNA contains the base contains the base uracil uracil (U)(U)

DNADNA has has thymine (T)thymine (T)

3.3. RNARNA molecule is molecule is single-single-strandedstranded

DNADNA is is double-strandeddouble-stranded

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Structure of RNAStructure of RNA

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. Three Types of RNAThree Types of RNA

• Messenger RNA (mRNA)Messenger RNA (mRNA) carries genetic carries genetic information to the information to the ribosomesribosomes

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

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

Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.

Ribosomes are made up of proteins and ribosomal RNA (rRNA).

During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.

Protein SynthesisDNADNA

moleculemolecule

DNA strandDNA strand(template)(template)

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TRANSCRIPTIONTRANSCRIPTION

CodonCodon

mRNAmRNA

TRANSLATIONTRANSLATION

ProteinProtein

3355

55

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Genes & ProteinsGenes & Proteins

ProteinsProteins are made of are made of amino amino acidsacids linked together by linked together by peptide bondspeptide bonds

2020 different amino acids different amino acids existexist

Amino acids chains are Amino acids chains are called called polypeptidespolypeptides

Segment of DNA that codes Segment of DNA that codes for the amino acid sequence for the amino acid sequence in a protein are called in a protein are called genesgenes

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Two Parts of Protein Two Parts of Protein SynthesisSynthesis

TranscriptionTranscription makes an makes an RNA molecule RNA molecule complementary to a complementary to a portion of DNAportion of DNA

TranslationTranslation occurs when occurs when the sequence of bases of the sequence of bases of mRNA mRNA DIRECTSDIRECTS the the sequence of amino acidssequence of amino acids in in a polypeptidea polypeptide

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Genetic CodeGenetic Code Every three bases on DNA Every three bases on DNA

stands for stands for ONE amino ONE amino acidacid

Each three-letter unit on Each three-letter unit on mRNAmRNA is called a is called a codoncodon

Most amino acids have Most amino acids have moremore than than oneone codon! codon!

The code is nearly The code is nearly universal universal among living among living organismsorganisms

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TranscriptionTranscription

TranslationTranslation

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Overview of TranscriptionOverview of Transcription During During transcriptiontranscription in the in the

nucleus, a segment of DNA nucleus, a segment of DNA unwinds and unzips, and unwinds and unzips, and the the DNA DNA serves as aserves as a template template forfor mRNA mRNA formationformation

RNA polymeraseRNA polymerase joins the joins the RNA nucleotides so that RNA nucleotides so that the the codons codons in mRNA are in mRNA are complementarycomplementary to the to the code in DNAcode in DNA

TranscriptionDNA is copied in the form of RNA

This first process is called transcription.

The process begins at a section of DNA called a promoter.

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RNA PolymeraseRNA Polymerase EnzymeEnzyme found in the found in the

nucleusnucleus Separates Separates the two DNA the two DNA

strands by strands by breaking breaking thethe hydrogen bondshydrogen bonds between the basesbetween the bases

Then moves along one Then moves along one of the DNA strands and of the DNA strands and links RNA links RNA nucleotides nucleotides togethertogether

RNA

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Messenger RNA Messenger RNA (mRNA)(mRNA)

• Carries the information for a Carries the information for a specific proteinspecific protein

• Made up of Made up of 500 to 1000500 to 1000 nucleotides longnucleotides long

• Sequence of 3 bases called Sequence of 3 bases called codoncodon

• AUGAUG – methionine or – methionine or start start codoncodon

• UAA, UAG, or UGAUAA, UAG, or UGA – – stopstop codonscodons

A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.

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Messenger RNA Messenger RNA (mRNA)(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

Copyright Pearson Prentice Hall

The Genetic Code

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Transfer RNA (tRNA)Transfer RNA (tRNA)• Picks up the appropriate Picks up the appropriate

amino acidamino acid floating in the floating in the cytoplasm cytoplasm

• Transports Transports amino acidsamino acids to the to the mRNAmRNA

• Have Have anticodonsanticodons that are that are complementary to complementary to mRNA mRNA codonscodons

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

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TranslationTranslation• Synthesis of proteins Synthesis of proteins

in the cytoplasmin the cytoplasm

• Involves the following:Involves the following:1.1. mRNA (codons)mRNA (codons)2.2. tRNA (anticodons)tRNA (anticodons)3.3. ribosomesribosomes4.4. amino acidsamino acids

Nucleus

mRNACopyright Pearson Prentice Hall

Translation

Translation is the decoding of an mRNA message into a polypeptide chain (protein).

Translation takes place on ribosomes.

During translation, the cell uses information from messenger RNA to produce proteins.

LysinetRNAPhenylalanine

Methionine

Ribosome

mRNAStart codon

The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.

TranslationProtein Synthesis

The process continues until the ribosome reaches a stop codon.

Polypeptide

Ribosome

• http://www.youtube.com/watch?v=NJxobgkPEAo