DNA The Code of Life

Topics Covered The DNA Molecule DNA Replication How DNA works Transcription Translation

DNA Deoxyribonucleic acid Discovered by Watson and Crick Made up of nucleotides Double helix 2 coiled strands (twisted ladder) Strands are complimentary

Nucleotide NB S P THREE PARTS Sugar Phosphate group Nitrogen Base Deoxyribose (in DNA) Ribose (in RNA) Phosphate group Nitrogen Base NB S P

The Four Nucleotides PURINES Guanine (G) Adenine (A) PYRIMIDINES Cytosine (C) T Thymine (T)

Two Complimentary Strands BASE PAIRING (Chargaff’s Rule) A – T or T – A G – C or C - G C G A T G C T A

The Double Helix

DNA Replication Why does DNA need to replicate (copy) itself? MITOSIS Replication preserves the sequence of bases in an organism’s DNA

DNA Replication: Step 1 T A C G T A C G The DNA molecule unzips

Replication: Steps 2 & 3 DNA polymerase adds the correct complimentary nucleotide to each exposed strand A complimentary strand is created for each original strand T A C G A T T A G C C G T A

DNA, Genes & Chromosomes long strands of DNA How many chromosomes do humans have? Genes part of a chromosome Each gene codes for a different protein

Proteins Gene Expression Amino Acids The use of genetic material to make a protein Protein ultimately determines a trait Amino Acids Building blocks of proteins

How does DNA code for a protein? Nucleotide bases “spell out” the message ORDER is important OIGLOBY BIOLOGY DNA alphabet has 4 letter G A T C

Protein Synthesis Transcription An RNA copy of DNA is made Translation RNA is translated in to a protein RNA transcription Protein translation DNA

RNA Ribonucleic acid Messenger for DNA Single stranded No thymine (T) has uracil (U) instead A G U

Transcription An RNA copy of DNA is made Occurs in the Nucleus Called mRNA Only one side of DNA is copied Occurs in the Nucleus Once mRNA is made it leaves the nucleus (through a pore)

TRC: Step 1 T A C G T A C G The DNA molecule unzips

TRC: Step 2 RNA polymerase binds to one strand of DNA at the promoter site T A C G

TRC: Step 3 RNA pol. Pairs each nucleotide base with its complimentary base One strand Only!! T A C G A U G C U A

TRC: Step 4 New messenger RNA (mRNA) leaves the nucleus through a nuclear pore nucleus cytoplasm A U G C U A A U U

Translation RNA translated into a protein Two types of RNA work together mRNA – messenger tRNA – transfer Occurs in the cytoplasm Genetic Code is the translator Each “word” is 3 letters GCA = alanine (see genetic code)

Genetic Code CODON ANTICODON three letter “word” in mRNA Specify a particular amino acid ANTICODON Three leter “word” in tRNA Complimentary to the codon

The Genetic Code

TRL: Step 1 mRNA “start” codon binds to a ribosome AUG = start AUG = methionine ribosome A U G C U A A U U

TRL: Steps 2 & 3 tRNA picks up an amino acid in the cytoplasm and carries to ribosome tRNA anticodon binds to complimentary mRNA codon A U G C U A A U U U A C met U A C met

TRL: Steps 4 & 5 Amino acid detaches from the tRNA and attaches to a growing protein chain tRNA leaves to find another amino acid A U G C U A A U U U A C met U A C met

TRL: Step 6 Continues as mRNA passes through ribosome and one tRNA after another is selected to match the mRNA codons G A U leu met A U G C U A A U U met G A U leu A U G C U A A U U met G A U leu G A U leu

TRL: Step 7 Ends when a “stop” codon is reached and the newly assembled protein is released into the cell leu met A U G C U A A U U stop

G G C C T A A C G A T T