PROTEIN SYNTHESIS

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DNA DNA AND AND GENEGENESS

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

GENES & PROTEINSGENES & PROTEINS

Proteins are made of amino acids linked together by peptide bonds

20 different amino acids exist

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AMINO ACID STRUCTUREAMINO ACID STRUCTURE

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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

cytosol 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 cytosoland taken to the cytosol In the cytosol, this In the cytosol, this code code

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

This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS

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RNARNA

DNA is the MASTER PLAN

RNA is the BLUEPRINT of the

Master Plan

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RNA DIFFERS FROM DNARNA DIFFERS FROM DNA

RNA has a sugar RNA has a sugar riboseribose

DNA has a sugar DNA has a sugar deoxyribosedeoxyribose

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OTHER DIFFERENCESOTHER DIFFERENCES

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

RNA molecule is RNA molecule is single-strandedsingle-strandedDNA is DNA is double-double-strandedstranded

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DNA

STRUCTURE OF RNASTRUCTURE OF RNA

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THREE TYPES OF RNATHREE TYPES OF RNA Messenger RNA (mRNA)Messenger RNA (mRNA)

copies DNA’s code & carries copies DNA’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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.

Long Straight chain of Nucleotides

Made in the Nucleus

Copies DNA & leaves through nuclear pores

Contains the Nitrogen Bases A, G, C, U ( no T )

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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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RIBOSOMAL RNA (RRNA)RIBOSOMAL RNA (RRNA)

rRNA is a single rRNA is a single strand strand 100 to 100 to 3000 nucleotides3000 nucleotides longlong

GlobularGlobular in shape in shape Made inside the Made inside the

nucleusnucleus of a cell of a cell Associates with Associates with

proteins to form proteins to form ribosomesribosomes

Site of Site of protein protein SynthesisSynthesis

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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

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

GGG? UCA? CAU? GCA? AAA?

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REMEMBER THE COMPLEMENTARY BASESREMEMBER THE COMPLEMENTARY BASES

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

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TRANSFER RNA (TRNA)TRANSFER RNA (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 RNA

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amino acidamino acidattachment siteattachment site

U A C

anticodonanticodon

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

Example: Codon ACU

Anticodon UGA

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UGA

ACU

TRANSCRIPTION TRANSCRIPTION AND TRANSLATIONAND TRANSLATION

PATHWAY TO MAKING A PROTEINPATHWAY TO MAKING A PROTEIN

DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProtein26

PROTEIN SYNTHESISPROTEIN SYNTHESIS

The production or synthesis of polypeptide chains (proteins)

Two phases: Transcription & Translation

mRNA must be processed before it leaves the nucleus of eukaryotic cells

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DNADNA RNARNA PROTEINPROTEIN

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Nuclearmembrane

TranscriptionTranscription

RNA ProcessingRNA Processing

TranslationTranslation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

EukaryotEukaryotic Cellic Cell

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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QUESTION:QUESTION:

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

DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’

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ANSWER:ANSWER:

DNA 5’-GCGTATG-DNA 5’-GCGTATG-3’3’

RNA 3’-CGCAUAC-RNA 3’-CGCAUAC-5’5’

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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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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

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MRNA PROCESSINGMRNA 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

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MRNA EDITINGMRNA EDITING Exons, segments of DNA that code for proteins, are then rejoined by

the enzyme ligase A guanine triphosphate 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

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38CAP

TailNew Transcript

Result of TranscriptionResult of Transcription

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

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

RIBOSOMESRIBOSOMES

Made of a large and small subunit

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

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

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STEP 1- INITIATIONSTEP 1- INITIATION

mRNA transcript start codon AUG attaches to the small ribosomal subunit

Small subunit attaches to large ribosomal subunit

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mRNA transcript

RIBOSOMESRIBOSOMES

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PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome

Peptide bonds join the amino acids

INITIATIONINITIATION

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mRNAmRNA


2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogenbonds codon

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mRNAmRNA


1-tRNA 2-tRNA

U A C G

aa1 aa2

A UA

anticodon

hydrogenbonds codon

peptide bond

3-tRNA

G A A

aa3

ElongationElongation

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mRNAmRNA


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)

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mRNAmRNA


2-tRNA

G

aa1

aa2

A UA

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

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mRNAmRNA


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)


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mRNAmRNA

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

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mRNAmRNA

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


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mRNAmRNA

A C A U G U

aa1

aa2

U

primaryprimarystructurestructureof a proteinof a protein

aa3

200-tRNA

aa4

U A G

aa5

C U

aa200

aa199

terminatorterminator or stopor stop codoncodon

TerminationTermination

END PRODUCT –THE PROTEIN!END PRODUCT –THE PROTEIN!

The end products of protein synthesis is a primary structure of a protein

A sequence of amino acid bonded together by peptide bonds

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aa1

aa2 aa3 aa4aa5

aa200

aa199

MESSENGER RNA (MRNA)MESSENGER RNA (MRNA)

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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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PROTEIN SYNTHESIS