DNA (Deoxyribonucleic Acid)  What is it? Read Chap 13 Read Chap 13  How does it work? Read Chap 14 Read Chap 14  How do we know? Read 13, 14 & class notes Read 13, 14 & class notes

The Central Dogma DNA makes PROTEINS and PROTEINS make LIFE

 But how?  At its essence, DNA is a set of instructions for making proteins. “DNA is a cookbook and the genes are recipes” “DNA is a cookbook and the genes are recipes”  Proteins are made from different arrangements of protein building blocks called Amino Acids.  There are 20 different Amino Acids. You get them from your food.

So how do you change the protein in a tuna fish sandwich into human hemoglobin, hair, enzymes, etc.???

There’s a little problem here…

Step 1: Transcription Copying the DNA DNA  mRNA

Transcription: Copying the DNA DNA  mRNA

Transcription: Copying the DNA DNA  mRNA COMPARISON OF DNA AND MESSENGER RNA

DNAmRNA StructureDoubleHelixSingleStrand SugarDeoxyribose C 5 H 10 O 4 Ribose C 5 H 10 O 5 Bases A,G,C,T A,G,C,U Uracil

How can 4 bases tell you how to make proteins from 20 amino acids???  Law of Parsimony (The simplest answer is often the right answer. Sort of, not always but a lot.) 4 letter alphabet making 1–letter words? 4 letter alphabet making 1–letter words? 4-letter alphabet making 2-letter words? 4-letter alphabet making 2-letter words? AGCT AAGACATAAGGGCGTG ACGCCCTC ATGTCTTT

mRNA & Codons The 3-base units of information on mRNA are called codons. AAU,GCC,CAU,GGG,CGA……………. Codons “spell out” the names of the specific amino acids to be used in making a specific PROTEIN. The sequence of bases on DNA or RNA is called, duh, the “base sequence”

The Universal Genetic Code is 64 triplets It’s a 4-letter alphabet that makes 64 3-letter words

Protein Synthesis (makin’ proteins) So this movie requires another actor… TRANSFER RNA (tRNA)

Transfer RNA (tRNA)

Protein Synthesis  Some terms that you MUST know… DNA codes or triplets (the genetic code of DNA) DNA codes or triplets (the genetic code of DNA) TRANSCRIPTION (of DNA to make mRNA) TRANSCRIPTION (of DNA to make mRNA) mRNA CODONS (3-base information units of mRNA mRNA CODONS (3-base information units of mRNA tRNA ANTICODONS (anticodons pair with codons) tRNA ANTICODONS (anticodons pair with codons) TRANSLATION (tRNA reads mRNA to make a protein) TRANSLATION (tRNA reads mRNA to make a protein)

OK, so you want to make some protein…

Hook together AMINO ACIDS with PEPTIDE BONDS

Protein Synthesis = Translation (makin’ proteins)

Codons

Transfer RNA (tRNA) “Picks up and transfers the amino acids over to the ribosome and mRNA”

codon in mRNA anticodon in tRNA amino acid Fig. 14-7, p.223 tRNA Structure

Protein Synthesis (makin’ proteins)

“Poly-ribosomes”

Overview Transcription Translation mRNA rRNAtRNA Mature mRNA transcripts ribosomal subunits mature tRNA

binding site for mRNA P (first binding site for tRNA) A (second binding site for tRNA) initiation elongation Amino Acid 1 Amino Acid 2 Amino Acid 1 Amino Acid 2 a A mature mRNA transcript leaves the nucleus through a pore in the nuclear envelope. c Initiation ends when a large and small ribosomal subunit converge and bind together. b Initiation, the first stage of translating mRNA, will start when an initiator tRNA binds to a small ribosomal subunit. d The initiator tRNA binds to the ribosome. e One of the rRNA molecules Fig. 14-9a-e, p.224

f The first tRNA is released g A third tRNA binds with the next codon h Steps f and g are repeated termination i A STOP codon moves into the area where the chain is being built. j The new polypeptide chain is released from the ribosome. k The two ribosomal subunits now separate, also. Fig. 14-9f-k, p.224

and all this requires just 28 molecules…

THE END. TEST NEXT TIME.

Extra slides below.  Disregard the remaining slides…

HersheyandChase

REPLICATION OF DNA