Cells Lecture Cells Lecture IVIVDNA and Protein SynthesisDNA and Protein Synthesis

Biology Standards CoveredBiology Standards Covered

• 1d ~ students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm

The Structure of DNAThe Structure of DNA

• DNA is a long molecule made up of nucleotides

• Each nucleotide is made up of three parts:– 5-carbon sugar

called deoxyribose

– Phosphate group– Nitrogen Base

Adenine Guanine

Phosphate group

Cytosine Thymine

(Deoxyribose)

5-Carbon Sugar

The NucleotidesThe NucleotidesNitrogen Bases A- adenine

G- guanine

C- cytosine

T- thymine

Chargaff’s RulesChargaff’s Rules

• According to Erwin Chargaff:– AAdeninedenine always pairs with TThyminehymine

– CCytosineytosine always pairs with GGuanineuanine

The Double HelixThe Double Helix

• base pairing- hydrogen bonds forming only between certain “base pairs”

Sugar-phosphate backbone

Hydrogen bonds

Nucleotide

Key

Adenine (A)

Thymine (T)

Cytosine(C)

Guanine (G)

DNA Arranged in a DNA Arranged in a ChromosomeChromosome

Central DogmaCentral Dogma

• The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA

• An equation to remember for Central Dogma would be:

DNA mRNA Amino Acid ChainDNA mRNA Amino Acid Chain

TranscriptionTranscription TranslationTranslation

TranscriptionTranscription inside inside the Nucleusthe Nucleus

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

RNA DNA

RNApolymerase

TranscriptionTranscription• PromotersPromoters – specific sites where the

enzyme-protein RNA PolymeraseRNA Polymerase binds to the strand of DNA to begin transcriptiontranscription

Central DogmaCentral Dogma• Proteins are assembled into

polypeptidespolypeptides– These are long chains of amino amino

acidsacids

– There are 20 different types of amino acidsamino acids

– The properties of proteins are The properties of proteins are determined by which order determined by which order these amino acids are joinedthese amino acids are joined

Central DogmaCentral Dogma• Each of these amino acids that mRNA

“codes” for recognizes the three base three base pair sequencepair sequence

• A codoncodon consists of “three nucleotides in a row” that code for a single amino acid– AUG codes for the amino acid Methionine

The (20) Amino AcidsThe (20) Amino Acids

Methionine is the universal “start codon” for all

proteins

Central DogmaCentral Dogma• Along with the twenty amino twenty amino

acidsacids there are “special” base pair sequences that “code for” startstart and stopstop codons

•Stop codons are like the “period at the end of a sentence”.– They signify the end of a

polypeptide (amino acid chain)

The The (20) (20)

Amino Amino AcidsAcids

TranslationTranslation

• The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA

• An equation to remember for Central Dogma would be:

DNA mRNA DNA mRNA Amino Acid ChainAmino Acid Chain

TranscriptionTranscription TranslationTranslation

Transfer RNA

mRNA Start codon

Ribosome

MethioninePhenylalanine tRNA Lysine

Nucleus

 Translation

mRNA

TranslationTranslation• Each strand of mRNA is separated into three

base pairs called codons

• AUG —- UUC --- AAA (mRNA)AUG —- UUC --- AAA (mRNA)• This is where This is where transfer RNAtransfer RNA

comes in comes in (tRNA)(tRNA)

TranslationTranslation• tRNA is responsible for getting the right

anticodon with each of the mRNA codons• An amino acid is attached to each

anticodon

tRNAtRNA

mRNA

Ribosome

Lysine (Amino Lysine (Amino Acid)Acid)

The Polypeptide “Assembly Line” The ribosome joins the two amino acids & breaks the bond between the tRNA & it’s amino acid

mRNARibosome

Translation direction

Lysine tRNA

tRNARibosome

Growing polypeptide chain

mRNA Completing the Polypeptide

The process continues until the ribosome reaches one of the three

stop codons. The result is a growing polypeptide chain.

TranslationTranslation