Cells Lecture IV
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Transcript of Cells Lecture IV
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